Dim ime ens nsio ioni ning ng and de desi sign gn of nit nitro roge gen n re remo mova vall te techn chnol olog ogie ies s Di p l .-Ing .-Ing.. S. Ret t i g TU Berli Berlin, n, De Department of Urban water water manageme management nt Gustav-M Gust av-Meyer-All eyer-Allee ee 25, 25, D - 1335 13355 5 Berlin Berl in Phon Pho n e: +49 / (0) 30 / 314 72356; 72356; Fax: Fax : +49 / (0) 30 / 314 72248
e-mail:
[email protected]
Introduction
Biological wastewater treatment: Fixed film (trickling filter, rotating rotating disk filter) or suspended biomass (a (activ ct iva ated sludge slud ge sy syst ste em )
Predominantly Predominantly the activated sludge system is practiced
Municipal and industrial wastewater treatment
Basic of the activated sludge system: Combination of aeration tank
+ subsequent sedimentation (clarifier) + return of the separated biomass (return sludge)
Carrier of biological treatment - activated sludge -
Invention of the activated sludge system 1914 (Ardern, Lockett )
Introduction
Biological wastewater treatment: Fixed film (trickling filter, rotating rotating disk filter) or suspended biomass (a (activ ct iva ated sludge slud ge sy syst ste em )
Predominantly Predominantly the activated sludge system is practiced
Municipal and industrial wastewater treatment
Basic of the activated sludge system: Combination of aeration tank
+ subsequent sedimentation (clarifier) + return of the separated biomass (return sludge)
Carrier of biological treatment - activated sludge -
Invention of the activated sludge system 1914 (Ardern, Lockett )
Basis Basis of dime di mension nsioning ing basic ba sic pos possibi sibilit litie ies s 1. Evalua valuation tion of ava availa ilable ble data data (no norm rma al ca c ase) 2. Ad A d d i t i o n al s p eci ec i f i c i n v est es t i g ati at i o n s (ser (s erii es o f measurements), measurements), i f d at a i s i n s u f f i c i en t 3. Mathema themati tica call dete determ rmina inatio tion n with wit h known kno wn (exceptional case)
Conside onsid eration ration of future deve developm lopme ent (most mo stly ly with wi th the th e help help of cha ch aract racte erist ri stic ic valu value es)
Demography mography (population population deve developme lopment) nt)
Reside sid ential area reas
Industry
Tourism
Cumulative frequency / Undercut frequency Inflow rate 10 0 90
] 80 ] % [ % [ 70 y t i c e n k 60 g e i f u u 50 q ä h e r n f e 40 m e v m 30 i u t S a l 20 u m10 u C 0
COD-load, inflow Undercut [%]
0
100
200
300
400 3
Qo in m /d
500
600
Dimensioning Flows and Loads
The following values are required from the influent to the biological reactor: lowest and highest wastewater temperature organic load (Bd,BOD Bd,COD), load of suspended solids (Bd,SS) and of
phosphorus (Bd,P) for the determination of the sludge production and thus the calculation of the volume of the aeration tank organic load and nitrogen load for the design of the aeration facility
for (as a rule) the highest relevant temperature –Loading condition: BOD/N; highest saisonal peak maximum inflow rate with dry weather QDW,h (m³/h) for the design of
the anaerobic mixing tank and the internal recirculation flow rate dimensioning inflow rate QWW,h (m³/h) for the design of the
secondary settling tanks
Biological Standard Processes Activated sludge processes Elimination of: COD, BOD5, NH4-N, NO3-N, P anoxic zone denitrification Influent (primary-treated)
aerobic zone COD-elimination & nitrification
Effluent
Aer ati on Recirclation sludge
Clarifier
Return sludge
Excess sludge
Inhabitant-specific loads
g/(Inhabitant·d)
German standard (ATV-DVWK A 131) During biological wastewater treatment process for each kg BOD5 about 0,04-0,05 kg Nitrogen and about 0,01 kg Phosphorus are needed for the development of biomass and discharged in the waste sludge. *) The share returned in the sludge liquor has to be concerned. Thus the loads in the influent of the biological treatment stage can increase up to 20 %.
