GERMAN ATV-DVWK RULES AND STANDARDS
Standard ATV-DVWK-A 198E Standardisation and Derivation of Dimensioning Values for Wastewater Facilities
April 2003 ISBN 3-924063-63-X
Publisher/marketing: ATV-DVWK German Association for Water, Wastewater and Waste, Theodor-Heuss-Allee 17 y D-53773 Hennef Tel. ++49-22 42 / 8 72-120 y Fax:++49 22 42 / 8 72-100 E-Mail:
[email protected] y Internet: www.atv-dvwk.de
ATV-DVWK-A 198E
User Notes This ATV Standard is the result of honorary, technical-scientific/economic collaboration which has been achieved in accordance with the principles applicable therefor (statutes, rules of procedure of the ATV and ATV Standard ATV-A 400). For this, according to precedents, there exists an actual presumption that it is textually and technically correct and also generally recognised. The application of this Standard is open to everyone. However, an obligation for application can arise from legal or administrative regulations, a contract or other legal reason. This Standard is an important, however, not the sole source of information for correct solutions. With its application no one avoids responsibility for his own action or for the correct application in specific cases; this applies in particular for the correct handling of the margins described in the Standard.
The German Association for Water, Wastewater and Waste, ATV-DVWK, is the spokesman in Germany for all universal questions on water and is involved intensively in the development of secure and sustainable water management. As politically and economically independent organisation it operates specifically in the areas of water management, wastewater, waste and soil protection. In Europe the ATV-DVWK is the association in this field with the greatest number of members and, due to its specialist competence it holds a special position with regard to standardisation, professional training and information of the public. The ca. 16,000 members represent the experts and executive personnel from municipalities, universities, engineer offices, authorities and businesses. The emphasis of its activities is on the elaboration and updating of a common set of technical rules and standards and with collaboration with the creation of technical standard specifications at the national and international levels. To this belong not only the technical-scientific subjects but also economical and legal demands of environmental protection and protection of bodies of waters.
Publisher/Marketing:
Setting-up and printing:
ATV-DVWK German Association for Water Wastewater and Waste Theodor-Heuss-Allee 17 D-53773 Hennef Tel.: ++49-22 42 / 8 72-192 Fax: ++49- 22 42 / 8 72-100 E-Mail:
[email protected] Internet: www.atv-dvwk.de
DCM, Meckenheim
ISBN: 3-924063-63-X Printed on 100 % recycled paper
© ATV-DVWK Deutsche Vereinigung für Wasserwirtschaft, Abwasser and Abfall e. V., Hennef 2002
All rights, in particular those of translation into other languages, are reserved. No part of this Standard may be reproduced in any form - by photocopy, microfilm or any other process - or transferred into a language usable in machines, in particular data processing machines, without the written approval of the publisher.
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April 2003
ATV-DVWK-A 198E
Authors This Standard has been elaborated by the ad-hoc Working Group “Dimensioning-Principles for Wastewater Facilities“ within the ATV-DVWK Main Committee ES “Drainage Systems” and KA “Municipal Wastewater Treatment”. The following are members of the Working Group: Prof. Dr.-Ing. Dr. h. c. R. Kayser, Braunschweig (Chairman) Dr.-Ing. E. Meißner, München Dipl.-Ing. H. Schmidt, Erkrath Prof. Dr.-Ing. Th. Schmitt, Kaiserslautern Dr.-Ing. M. Schröder, Aachen Bauass. Dipl.-Ing. G. Willems, Essen
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ATV-DVWK-A 198E
Contents User Notes ............................................................................................................................................... 2 Authors .............................................................................................................................................................3 1
Area of Application ...........................................................................................................................6
1.1 1.2 1.3
Preamble ................................................................................................................................... 6 Objective.................................................................................................................................... 6 Scope ........................................................................................................................................ 6
2
Symbols..............................................................................................................................................7
2.1 2.2 2.3 2.4 2.5 2.6 2.7
General...................................................................................................................................... 7 Surface Parameters and Runoff Coefficients............................................................................ 8 Flow/Discharge Parameters ...................................................................................................... 9 Concentration Parameters ........................................................................................................ 9 Sludge Parameters.................................................................................................................... 11 Load Parameters....................................................................................................................... 11 Other Characteristic Values ...................................................................................................... 11
3
Preparatory Work for the Derivation of Dimensioning Values ...................................................12
3.1 3.2 3.2.1 3.2.2 3.3 3.3.1 3.3.2 3.3.2.1 3.3.2.2 3.3.2.3
Initial Situation ........................................................................................................................... 12 Data Gathering .......................................................................................................................... 12 Flow Measurement.................................................................................................................... 12 Sampling for the Derivation of Loads ........................................................................................ 13 Data Required for Dimensioning ............................................................................................... 13 Flow Data .................................................................................................................................. 13 Loads and Concentrations ........................................................................................................ 14 For the Size-Classification and the Determination of the Design Capacity of Wastewater Treatment Plants 14 For the Dimensioning of Combined Sewer Overflows 14 For the Dimensioning of Wastewater Treatment Plants 15
4
Determination of Data about the Actual Condition ......................................................................16
4.1 4.2 4.2.1 4.2.2 4.2.2.1 4.2.2.2 4.2.2.3 4.2.2.4 4.2.2.5 4.2.2.6 4.2.3 4.3 4.3.1 4.3.1.1 4.3.1.2 4.3.1.3 4.3.1.4
General Documents and Data................................................................................................... 16 Determination of Discharge Data .............................................................................................. 16 Data on Water Consumption ..................................................................................................... 16 Data on Sewage Flow ............................................................................................................... 17 Determination of Essential Flow Data 17 Determination of the Annual Mean Dry Weather Flow 18 Determination of the Wastewater Flow 18 Determination of the Infiltration Water Flow 18 Determination of Daily Peaks and Nightly Minima 19 Determination of the Combined Wastewater Flow to the Wastewater Treatment Plant 20 Flow Data on the Basis of Empirical Values ............................................................................. 21 Determination of Loads and Concentrations............................................................................. 22 Determination through Evaluation of Measured Values............................................................ 22 Sampling Frequency and Necessary Parameters 22 Examination of Available Information 23 Location of the Sampling 23 Summary of Measured Data and Calculation of the Daily Load as well as the Values of the Concentration Ratio 24
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ATV-DVWK-A 198E 4.3.1.5 4.3.1.6 4.3.1.7 4.3.1.8 4.3.2
Determination of the Relevant Loads on the Basis of Weekly Means 25 Determination of the Relevant Loads as 85 % Values 26 Determination of the Relevant Concentrations 26 Determination of the Peak Factor for Nitrogen 26 Estimation of Pollutant Loads and Concentrations on the Basis of Empirical Values ...............27
5
Forecast Data.....................................................................................................................................28
6
Costs and Environmental Effects ...................................................................................................28
7
Relevant Regulations, Standards and Standard Specifications ................................................28
8
Literature [Translator’s note: Apart from [4] no known translation available in English] ......30
Appendix A: Explanatory notes for surface characteristic values and catchment area related values..................................................................................................................................................31 A1 A 1.1 A 1.2 A 1.3 A 1.4 A. 1.5 A2
Surface characteristic values .....................................................................................................31 Surface areas.............................................................................................................................31 Calculated value “Impermeable surface” Aimp ............................................................................32 Degree of paving and runoff coefficients ...................................................................................32 Numerical example for surfaces and surface parameters .........................................................35 Catchment area related values ..................................................................................................36 Surface reference parameters ...................................................................................................36
Appendix B 1: Summary of flow values from the English translations of respective ATV-DVWK Standards ...........................................................................................................................................38 Appendix B 2: Summary of flow values from the original German ATV-DVWK Standards ...................39 Appendix C: Example for the evaluation of measured values....................................................................40 C1 C 1.1 C 1.2 C 1.3 C 1.4 C 1.5 C 1.6 C 1.7 C 1.8 C2 C 2.1 C 2.2 C 2.3 C 2.4 C 2.5 C 2.6 C 2.7
Flows ..........................................................................................................................................40 Summary of measured values ...................................................................................................40 Daily flows ..................................................................................................................................41 Determination of the dry weather flow .......................................................................................41 Determination of the wastewater flow as annual mean .............................................................42 Determination of the infiltration water flow .................................................................................43 Determination of the maximum and minimum dry weather flow ................................................43 Maximum and minimum wastewater flow ..................................................................................44 Determination of the combined wastewater flow .......................................................................44 Loads and concentrations ..........................................................................................................45 Summary of measured values ...................................................................................................45 Planning of sampling..................................................................................................................46 Determination of the relevant COD load on the basis of weekly means ...................................47 Determination of the relevant COD load as 85 % value ............................................................48 Ratio values of important parameters ........................................................................................48 Determination of the concentrations ..........................................................................................49 Determination of the peak factor for the nitrogen loading..........................................................50
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ATV-DVWK-A 198E
1
Area of Application
1.1 Preamble In the course of the self-monitoring of wastewater treatment plants data are collected which can form a valuable basis with the planning of expansion or optimisation of both drainage systems and also wastewater treatment plants. Unfortunately, in the past, the collection and evaluation often took place unilaterally, either for wastewater treatment plants only or for sewer systems only. Terms and symbols were not always harmonised with each other, frequently the same symbols with different significance have been used in different standards. The reason was the lack of clear specifications. After even more municipalities, associations and operating companies are managing data banks in which a great deal of basic data for water management planning are kept, a clear definition and common further processing of these data have gained in significance. The planning of wastewater facilities should as far as possible take place on the basis of measured values. As the planning process for the expansion of existing wastewater facilities or new construction measures in individual locations as a rule spread over several years, this time should, if possible, be used to widen the data base. A reliable databasis is a basic prerequisite for an ecologically and economically practical planning, construction and operation of wastewater facilities. Sewer systems and wastewater treatment plants are to be operated for the same flow. Due to the different planning horizons the sewer system can be dimensioned for another flow than that for the wastewater treatment plant. Previously the permitted combined wastewater flow was determined primarily according to dimensioning data or the hydraulic capacity of the wastewater treatment plant. In order to make possible an optimisation between permitted charging of the wastewater treatment plant and the dimensioning of stormwater tanks, an approach using a bandwidth of the permitted combined wastewater flow is recommended.
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1.2 Objective This Standard is concerned with the definition, collection, evaluation and examination of data as well as with the subsequent derivation of dimensioning values based on these for wastewater treatment plants and drainage systems. Forecast data for various time horizons can subsequently be derived from measured data. With this Standard the objective is pursued, globally for all ATV-DVWK Standards and Advisory Leaflets, as far as possible and practical to standardise the derivation of values for the dimensioning of drainage systems and municipal wastewater treatment plants as well as the symbols for dimensioning values. The discharges, loads and concentrations necessary for dimensioning are, as previously, laid down in the appropriate ATV-DVWK-Standards. The following are introduced in this standard: – a homogeneous system for symbols; – for hydraulic calculations a mathematical determination of the dry weather flow dissociated from meteorological records; – for the interface sewer - wastewater treatment plant a new approach for the determination of the combined wastewater flow QCWW; – the concentration of the frequently to be determined COD as master parameter and the ratios to the less frequently determined other parameters (e.g. BOD5, filterable solids, nitrogen and phosphorus), in order to keep the costs for chemical analysis within limits. Should, after the publication of this Standard, divergent definitions be given in other ATV-DVWKStandards then the latter apply.
1.3 Scope The here summarised terms and bases for the determination of – – – –
catchment areas, flows/discharges, loads and concentrations
ATV-DVWK-A 198E concern all ATV-DVWK Standards and Advisory Leaflets which deal with dimensioning and application of simulation models for drainage systems, combined wastewater or stormwater treatment facilities and wastewater treatment plants (see Chap. 7, ATV-DVWK Standards).
2
Symbols
2.1 General A common system is introduced for all symbols according to which, behind the respective main term (A for surfaces, Q for flows/discharges, C, S and X for concentrations and B for loads), an index or further indices separated by commas can follow. Alternatively, instead of the index style one can work with lowered hyphen. Special indices are continued in later chapters, however, they can also be selected sensibly, for certain applications in the respective Standards. Authors’ afternote: In agreement with EN 752-1 it is differentiated between “wastewater” (water changed by use and discharged to a sewer system, e.g. domestic wastewater and/or commercial/industrial wastewater) [in German: Schmutzwasser] and “sewage” (wastewater and/or surface water conveyed by a sewer) [in German: Abwasser]. Translator’s note: While the main terms remain unchanged as they are recognised internationally, the indices used reflect the English translation of the individual German parameter. For simplicity and clarity these have been chosen to match as far as possible the German indices. Where this is not possible the original German symbol is placed in square brackets after the English version. This procedure is not intended to create new symbols for the English-speaking engineering community but serves solely to make German symbols/indices comprehensible to non-German speakers.
AC,Sep [AE,Tr] – area with separate sewer system AC,Comb [AE,Mi] – area with combined sewer system AC,Ind [AE,G] – commercial/industrial area Further ple: p [b] np [nb] s [k]
differentiation in lower case, for exam-
– with paved surface (AC,p) [AE,b] – non-paved surface (AC,np) [AE,nb] – with sewers (AC,s [AE,k] and, for example, AC,s,p [AE,k,b]) ns [nk] – without sewers (AC,ns) [AE,nk] – Types of flow: [in German upper case, 1 or 2 letters], for example: WW [S] – wastewater flow (QWW) [QS] DW [T] – dry weather flow (QDW) [QT] Inf [F] – infiltration water flow (QInf) [QF] Comb [M] – combined wastewater flow (QComb) [QM] Thr [Dr] – throttle flow (QThr) [QDr] – Periods of time: lower case, for example: a – year m – month t – a certain period of time, e.g. from 13.7.02 to 18.9.02 w – week d – day h – hour min – minutes With no details: interval ≤ 5 minutes – Divisor for wastewater flows: x in h/d, (24, 16, x for general) xQmax in h/d for peak values – Mean values for periods, e.g.: aM – annual mean mM – monthly mean pM – mean for a period wM – weekly mean 2wM – 2-weekly mean dM – daily mean hM – hourly mean
For the main meanings below the indices are specified in the following order:
− Catchment areas (AC) [AE], further subdivision, for example:
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ATV-DVWK-A 198E 2.2 Surface Parameters and Runoff Coefficients
from the locality, others first result through multiplication using a runoff coefficient and represent numerical values.
As the conceptual limitation of catchment areas in practice continues to cause confusion, the areas which are possible within water management are listed below. The majority are assignable Symbol English
Unit
In Appendix A further explanatory notes can be found on surface parameters and the values derived from these. Designation
German
AC
A_C
AE
A_E
ha
Catchment area; e.g. of a wastewater disposal region
AC,s
A_C,s
AE,k
A_E,k
ha
AC,ns
A_C,ns
AE,nk
A_E,nk
ha
AC,p
A_C,p
AE,b
A_E,b
ha
AC,np
A_C,np
AE,nb
A_E,nb
ha
Catchment area served by sewers or covered by a drainage system Catchment area not served by sewers or not covered by a drainage system Sum of all paved surfaces of a catchment area; is to replace Ared, i. a. in ATV-A 128E (1992) Sum of all non-paved surfaces of a catchment area
AC,Ind
A_C,ind
AE,G
A_E,G
ha
Commercial and/or industrial catchment area
Aimp
A_imp
Au
A_u
ha
I_G
ED IG
I_G
I/ha E/ha %
Impermeable surface area, application-related numerical value: Aimp = AC,s ⋅ Ψ or Aimp = AC,p ⋅ Ψ [Au = AE,k ⋅ Ψ or Au = AE,b ⋅ Ψ ] (dependent on terms of reference), if required also sum of several flow-effective surface components: Aimp = Σ(AC,i ⋅ Ψi) [Au = Σ(AE,i ⋅ Ψi)] Population density, quotient of number of inhabitants and catchment area Surface ground slope; area-weighted average slope of a catchment area Degree of paving of a catchment area, γ = AC,p/AC [γ = AE,b/AE]
PD IG γ
γ
-
Ψ
Ψ
-
Ψm
Ψ_m
Ψm
Ψ_m
-
Ψs
Ψ_s
Ψs
Ψ_s
-
ΨA128
Ψ_A128
ΨA128
Ψ_A128
-
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April 2003
Runoff coefficient; application-related ratio to quantify the flowinfluencing part of the precipitation; calculation as quotient of stormwater flow and associated precipitation dependent on application, e.g. as Ψm, Ψpeak [Ψm, Ψs] Mean runoff coefficient; quotient of stormwater flow volume and precipitation volume for a defined period of time (e.g. duration of a single rainfall event, period of time); previously mean discharge coefficient Peak runoff coefficient; quotient of maximum runoff rate qmax and associated maximum rainfall intensity rmax; mainly for flow time procedures and block rainfall; previously runoff coefficient during storm peak Application-related runoff coefficient in accordance with ATV-A 128E (1992) and ATV-DVWK–M 177 (2001) for the determination of the numerical value Aimp from the size of the paved surface AC,p [AE,b]
ATV-DVWK-A 198E 2.3 Flow/Discharge Parameters Symbol English
Unit
Designation
German
fWW,QCW
f_WW,QCW
fS,QM
f_S,QM
-
QD QInd QWW QWW,max,85
Q_D Q_Ind Q_WW Q_WW,max,85
QH QG QS QS,max,85
Q_H Q_G Q_S Q_S,max,85
l/s l/s l/s l/s
QInf QDW QR QComb
Q_Inf Q_DW Q_R Q_Comb
QF QT QR QM
Q_F Q_T Q_R Q_M
l/s l/s l/s l/s
QR,Sep
Q_R,Sep
QR,Tr
Q_R,Tr
l/s
QThr
Q_Thr
QDr
Q_Dr
l/s
Qa Qd QDW,d QDW,d,aM
Q_a Q_d Q_DW,d Q_DW,d,aM
Qa Qd QT,d QT,d,aM
Q_a Q_d Q_T,d Q_T,d,aM
l/s l/s l/s l/s
QDW,aM Qd,Conc
Q_DW,aM Q_d,Conc
QT,aM Qd,Konz
Q_T,aM Q_d,Konz
l/s m3/h
Qh Q2h QWW,x
Q_h Q_2h Q_WW,x
Qh Q2h QS,x
Q_h Q_2h Q_S,x
m3/h m3/h m3/h, l/s
QDW,max QDW,h,max QDW,2h,max qInf
Q_DW,max Q_DW,h,max Q_DW,2h,max q_Inf
QT,max QT,h,max QT,2h,max qF
Q_T,max Q_T,h,max Q_T,2h,max q_F
l/s m3/h, l/s m3/h, l/s l/(s•ha)
qR
q_R
qR
q_R
l/(s•ha)
qInd
q_Ind
qG
q_G
l/(s•ha)
wd wWW,d
w_d w_WW,d
wd wWW,d
w_d w_WW,d
l/(I•d) l/(I•d)
2.4 Concentration Parameters Concentrations without additional details apply for 24-h composite samples, with index, for example, 2h is defined as the average concentration in a
Factor for the calculation of the wastewater flow with QCW [QM] Domestic wastewater flow Commercial and/or industrial wastewater flow Wastewater flow (QD + QInd [QH + QG]) Maximum hourly wastewater flow derived from the daily wastewater flow undercut on 85% of the days Infiltration water flow Dry weather flow (QWW + QIW [QS + QF]) Stormwater [rainfall] flow Combined wastewater flow to the wastewater treatment plant Unavoidable stormwater runoff in sanitary sewers of areas with separate sewer system Throttle flow with combined sewer overflows and stormwater tanks Annual flow Daily flow Daily dry weather flow Average daily dry weather flow (quotient of sum of daily flows of all dry weather days and the number of dry weather days of a year Dry weather flow as annual mean Daily flow for the calculation of concentrations from loads Hourly flow 2-hourly average of the flow Wastewater flow as fraction x of QWW,d [QS,d], e.g. flow as daily peak Peak dry weather flow (interval ≤ 5 minutes) Maximum hourly dry weather flow Maximum dry weather flow as 2-hourly mean Area-specific infiltration water flow rate, qInf = QInf / AC,s [qF = QF / AE,k] Area-specific stormwater discharge rate, qR = QR / AC,s [qR = QR / AE,K] Industrial/commercial wastewater discharge rate, qInd = QInd / AC,s [qG = QG / AE,k] Inhabitant-specific daily water consumption Inhabitant-specific daily wastewater yield
2 h interval. Average annual values are, for example, required with the calculation of pollution load simulation. For differentiation, grab samples receive the additional index GS, this also applies for qualified grab samples.