Dimensioning of the activated sludge process I 1. Determination of the relevant flows and loads 2. Selection of the treatment process => Nitrification/Denitrification
Activated sludge tank (Part 1) Set up of a Nitrogen-balance Selection of the treatment process
Nitrification/Denitrification; P-Elimination; Selector Selection of the return sludge ratio;
intermitting DN
time
Determination of the denitrification capacity Determination of the required sludge age Calculation of the sludge production
Nitrogen balance
Influent (primary-treated)
anoxic zone denitrification
aerobic zone COD-elimination & nitrification Effluent aeration
Recirculation sludge
Clarifier
Return sludge
Co,TKN
Excess sludge
N in influent: Co,N = Co,org.N + Co,NH
+ Co,NO
4-N
N in effluent: Ce,N = Ce,org.N + Ce,NH
+ Co,NO
3-N
+ Ce,NO
4-N
N in sludge: CNWS = 0,04 - 0,05 · Co,BOD
+ Ce,NO
3-N
5
2-N
2-N
German effluent regulations for municipal sewage; monitoring values
PE based on BOD inlet 60 g BOD5/(PE d )
COD
BOD5
NH4-N *)
Ntot anorg.
tot P
mg/l
mg/l
mg/l
mg/l
mg/l
1
< 1.000
150
40
–
–
–
2
1.000 bis < 5.000
110
25
–
–
–
3
5.000 bis < 10.000
90
20
10
–
–
4
10.000 bis < 100.000
90
20
10
18 **)
2
5
> 100.000
75
15
10
13 **)
1
Size Category
PE: population equivalent
*
Abwasserverordnung (AbwV vom 2004)
Nitrogen removal procedures
(DWA-A 131e, 2000)
Return Sludge Ratio I
The operating conditions in aeration tank and secondary settling tank are influenced through Mixed-liquor suspended solids concentration in the influent to the
secondary settling tank SSEAT Mixed-liquor suspended solids concentration of the return sludge
SSRS Return sludge ratio RS = QRS/Q.
Suspended solids mass balance (neglecting XSS,EST)
Return Sludge Ratio II
Influent QWW,h
Effluent
Recirculation sludge Return sludg e
QRS = 0.75·QWW,h max.QRS = 1.0 ·QWW,h
Denitrification capacity
(DWA-A 131e, 2000)
Important design parameter for activated sludge system Sludge age tSS:
[d]
Average retention time of activated sludge in the activated sludge system
tSS =
Amount of sludge in the aeration tank Removed amount of sludge
tSS = 1/(SPd·BSS)
tSS = 1/µmax
=
MLSS AT V AT QES MLSSES + Q MLSSE
tSS …..10 to 12 days
MLSS AT: Total amount of solids (MLSS) (measured)
[g/l or kg/m3]
MLSSES: Total amount of solids in the excess sludge
Enough time for the growth of microorganisms
Dimensioning sludge age in days dependent on the treatment target and the temperature as well as the plant size (intermediate values are to be estimated)
Required Sludge Age
(DWA-A 131e, 2000)
Sludge production SPd
SPd = SPd,BOD + SPd,P SPd,BOD= SPC,BOD * Bd,BOD,ZB
(DWA-A 131e, 2000) SPd,P [kg/d] = Qd [m³/d] (3 XP,BioP + 6,8 XP,Prec, Fe + 5,3 XP,Prec,Al)/1000
Dimensioning of the Secondary Settling Tank 1. Selection of the sludge volume index 2. Selection of t he sludge thickening time t Th ; dependent on the biological process selected 3. Determination of the return sludge suspend solids concentration (SSRS) 4. Selection of the return sludge ratio (RS) and estimation of the permissible suspended solids concentration of the activated sludge in the biological reactor (SS AT ). V AT reduces with increasing SS AT . A ST and t ST rises with increasing SS AT .
5.
Determination of the surface area of the scondary settling tank (A ST) from the permissible surface overflow rate q a or the sludge volume loading rate qav
6.
Determination of the depth of the secondary settling tank from partial depths for the functional zones and other sepcifications
7.
Dimensioning of the sludge removal (scraper)
8.
Verification of the selected thickening time by the sludge removal (scraper) performance
9.
Dimensioning of the return sludge and excess sludge pumps
Characteristic parameters
Mixed liquor suspended solids MLSS: Content of biomass Common values: 3 - 6 g/l
Sludge volume SV: Volume of sludge after 30 min. settling of 1000 ml activated
sludge
Measured value > 250 ml
dilution the sample (factor)
Common values: 200 – 600 ml
Sludge volume index SVI: Quotient of sludge volume and liquor suspended solids SVI = SV / MLSS Common values: 75 - 180 ml/g Bulking sludge SVI > 150 ml/g
(Steinke, 2009)
Standard values for the sludge volume index
= MLSS
Approximate values for the MLSS concentration in the biological reactor dependent on the sludge volume index for SSRS = 0.7·SSBS
(DWA-A 131e, 2000)
Settlement in horizontal flow tanks
(Austermann-Haun, 2011)
Permitted Thickening Time (t Th )
Type of wastewater tr eatment
Thickening time tTh [h]
Activated sludge plants without nitrification
1.5 - 2.0
Activated sludge plants with nitrification
1.0 - 1.5
Activated sludge plants with denitrification
2.0 - (2.5)
An exceeding of the thickening time of tE = 2.0 h requires a very advanced denitrification in the biological reactor.
Suspended Solids Concentration in the bottom sludge
Achievable suspended solids concentration in the bottom sludge SSBS can be estimated
empirically in dependence on the SVI and tTh
(DWA-A 131e, 2000)
Surface Overflow Rate and Sludge Volume Surface Loading Rate
The surface overflow rate q A is calculated from the permitted sludge volume loading rate qSV and the diluted sludge volume DSV as:
(DWA-A 131e, 2000)
Dimensioning of the Secondary Settling Tank
QWW,h (m³/h) - Max. inflow rate
SVI (l/kg) - Sludge volume index
SSEAT (kg/m³) - Suspended solids concentration in the influent to settling tanks
QRS Return sludg e
Effluent
Settling Tank Surface Area
The required surface area of the secondary settling tank results as follows:
(DWA-A 131e, 2000)
For vertical flow secondary settling tanks the effective surface area at the mid-point between inlet aperture and water level is to be set
With this the geometry of normal tank shapes is taken into account
Horizontal flow circular secondary settling tanks
Settling Tank Surface Area
(DWA-A 131e, 2000)
Dimensioning of the activated sludge process II Takeover: concentration of SS Activated
sludge tank (Part 2)
Calculation of the volume of the biological reactor Dimensioning of aeration (O2-demand; daily peak) Dimensioning of circulation units; design of circulation pumps Type of biological reactor Checking of acid capacity and pH
Volume of the Biological Reactor
Required mass of suspended solids in biological reactor: MSS, AT = tSS,Dim · SPd [kg]
Usual values of MLSS,AT: 2 - 6 g/l
The volume of the biological reactor is obtained as follows:
As comparative figures the BOD5 volume loading rate (BR) and the sludge loading rate (BSS) can be calculated:
Bd = BOD5
Qo
Nitrification BR =0,35 kg BOD5/(m³·d) Nitrification BSS= 0,10 kg BOD5/(kgSS·d)
Design of recirculation Influent QWW,h Effluent
Recirculation sludge Return sludg e
RC with
S NH 4 , N
S NO 3 , AN S NH 4 , N
1
C N ,O
S orgN , e
X orgN , BM
therefore : RC
Q RS Qt
Q RZ Qt
[]
Q RC
Qt * RF Q RS
bzw .
Q RZ Qt
RF
Q RS Qt
Dimensioning of aeration (O2-demand) Oxygen consumption for C-Elimination OUd,C [kg O2/d] = OUC,BOD,spez · Bd,BOD,I Specific oxygen consumption OUC,BOD [kg O2/kg BOD5, valid for CCOD,IAT/CBOD;IAT ≤ 2.2
(DWA-A 131e, 2000)
Oxygen consumption for Nitrification
OUd,N [kg O2/d] = Qd * 4,3*(SNO3,D – SNO3,IAT + SNO3,EST)/1000 Oxygen consumption for Denitrification
(+)
OUd,D [kg O2/d] = Qd * 2,9 * SNO3,D / 1000
Dimensioning of aeration (Daily peak OUh)
OU h [ kgO2 / h]
f C * (OU d ,C OU d , D ) f N * OU d , N
24
with f C and f N = Peak factors for load peaks (appear at different times) Load cases: I f N = 1 with f C = x
Sludge age in d
II f N = x with f C =1
4
6
8
10
15
25
f C
1.3
1.25
1.2
1.2
1.15
1.1
f N for BC,BOD,I ≤ 1.200 kg/d
-
-
-
-
2.5
2.0
2.0
1.8
1.5
-
f N for BC,BOD,I > 6.000 kg/d