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ATV-DVWK-A 198E Symbol English CXXX
C_XXX
CXXX,GS
Unit
Designation
German C_XXX
mg/l
Concentration of the parameter XXX, in the homogenised sample
C_XXX,GS CXXX,SP
C_XXX,SP
mg/l
Concentration of the parameter XXX, in the homogenised grab sample
SXXX
S_XXX
SXXX
S_XXX
mg/l
Concentration of the parameter XXX, in the filtered sample (0.45 µm membrane filter)
XXXX
X_XXX
XXXX
X_XXX
mg/l
Concentration of the filter residue, XXXX = CXXX - SXXX
CXXX,2h
C_XXX,2h CXXX,2h
C_XXX,2h
mg/l
Average concentration in a 2-h interval
CXXX,aM
C_XXX,aM CXXX,aM
C_XXX,aM
mg/l
Annual average value of a concentration
CBOD
C_BOD
CBOD
C_BOD
mg/l
Concentration of BOD5 in the homogenised sample
SBOD
S_BOD
SBOD
S_BOD
mg/l
Concentration of BOD5 in the sample filtered with 0.45 µm membrane filter
CCOD
C_COD
CCOD
C_COD
mg/l
Concentration of COD in the homogenised sample
SCOD
S_COD
SCOD
S_COD
mg/l
Concentration of COD in the sample filtered with 0.45 µm membrane filter
CN
C_N
CN
C_N
mg/l
Concentration of total nitrogen in the homogenised sample as N (CN = CorgN + SNH4 + SNO3 + SNO2)
CTKN
C_TKN
CTKN
C_TKN
mg/l
Concentration of Kjeldahl nitrogen in the homogenised sample (CTKN = CorgN + SNH4)
CorgN
C_orgN
CorgN
C_orgN
mg/l
Concentration of organic nitrogen in the homogenised sample as N (CorgN = CTKN – SNH4 or CorgN = CN – SNH4 – SNO3 – SNO2)
SinorgN
S_inorgN
SanorgN
S_anorgN
mg/l
Concentration of inorganic nitrogen as N (SinorgN = SNH4 + SNO3 + SNO2)
SNH4
S_NH4
SNH4
S_NH4
mg/l
Concentration of ammonia nitrogen in the filtered sample as N
SNO3
S_NO3
SNO3
S_NO3
mg/l
Concentration of nitrate nitrogen in the filtered sample as N
SNO2
S_NO2
SNO2
S_NO2
mg/l
Concentration of nitrite nitrogen in the filtered sample as N
CP
C_P
CP
C_P
mg/l
Concentration of phosphorus in the homogenised sample as P
SPO4
S_PO4
SPO4
S_PO4
mg/l
Concentration of phosphate in the filtered sample as P
SALK
S_ALK
SKS
S_KS
mmol/l Alkalinity
XSS
X_SS
XTS
X_TS
mg/l
XorgSS
X_orgSS
XorgTS
X_orgTS
mg/l
XinorgSS
X_inorgSS XanorgTS
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April 2003
CXXX
X_anorgSS mg/l
Concentration of suspended solids (0.45 µm membrane filter, drying at 105 °C) Concentration of organic suspended solids Concentration of inorganic suspended solids
ATV-DVWK-A 198E 2.5 Sludge Parameters Symbol
Unit
English QSl,d QWS,d SVI DRSl oDRSl DSWS
Q_Sl,d Q_WS,d SVI DR_Sl oDR_Sl DS_WS
Designation
German QSchl,d QÜS,d SVI TRSchl TRSchl TSÜS
Q_Schl,d Q_ÜS,d SVI R_Schl oTR_Schl S_ÜS
m3/d m3/d l/kg kg/m3 % kg/m3
Daily volume of sludge Daily volume of waste (activated) sludge Sludge Volume Index Concentration of the dry solids (evaporation residue) of sludge Percentage of organic dry solids of sludge Concentration of dry solids (filter residue) of waste (activated) sludge
2.6 Load Parameters Traditionally, with loads, the period of time is the first index before the index for parameter. Symbol English
Unit
Designation
2-weekly average of the daily load of a substance, e. g. for 2-weekly average of the daily COD load Bd,COD,2wM Hourly load of a substance (Bh,XXX = CXXX,h · Qh), e. g. for hourly BOD5-load Bh,BOD Hourly load of a 2-hour interval (B2h,XXX = CXXX,2h · Q2h), e. g. for 2-h TKN load B2h,TKN A days maximum 2-h-load as hourly load
German
Bd,XXX,2wM B_d,XXX,2wM
Bd,XXX,2wM
B_d,XXX,2wM
kg/d
Bh,XXX
B_h,XXX
Bh,XXX
B_h,XXX
kg/h
B2h,XXX
B_2h,XXX
B2h,XXX
B_2h,XXX
kg/h
B2h,XXX,max
B_2h,XXX,max
kg/h
B2h,XXX,max B_2h,XXX,max
Numbers of inhabitants or population equivalents [see EN 1085]
EGWXXX,ZZ EGW_XXX,ZZ
I [E] I [E]
EW
I [E]
P EZ PEXXX,ZZ
PE_XXX,ZZ
PT
Number of inhabitants (Population) Population equivalents, e. g. for the characterisation of the industrial wastewater, always with reference parameter and associated inhabitant-specific load, e. g. PECOD,120, i.e. dependent on the parameter there can be various PEs for a specific wastewater Total number of inhabitants and population equivalents (PT = P + PE), depending on the parameter possibly different PTs
2.7 Other Characteristic Values Indices for the location or for the purpose of sampling (always as last index). Indices English German In InB ESST EF EP
Z ZB AN AF AT
Designation
Sample from the inflow to the wastewater treatment plant, e. g. CBOD,In; XDS,In [CBSD,Z; XTS,Z] Sample from the inflow to the biological stage, e. g. CCOD, InB [CCSB,ZB] Sample from the effluent of the secondary settling stage [EPST for primary settling] Sample from the effluent of a filter Sample from the effluent of a pond
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ATV-DVWK-A 198E
3
Preparatory Work for the Derivation of Dimensioning Values
3.1 Initial Situation As a rule, there are records of the sewage flow, the weather (rainfall days, dry weather days), the temperature of the wastewater and the concentration of certain parameters available in wastewater treatment plants and, in individual cases, from sewer networks or from stormwater tanks. With these data the values for the effluent from the sewer system and for the loading of the wastewater treatment plant can be determined. However, it is always to be examined whether the sewer system is being operated correctly, for example whether any inadmissible overflows or nonstatutory discharges are present, which are not contained in the records. It is recommended that first, a correct situation is established.
If one or more of the above criteria are not met it has to be decided whether missing data is to be determined through additional measurements, or are to be estimated on the basis of empirical values. Empirical values are enlisted for plausibility checks of the dimensioning values derived from measured values. They can be used as basis for the dimensioning of wastewater treatment plants, if the costs for measurements are disproportionate compared with utilisation, in particular for small catchment areas without industrial or commercial developments. Sewage flow values should, as far as possible, be derived from measured values. The concentration of a parameter, as a rule, shows a typical diurnal variation as for the wastewater flow. In addition, as a result of dilution with rain and/or infiltration water, through remobilisation of sewer deposits or as a result of draining stormwater tanks, they can vary considerably. Average concentration values can therefore only be derived from the average values of loads and the associated flows.
As every evaluation has a very definite aim it must first be determined which values are required, see Chap. 3.3.
3.2
Then, inter alia, it is to be examined ,
3.2.1 Flow Measurement
– whether the available measured values are acceptable or not, for example due to inaccurate or missing flow measurements or inappropriate sampling and/or analysis; – whether the flow values are available with sufficient frequency in representative periods of time (including weekends), in order to create time series; – whether and in which manner the laboratory is subject to analytical quality assurance; if required an external examination is to be carried out; – whether measured values [of concentrations] of volume- or flow-proportional daily composite samples for the required parameters are available; – whether the sampling point is suitable for the desired information (e. g. due to internal backflows). With the discharge of back-flows with a high suspended solids concentration, implausible concentrations can, for example, be measured.
For each type of evaluation it has to be checked when the last calibration of the flow measurement equipment took place. Under certain circumstances a new calibration is to be initiated. The existing flow data then may be corrected appropriately.
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Data Gathering
In the ideal case, in addition to the daily flow Qd in m³/d, the daily flow variation is available in the form of print-outs or on data carriers. It is recommended, that 5 minute or 1 hour averages of the dry weather flow are applied for evaluations of the daily variation on dry weather days for the sewer system, and 2-hourly means for wastewater treatment plants.
ATV-DVWK-A 198E 3.2.2 Sampling for the Derivation of Loads A continuous (on-line) measurement of the concentrations of the essential parameters is desirable, in order to be able to limit the expense for sampling and analysis and to indicate diurnal and seasonal variations and, from these, derive maxima and minima. In the wastewater treatment plant inflow or in the discharge from the primary settling stage, however, it is almost impossible to measure on-line any of the typical parameters without great expense for the processing of the sample stream. As an aid the Spectral Absorption Coefficient (SAC) in accordance with DIN 38404, Part 3, with a measuring probe submerged directly in the wastewater in the outflow of the primary settling stage, can be used as an indicator for the variation of the organic loading. The relationship to the COD is, in each case, to be derived based on parallel chemical analysis. The continuous measurement of the ammonia concentration is also possible but very expensive due to the processing of the sample stream. A daily load is the product from the volume- or flow-proportional 24-hourly mean (daily composite sample) of the concentration of a parameter, e.g. CCOD in mg/l, and of the flow volume of the day Qd in m³/d. It is, for example, designated with Bd,COD in kg/d. Grab samples are unsuitable for the calculation of daily loads. The diurnal load fluctuation for reasons of cost, is formed from the 2-hourly mean of the concentration, e.g. CTKN,2h in mg/l, and from associated 2hourly mean of the flow Q2h in m³/h. For sampling there are the following possibilities: – Volume- or flow-proportional sampler Flow-coupled samplers require a measurement signal of the flow-meter. As a rule a daily composite sample is collected. If the samplers are also equipped with a bottle exchanger, 2-hourly composite samples can also be collected to analyse the diurnal fluctuation. – Time-proportional sampler This is employed if the conduction of the flow signals, e. g. for temporary applications, is too
expensive. The samplers must be equipped with a bottle exchanger, in order to obtain twelve 2-hourly composite samples a day. A daily composite sample is obtained by weighting the sample volumes of the 2-hourly samples with the inflows of the associated 2-hourly intervals. – Manual sampling Grab samples are taken at half-hourly or hourly intervals and combined into 2-hourly samples. The further procedure corresponds with the time-proportional sampling. Grab samples are, as a rule taken from the sludge flows. A sampling point is to be chosen at which the concentration is not subjected to heavy time variations, e.g. at the outlet of a pre-thickener; if necessary several grab samples are to be taken each day in order to obtain a usable average daily value. Fundamentally a rough sketch of the wastewater treatment plant with clear marking of the sampling points should be made from which it is plain to see which wastewater stream is sampled where.
3.3
Data Required for Dimensioning
3.3.1 Flow Data For applications within wastewater engineering mean values and peak values are required dependent on the terms of reference. Mean values are always based on a given period of time, e. g. daily dry weather flow QDW,d in m³/d or dry weather flow as annual mean QDW,aM in l/s. Peak values are used when, for short intervals, specific functions have to be maintained and safe operation has to be guaranteed. With this also the appropriate reference period of time (e. g. 2h, h) is to be given; without these details the reference interval is ≤ 5 minutes. A summary of the necessary inflows or discharges from the relevant ATV-DVWK Standards is to be found in Appendix B. In the Standards and Advisory Leaflets listed in Appendix B it is not clearly defined with what infiltration water flow is to be reckoned. Therefore the following definition is made: for hydraulic dimen-
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13
ATV-DVWK-A 198E sioning the infiltration water flow should be the maximum monthly mean (QInf,mM,max in l/s) of a multiple annual series (see Chap. 4.2.2.4). As a rule the following values can be derived from flow data measured in the wastewater treatment plant or in the sewer network: – mean annual dry weather flow QDW,d,aM in m3/d or QDW,aM in l/s. – maximum monthly mean of the infiltration water flow of a multiple annual series QInf,mM.max in l/s and the annual mean of the infiltration water flow QInf,aM in l/s. – mean annual wastewater flow QWW,aM in l/s, if the mean infiltration water flow QInf,aM in l/s has been determined through nightly measurements – maximum flow as 1-hourly or 2-hourly mean Qh,max or Q2h,max in m³/h or l/s. – maximum and minimum mean hourly dry weather flow as 1- or 2-hourly mean QDW,h,max or QDW,2h,max and QDW,h,min or QDW,2h,min in m3/h or l/s. – maximum and minimum flow Qmax and Qmin in l/s both from areas with separate as well as with combined sewer systems if the flow data are available for short time intervals of, for example, 5 minutes. For the derivation of data see Chap. 4.2.2. For hydraulic calculations with wastewater treatment plants on catchment areas with pure separate sewer systems, the maximum inflow with wet weather as 1-hourly mean (QDW,h,max in l/s) and in all other cases the combined wastewater flow (QComb in l/s) as well as the minimum flow with dry weather as 2-hourly mean (QDW,2h,min in l/s) are required. The dimensioning of the primary settling tanks depends on the maximum inflow as 2-hourly mean with dry weather (QDW,2h,max in m3/h) and with the combined wastewater flow (QComb in m3/h) or with the maximum flow from separate systems (QSep,h,max in m³/h).
3.3.2
Loads and Concentrations
3.3.2.1 For the Size-Classification and the Determination of the Design Capacity of Wastewater Treatment Plants The classification of wastewater treatment plants into the size-category [Authors’ afternote: In Germany the effluent standard depends on the sizecategory] and the determination of the design capacity is to be based on the BOD5 load in the inflow to the wastewater treatment plant which is achieved or undercut on 85% of the dry weather days (Bd,BOD,In in kg/d) without internal return flows plus a planned reserve of capacity. If only data from the effluent of the primary tanks are available then, in accordance with the [German] Wastewater Ordinance, the 85% value of the BOD5 load derived from these for dry weather can be applied. If necessary, existing internal back-flows are to be determined and deducted. The determination of the 85% values should in any case be based on at least 30 BOD5 load values of dry weather days distributed evenly over the period of time considered, insofar as no significant changes in the catchment area (e.g. connection of areas, changes with indirect dischargers) occur. Note: The separate determination of the design capacity and of the dimensioning value, for example for the biological stage, is necessary as this is dimensioned, dependent on the type of process, for various loads (e.g. 2- or 4-weekly mean with activated sludge plants or 2-hourly mean with biofilters).
3.3.2.2 For the Dimensioning of Combined Sewer Overflows For the dimensioning of combined sewer overflows and subsequent stormwater retention facilities in accordance with ATV-A 128E (1992) the mean annual value of the concentration of the COD in the inflow to the wastewater treatment plant (CCOD,In,aM in mg/l) with dry weather is required. If it is known through previous measurements, that the average
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ATV-DVWK-A 198E concentration is smaller than CCOD,In,aM = 600 mg/l, the determination is only necessary for the application of simulation models and, if applicable, with stringent discharge requirements.
3.3.2.3 For the Dimensioning of Wastewater Treatment Plants For the dimensioning of activated sludge plants with the removal of nitrogen and phosphorus the following are required in accordance with ATVDVWK-A 131E (2000): – The annual variation of the water temperature, in particular the lowest and highest temperature in the effluent of the biological reactors, from the 2-weekly means over at least two years. If no temperature measurement in the biological stage is available, the water temperature of the inflow or the effluent of the primary settling stage can be applied. – As relevant loads the maximum 2- or 4-weekly mean of the isochronous loads of: – COD (Bd,COD,InB in kg/d) and ratio SCOD/CCOD, if dimensioning using COD, – BOD5, (Bd,BOD,InB in kg/d), – suspended (filterable) solids (Bd,SS,InB in kg/d), – nitrogen (Bd,TKN,InB; Bd,NO3,InB and, if required, Bd,NO2,IB in kg/d) as well as – phosphorus (Bd,P,InB in kg/d) respectively for the periods with the dimensioning temperature, with the lowest and the highest temperature. For determination see Chap. 4.3.1.5. If the intense sampling required for the formation of 2- or 4-weekly average is out of proportion with the use, the relevant daily loads can be determined as those daily loads achieved or undercut on 85% of the days (“85 percentile value“). The data collection for this should include at least 40 daily loads distributed evenly over up to three years. The combination of loads which are not isochronous, for example of the COD and of the nitrogen, must be avoided. For the calculation see Chap. 4.3.1.6. For small wastewater treatment plants the relevant loads can be estimated from empirical values. With a distinct seasonal variation of loads, at least two different (maximum) 2- or 4-weekly
means are to be determined or 2 x 40 daily loads are required for the formation of the corresponding 85% values. A distinct seasonal variation exists if the maximum or minimum monthly average of the load varies by more than ± 20% of the annual mean. – Relevant concentrations of nitrogen and phosphorus: if it is required to maintain certain effluent concentrations, the relevant concentrations CTKN,InB in mg/l, SNO3,InB in mg/l and CP,InB in mg/l are to be arived, comp. Chap. 4.3.1.7. – Peak factor: for the design of the oxygen supply the ratio of the highest daily 2-hourly load of the TKN (B2h,TKN,max,InB in kg/h) to the daily average (Bh,TKN,dM,InB in kg/h) is required, comp. Chap. 4.3.1.8. – Sludge Volume Index with the expansion of activated sludge plants: as a result of a frequent seasonal variation of the Sludge Volume Index the critical load case should be determined in context using the associated loading from the seasonal fluctuation of the Sludge Volume Index (as 2-weekly average, as far as possible over three years). Alternatively, it should be based on the 85-percentile value at least from the last two years. It should be noted that changes of the process and of the sludge age also lead to changes of the Sludge Volume Index. The efficiency of the secondary settling stage is to be taken into account. For the dimensioning of trickling filters and rotating biological contactors in accordance with ATV-DVWK-A 281E (2001) the following are required as relevant loads: – BOD5, (Bd,BOD,InB in kg/d), – Nitrogen (Bd,TKN,InB in kg/d) Applicable as being relevant are those loads which are undercut on 85% of the days. At least 40 load values over one to three years are to be used. The combining of BOD5 loads and nitrogen loads which do not occur isochronously must be avoided. For the calculation see Chap. 4.3.1.6. For small facilities the relevant loads can be estimated from empirical values. – Relevant concentrations of nitrogen and phosphorus: if it is required to maintain certain effluent concentrations the relevant concentra-
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15
ATV-DVWK-A 198E tions CTKN,InB in mg/l, SNO3,InB in mg/l and CP,InB in mg/l, are to be derived, comp. Chap. 4.3.1.7. Treatment processes with short retention periods: certain biological processes such as, for example, biofilters, are dimensioned for the relevant (highest) 2-hourly loads of COD (B2h,COD,max,InB in kg/h) and of TKN (B2h,TKN,max,InB in kg/h). Dynamic simulation: depending on the programme and planning specifications comprehensive data collection is to be carried out for dynamic simulation. Presentation of this is dispensed with in this Standard [1, 2].
charges and effluents from wastewater treatment plants); – local conditions (inter alia inventory documents with details on conditions, soil and groundwater conditions, water levels in the surface waters, urban land use planning documents); – surface restrictions (inter alia pipelines and cables, contaminated soil). The sources of information and publishers or data managers can vary depending on the structure of the administration of the Federal [German] State.
4.2 For the dimensioning of facilities for sludge treatment the daily sludge volume QSl,d in m3/d, the dry solids concentration DRSl in kg/m3 and the organic fraction of the dry solids oDRSl in % are required. It is recommended that the mean of the sludge load is based on several weeks with dry and wet weather. The masses to be disposed of – screenings (depends on the bar spacing of the screen) and – grit chamber material (also depends on whether a washing takes place) can be determined as a mean only over several weeks. With sewer systems susceptible to deposits the masses of all residues can vary extremely sharply over time.
4
Determination of Data about the Actual Condition
4.1 General Documents and Data For the planning of wastewater facilities, in addition to the dimensioning values, which characterise the loading, further data, documents and information are required, such as for example: – requirements on the quality of the wastewater to be discharged (combined sewer overflow dis-
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Determination of Discharge Data
4.2.1 Data on Water Consumption The potable and process water input into the catchment area and the water produced in own water works of industry correspond approximately with the wastewater discharged to the sewer system. Water which is not discharged, for example from breweries or in agriculture, is to be taken into account. The seasonal variation of the daily water consumption serves as plausibility check of the seasonal variation of the daily wastewater flow; seasonal influences can thus be clearly recognised. A trend can be better recognised in a time series of the annual water consumption than in a time series of the annual dry weather flow which is influenced by differing precipitation and/or infiltration water flow. Attention is to be paid that in many cases the water service area and the catchment area of the sewer system are not congruent. The water consumed in the catchment area can be determined through addition of the annual water quantities of all consumers and subtraction of the water consumption outside the catchment area. This can, however, mean expensive calculations for the water suppliers. In accordance with the significance of the planning task it is recommended, even if the water service area and the wastewater catchment area are different, to take the following points into consideration: – collection of the annual water supply rates, if possible including the inherent water production
ATV-DVWK-A 198E of businesses, for the last 5, better 10 years, in order to identify a possible existing trend. – collection of the seasonal variation of the daily water consumption including the inherent water production of industries in order to obtain information on seasonal fluctuations of the wastewater flow. – determination of the mean specific water consumption wd,aM in l/(I·d). For this the following are to be collected: the number of inhabitants in the service area (P) and the annual feeding of water into the service area as mean of the last two to three years if no strong trend is present, otherwise from the previous year, in each case reduced by the recorded water utilisation of industries. If a value is found for wd,aM which lies far outside the normal range of from 100 to 150 l/(I·d), the reasons are to be explored.
4.2.2
Data on Sewage Flow
4.2.2.1 Determination of Essential Flow Data As a rule, one finds devices for the measurement of the sewage flow with associated recording facilities in wastewater treatment plants and, possibly, at pumping stations and stormwater tanks. Attention is already drawn to the checking of measurement devices in Chap. 3.2.1. The evaluation of sewage flow data should cover one year (with little infiltration water), better three to five years (with a great deal of infiltration water), as the precipitation events of only one year, under certain circumstances, can lead to false initial data (dry or wet year). An example for an evaluation is contained in Appendix C. In the first place the following data are to be collected or calculated: 1. Days with dry weather flow. Although, as a rule, it is recorded in wastewater treatment plants whether it has rained or snowed, the definition of a dry weather day should, however, come better from existing representative rainfall recorders in the catchment area in combination with a limiting amount of precipitation of, for example, 1 mm/d and normally one, and in larger catchment areas, up to two follow-on days [Author’s afternote: For the emptying of stormwater reservoirs]. Days with melting snow and days
with the discharge of groundwater from larger construction sites are not dry weather days. If the determination of the dry weather flow takes place with calculation in accordance with the method of sliding minimum (comp. 4), the weather records serve as plausibility check. 2. Daily sewage flow Qd in m3/d. 3. Daily sewage flow with dry weather QDW,d in m3/d (combination from 1 and 2). 4. For the mathematical derivation of the daily dry weather flow it is recommended, based on Fuchs et al. [3], that the polygon of the sliding 21-day minima of the daily flows be formed (interval 10 days before and 10 days after the day under consideration). All up to 20% over this polygon available daily flows then apply as dry weather flows, comp. Appendix C, Chap. C 1.3. The value of 20% corresponds approximately with the fluctuation bandwidth of the daily dry weather flow with constant infiltration water flow. Note: the procedure of sliding minima is new and still not a rule of technology. It is accepted that the day with the smallest daily flow within the interval is to be considered as dry weather day. A duration for the interval of 21 days is proposed. With a reduction of the duration of the interval the number of dry weather days and the annual mean of the dry weather flow increase. 5. Daily maximum and minimum flow with dry weather as peak values QDW,max and QDW,min in l/s or as hourly values QDW,h,max and QDW,h,min in l/s or m3/h, if inflow data for short time intervals of, for example, 5 minutes or hours are available. Attention: the values can, for example, be influenced by upstream pumping stations. 6. Daily maximum and minimum flow with dry weather as 2-hourly mean QDW,2h,max and QDW,2h,min in m3/h (only if the flow data are available on data carriers or printer carriage tape). 7. Daily maximum flow from areas with separate sewer system as hourly values QSep,h,max or as 2hourly mean QSep,2h,max in m3/h (only if the inflow data are available on data carriers or printer carriage tape).
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17
ATV-DVWK-A 198E The following graphical representation is recommended: – time series of the daily sewage flow for all days (Qd) and separately for dry weather days (QDW,d), comp. Figs. C-1 to C-5. – time series of the daily maximum, mean and minimum dry weather flows possibly separate for 5-minute intervals, hourly- and 2-hourly mean, comp. Figs C-7 and C-8. Freak values in the hydrographs of the dry weather flow QDW,d indicate i. a. undetected rainy weather days, emptying of stormwater reservoirs or false measurements. If the associated maxima and minima (e. g. QDW,h,max and QDW,h,min in l/s) indicate similar deviations from the other dry weather days such days are, if necessary, to be omitted for the evaluation.
4.2.2.2 Determination of the Annual Mean Dry Weather Flow The annual mean dry weather flow QDW,aM in l/s which, for example, is required for pollution load simulations, results from the arithmetic mean of all daily dry weather flows QDW,d,aM in m3/d through simple conversion in l/s: QDW ,aM =
QDW ,d ,aM 86.4
[l/s]
(1)
For the determination of the wastewater flow as annual mean QWW,aM in l/s or as mean of a certain period two routes are possible: 1. With the first route, the infiltration water flow must have been determined through night measurements as annual mean QInf,aM in l/s (Eqn. 2) or for a certain period QInf,pM in l/s (Eqn. 3), comp. 4.2.2.4. [l/s]
(2)
If the infiltration water is subject to a marked seasonal variation and if it is known from water consumption data, that the wastewater flow in-
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QWW ,aM = QDW ,pM − QInf ,pM
[l/s]
(3)
2. With the second route the mean annual wastewater flow QWW,aM is determined from water consumption data. For this the mean annual water consumption in the catchment area including the water production of industry and the water used by commerce and industry but not discharged are to be collected with sufficient accuracy. If the water consumption indicates a seasonal variation, then appropriate period means QWW,pM are to be determined.
If this is not possible, the mean annual wastewater flow QWW,aM can be calculated (Eqn. 4) as sum of the domestic flow QD,aM and of the industrial wastewater QInd,aM with the aid of specific values. The specific wastewater flow wWW,d,aM should be derived from water consumption data. QWW ,aM = Q D,aM + Q Ind ,aM = P⋅
4.2.2.3 Determination of the Wastewater Flow
QWW ,aM = QDW ,aM − QInf ,aM
dicates no pronounced seasonal variation, it is appropriate to determine the wastewater flow for a period with constant dry weather flow, e.g. in summer, through more frequent measurements of the infiltration water in accordance with Eqn. 3.
w WW ,d ,aM 86400
+ AC ,Ind ⋅ q Ind
[l/s] (4)
In addition the annual amount of wastewater from the annual reports of the wastewater treatment plant can be included for comparison. As thoroughly different results can be expected it is recommended that the results are compared with each other and that the “most probable” value is selected following critical assessment and justification why calculation should be carried out using it.
4.2.2.4 Determination of the Infiltration Water Flow The infiltration water flow is subject to seasonal variations due to the seasonal fluctuation of the precipitation. The assumption of a suitable infiltration water flow is decisive for the correct function of wastewater facilities and the loading of surface waters [receiving water].
ATV-DVWK-A 198E The infiltration water flow can be determined through night measurements or as difference of the dry weather flow and the wastewater flow. 1. Annual mean on the basis of night measurements: night measurements are, as a rule, only significant in catchment areas with negligible water consumption at the time of measurement. Favourable times are the early morning hours of nights from Saturday to Monday. The measurements are to be carried out regularly at least twice per month, in order to obtain sufficient values for the annual mean of the infiltration water flow QInf,aM in l/s. 2. Maximum monthly mean on the basis of night measurements: if a distinct seasonal variation of the infiltration water flow is present, the maximum infiltration water flow as monthly mean QInf,mM,max is determined in l/s. For this, night measurements on at least six days of the months involved from three years are necessary. As such intensive measurements are not, as a rule, undertaken, in retrospect an appropriate value cannot be determined. 3. Maximum monthly mean as difference of the dry weather flow and of the wastewater flow: here the variation of the dry weather flow for a multiple year series is determined in accordance with Chap. 4.2.2.1, Para. 4. From this the maximum monthly mean of the dry weather flow QDW,mM,max is determined. The wastewater flow is based on Chap. 4.2.2.3, Para. 2 as annual or period mean and is deducted.
– sewage flow data are available on data carriers for short time intervals of, for example, 5 minutes or for one hour, so that QDW,max and QDW,min or QDW,h,max and QDW,h,min can be extracted for each dry weather day. – the flow rate is not influenced by the operation of upstream pumping stations. – a period with approximately constant infiltration water flow is detectable, this must be documented through a sufficient number of measured values for the determination of QInf,pM . The period can cover one or more months with as few as possible rainy weather days. In the first instance, for each dry weather day, the differences QDW,h,max – QInf,pM and QDW,h,min – QInf,pM and QDW,d – QInf,pM in l/s are formed as hourly flow (or, for example, for 5 minute intervals). Then for each dry weather day the ratio values QDW ,h ,max − QInf ,pM QDW ,d − QInf ,pM
and
QDW ,h ,min − QInf ,pM QDW ,d − QInf ,pM
are calculated. Finally the mean maximum and minimum hourly wastewater flow is calculated by using the arithmetic means of the ratio values and the period mean of the wastewater flow QWW,d,pM : QDW ,h ,max − QInf ,pM QWW ,h ,max,pM = QWW ,d ,pM ⋅ [l/s] (5) QDW ,d − QInf ,pM pM
QDW ,h ,min − QInf ,pM [l/s] QWW ,h ,min,pM = QWW ,d ,pM ⋅ QDW ,d − QInf ,pM pM
(6)
The Divisor xQmax in h/d results as follows:
24
An ATV-DVWK Advisory Leaflet, which deals with the determination of the infiltration water flow is in preparation.
xQ max =
4.2.2.5 Determination of Daily Peaks and Nightly Minima
Maximum and minimum flow with dry weather as 2-hourly mean
Maximum and minimum wastewater flow
If the daily dry weather flow is subject to no marked seasonal variation, the annual mean of the maximum and minimum 2-hourly mean QDW,2h,max,aM and QDW,2h,min,aM in m³/h is produced from all dry weather days.
The maximum or minimum wastewater flow QWW,max and QWW,min or QWW,h,max and QWW,h,min in l/s can be determined with the presence of the following prerequisites only:
QDW ,h ,max − QInf ,pM QDW ,d − QInf ,pM pM
[h/d]
April 2003
(7)
19
ATV-DVWK-A 198E If the daily dry weather flows show a marked seasonal variation then, for the month with the highest mean dry weather flow, the mean of the maximum 2-hourly mean of the dry weather days QDW,2h,max,mM is formed in m3/h and for the month with the lowest mean dry weather flow the mean of the minimum 2-hourly mean of the dry weather days is calculated. If the period with low daily dry weather flow is of longer duration, for example, always continues for the complete summer, the maximum 2-hourly mean of this period QDW,2h,max,pM in m3/h can be significant for process layout. Maximum flow from purely separate systems
For hydraulic calculations, i. a. in the area of the wastewater treatment plant, with purely separate sewer systems the highest plausible measured value of the flow QSep,h,max in l/s of a period of at least one, better three or more years is assumed; if necessary, a safety factor is to be taken into account.
4.2.2.6 Determination of the Combined Wastewater Flow to the Wastewater Treatment Plant The combined wastewater flow to the wastewater treatment plant or the effluent of the last combined sewer overflow upstream of the wastewater treatment plant QCW has been calculated in accordance with ATV-A 131E (1991) [4] from double the wastewater flow QWW plus the infiltration water flow QInf QComb = 2 · QWW + QInf,aM With this, QWW was derived from the value of the daily flow QDW,d in m³/d which is undercut in 85% of the dry weather days. With multiplication of this value by an hourly peak factor (divisor xQmax) there results the daily peak value QWW, which is designated below as QWW,max,85. According to the earlier ATV Standard ATV-A 131E (1991) [4] the infiltration water flow is defined as annual mean. In order to obtain a margin for the optimisation of the hydraulic loading of the wastewater treatment plant and the treatment of the stormwater, a new approach to the calculation in accordance with
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Schleypen and Meißner [5] is introduced. With this a mean annual wastewater flow QWW,aM in l/s and a factor fWW,QComb are assumed. The salient points of the approach are derived as follows: For small residential areas the ratio of the 85 % value to the annual mean QWW,d,85 /QWW,aM is ca. 1.5 and the divisor for the peak xQmax = 8. From this results for the previous peak flow in accordance with ATV-A 131E (1991) QWW = QWW,max,85 = (1.5 · 24/8) · QWW,aM = 4.5 QWW,aM and 2 QWW,max,85 = 9 QWW,aM. For larger towns the ratio QWW,d,85 /QWW,aM with ca. 1.15 and xQmax = 16 can be applied. With this 2 QWW,max,85 = 3.5 QWW,aM. Using this approach up until now in small towns relatively much and in large cities relatively little stormwater has been accepted in the wastewater treatment plant. Editorial note: ATV Standard ATV-A 131E (1991) is no longer the valid dimensioning regulator. Currently, for the dimensioning of single-stage activated sludge plants, ATV-DVWK-A 131E (May 2000) is valid. The explanatory notes given at this point for the determination of the combined wastewater flow serve for the better understanding of the procedure in ATV-DVWK Standard ATV-DVWK-A 198E.
Within the sense of pollution control, equal treatment of large and small residential areas is to be sought. In order also to ensure that, with the start [Authors’ afternote: due to rainfall] of combined wastewater flow, the ammonia concentration in the plant effluent does not increase too sharply, it would be sensible to limit the combined wastewater flow QCW uniformly to QComb = 6 · QWW,aM + QInf,aM [corrected from QInf,pM] Instead of the rigid factor of 6 in the equation above a bandwidth of the factor for the wastewater flow fWW,QCW (Fig. 1), however, shall be used for calculation. Through this an optimisation between the necessary storage volume for stormwater in the sewer system and the loading capacity of the wastewater treatment plant is made possible. The factor should be selected between 6 and 9 for small catchment areas and between 3 and 6 for wastewater treatment plants of large cities. The
ATV-DVWK-A 198E combined wastewater flow QCW, using the factor selected from Fig. 1, results as follows: QComb = fWW ,QCW ⋅ QWW ,aM + QInf ,aM
[l/s]
(8)
The annual mean of the infiltration water flow QInf,aM is to be determined according to Chap. 4.2.2.4. If the infiltration water flow is subject to a marked seasonal variation and the highest monthly mean QInf,mM,max, for example, is more than twice the annual mean, a higher infiltration water flow is, if necessary, to be applied in order still to ensure an emptying of the stormwater tanks with the daily peak of the dry weather flow. Seen as an advantage of this approach is that the mean wastewater flow QWW,aM can present the same initial basis both for the layout of combined sewer overflows and also for the combined wastewater flow to the wastewater treatment plant.
If no water consumption data is available the inhabitant specific wastewater yield can be assumed to be wWW,d = 100 to 150 l/(I·d). The area-specific industrial respectively commercial wastewater discharge rate qInd in l/(s·ha) is to be estimated for areas with firms producing little wastewater (commerce, offices, certain firms, for example, wood processing) on the basis of the number of employees and, if necessary, visitors. Here, it should be avoided that employees resident in the catchment area are additionally included with the firms. If water-intensive firms, for example food processing, are based in the catchment area surveys of the water consumption and/or the wastewater flow are to be undertaken. The annual mean the dry weather flow is: QDW ,aM = QWW ,aM + QInf ,aM
[l/s]
(10)
For the infiltration water flow see Chap. 4.2.2.3. If no measured values are available a sensible assumption must be made and justified. If no measured data are available the daily peak of the wastewater flow can be determined with the aid of divisor xQmax in accordance with Fig. 2. In this the lower line can be related approximately to QWW,max or QWW,h,max and the upper line to QWW,2h,max. The daily peak flow with dry weather thus results as follows: Q DW ,max , Q DW ,h ,max resp . Q DW ,2 h ,max =
Fig. 1: Range of the factor fWW,QComb for the determination of the optimum combined wastewater flow to the wastewater treatment plant on the basis of the mean annual wastewater flow
24 ⋅ QWW ,aM x Q max
+ Q Inf ,aM
[l/s] (11)
4.2.3 Flow Data on the Basis of Empirical Values The annual wastewater flow QWW,aM in l/s can be estimated on the basis of the inhabitant-specific wastewater yield wWW,d in l/(I·d) as well as the area-specific commercial and/or industrial wastewater discharge rate qInd in l/(s·ha) as follows:
QWW ,aM =
P ⋅ w WW ,d 86400
+ AC ,Ind ⋅ q Ind
[l/s]
(9) Fig. 2: Divisor xQmax dependent on the size [number of residents] of the [catchment] area [Authors’ afternotes]
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21
ATV-DVWK-A 198E Further suitable estimated values for dimensioning or for plausibility checks are to be found, application specific, in the relevant ATV-DVWK Standards and Advisory Leaflets.
4.3
Determination of Loads and Concentrations
4.3.1
Determination through Evaluation of Measured Values
4.3.1.1 Sampling Frequency and Necessary Parameters As prerequisite for the assessment of available data and/or the planning of a sampling it must be known for which purpose the data are to serve. Subsequently the necessary parameters and the frequency of sampling are to be laid down. The necessary parameters result in accordance with the relevant ATV-DVWK Standards, see Chap. 3.3.2. The BOD5 load in the inflow with dry weather without internal return flows is relevant for the size classification of wastewater treatment plants, see Chap. 3.3.2.1. The annual mean value of the concentration of the COD in the inflow with dry weather is required for the dimensioning of stormwater overflow facilities in accordance with ATV Standard ATV-A 128E (1992), see Chap. 3.3.2.2. For this it is sufficient once in every month with dry weather, to determine a daily COD load of the inflow to the wastewater treatment plant not loaded by internal backflows. The mean concentration CCOD,In,aM is the quotient of the sum of the COD loads and the sum of the flows of days from which the loads have been formed. If measured values of the raw wastewater inflow are not available in sufficient numbers, CCOD,In,aM, can be extrapolated approximately from the mean COD load in the effluent from the primary settling stage, taking into account the measured settling effect of the primary settling tanks. For the dimensioning of the biological treatment stage with nitrogen and phosphorus removal, as a rule the following necessary parameters in the in-
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flow to the biological stage are to be determined (see Chap. 3.3.2.3): – – – –
CBOD,InB in mg/l, CCOD,InB and, if required, SCOD,InB in mg/l, XSS,InB and, if required, XinorgSS,InB in mg/l, CTKN,InB, SNH4,InB, SNO3,InB, and, if required, SNO2,InB in mg/l, – CP,InB in mg/l, – SAlk,InB in mmol/l. In order to keep the costs for chemical analysis within limits, the relatively easy to determine COD is introduced as master parameter. CCOD is to be determined frequently, if possible daily. The other necessary parameters can be analysed less frequently. Using the ratio values determined on the basis of the measurements, loads and the relevant concentrations of the less frequently analysed parameters can be calculated.
For the determination of the relevant 2- and 4weekly means of the COD loads (master parameter), the calendar weekly mean of the COD (Bd,COD,wM) is introduced as auxiliary for the dimensioning of activated sludge plants. At least 4 daily loads of a calendar week are required for the creation of a weekly mean. Note: At least 5, better 6 days of each calendar week must be sampled in order to obtain 4 usable COD daily loads in the case of freak values, for example obvious errors in analysis.
If the seasonal variation of the daily loads is known, the intensive sampling can be limited to respectively 4 to 10 weeks, for example in the cold and warm seasons and, if required, to seasonally weak or high load periods. For each period the maximum 2- or 4-weekly mean of the COD loads are to be formed from the means of coherent weeks (sliding mean value). For the determination of the parameters of the sewage sludge, in view of the possible heavy fluctuations both of the volume and of the concentration, the daily determination of the solids concentration (DRSl in kg/m3) as well as of the organic fraction (oDRSl in %) is recommended several times a year in periods of two and more weeks. The associated daily volume (QSl in m3/d) is to be documented for the determination of the daily mass of [sludge] solids.
ATV-DVWK-A 198E 4.3.1.2 Examination of Available Information Using the available records of the daily sewage flow, the concentration of certain parameters and thus the calculated loads the following questions are first to be clarified: – are the measured values plausible? Do, for example, the ratio values of parameters deviate significantly (more than 20%) from the values according to Table 1, then the cause should be explored. – is there a trend within the last 3 to 4 years with the sewage flow, the pollutant loads and/or the ratio values of certain parameters, for example COD/N, to be observed? Are there reasons for the observed trend? Is the sewage flow, for example, influenced by the annual precipitation? Loads can, for example, be influenced through decrease or new establishment of commercial and/or industrial activity. If there is a trend with the loads or with the relationship of certain parameters which has a gradient of more than ±10% per year then the data from previous years have only a limited value for application. – has a seasonal variation of the [daily] sewage [flow] produced, the pollutant loads and/or of the ratio values of certain parameters, for example COD/N, been observed? Are there reasons for this variation, for example seasonal operating industry, tourism, infiltration water? If the monthly mean of the period with higher or lower loading deviates by more than 20% of the annual mean, then the data is to be evaluated separately for typical periods of the year. – does the frequency of the previous sampling suffice for the current questioning? – do the parameters previous analysed routinely suffice for the current questioning? Then the following two situations are possible for further action: 1. The current routine sampling is insufficient with regard to the frequency of sampling and/or the parameters investigated. As a possible seasonal variation is to be recorded the routine analysis is to be intensified appropriately. Thereby a sampling for the determination of the relationship of the highest daily 2-hourly TKN
load to the mean daily TKN load can be taken up, comp. 4.3.1.8. 2. The current routine sampling with regard to frequency of sampling as well as the parameters examined for the recording of the seasonal variation is considered essentially to be sufficient. In favourable cases calendar-weekly means of the COD loads can be created for interesting periods or there are available at least 40 evenly distributed COD loads for the determination of the 85% value. Previously unmeasured parameters can, in addition to the master parameter COD, be determined in a two to four week continuous sampling. The ratio of the highest daily 2-hourly TKN load to the mean daily TKN load (peak factor) can also be determined, comp. Chap. 4.3.1.8.
4.3.1.3 Location of the Sampling In wastewater treatment plants there are practically only three locations for a representative sampling: the raw sewage inlet, the outlet from the primary settling stage or the inlet to the biological stage and the outlet to the surface [receiving] waters. Basically the sample from the raw sewage is to be taken at a location with sufficient turbulence, if necessary mixers or a chicane are to be installed for the sampling. If several main sewers discharge into one wastewater treatment plant and the separate determination of the loads of the individual main sewer is necessary for a certain question, attention is to be paid that, in addition to the sampling, flow measurements for each main sewer must also be available. For practical reasons the sampling for the raw sewage, takes place usually in the outlet of the grit chamber. At this location, if applicable, the streams from different main sewers are well mixed. If a pumping station is upstream from the sampling point in many cases the internal return flows from sludge treatment are fed in there. In particular, due to thickener overflows which are [may be] heavily
April 2003
23
ATV-DVWK-A 198E loaded with suspended solids, the organic loading can also be increased. If possible the loads of sludge liquor and faecal matter discharges should be determined separately with an inflow sampling. A possible discharge of filter washing water should also be recorded. The advance construction of a sludge liquor equaliser can be sensible. This is, in any case, expedient for all types of advanced sludge liquor treatment; even without liquor treatment, in particular, with surge-type sludge liquor production, an equaliser is strongly recommended. At many points the fraction of the nitrogen load to the nitrogen load of the plant is properly identified through the deliberate collection and volume flow measurement of the sludge liquor. If the sampling serves for the creation of the basis for the expansion of the biological stage of a wastewater treatment plant, then one should bear in mind that, with the expansion this, in many cases, is accompanied by process changes in the area of the mechanical [primary] stage. Thus, under certain circumstances, consideration can be given to reducing the existing too large a primary settling tanks and/or to carry out a separate treatment or an equalising of the centrifuge/filter effluent of the sludge dewatering facility. With a planned reduction of the primary settling stage the question arises whether a sampling of the outflow of the (too large) primary settling stage provides false values. The alternative is therefore seen frequently in the sampling of the inflow to the wastewater treatment plant, which however, can also deliver problematic values (see above). One usually makes the lesser error if one samples the effluent of the existing primary settling stage and takes into account a possible later reduction of the volume through a slight increase of the organic loads. With sampling attention must be paid to the internal back-flows (surplus [waste activated] sludge, process water etc.) into the primary settling stage. For sampling for the determination of the parameters of the sewage sludge see Chap. 3.3.2.3.
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April 2003
4.3.1.4 Summary of Measured Data and Calculation of the Daily Load as well as the Values of the Concentration Ratio The calculation of the COD loads and the ratio values of the less frequently measured parameters to the master parameter COC normally takes place in tabular form. In Appendix C an evaluation is demonstrated as an example. The following are to be listed for a period of approximately one year: 1. Date and day of the week (the latter to identify the effects of the weekend). 2. Characterisation of the dry weather days. 3. Wastewater temperature in the effluent from the biological reactor, alternatively in the wastewater inflow to or effluent from the primary settling stage. The 2-weekly mean of the temperature should be produced separately for at least two of the preceding years. 4. Sludge Volume Index SVI in l/kg. The 2-weekly mean should be produced for at least two of the preceding years. 5. Daily wastewater flow Qd in m3/d. 6. Dry weather flow QDW,d in m3/d (combination of 2 and 5 or determined arithmetically, comp. Chap. 4.2.2.1, Para. 4). 7. Measured concentrations in mg/l from 24 hourcomposite samples from the inflow into the biological stage: – COD homogenised, CCOD,InB – COD of the filtrates of the sample, SCOD,InB – BOD5 homogenised, CBOD,InB – suspended solids, XSS,InB – Kjeldahl nitrogen, TKN, homogenised, CTKN,InB – ammonia nitrogen, SNH4,InB – nitrate nitrogen, SNO3,InB – total phosphorus, homogenised, CP,InB – alkalinity, SAlk,InB in mmol/l 8. Calculation of the COD loads in the inflow to the biological stage: – COD daily load, Bd,COD,InB in kg/d (= Qd · CCOD,InB/1000). – weekly mean (calendar week) of the COD load Bd,COD,InB,wM in kg/d, can be produced if at least four daily loads have been determined in the week. 9. Calculation of the ratio values of the concentrations: – dissolved [filtered] to homogenised COD, SCOD,InB / CCOD,InB
ATV-DVWK-A 198E – – – – – –
BOD5 to COD, CBOD,InB/CCOD,InB suspended solids to COD, XSS,InB/CCOD,InB Kjeldahl nitrogen to COD, CTKN,InB/CCOD,InB ammonia nitrogen to COD, SNH4,InB/CCOD,InB phosphorus to COD, CP,InB/CCOD,InB alkalinity to COD, SAlk,InB/CCOD,InB
4.3.1.5 Determination of the Relevant Loads on the Basis of Weekly Means The following load cases can be differentiated for the dimensioning of activated sludge plants:
The inflow of sludge liquor, significant discharges of faecal sludge and filter washing water should at least be documented through details of the start and finish of each discharge; also necessary is the recording of the volumes discharged. These details are particularly useful on days with investigations for the peak factor, as irregularities can be identified. For plants with sludge digestion and mechanical dewatering the following are, for example, to be documented:
Load with the dimensioning temperature The relevant 2- or 4-weekly mean of the organic load (Bd,COD,InB,2wM) is found in the period in which the 2-weekly mean of the temperature (T2wM) lies in the range of the dimensioning temperature (Tdim). Using the ratio values CBOD,InB/CCOD,InB, CTKN,InB/CCOD,InB, XDS,InB/CCOD,InB and CP,InB/CCOD,InB one finds the associated loads and concentrations of the other parameters.
– daily volume of sludge liquor QSl,d in m3/d (can be approximated with the daily volume of the sludge drawn from the digester). – ammonia nitrogen concentration of sludge liquor, SNH4,Sl. – start and finish (time) of the sludge liquor discharge. – ratio of the ammonia nitrogen load of the sludge liquor to the TKN load in the inflow to the biological stage.
Load with the lowest temperature It is to be examined whether the 2- (or 4-) weekly mean of the organic load for the lowest range of the temperature is higher by more than 10% than with Tdim. If this is the case then the proof of the maintenance of nitrification in accordance with ATV-DVWK-A 131E (2000) is based on the 2- (or 4-) weekly mean of the measured load. The under certain circumstances deviating ratio values CBOD,InB/CCOD,InB, CTKN,InB/CCOD,InB, XDS,InB/CCOD,InB and CP,InB/CCOD,InB are to be taken into account.
So far as no data is available about later sludge production and its properties, the back-flow loads can be estimated with the aid of empirical approaches [6]. In order in particular to identify seasonal influences it is recommended that the following annual time series are shown graphically: – – – –
wastewater temperature, comp. Fig. C-9 Sludge Volume Index COD loads, Bd,COD,InB, comp. Fig. C-10 weekly mean of the COD loads Bd,COD,InB,wM, comp. Fig. C-11 – 2- (or 4-) weekly mean of the COD loads Bd,COD,InB,2wM, comp. Fig. C-12 – ratio values CBOD,InB/CCOD,InB, CTKN,InB/CCOD,InB, XDS,InB/CCOD,InB and CP,InB/CCOD,InB, comp. Figs. C-15 to C 17
Load with the highest temperature For the layout of the aeration system the 2- (or 4-) weekly mean of the COD load for the range of the highest temperature (T2wM,max) as well as the associated ratio values CBOD,InB/CCOD,InB, CTKN,InB/CCOD,InB, XSS,InB/CCOD,InB and CP,InB/CCOD,InB are to be determined. Special load cases There are cases with commerce or industry which operate seasonally or in tourist areas with which the maximum organic and/or nitrogen loading do not fall within the three above load cases. For these the highest 2- (or 4-) weekly mean of the COD load, the associated wastewater temperature and the associated ratio values CBOD,InB/CCOD,InB, CTKN,InB/CCOD,InB, XSS,InB/CCOD,InB and CP,InB/CCOD,InB are to be determined.
At a glance one can identify the dependencies and dispersions of the [daily] inflows, loads and concentrations in a plot of the COD loads Bd,COD,InB via the wastewater flows Qd, comp. Fig. C-13.
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25
ATV-DVWK-A 198E 4.3.1.6 Determination of the Relevant Loads as 85 % Values The dimensioning of trickling filters and rotating biological contactors is to be based on the relevant BOD5 and TKN loads as 85% values. With this it is to be avoided that non-isochronous loads are combined together. It is assumed that, in addition to BOD5 and TKN, the COD is also determined and that the COD analysis is more reproducible than the determination of the BOD5 practised in wastewater treatment plants. Therefore the procedure should be as follows: 1. The COD load is determined which has been achieved or undercut in 85% of the cases. For this at least 40 daily loads Bd,COD,InB are required in kg/d. These can be distributed over a period of up to three years, provided there is no trend or seasonal variation of the BOD5 and/or of the TKN loads present, comp. Fig. C-14. If there is a marked seasonal variation present then periods of similar loads are to be selected and 85% values formed separately for these periods. In this case every period should also cover at least 40 values. 2. For all days in which samples are taken the ratio values CBOD,InB/CCOD,InB and CTKN,InB/CCOD,InB are formed and mean values are to be determined. Using the mean values of the ratios the relevant BOD5 load and the relevant TKN load can then be determined. If, in special cases, activated sludge plants are to be dimensioned with the 85% load value, one has to proceed accordingly. The load cases are named as under Chap. 4.3.1.5 with the exception that, as a rule, only the determination of the lowest and highest temperature is required. The relevant loads are the same in all cases unless, with the presence of a seasonal variation, two 85% values have to be determined.
4.3.1.7 Determination of the Relevant Concentrations If the relevant COD load has been determined as 2(or 4-) weekly mean, the relevant concentration CCOD from the relevant load Bd,COD,2wM and the mean of the dry weather flow of the associated sampling period (e.g. 6 weeks) are to be deter-
26
April 2003
mined; this value is designated as Qd,conc in m3/d. In the simplest case the mean dry weather flow of the period sampled is to be applied. If it is required to keep certain effluent concentrations, it is decisive which initial concentration has to be reckoned with, the correct assumption to the wastewater flow, therefore, has the greatest significance. At best the associated value of Qd,conc can be identified from the hydrograph curve of the flow also of previous years as in this way, for example, increased dry weather flows caused by high infiltration water flows, can be excluded. All further necessary concentrations can be obtained with the aid of the mean ratio values or on the basis of measured loads. If the relevant loads have been determined as 85% values in accordance with Chap. 4.3.1.6, then the monthly mean of the dry weather flow for the range of the dimensioning temperature is to be selected for the determination of the concentration.
4.3.1.8 Determination of the Peak Factor for Nitrogen In accordance with ATV-DVWK-A 131E (2000) the peak factor fN =
B 2 h,TKN,InB,max B d,TKN,InB
must be derived from measured values for the determination of the oxygen transfer. For this at least 14 days, if possible with dry weather, are to be sampled. The peak factor fN is determined for each day and finally the mean value is formed. If the ratio value CTKN,InB/CCOD,InB indicates a seasonal variation then in the appropriate periods respectively 14 days are to be sampled and two mean values for fN are to be produced. As, as a rule, one more or less knows the daily variation of the TKN load, it is usually sufficient, for example in the period from 10:00 h to 16:00 h, to analyse three 2-hourly samples and the daily composite sample, comp. Chap. C 2.7.
ATV-DVWK-A 198E 4.3.2 Estimation of Pollutant Loads and Concentrations on the Basis of Empirical Values If so few measured values are available that even an 85% value (comp. Chap. 4.3.1.6) cannot be determined and the recording of additional values is too expensive, there are the following possibilities for the estimation of the pollutant loads. – transfer of pollutant loads from analogously or similarly populated (structured) areas. – derivation of pollutant loads from the number of connected inhabitants and inhabitant-specific pollutant loads as well as the connected commercial and/or industrial areas using productionspecific values. Most convenient is the derivation of the pollutant loads using inhabitant-specific loads, as are listed in Table 1. Production-specific values of commerce and industry have, in the past, been frequently given for the purpose of comparison as population equivalents (PE). In the future, in accordance with DIN EN 1085, this must be given an index, which designates from what the value has been determined (e.g. PECOD,120 = 25,000 I, PEBOD5,60 = 15,000 I). Always necessary is the separate determination of the dimensioning-relevant values for BOD5, COD, suspended solids, nitrogen, phosphorus and, if required, further parameters. The area-specific wastewater flow rate from commercial/industrial areas is frequently applied as qInd = 0.5 l/(s·ha) with the dimensioning of the sewer system (in the planning stage) (comp. ATV-A 118E, 1999). This presents hourly peak values for the dimensioning of sewers and drains. These are not suitable for the determination of annual values of the wastewater flow and are to be appropriately reduced. It is not permitted to derive population equivalents from estimated wastewater flows from commercial areas and then determine loads using these. As an aid a minimum value for the loads can be found using the (estimated) number of those employed in the commercial area.
Table 1: Inhabitant-specific loads in g/(I·d), which are undercut on 85% of the days, see also ATV-DVWK StandardATV-DVWK-A 131E (2000)
Parameter BOD5 COD SS TKN P
Rawwastewater 60 120 70 11 1.8
After primary settling with retention time with QDW,2h,max 0.5 to 1.0 h 1.5 to 2.0 h 45 40 90 80 35 25 10 10 1.6 1.6
The monthly mean of the dry weather flow for the range of the dimensioning temperature should be used for the calculation of the concentrations. The flow value should be derived from measurements (comp. Chap. 4.2.2.1) or, if that is not possible, determination should be in accordance with Chap. 4.2.3. The concentrations determined with this must be compared with the measured values of the concentrations with dry weather. With heavy deviations, if required, a suitable value Qd,conc is to be selected. It should be noted that the calculated concentrations of COD and BOD5 as a rule are higher than measured concentrations. The reason for this is that, with the specific loads in Table 1, one is concerned with the 85% value and not with mean values. In individual cases higher inhabitantspecific loads of suspended solids (SS) were measured. With heavy seasonal differences different values for Qd,conc must be used as a basis. For the determination of the flow in the daily peaks with dry weather QDW,2h,max see Chaps. 4.2.2.5 or 4.2.3 and for the calculation of the combined wastewater flow QComb, see Chap. 4.2.2.6.
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ATV-DVWK-A 198E
5
Forecast Data
Forecasts are to be made according to the planning horizon of the facilities, if necessary separated according to structures, mechanical installations, measuring and control facilities etc. In Germany overall one assumes a reducing population number. It depends, however, in individual cases on the attractiveness of the communities whether one has to reckon with an increase or decrease of the number of inhabitants. At the same time the further development of the inhabitantspecific domestic water consumption is to be taken into account. Currently, in many places, the specific water consumption is stagnating, frequently it is rather decreasing Firms are increasingly applying water-saving production procedures. An increase of the wastewater production and of the pollution loads from firms already established is therefore to be expected only with mergers or the commissioning of new production lines. In urban land use planning normally additional residential and commercial areas are identified. The additional numbers of inhabitants are to be estimated very accurately on the basis of the characteristic numbers for building utilisation and to be assessed with possible changes (reductions) in other areas. With the commercial/industrial areas there should be differentiation between firms with low specific water consumption and those with medium to high water consumption (see Chap. 4.2.3 and ATV-A 118E, 1999). If no clear plans for certain [new] businesses exist, one should, as a rule, assume businesses with medium water consumption for the dimensioning of wastewater treatment plants. In larger catchment areas the forecast data for the dimensioning of wastewater treatment plants and for example the dimensioning of combined sewer systems may deviate from one another.
6
Costs and Environmental Effects
With this standard planners and examiners obtain a differentiated work basis for the derivation of di-
28
April 2003
mensioning values from measured data. False interpretations are avoided through the standardisation of the terms and symbols. Investment costs for wastewater facilities can, inter alia, be limited to the required degree through the specification of realistic dimensioning values. To that end existing measured data are to be evaluated and, if necessary, to be supplemented through well-directed investigations. The costs for this stand in no relation to the possible savings. In addition ways are indicated as to how the costs for chemical analysis can be limited to a justifiable degree without giving up any of the informative value.
7
Relevant Regulations, Standards and Standard Specifications
• Wastewater Ordinance Verordnung über Anforderungen an das Einleiten von Abwasser in Gewässer (AbwV). [(German) Ordinance on the Requirements for the Discharge of Wastewater into Surface Waters] Bundesgesetzblatt 2002, Part 1, No. 6 dated 2. 7. 2002 • ATV-DVWK Standards ATV-DVWK-A 110E Hydraulic Dimensioning and Performance Verification of Sewers and Drains ATV-A 111E Standards for the Hydraulic Dimensioning and Verification of Stormwater Overflow Installations in Sewers and Drains ATV-A 112 [Not available in English] Richtlinien für die hydraulische Dimensionierung und den Leistungsnachweis von Sonderbauwerken in Abwasserkanälen und -leitungen [Standards for the Hydraulic Dimensioning and Performance Verification of Special Structures in Sewers and Drains]
ATV-DVWK-A 198E ATV-A 116E Special Sewer Systems Vacuum Drainage Service – Pressure Drainage Service ATV-DVWK-A 117 [Not available in English in the latest version (2001)] Bemessung von Regenrückhalteräumen [Dimensioning of Stormwater Retention Facilities] ATV-A 118E Hydraulic Dimensioning and Verification of Drainage Systems ATV-A 126E Principles for Wastewater Treatment in Wastewater Treatment Plants According to the Activated Sludge Process with Joint Sludge Stabilisation with Connection Values between 500 and 5,000 Total Number of Inhabitants and Population Equivalents ATV-A 128E Standards for the Dimensioning and Design of Stormwater Structures in Combined Sewers ATV-DVWK-A 131E Dimensioning of Single-Stage Activated Sludge Plants ATV-A 134 [Not available in English in the latest version (2000)] Planung und Bau von Abwasserpumpanlagen [Planning and Construction of Pumping Stations] ATV-A 138 [Not available in English in the latest version (2000)] Planung, Bau und Betrieb von Anlagen zur Versickerung von Niederschlagswasser [Planning, Construction and Operation of Facilities for the Percolation of Precipitation Water] ATV-A 200E Principles for the Disposal of Wastewater in Rurally Structured Areas ATV-A 257E Principles for the Dimensioning of Wastewater Lagoons and In-line Biological Filters or Biological Contactors
ATV-DVWK-A 281E Dimensioning of Trickling Filters and Rotation Biological Contactors ATV-DVWK-M 153 [Not yet available in English] Handlungsempfehlungen zum Umgang mit Regenwasser [Recommendations on the handling of Stormwater] ATV-DVWK-M 177 [Not yet available in English] Bemessung und Gestaltung von Regenentlastungsanlagen in Mischwasserkanälen - Erläuterungen und Beispiele [Dimensioning and Design of Stormwater Overflow Facilities in Combined Sewers - Explanatory Notes and Examples -] • Standard Specifications EN 752-1: 1995 Drain and sewer systems outside buildings, Part 1: Generalities and definitions EN 752-2, 1996 Drain and sewer systems outside buildings, Part 2: Performance requirements EN 752-3, 1996 Drain and sewer systems outside buildings, Part 3: Planning EN 752-4, 1997 Drain and sewer systems outside buildings, Part 4: Hydraulic design and environmental considerations EN 752-5, 1997 Drain and sewer systems outside buildings, Part 5: Rehabilitation EN 752-6, 1998 Drain and sewer systems outside buildings, Part 6: Pumping installations EN 752-7, 1998 Drain and sewer systems outside buildings, Part 7: Maintenance and operations EN 1085, 1997 Wastewater treatment – Vocabulary; Trilingual version
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29
ATV-DVWK-A 198E DIN 4045, 1985 Wastewater engineering; Vocabulary DIN 4049-3, 1994 [Not yet available in English] Hydrologie – Teil 3: Begriffe der quantitativen Hydrologie [Hydrology - Part 3: Terms for quantitative hydrology] EN 12255-11, 2001 Wastewater Treatment plants - Part 11: General data required
[3]
Fuchs, S., Lucas, S., H. Brombach, Weiß, G. and Haller, B.: Fremdwasserprobleme erkennen - methodische Ansätze [Identification of Infiltration Water Problems Methodic Approaches]. KA - Abwasser, Abfall 50 (2003), 28 - 32
[4]
ATV-A 131E (1991): Dimensioning of SingleStage Activated Sludge Plants upwards from 5,000 Total Inhabitants and Population Equivalents
[5]
Schleypen, P. and Meißner, E.: Abflüsse aus Kanalisationsgebieten und Zuflüsse zu kommunalen Kläranlagen bei Trockenwetter- und Regenwasserverhältnissen [Flows from Areas with Sewers and Flows into Municipal Wastewater Treatment Plants with Dry Weather and Wet Weather Conditions]. Korrespondenz Abwasser 46 (1999), 42 - 46 ATV-DVWK-Arbeitsbericht: Rückbelastung aus der Schlammbehandlung - Menge und Beschaffenheit der Rückläufe [Loads from Sludge Treatment - Quantity and Properties of the Return Flows]. Korrespondenz Abwasser 47 (2000), 1181 -1187
DIN 38404-3, 1976 German standard methods for the analysing of water, wastewater and sludge: physical and physicalchemical parameters (Group C); Determination of absorption in the field of UV radiation (C3)
8
Literature
[6]
[Translator’s note: Apart from [4] no known translation available in English] [1]
[2]
30
ATV-Arbeitsbericht „Simulation von Kläranlagen“ [ATV Report “Simulation of Wastewater Treatment Plants”]. Korrespondenz Abwasser 44 (1997), 2064-2074. ATV-Arbeitsbericht „Grundlagen und Einsatzbereich der numerischen NachkläbeckenModellierung“ [ATV Report “ Principles and Area of Application of Numerical Modelling of Secondary Settling Tanks]. Korrespondenz Abwasser 47 (2000), 893-896.
April 2003
[7]
Schmitt, T. G., Illgen, M.: Abflusswerte in der Bemessung und Abflusssimulation von Entwässerungsanlagen [Flow values in the Dimensioning and Flow Simulation of Drainage Systems]. KA - Wasserwirtschaft, Abwasser, Abfall 48 (2001), 1720 - 1728
[8]
Stier, E., Fischer, M. and Felber, H.: Betriebstagebuch für Kläranlagen [Logbooks for Wastewater Treatment Plants]. F. Hirthammer Verlag, München
ATV-DVWK-A 198E
Appendix A: Explanatory notes for surface characteristic values and catchment area related values Due to the large effect of the surface characteristic values (catchment areas and parameters) and the surface-related characteristic values on the wastewater engineering calculations, standard definitions for the comprehension of terminology as well as clear specifications on the arithmetical determination of the individual quantities are particularly important. The terminological determination of these quantities as well as their significance and quantitative determination are explained in detail below. Particular attention is drawn to the catchment area and the runoff coefficients.
A1
Surface characteristic values
A 1.1
Surface areas
In future, with wastewater engineering calculations, only the terms and symbols defined in Fig. 1 are to be applied. All other derived area specifications such as, for example, Aimp, are numerical values which can be additionally calculated depending on the application.
• Catchment area AC [ha] Surface of a catchment area, e. g. surface area of a wastewater disposal catchment. The catchment area must be clearly bounded in accordance with the respective problem. For more detailed characterisation of the surface AC further indices are added, for example AC,s as catchment area with sewers (see below.) etc. • Sewered catchment area AC,s [ha] Surface of the catchment area served by sewers or other types of drainage system. For construction areas the boundaries of the catchment area with sewers are as a rule laid down corresponding with the boundaries of the parcel of land which is connected through the drainage system. The surface of the outer area possibly drained in the direction of the development is not included in this. In areas with separate sewer systems AC,s for the wastewater and stormwater sewers may be different. • Catchment area without drainage system AC,ns [ha] Catchment area without sewers or not covered by a drainage system. The drainage area without sewers AC,ns results as the difference between the surface of the catchment area AC and the surface of the catchment area with sewers AC,s: AC,ns = AC – AC,s
(A-1)
• Paved surface area AC,p [ha] Sum of all paved surfaces of a catchment area.
Fig. A-1:
Schematic representation for catchment area definition (not a plan drawing!)
The quantity AC,p includes all paved sub-areas in the catchment under consideration, independent of whether these surfaces are connected to the drainage system and a discharge into the sewer system takes place. The designation AC,p replaces the quantity Ared which is contained, inter alia, in the ATV Standard ATV-A 128E (1992).
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ATV-DVWK-A 198E Paved surfaces can be impermeable (tiled, metal or glass roofs, asphalt roads) or be of different permeability (gravel paths, grassed ballast). Their flow effectiveness is described via application-specific runoff coefficients ψ (see A 1.3). • Unpaved surfaces AC,np [ha] Sum of all unpaved surfaces of a catchment area as the difference between total catchment area and paved catchment area under consideration, general: AC,np = AC – AC,p
(A-2)
The possible runoff contribution of unpaved surfaces and their consideration in the design or with flow calculations is dependent on the local circumstances (ground slope, limitation of the parcel of land, structural facilities) and the respective problem. Unpaved areas can have a considerable contribution in particular with the consideration of less frequent heavy rainfall events in the sewer network calculation or the dimensioning of stormwater retention facilities. • Industrial catchment area AC,Ind [ha] Area of a commercial or industrial catchment. The industrial catchment area AC,Ind refers in general to the catchment of commercial or industrial areas identified in the development plan. For definition or more detailed description further indices can be applied, e.g. as area with sewers AC,Ind,s.
A 1.2 Calculated value “Impermeable surface” Aimp Application-related calculated value for quantifying the portion of the catchment area from which the stormwater runoff, following deduction of the wetting effect and filling of depression storage, entirely gets runoff effective in a drainage system.
Aimp is a calculated quantity and is a nonmeasurable surface area in a locality. It results from the application-related precipitation runoff balance of a catchment area: hP ⋅ AC ⋅ ψ = hP ⋅ Aimp => Aimp = AC ⋅ ψ
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April 2003
(A-3)
The quantity Aimp, through the coupling with the application-specific runoff coefficient ψ (see above), is event-dependent and represents the respective “runoff-effective surface”. Aimp is determined in the concrete application case from the sum of all sub-surfaces AC,i connected to the drainage system, multiplied by the associated application- and surface-specified discharge coefficient ψi: Aimp = Σ (AC,i ⋅ ψi)
(A-4)
With restriction to paved sub-areas AC,p,i and exclusion of the unpaved surfaces, the following simplification applies: Aimp = Σ (AC,p,i ⋅ ψi)
(A-5)
In ATV Standard ATV-A 128E (1992) Aimp is defined with reference to the annual amount of stormwater runoff as long-term mean and limitation to the paved surface AC,p (Ared in accordance with A 128E (1992)). For these, Aimp,A128 is determined via the runoff coefficient ψA128,i of the paved sub-areas AC,p,i determined with the same reference. Paved sub-areas not connected to the sewer system are evaluated here with ψA128,i = 0.0 (see A 1.3). Aimp,A128 = Σ (AC,p,i ⋅ ψA128,i)
(A-6)
If no differentiated consideration of the individual surfaces takes place within the drainage area, Aimp is to be set equal to the paved surface AC,p. Stormwater runoff models as a rule contain distinct modelling approaches for the calculation of the losses (flow formation) and should therefore build upon the actual connected surface area AC,s or, with the disregard of the contribution to the runoff of non-paved surfaces, upon the paved surface AC,s,p. The surface approaches used as a basis are to be identified.
A 1.3
Degree of paving and runoff coefficients
• Degree of paving γ [-] corresponds with the fraction of the paved surfaces in the overall catchment area; generally:
γ =
AC ,p AC
(A-7)
ATV-DVWK-A 198E As a rule the degree of paving refers to the catchment area with sewers AC,s. Indices can be employed for elucidation and further differentiation, e.g.:
γC,s = AC,p,s / AC,s.
(A-8)
In built-up areas the degree of paving results from the assessed size of the paved surface areas (see A 1.1) and the associated overall catchment area. With planned developments the degree of paved areas is selected on the basis of specifications on the type and extent of the constructional utilisation from the development plan (empirical values). • Runoff coefficient ψ [-] application-related coefficient quantifying the runoff effective precipitation fraction; calculation as quotient of runoff and associated precipitation quantity, depending on the problem, as ψm, ψs etc. The runoff coefficient of a catchment area is always to be given as application-related according to the respective problem. It is, to a large degree, dependent on the local conditions (i. a. surface properties and ground slope, type of property drainage and implementation of (decentralised) measures of stormwater management) as well as on the precipitation event or period considered. With existing systems and clearly defined sub-catchments the coefficient of discharge can be determined mathematically via a discharge and precipitation measurement. With runoff coefficients, in addition to the application reference, it is to be differentiated whether they are given as dimensioning value or as result of a discharge/flow calculation, see also [7]. a) Runoff coefficients for dimensioning (design) Runoff coefficients are used for various dimensioning details. They serve for the determination of a flow quantity (flow in l/s or m3/s; volume in m3) from a specified precipitation loading (e.g. block rain with rainfall intensity r in l/(s⋅ha) or amount of precipitation in mm together with a surface area). The size of the selected runoff coefficients has a deci-
sive influence on the result of the runoff calculation. In specialist literature there exist standard values for different problems and dimensioning details, if required broken down for various precipitation loads as well as types, uses and slopes of surfaces. The standard values can be converted, using surface-weighted meaning, to area-specific coefficients of runoff and adopted in simplified approaches for the determination of discharge (e.g. as coefficient of maximum discharge ψs in the time coefficient process). Discharge coefficients for dimensioning can, quantitatively, be specified only together with their application reference. This is to be given. It can be elucidated using additional indices, for example ψs as coefficient of peak runoff or ψm for a defined period (see below). b) Runoff coefficients as calculation result of discharge modelling Runoff coefficients can be derived as calculation result from the application of precipitation runoff modelling. These determine the resultant runoff directly from the specified precipitation loading, the surface characteristic values and the model parameters for the flow formation. Here the runoff coefficients result again with different reference - as ratio value of calculated discharge quantity (flow in l/s; flow volume in m3) to the associated, specified precipitation loading (momentary or mean rainfall intensity in l/(s⋅ha) or amount of precipitation in mm together with the catchment area).
• Mean runoff coefficient ψm [-] Quotient from flow volume and precipitation volume for a defined period (e.g. limited precipitation event or seasonal period). The mean runoff coefficient ψm can, depending on the problem, refer to a limited, individual precipitation event or a defined period, e.g. as annual value in the long-term mean. In this way it is used in the ATV-DVWK Advisory Leaflet ATVDVWK-M 153 (2000) [not available in English] as event-related value - with reference to heavy rain appropriate to the question. As long-term annual mean value it serves in ATV Standard
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33
ATV-DVWK-A 198E ATV-A 128E (1992) for the estimation of the discharge-effective annual amount [height] of precipitation hP,a,eff. As dimensioning [design] value, ψm allows the determination of the runoff amount of precipitation of a specified precipitation loading or a discharge volume with inclusion of the associated surface area in accordance with Eqn. A-9.
The specification should always be with reference to a specified precipitation event (amount of rain hP and duration D) or an appropriate range of values. hP,eff = hP ⋅ ψm or VPR = 10 · hP ⋅ ψm ⋅ AC,s
(A-9)
with hP hP,eff VPR AC,s
– – – –
amount [height] of precipitation in mm discharge effective precipitation [rain] in mm precipitation runoff volume in m3 catchment area with sewers in ha
In the same way ψm can be determined via Eqn. (A-9) as result of a measurement of the amounts of precipitation and runoff for a clearly defined area AC,s. As calculation result of the runoff modelling
ψm in accordance with Eqn. (A-10) is determined as
ψm = VPR / (10 · hP ⋅ AC,s)
(A-10)
The amount of precipitation hN specified in the calculation and the calculated loss hL,i can refer to a limited, individual event or a defined period of time, e.g. one year, or can represent the long-term mean. • Peak runoff coefficient ψs [-] Quotient from the peak runoff rate qmax and associated maximum rainfall intensity rmax, in the first instance for flow time procedures and block rain. The peak runoff coefficient ψs (previously also runoff coefficient during storm peak) refers to an individual rainfall event (e.g. dimensioning rainfall) and is adopted in the sewer network calculation in accordance with ATV Standard ATV-A 118E (1999) together with flow time procedures
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and block rain. It is defined as quotient of the maximum amount of precipitation runoff to the maximum rainfall intensity defined via Eqn. (A11)
ψs = qmax / rmax with qmax rmax
– –
(A-11) maximum runoff rate in l/(s⋅ha) maximum rainfall intensity in l/(s⋅ha)
Eqn. (A-11) is oriented on the consideration of precipitation of constant intensity and the application of flow time procedures for the calculation of maximum discharges in dimensioning in accordance with Eqn. (A-12). Qmax = AC,s ⋅ rD,n ⋅ ψs with Qmax rD,n
– –
(A-12)
calculated maximum discharge in l/s rainfall intensity (block rain) for the duration D and frequency n in l/(s⋅ha)
The specification of peak runoff discharge coefficients for the dimensioning should always be with reference to a certain rainfall intensity or an appropriate range of values. The peak runoff coefficient ψs can be identified via Eqn. (A-11) as result of a runoff modelling. Through the employment of time-variable precipitation (for example model rainfall) and statements on loss (initial losses, long-term losses) using Eqn. (A-11) both the significantly reduced as well as essentially increased coefficients of maximum discharge in comparison with the standard values in literature can result. While discharge models reflect the surface runoff for rainfall events of “arbitrary” magnitude (for example return times Tn = 0.5 years to Tn = 50 years), the coefficients of maximum discharge named in literature are derived and can be used in regulation for a narrowly limited range of rainfall intensities (for example reference rainfall intensity r15,n). • Runoff coefficient ψA128 [-] application-related runoff coefficient in accordance with ATV Standard ATV-A 128E (1992) and/or Advisory Leaflet ATV-DVWK-M 177 (2001) [not available in English] for the determination of the calculation value Aimp,A128 from the size of the paved surface area AC,p.
ATV-DVWK-A 198E In the context of ATV-A 128E (1992) and ATVDVWK-M 177 (2001) the runoff coefficient ψA128 corresponds with the ratio value between the calculation value Aimp,A128 and the paved surface area AC,p
ψA128 = Aimp,A128 / AC,p or Aimp,A128 = AC,p ⋅ ψA128 (A-13) and at the same time serves for the valuation of the contribution of pervious paved areas to the runoff. With limitation to the paved surfaces it describes the part of the surface which, in the annual mean, after covering wetting and filling of hollows, contributes entirely to the runoff. The runoff coefficient ψA128 thus serves for the valuation of the flow reducing effect of impervious or pervious paved areas in the catchment related to the problem in ATV-A 128E “Dimensioning of Stormwater Overflow Facilities”. Its magnitude is influenced by the type of surface pavement and, possibly, through the type of soil and the covering of vegetation. Impermeably paved sub-surfaces (roofs, asphalt roads etc.), by definition, have a coefficient of discharge ψA128= 1.0. Permeable surface pavements are evaluated according to their effectiveness with the relevant rainfall event with coefficients of discharge ψA128 < 1.0. Thus, in the difference to 1.0 the coefficient of discharge ψA128 quantifies the flow reducing effect of the percolation whereby, with the application ATV-A 128E, relief-relevant precipitation events are in the foreground. Paved areas, which can be verified as not being connected to the drainage system, are valuated as ψA128 = 0.0.
Advisory Leaflet ATV-DVWK-M 177 (2001), for selected types of surface, contains different runoff coefficients ψA128 for application in the design process in accordance with ATV-A 128E (1992). With this a detailed determination of the calculated quantity Aimp,A128 according to Eqn. A-6 can take place (see numerical example below).
[with hL,perc hP hL,W+M
loss due to percolation amount of precipitation loss due to wetting (W) and suppression storage (M) effects]
From long-term simulation, coefficients of discharge ψA128 significantly smaller than identified in Advisory Leaflet ATV-DVWK-M 177 (2001) can result through the involvement of all rainfall events in the annual period.
A 1.4 Numerical example for surfaces and surface parameters AC AC,p AC,np AC,s,p AC,s,np γC,s
120 ha 100 ha 20 ha (AC,np = AC – AC,s) 40 ha 60 ha (AC,s,np = AC,s – AC,s,p) = AC,s,p / AC,s = 40 / 100 = 0.40
Using the value calculated in Table A-1 ψA128 = 0.83 one obtains: Aimp,A128 = AC,s,p ⋅ ψA128 = 40 ⋅ 0.83 = 33.2 ha Table A-1: Example for the determination of the runoff coefficient ψA128 (various subsurfaces of a residential area assumed as examples and ψA128,i - values in accordance with ATV-DVWKM 177 (2001)) Type of surface
Surface frac-
ψA128,i
AC,s,p·ψA128,i
tion
[-]
[-]
AC,s,p[%] Roof surfaces
30 (0.30)
1.00
0.3
Roads, asphalt
25 (0.25)
1.00
0.25
Parking areas and
20 (0.20)
0.85
0.17
10 (0.10)
0.75
0.075
Grassed ballast
5 (0.05)
0.60
0.03
Non-connected
10 (0.10)
0.00
0
ψA128
0.825 ≈
places, courtyards, continuous pavement Parking areas, courtyards, jointed pavement
For the identification of the coefficient of discharges ψA128 in flow models - referred to individual surfaces or the (sub-) catchment area under consideration - the employment of the definition equation (A-14) is recommended.
ψA128 = 1 – (hL,perc / (hP – hL,W+M) )
paved surfaces 0.83
(A-14)
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ATV-DVWK-A 198E A. 1.5 Catchment area related values • Concentration [flow] time tf [min] Time, which the relevant stormwater runoff requires from the catchment area to a determined point of the drainage system. The concentration time is an auxiliary value for the characterisation of the flow behaviour with rainfall. It is determined for existing sewer systems via the maximum flow rate with dimensioning rainfall and the lengths of the individual sewers and channels. With new planning, as an approximation, one assumes the flow velocity with complete filling of the selected profile. With extreme dissimilar flows and at confluences, branches and special structures which effect a marked change of the discharge wave through throttling, storage and/or reduction (flattening, extension), special considerations are to be made depending on the problem. • Surface ground slope IG [%] Gradient of an area, details are in % and is frequently allocated to slope groups (Table A-2). Table A-2:
Slope groups SG of the ground slope IG (e.g. in accordance with ATV-A 128, 1992)
Slope Group SG 1 2 3 4
Ground slope IG ≤1% 1%-4% 4 % - 10 % > 10 %
The mean ground slope characterises the gradient conditions in the respective catchment area independent of the prevailing flow direction in the sewers.
A2
Surface reference parameters
• Population density PD [I/ha] Quotient from the number of inhabitants (I) and the area of the catchment. With the consideration of existing areas the population density can be calculated from the number of inhabitants and the associated surface, whereby this is often related to the surface area with sewers AC,s (PD = I / AC,s). With
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April 2003
planned areas the population density, for example from existing development plans, is adopted. With this the respective reference surface area is to be observed. • Industrial wastewater discharge rate qInd [l/(s⋅ha)] Industrial wastewater flow QInd referred to the catchment area AC,Ind of the commercial or industrial area under consideration. With the planning of commercial and industrial areas the quantity qInd can be selected from empirical values. If the calculation refers to existing areas the industrial wastewater discharge per unit area can be calculated from the flow QInd and the associated area. It should be given related to the surface area of the commercial or industrial area AC,Ind,s which has sewers. • Infiltration water discharge rate qInf [l/(s⋅ha)] Infiltration water flow QInf (with dry weather) related to the catchment area with drainage system AC,s under consideration. With new planning of residential and commercial/industrial areas the infiltration water discharge qInf is used for the estimation of the anticipated amount of the infiltration water flow. With the consideration of existing areas it can be determined from the infiltration water flow QIW and the associated surface. For reasons of comparability it should always be related to the area with sewers AC,s. • Stormwater discharge rate in sanitary [sewage] sewers qR,Sep [l/(s⋅ha)] Unavoidable stormwater runoff QR,Sep in sanitary sewers from areas served by separate sewer system related to the associated drainage area AC,s. • Throttle discharge rate qThr [l/(s⋅ha)] Throttle flow QThr from stormwater overflows and stormwater tanks referred to the associated catchment area. The reference catchment area, depending on the scope and problem, can be differentiated; e.g. direct catchment area or overall area with sewers upstream. For clarification additional indices can be employed, e.g. qThr,s = QThr / AC,s.
ATV-DVWK-A 198E • Rainfall fraction of the throttle discharge rate qThr,R [l/(s⋅ha)] Rainfall fraction in the throttle flow QThr,R from stormwater overflows and stormwater tanks related to the surface of the associated catchment areas. In combined sewer systems the separate identification of the rainfall fraction often takes place in the throttle flow of a monitoring facility (comp. qR). The reference catchment area, depending on the scope and problem, can be differentiated; e.g. direct catchment area or overall area with sewers upstream of the monitoring facility.
• Stormwater discharge rate qR [l/(s·ha)] Stormwater flow of an area related to an associated surface area AC. • Stormwater discharge rate in accordance with ATV-A 128E (1992) qr [l/(s·ha)] In ATV-A 128E (1992) the stormwater discharge rate (using the symbol qr) is to be seen as annual mean value in the throttle flow of a stormwater overflow tank or sewer with storage capacity. It derives from the fraction of the stormwater runoff in the throttle flow Qr with regard to the impermeable surface Aimp,A128 (qr = Qr / Aimp,A128) and thus represents an applicationrelated quantity.
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37
ATV-DVWK-A 198E
Appendix B 1: Summary of flow values from the English translations of respective ATV-DVWK Standards In the following summary only those flow values have been incorporated which are required as initial quantities. Values which are derived from calculations in the standards such as, for example,
the throttle flow from retention facilities, have therefore not been listed. This is also the reason why a series of standards which, for example, are directed at hydraulic calculations, are not listed.
[Translator’s note: here only the English versions of the symbols are compared. For a comparison of the German symbols please refer to Appendix B2 below.]
Symbol Old
A 198E
Unit
Definition/Explanation A 198E
ATV-A 118E (1999): Hydraulic Dimensioning and Verification of Drainage Systems Infiltration water as annual mean Qiw QInf,aM l/s Max. hourly commercial resp. industrial wastewater flow Qc QInd,h,max l/s Max. hourly domestic wastewater flow l/s Qd QD,h,max Max. hourly stormwater runoff l/s Qs QR,h,max Max. hourly unavoidable stormwater runoff in sanitary sewers from areas with Qs,S QR,Sep,h,max l/s separate sewer system Max. hourly dry weather flow l/s Qdw QDW,h,max ATV-A 126E (1993): Principles for the Wastewater Treatment in Sewage Treatment Plants according to the Activated Sludge Process with Joint Sludge Stabilisation with Connection Values between 500 and 5000 Total Number of Inhabitants and Population equivalents Infiltration water flow as annual mean QInf,aM m³/h Qi Max. hourly domestic wastewater flow as 2-hourly mean m³/h Qd24 QD,2h,max Max. hourly commercial resp. industrial wastewater flow as 2-hourly mean m³/h QC QInd,2h,max As above (QC and Qi are no longer differentiated, instead QInd) m³/h QI QInd,2h,max m³/h Qcs QComb Combined wastewater flow to the wastewater treatment plant m³/h Unavoidable stormwater runoff in sanitary sewers from areas with separate Qr QR,Sep sewer system Max. wastewater flow as 2-hourly mean QDI QWW,2h,max m³/h m³/h Max. dry weather flow as 2-hourly mean Qdw QDW,2h,max m³/d Daily sewage flow Q Qd ATV-A 128E (1992): Standards for the Dimensioning and Design of Stormwater Structures in Combined Sewers Infiltration water flow as annual mean Qiw24 QInf,aM l/s Max. hourly domestic wastewater flow as annual mean Qd24 QD,aM l/s Max. hourly commercial resp. industrial wastewater flow as annual mean l/s Qc24 QInd,aM As above (QC and Qi are no longer differentiated, instead QG) l/s Qi24 QInd,aM l/s Qcw QComb Combined wastewater flow to the wastewater treatment plant l/s Unavoidable stormwater runoff in sanitary sewers from areas with separate QrS24 QR,Sep sewer system l/s Wastewater flow as annual mean Qw24 QWW,aM Wastewater flow from areas with separate sewer system as annual mean QwST24 QWW,Sep,aM l/s l/s Dry weather flow as annual mean Qdw24 QDW,aM l/s Max. hourly dry weather flow Qdwx QDW,h,max ATV-DVWK-A 131E (2000): Dimensioning of Single-Stage Activated Sludge Plants Combined wastewater flow to the wastewater treatment plant QCW m³/h QWW,h Daily dry weather flow as annual mean m³/d QDW,d QDW,d,aM Max. dry weather flow as 2-hourly mean m³/h QDW,h QDW,2h,max ATV-DVWK-A 281E (2001): Dimensioning of Trickling Filters and Rotating Biological Contactors [Translator’s note: This Standard was translated after A198 and therefore the symbols in English are standardised]
QCW QDW,d,aM QDW,2h,max
38
QComb QDW,d,aM QDW,2h,max
April 2003
m³/h m³/d m³/h
Combined wastewater flow to the wastewater treatment plant Daily dry weather flow as annual mean Max. dry weather flow as 2-hourly mean
ATV-DVWK-A 198E
Appendix B 2: Summary of flow values from the original German ATV-DVWK Standards In the following summary only those flow values have been incorporated which are required as initial quantities. Values which are derived from calculations in the standards such as, for example, Symbol Old
A 198
Unit
the throttle flow from retention facilities, have therefore not been listed. This is also the reason why a series of standards which, for example, are directed at hydraulic calculations, are not listed.
Definition/Explanation A 198E
ATV-A 118 (1999): Hydraulic Dimensioning and Verification of Drainage Systems Infiltration water as annual mean Qf QF,aM l/s Max. hourly commercial resp. industrial wastewater flow Qg QG,h,max l/s Max. hourly domestic wastewater flow l/s Qh QH,h,max Max. hourly stormwater runoff l/s Qr QR,h,max Max. hourly unavoidable stormwater runoff in sanitary sewers from areas with l/s Qr,T QR,Tr,h,max separate sewer system Max. hourly dry weather flow l/s Qt QT,h,max ATV-A 126 (1993): Principles for the Wastewater Treatment in Sewage Treatment Plants according to the Activated Sludge Process with Joint Sludge Stabilisation with Connection Values between 500 and 5000 Total Number of Inhabitants and Population equivalents Infiltration water flow as annual mean QF,aM Qf m³/h Max. hourly domestic wastewater flow as 2-hourly mean Qh QH,2h,max m³/h Max. hourly commercial resp. industrial wastewater flow as 2-hourly mean m³/h Qg QG,2h,max As above (QC and Qi are no longer differentiated, instead QInd) m³/h Qi QG,2h,max m³/h Qmz QM Combined wastewater flow to the wastewater treatment plant m³/h Unavoidable stormwater runoff in sanitary sewers from areas with separate Qr QR,Tr sewer system m³/h Max. wastewater flow as 2-hourly mean Qs QS,2h,max m³/h Max. dry weather flow as 2-hourly mean Qt QT,2h,max m³/d Daily sewage flow Q Qd ATV-A 128 (1992): Standards for the Dimensioning and Design of Stormwater Structures in Combined Sewers Infiltration water flow as annual mean Qf24 QF,aM l/s Max. hourly domestic wastewater flow as annual mean Qh24 QH,aM l/s Max. hourly commercial resp. industrial wastewater flow as annual mean Qg24 QG,aM l/s As above (QC and Qi are no longer differentiated, instead QG) l/s Qi24 QG,aM l/s Qm QM Combined wastewater flow to the wastewater treatment plant l/s Unavoidable stormwater runoff in sanitary sewers from areas with separate QrT24 QR,Tr sewer system l/s Wastewater flow as annual mean Qs24 QS,aM l/s Wastewater flow from areas with separate sewer system as annual mean QsT24 QS,Tr,aM l/s Dry weather flow as annual mean Qt24 QT,aM l/s Max. hourly dry weather flow Qtx QT,h,max ATV-DVWK-A 131 (2000): Dimensioning of Single-Stage Activated Sludge Plants Combined wastewater flow to the wastewater treatment plant QM m³/h Qm Daily dry weather flow as annual mean m³/d Qd QT,d,aM Max. dry weather flow as 2-hourly mean m³/h Qth QT,2h,max ATV-DVWK-A 281E (2001): Dimensioning of Trickling Filters and Rotating Biological Contactors Combined wastewater flow to the wastewater treatment plant QM m³/h Qm Daily dry weather flow as annual mean m³/d Qd QT,d,aM Max. dry weather flow as 2-hourly mean m³/h Qt QT,2h,max
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ATV-DVWK-A 198E
Appendix C: Example for the evaluation of measured values C1
Flows
C 1.1
Summary of measured values
As a rule the evaluation takes place with the aid of a tabular calculation programme. The scheme with
QDW,h,min/QDW,d
QDW,h,max/QDW,d
min. hourly DW flow (QDW,h,min)
2 Fr Sa
24.5. 25.5.
Mo Tu
DW 15845 15845 260 DW 17156 17256 263
105 111
1.42 0.57 1.32 0.56
31.12 Fr Mean (aM)
43502 30579 16820 259
112
1.35 0.55
Column 3, Weather: In the wastewater treatment plant the weather code recommended in the logbook [8] can be used as the basis: 1-dry; 2-frost; 3-rain; 4-thunder; 5snow melt; 6-snowfall; 7-rainfall follow-up. According to this, only days with 1 or 2 are dry weather days. At the same time there are [German] Federal State regulations, for example in North Rhine Westphalia, it counts as a dry weather day if, on the day considered or the day before N ≤ 1 mm/d. In Column 3 one can limit this to the designation dry weather days (“DW“). Column 4, Flow: Taken over from the logbook or determined from digital records.
April 2003
max. hourly DW flow (QDW,h,max)
1 1.1. 2.1.
m3/d m3/d l/s 3 4 5 6 DW 24077 24077 348 35041
The following on the contents of the columns should be noted:
40
Dry weather flow(QDW,d)
Flow (Qd)
Weather
Weekday
Summary of flow data
Date
Table C-1:
a table with data and some calculations are shown as examples in Table C-1.
l/s 7 210
8 9 1.25 0.76
Column 5, Dry weather (DW) flow: for dry weather days (see Col. 3) taken over from Column 4. Columns 6 and 7: maximum and minimum hourly flow (QDW,h,max and QDW,h,min). For dry weather days (see Col. 3) determined from (digital) records. Columns 8 and 9: ratio values from Columns 6 and 7 for the mean dry weather flow (QDW,d in l/s) each day.
For Columns 4 to 9 the annual means have been formed in the last line.
ATV-DVWK-A 198E C 1.2
Daily flows
C 1.3 Determination of the dry weather flow
As overview of the daily sewage flow as well as for plausibility check the graphical presentation is practical using the data from Table C-1. Q [1000 m³/d] Daily flow, all days d 100 80 60 40 20 0
J
F M A M J
J A S O N D
The annual mean of the dry weather flow is calculated as mean of the values in Column 5 of Table C-1. The dry weather flows in Fig. C-3 show a trend similar to the smallest daily flows in Fig. C-1. Freak values can not be identified in the time series of the dry weather flow. From Column 5 of Table C-1, for this example a dry weather flow of QDW,d,aM = 16,820 m3/d corresponding with QDW,aM = 195 l/s results, which is confirmed optically by Fig. C-3. Typical dry weather conditions with approximately constant infiltration water flow predominate in 1999 from 01 July to 31 October. In this period the mean with QDW,d,pM = 13,565 m³/d is significantly lower than the annual mean.
Fig. C-1: Time series of the daily flow in 1999 Q [1000 m³/d] Daily flow, dry weather days T,d 100
Q [1000 m³/d] Daily flow, all days d 100 80
60
60
01 July to 31 Okt. Mean 13,565 m³/d
40
40
20
20 0
Annual mean 16,820 m³/d 70 DW days
80
0
J
F M A M J
J A
S O N D
J
F M A M
J
J A S O N D
Fig. C-2: Time series of the daily flow in 1997, 1998 and1999
Fig. C-3: Time series of the flow on dry weather days in 1999
Fig. C-1 shows that, in the months January to May and November/December 1999, there are many days with high flows. The minimum flow values indicate a seasonal variation; they are higher in the winter months than, for example, in summer. From precipitation records it can be seen that in the months of January to May and November/December it rained a great deal. These rainfall periods have evidently caused a seasonal variation of the infiltration water flow. The flows of the three years 1997 to 1999 (Fig. C-2) show clearly that the course of the flow can also be different.
The dry weather flow can, in accordance with Chap. 4.2.2.1, Para 4, also be determined independently from the weather conditions. This is demonstrated for 1999. For this the lowest daily flow for each day of the preceding 10 days, of the day considered and the following 10 days (sliding 21-day value) is sought. The polygon resulting from this is shown by the continuous line in Fig. C4. All flows which lie by up to 20% above the polygon are considered as dry weather flows, see Fig. C-5.
April 2003
41
ATV-DVWK-A 198E Frequency of undercutting [%]
Q [1000 m³/d] Daily flow, all days d
100
100
+ f lo w f r o m d ry w e a th e r d a y s ( 7 0 v a lu e s )
90 80
80
70 60
60
F lo w f r o m c a lc u la t e d d ry w e a th e r d a y s (1 4 1 v a lu e s )
50
40
40
20
20
30
1 9 99
10
0
J
F M A M J
J
A
S O N D
0 0
Fig. C-4: Polygon of the lowest flows in 21-day intervals (1999) Q [1000 m³/d] flow, calculated DW days d 100 Annual mean 17,790 m³/d 141 DW days
80 60
01 Jul to 31 Oct. Mean 13,710 m³/d
40 20 0
J
F M A M
J
J
A S O N D
Fig. C-5: Time series of flows from calculated dry weather days in 1999
The annual mean of the dry weather flows defined using weather records and the calculated dry weather flows differ only very slightly, even the summer means are practically equal. The usefulness of this procedure is also confirmed by the very great similarity of the frequency of undercutting of the dry weather flows, comp. Fig. C-6.
10 20 30 [1 0 0 0 m ³/d ] , T k tt b fflow l QDW,d [1000 m³/d] dry weather
40
Fig. C-6: Frequency of the undercutting of the flow on dry weather days and those calculated as dry weather days of 1999
C 1.4 Determination of the wastewater flow as annual mean There are 75,400 inhabitants living within the catchment area of the wastewater treatment plant involved in the measurement. The responsible water supply company gives the mean water consumption incl. small commercial consumers, as 150 l/(I·d). Larger industrial and commercial businesses drew together an annual amount of 418,000 m³ they, however, discharged only 391,000 m³ into the sewer network. With this one obtains the annual mean of the wastewater flow as QWW ,d ,aM =
3 75,400 ⋅ 150 391,000 + = 12,380 m /d 1,000 365
respectively QWW,aM = 143 l/s The daily water consumption shows no marked seasonal variation.
42
April 2003
ATV-DVWK-A 198E C 1.5 Determination of the infiltration water flow Measurements of the infiltration water flow are not available. Therefore the infiltration water flow is calculated as the difference between the dry weather sewage flow and the wastewater flow. Here, as an example, the infiltration water flow for 1999 is determined on the basis of weather data (Fig. C-3) and using calculated dry weather days (Fig. C-5) in Table C-2. Using the calculated dry weather days one obtains higher mean dry weather and infiltration water flows than with the flows derived from weather data because many high flow values in the period January to March are not recorded as dry weather days. Table C-2: Designation
QDW,d,aM QDW,aM QWW,aM QInf,aM QInf,aM/QDW,aM
Determination of the infiltration water flow in 1999 Unit
m3/d l/s l/s l/s %
QD,d in accordance with weather data 16,820 195 143 52 27
QDW,d from calculated dry weather days 17,790 206 143 63 31
From the three year series investigated 1999 shows the highest monthly mean of the daily dry weather flow. According to Fig. C-5 these occur in the months January to March with ca. QDW,d,mM,max = 30,000 m3/d corresponding with = 347 l/s. In Fig. C-3 also (according to weather data) one finds individual values of QDW,d ≅ 30,000 m3/d. Under the premise of the constant wastewater flow of QDW,aM = 143 l/s there results the maximum monthly mean of the infiltration water of:
QInf,mM,max = 347 - 143 = 204 l/s
C 1.6 Determination of the maximum and minimum dry weather flow The daily maximum, mean and minimum hourly flows show a similar seasonal variation as for the daily dry weather flows (comp. Fig. C-7). The following monthly means have been calculated: March: September:
Maximum QDW,h,max,mM = 370 l/s Minimum QDW,h,min,mM = 80 l/s
Due to the almost constant infiltration water flow the mean of the maximum hourly flows of the summer is of interest, it is QDW,h,max,pM = 225 l/s. In Table C-1 the ratio values QDW,h,max/QDW,d and QDW,h,min/QDW,d have been formed, whose time series is shown in Fig. C-8. As a result of the, for example, in March high fraction of infiltration water in the dry weather flow the ratio value with QDW,h,max/QDW,d = 1.25 is significantly lower than, for example, in August/September with QDW,h,max/QDW,d = 1.45. bzw. [l/s] QT,h or Q QDW,d DW,h T,d [l/s] 500 400 QDW,h,max 300 200
QDW,d QQ DW,h,min DW,h,min
100 0
J
F
M
A
M
J
J
A
S
O
N
D
Fig. C-7: Maximum, mean and minimum hourly dry weather flows in 1999 /Q DW,dbzw. QDW,h,min/Q [-] [-] QQDW,h,max or Q DW,d T,h,max T,d T,h,min /QT,d
The maximum monthly mean of the infiltration water is thus 204/52 = 4-times (QDW,d according to weather data) or 204/63 = 3.2-times (QDW,d of calculated dry weather days) of the annual mean. In summer the dry weather flows with, on average, QDW,d = 13,565 m3/d or 13,710 m3/d corresponding with ≅ 157 l/s are the least both according to weather data and for calculated dry weather days. The minimum infiltration water flow of this period then results as:
2.0
QInf,pM,min = 157 - 143 = 14 l/s
Fig. C-8: Ratio values QDW,h,max/QDW,d and QDW,h,min/QDW,d in 1999
QDW,h,max /QDW,d 1.5
1.0
0.5 QDW,h,min/QDW,d 0.0
J
F
M
A
M
J
J
A
S
O
N
April 2003
D
43
ATV-DVWK-A 198E C 1.7 Maximum and minimum wastewater flow For the summer the maximum hourly dry weather flow has been determined in Chap. C 1.6 as QDW,h,max,pM = 225 l/s. The infiltration water flow is QInf,min,pM = 14 l/s (Chap. C 1.5). Thus the maximum hourly wastewater flow for the summer is:
QWW,h,max,pM = 225 - 14 = 211 l/s The ratio of the maximum wastewater flow and daily average is
QWW,h,max,pM /QWW,aM = 211 / 143 = 1.48 The divisor xQmax, according to Eqn. 7, results as follows:
xQ max =
24 ≈ 16.2 1.48
This value, in comparison with Fig. 2, appears plausible. With a forecast mean wastewater flow one can determine the maximum and minimum wastewater flows either with the aid of the ratio value or the divisor.
C 1.8 Determination of the combined wastewater flow
with fWW,QComb = 3.5:
QComb = 143 ⋅ 3.5 + 52 = 500 + 52 = 552 l/s with fWW,QComb = 6.5:
QComb = 143 ⋅ 6.5 + 52 = 930 + 52 = 982 l/s According to Fig. C-7 the maximum hourly dry weather flows in the wet weather periods are QDW,h,max ≅ 400 l/s. If one calculates with QComb = 551 l/s, then in the daytime hours the emptying of a stormwater reservoir would be very slow. Therefore, for the combined wastewater flow, a value between QComb = 700 and 900 l/s should be selected. If, for example, the secondary settling tanks of the wastewater treatment plant have reserves, one can apply the higher combined sewage flow in order to save volume for combined sewage reservoirs and to further relieve the receiving water. According to the previously usual approach the following would have resulted: the 85-Percentile value of the daily wastewater flow is applied as 1.25·QDW,aM. The peak flow is then calculated using the divisor xQmax = 16.2, according to Chap. C 1.7. The peak flow then results as
QWW,max,85 = 1.25 · 143 · (24/16.2) = 265 l/s
Using the following initial data, calculated above, an estimate of the combined wastewater flow is to be undertaken:
The infiltration water flow is the applied as above with 52 l/s.
QWW,aM = QInf,aM = QInf,mM,max =
530 + 52 = 582
143 l/s 52 l/s 204 l/s
Connected inhabitants and total numbers of inhabitants and population equivalents: ca. 75,000 I. According to Fig. 1 the factor for this population can be assumed as being between fWW,QCW = 3.5 and 6.5. The maximum monthly mean of the infiltration water flow is higher than two-times the annual mean. According to Chap. 4.2.2.6 a higher value than the annual mean can be applied for the infiltration water flow. Initially, however, QComb is calculated using the annual mean of the infiltration water flow:
44
April 2003
Q Comb = 2 ⋅ Q WW + Q Inf = 2 ⋅ 265 + 52 =
l/s
The value for QComb calculated according to the previous approach lies nearer to the smallest value according to the new approach. The emptying of the storage facility in wet weather periods would have taken place also appropriately slowly (see above). If one were to calculate using QInf,mM,max = 204 l/s instead of QInf,aM = 52 l/s, one would enter the more convenient range of QComb = 700 to 900 l/s.
ATV-DVWK-A 198E C2
Loads and concentrations
C 2.1
Summary of measured values
year should be evaluated. As here all concentrations and load values refer to the inflow to the biological stage, the index INB is left out for the sake of simplicity.
Table C-2 shows, as an example, a listing of measured values as well as the determination of loads and ratio values. A period of at least one
mg/l 10
mg/l mg/l mg/l mg/l 11 12 13 14
Alkalinity (SAlk)
mg/l 9
Phosphorus, homog. (CP)
mg/l 8
Nitrate nitrogen (SNO3)
m3/d 6
Ammonia nitrogen (SNH4)
All days (Qd)
m3/d 5
TKN homog. (CTKN)
suspended solids (XSS)
mg/l 7
DW-days (QDW,d)
BOD5, homog. (CBOD)
Fr
Concentrations
COD, filtered (SCOD)
31.12.
3
°C 4
Inflows COD, homog. (CCOD)
2 Fr Sa So Mo
Wastewater temperature (T)
1 1.1. 2.1. 3.1. 4.1.
Weather (give DW only)
Summary of the measured values, the calculated COD loads and the ratio values of the master parameter COD
Weekday
Date
Table C-2:
mmol/l 15
Mean
End
Bd,COD
Weekly mean Bd,COD,WM
2-weekly mean Bd,COD,2WM
SCOD/CCOD
CBOD/CCOD
XSS/CCOD
CTKN/CCOD
SNH4/CCOD
CP/CCOD
SAlk/CCOD
Qd,SL
Ratio values
Start
2 Fr Sa So Mo
m3/d 16
COD loads
SNH4,SL
1 1.1. 2.1. 3.1. 4.1.
Weekday
Date
Sludge liquor [SL]
mg/l 17
h 18
h 19
kg/d 20
kg/d 21
kg/d 22
23
20
24
25
26
27
28
31.12. Fr Mean
April 2003
45
ATV-DVWK-A 198E
The following is to be noted for the individual columns: Column 3, Weather code: It is sufficient to designate the dry weather days, comp. also Chap. C 1.1. Column 4, Wastewater temperature: The temperature is measured in the outlet of the biological reactor. If there is still no wastewater treatment plant available, the sewage temperature can be used. Column 5, Inflow on all days: Transferred from the logbook or Table C-1, Col. 4.
Columns 23 to 28, Ratio values: The ratios of the concentrations from Cols. 8 to 15 to the concentration of the master parameter COD (Col. 7) are entered.
In the last line the mean value is formed from a series of columns, some of which are only informative others are used for further calculations. Not listed in Table C-2 are the BOD5 and COD loads in the inflow to the wastewater treatment plant with dry weather which are possibly required for the determination of the design capacity and/or for the dimensioning of combined sewer overflows, (comp. Chap. 3.3.3.1 and 3.3.3.2) as well as the Sludge Volume Index of existing facilities.
Column 6, Inflow on dry weather days: Transferred Column 5 together with Column 3.
C 2.2 Columns 7 to 15, Concentrations: Measured values are entered. Columns 16 to19, Sludge liquor [SL] discharge: To be recorded are: the daily volumes of sludge liquor (Col 16); the ammonia nitrogen concentration (Col.17) is not necessary each day; the start and end of the discharge (Cols. 18 and 19). If considerable volumes of faecal sludge or other sludge as well as filter washing water are to be discharged, appropriate columns should be added for these. Essential are the daily volume and start and end of the discharge. These entries are valuable, in particular on days with investigations of the peak factor as irregularities can be identified. Columns 20 to 22, COD loads: First the daily loads are formed as product of the values of Columns 5 and 7 (divided by 1000) (Col. 20). Columns 21 and 22 are necessary for the dimensioning of activated sludge plants only, if the dimensioning is to take place in accordance with 2- or 4-weekly means. If at least four loads have been calculated per calendar week, the weekly mean is entered in Column 21, respectively on Sunday (end of the week) and in Column 22, for example, the 2-weekly means, which are the mean of respectively two consecutive weekly loads (“Sunday values” from Column 21).
46
April 2003
Planning of sampling
Fundamentally there are two possibilities: 1.
2.
Consolidation of routine sampling with the aim of carrying out dimensioning on the basis of loads undercut on 85% of the days. It is sufficient for this if, during a year, at least one sampling takes place per week. The determination of the relevant loads on the basis of the 85-percentile value is necessary for the dimensioning of trickling filters and rotating biological contactors in accordance with ATVDVWK-A 281E (2001). For the dimensioning of activated sludge plants this should take place in accordance with ATV-DVWK-A 131E (2000) for small plants or in special cases only. Consolidation of the sampling in certain periods with the aim of forming weekly means for the loads. This is to be the standard case for the dimensioning of activated sludge plants in accordance with ATV-DVWK-A 131E (2000).
For the following example, a sampling for the weekly mean for the dimensioning of activated sludge plants is demonstrated. The sampling for this is planned on the basis of the seasonal variation of the COD loads, the ratios of the important parameters to the COD as well as the time series of the temperature of the previous years.
ATV-DVWK-A 198E Both the COD loads as well as the ratio values [of previous years] indicate no marked seasonal variation. In the meanwhile no seasonal operating industrial and/or commercial firms have been established. Sampling can therefore be oriented to the wastewater temperature. In order to exclude coincidences the time series of the 2-weekly mean of the temperature of the previous three years is considered, Fig. C-9. One can form sliding 14-day means, as in Fig. C-9, or means from two calendar weeks. The content of information is the same with both representations. For the dimensioning of an activated sludge plant the following periods are selected in which the sampling is so consolidated that weekly means can be formed: – 25. 1 to 26. 3 as period for the dimensioning temperature and the lowest temperature. – 23. 8. to 1. 10. as period for the highest temperature (July and August inappropriate due to holidays). Alternatively in Chap. C 2.4 the determination of the relevant COD load as 85% value is demonstrated. Temperature in the aeration tank [°C] 20 18 16 14 12 10 8 6 4 2 0
with daily sampling are marked by dashes. For this the weekly means are presented in Fig. C-11. B [1000 kg/d] COD load to biol. stage d,COD 20 18 16 14 12 10 8 6 4 2 0 J F M A M J J A S O N D
Fig. C-10: Time series of COD loads in 1999 B [1000 kg/d] weekly mean COD load d,COD,wM 20 18 16 14 12 10 8 6 4 2 0 J F M A M J J A S O N D
Fig. C-11: Weekly mean of the COD loads from 1999 B
J
F M A M J
J
A S O N D
Fig. C-9: Time series of the temperature from three years (sliding 2-weekly mean)
C 2.3 Determination of the relevant COD load on the basis of weekly means At this wastewater treatment plant the inflow to the biological stage is sampled once a week on different week days. In the periods given in Chap. C 2.2 a daily sampling took place with the exception of Sundays. Fig. C-10 shows the result. The periods
d,COD,2wM
20 18 16 14 12 10 8 6 4 2 0
J
[1000 kg/d] 2-weekly mean COD load
F M A M
J
J
A S O N D
Fig. C-12: Two-weekly mean of the COD loads from 1999 (overlapping)
For the dimensioning of an activated sludge plant 2-weekly means of the COD loads form the basis.
April 2003
47
ATV-DVWK-A 198E In order to find the maximum 2-weekly means, means from respectively consecutive weeks are formed. As each week can lie once as first and once as second in a 2-weekly interval, one obtains, for example, for a 10 week period, nine 2-weekly means, comp. Fig. C-12. The highest 2-weekly mean lies in September with Bd,COD = 7,500 kg/d. In February/March one can reckon with Bd,COD = 6,700 kg/d. Additions are to be made (comp. Chap. 5) for growth in population or connection of further residential developments and industrial/commercial firms. The plotting of the COD loads over the flows shows at a glance the dependencies and the widths of scatter of the flows, of the loads and of the concentrations, Fig. C-13. Here it is apparent, for example, that with increased combined wastewater flows, the loads remain almost constant and the concentrations reduce accordingly. One can also easily identify the “cloud” of the flows of dry weather days with Qd = 13,000 and 18,000 m³/d and the associated loads of Bd,COD = 5,000 and 7,000 kg/d, whereby concentrations of CCOD = 300 to 500 mg/l appear. It is to be noted that, due to the lower sampling frequency in summer, many values with higher concentrations and flows below 13,000 m3/d are missing in the plot.
C 2.4 Determination of the relevant COD load as 85 % value The determination of the relevant COD load as 85% value is necessary for the dimensioning of trickling filters and rotating biological contactors, for activated sludge plants it should only serve in special cases, for example if the consolidation of the sampling is out of proportion to the usage. In 1998 a sampling took place weekly on differing days. Through this some 50 load values are available. A seasonal variation of the COD loads and in particular the ratio values CTKN/CCOD was not identifiable. The value achieved or undercut on 85% of the days is Bd,COD = 7,500 kg/d, comp. Fig. C-14. It is purely coincidental that here the 85% value of the COD load from 1998 is practically the same as the relevant load of Summer 1999, derived from the 2-weekly means.
Frequency of undercutting [%] 100 90 80 70 60 50 40
B [1000 kg/d] daily COD load d,COD 15 300 200 500
30 20 10 0
10
100
0
5
10
15
B [1000 kg/d] daily COD load d,COD Fig. C-14: Undercutting frequency of COD loads for 1998
5
C 2.5 Ratio values of important parameters
Parameter C [mg/l] COD
0
0
20
40
60
80
100
Q [1000 m³/d] daily sewage flow d
Fig. C-13: Plot of the daily flows and COD loads (1999)
48
April 2003
As a rule, all important parameters were determined with the weekly sampling. This was maintained in the phases with daily sampling. Here, for example, TKN/COD, P/COD and BOD5/COD were considered. The ratios CTKN/CCOD appear to be subject to a certain seasonal variation, Fig. C-15. In the period February/March the ratio was, as a mean,
ATV-DVWK-A 198E CTKN/CCOD = 0.22, while in September the mean was CTKN/CCOD = 0.17. Rather constant with only a slight scatter CP/CCOD = 0.017 as a mean in February/March and CP/CCOD = 0.016 in September is found, Fig. C-16.
C /C [-] BOD COD 0,8 Mean 0,40 kg/kg
0,6 0,4
C /C [-] TKN COD 0,4
0,2 0
0,3
Fig. C-17: Time series of the ratio CBOD/CCOD
0,2
C 2.6 Determination of the concentrations
0,1 0
J
F M A M
J
J
A S O N D
Fig. C-15: Time series of the ratio CTKN/CCOD C /C [-] P COD 0,04
In accordance with Chap. 4.3.1.5 the relevant loads and concentrations are to be determined for at least three different temperatures. The dimensioning temperature is specified as TDim = 12 °C. The lowest temperature is T2wM,min = 8 °C and the highest T2wM,max = 21 °C, comp. Fig. C-9. To the COD loads presented in Figs. C-10 to 12 belong the flows shown in Fig. C-1. Initial figures for the calculation of the relevant concentration of the COD are respectively the COD loads of Bd,COD = 6,700 and 7,500 kg/d determined in Chap. C 2.3. Dividing by the appropriate flow gives the relevant concentration.
0,03 0,02 0,01 0
J F M A M J J A S O N D
J
F M A M
J
J
A S O N D
Fig. C-16: Time series of the ratio CP/CCOD
The ratio values CBOD/CCOD show the largest scatter (Fig. C-17). The scatter is a sign for the possible proneness to error of the BOD5 determination. This is, therefore, a reason in future to carry out dimensioning on the basis of the COD. A seasonal variation of the ratio BOD5/COD is also not identifiable here.
The dry weather flow in February/March 1999, caused by high rainfalls, is Qd ~ 25,000 m3/d. With less rainfalls, flows of Qd ~ 17,000 m3/d were measured in other years, therefore, for the winter calculation was carried out using Qd,conc = 17,000 m3/d. In Summer one can calculate using Qd,conc = 13,000 m3/d, comp. Fig. C-2. The results in Table C-3 show, that this wastewater, in comparison with normal domestic wastewater, contains higher nitrogen loads. These are caused by an industrial discharger.
April 2003
49
ATV-DVWK-A 198E Table C-3:
Derivation and summary of selected dimensioning values
Designation T Bd,2wM,max
Unit °C kg/d m3/d mg/l mg/l mg/l mg/l
Qd,conc CCOD CTKN/CCOD CP/CCOD CBOD/CCOD CTKN CP CBOD
Dimensioning temperature 12 6,700
Lowest temperature 8 6,700
Highest temperature 21 7,500
17,000 394 0.22 0.017 0.4 87 6.7 158
17,000 394 0.22 0.017 0.4 87 6.7 158
13,000 577 0.17 0.017 0.4 98 9.8 231
CTKN in mg/l and Bd,TKN in kg/h are listed in Column 7. The highest value from Columns 4 to 6 is transferred into Column 8 and the ratio value B2h,TKN/Bd,TKN is formed in Column 9. The mean values are calculated in the last line. Sampling should be for at least 14 days. If a seasonal variation for CTKN/CCOD is observed, then in the corresponding periods of sampling should be twice in a minimum of 14 days.
C 2.7 Determination of the peak factor for the nitrogen loading In a plant it is known that the maximum 2-hourly load of nitrogen B2h,TKN in kg/h with dry weather always occurs between 10 h and 16 h. Some measured values are listed in Table C-3 as an example. As far as possible only dry weather days should be included for the evaluation. In columns 4 to 6, for each day one below the other are the flows QDW,2h in m³/h, the concentrations CTKN,2h in mg/l from 2hourly composite samples and the loads as 2hourly mean B2h,TKN in kg/h. The values for the daily average corresponding with QDW,d in m3/h,
Parameter
Unit
10 - 12 h
12 - 14 hr
14 - 16 h
24-h mean
Maximum 2-h load
Max. 2-h load/ 24-h mean
1
2
3
4
5
6
7
8
9
QDW,2h (QDW,d) CTKN B2h,TKN (Bd,TKN)
3
m /h mg/l kg/h
789 67 52.9
957 58 55.5
896 61 54.7
623 54 33.6
55.5
1.65
QT,2h (QT,d) CTKN B2h,TKN (Bd,TKN)
3
m /h mg/l kg/h
870 65 56.6
1023 61 62.4
977 58 56.7
678 51 34.6
62.4
1.80
QT,2h (QT,d) CTKN B2h,TKN (Bd,TKN)
3
Mean
59.3
1.77
10.2. Wed 4.3. Thur
50
Example for the determination of the peak factor for the nitrogen load
Date
Table C-4:
With this procedure, with three additional analyses daily in addition to the in any case analysed daily composite sample one has sufficient information. What is required is the mean of the ratio as peak factor, inter alia for the calculation of the oxygen consumption of activated sludge plants, here fN = 1.77.
April 2003
m /h mg/l kg/h
