GERMAN ATV-DVWK RULES AND STANDARDS
Advisory Leaflet ATV-DVWK-M 206E Automation of chemical phosphate removal
November 2001 ISBN 3-937758-63-1
Publisher/marketing: GFA the publishing company of the 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:
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ATV-DVWK-M 206E
Die Deutsche Bibliothek [The German Library] – CIP-Einheitsaufnahme ATV-DVWK, German Association for Water, Wastewater and Waste: ATV-DVWK Rules and Standards (Medium combination) / ATV-DVWK, Wasserwirtschaft, Abwasser, Abfall. - Hennef : GFA, Publishing Company of the ATV-DVWK Formerly under the [German] title: Abwassertechnische Vereinigung: ATV-Regelwerk Advisory Leaflet M 206E. Automation of chemical phosphate removal ISBN 3-937758-63-1
The main fields of activity of the ATV-DVWK are technical-scientific subjects and the economic as well as the legal concerns of environmental protection. The politically and economically independent association works nationally and internationally in the fields of pollution control, wastewater, water-hazardous substances, waste, hydraulic engineering, hydraulic power, hydrology, soil protection and contaminated sites. The ca. 16,000 members are active in municipalities, engineer offices, authorities, firms and associations and also in universities. Of these there are 10,000 specialists with personal membership; these are engineers, scientists, lawyers, business persons, operating personnel and technicians. Via the corporate membership in the ATVDVWK there is access to ca. 160,000 specialists. All rights, in particular those of translation into other languages, are reserved. No part of this Advisory Leaflet 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.
Publisher:
ATV-DVWK Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V., Theodor-Heuss-Allee 17, 53773 Hennef
Marketing:
GFA Gesellschaft zur Förderung der Abwassertechnik e.V., Hennef
Setting and printing of the German original:
DCM, Meckenheim
© GFA Gesellschaft zur Förderung der Abwassertechnik e. V., Hennef 2001
2 November 2001
ATV-DVWK-M 206E
Foreword Since the publication of Advisory Leaflet ATV-M 206 “Automation of the Chemical Removal of Phosphate” in July 1994 a continuous technical further development has taken place in this field. As a result of the increasing expansion of process analysis technology in wastewater treatment plants, the further development of regulation and control strategies as well as new knowledge on the combination of a deliberate biological with a chemical removal of phosphorus a revision and amendment of the 1994 edition has become necessary.
Authors The original German Advisory Leaflet ATV-DVWK-M 206 was elaborated by the ATV-DVWK Specialist Committee KA-13 “Automation of wastewater treatment plants”. The following have collaborated in the preparation: Dr. rer. nat. J.-U. Arnold, Bergisch-Gladbach Dr.-Ing. P. Baumann, Stuttgart Dipl.-Ing. U. Blöhm, Berlin Dr.-Ing. P. Hartwig, Hannover Dr.-Ing. U. Jumar, Magdeburg Dipl.-Ing. E. Michel, Waldbronn Dr.-Ing. J. Reichert, Viersen Dr.-Ing. S. Schlegel, Essen (Chairman) Dr.-Ing. H.-H. Schneider, Berlin Dipl.-Phys. Ing. W. Worringen, Düsseldorf
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ATV-DVWK-M 206E
Contents Foreword ........................................................................................................................................................3 Authors ..........................................................................................................................................................3 User Notes......................................................................................................................................................5 1
Area of Application ........................................................................................................................5
2
Abbreviations .................................................................................................................................5
3
Introduction ....................................................................................................................................5
4
Basic Elements and Process Description ...................................................................................6
5
Continuous Measurement of the Phosphate or Phosphorus Concentration ..........................7
5.1 5.2 5.2.1 5.2.2 5.3 5.4
General.............................................................................................................................................7 Measurement of Orthophosphate (SPO4)..........................................................................................7 Molybdenum Blue Process ..............................................................................................................7 Vanadate Molybdate Process ..........................................................................................................8 Measurement of Total Phosphorus (CP) ..........................................................................................8 Operation and Maintenance.............................................................................................................8
6
Automation Concept involving Metal Salts and Sodium Aluminates ........................................8
6.1 6.2 6.3 6.3.1 6.3.2 6.3.3 6.3.4 6.3.5 6.3.6
Preamble ..........................................................................................................................................8 Measuring Sites and Dosing Points .................................................................................................8 Control and Regulation Concept for Phosphate Removal ...............................................................10 Control according to Timeplan .........................................................................................................10 Control according to P-Load ............................................................................................................11 Control according to Wastewater Flow ............................................................................................11 Regulation of SPO4 ............................................................................................................................12 Other Control Concepts....................................................................................................................14 Substitutional Value Strategies ........................................................................................................14
7
Storage and Dosing Technology ..................................................................................................15
7.1 7.2 7.3 7.3.1 7.3.2 7.3.3 7.4 7.5
General.............................................................................................................................................15 Dosing Facilities ...............................................................................................................................16 Storage and Dosing..........................................................................................................................17 Liquid Precipitants ............................................................................................................................17 Non-Pourable Precipitants ...............................................................................................................18 Pourable Precipitants .......................................................................................................................19 Measurement of the Precipitation Concentration.............................................................................21 P-Removal by Raising the pH-Value................................................................................................21
8
Economic Efficiency ......................................................................................................................21
9
Ordinances, Standard Specifications and Standards ................................................................22
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ATV-DVWK-M 206E
User Notes This Advisory Leaflet 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-DVWK and the Standard ATVDVWK-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 Advisory Leaflet is open to everyone. However, an obligation for application can arise from legal or administrative regulations, a contract or other legal reason. This Advisory Leaflet 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 Advisory leaflet.
1
Area of Application
This Advisory leaflet applies for activated sludge and fixed bed plants for the treatment of wastewater which essentially originates from households or from facilities which serve commercial or agricultural purposes provided that the harmfulness of this wastewater can be reduced using biological processes with the same result as with wastewater from households.
2 AbwV XSS SPO4,des CP,MV CP,Part CP CCOD,InB I PT F
Abbreviations Abwasserverordnung [German Wastewater Ordinance Concentration of suspended solids (0.45 µm) PO4-P design value at the dosing point e.g. in mg/l Monitoring value for the Ptot concentration in the effluent e.g. in mg/l P-concentration in the effluent of the plant due to residual suspensions e.g. in mg/l Measured concentration of phosphorus, e.g. in mg/l COD in the inflow to the biological reactor Inhabitant Total number of inhabitants and population equivalents Safety factor as empirical value, e.g. in mg/l
f FM k mMe
Safety factor Precipitant Proportionality factor Effective metal content of a precipitant solution, e.g. in mol/l mP,SS Phosphorus content of the suspended solids, e.g. in mg/kg SPO4 Orthophosphate-P Q Wastewater flow at the point of the Pconcentration measurement, e.g. in m3/h QPF Precipitant flow, e.g. in m3/h UV Ultraviolet VAwS Verordnung über Anlagen zum Umgang mit wassergefährdenden Stoffen und über Fachbetriebe [German Ordinance on plants for the handling of water-hazardous substances and on technical operations] WGK Wassergefährdungsklasse [German Water Hazard Class] WHG Wasserhaushaltsgesetz [German Water Resources Management Law] ß-value Ratio of mol metal to mol phosphorus related to the P-content in the influent to the precipitation reactor. In order to be able to assess the effectiveness of the precipitation the ß-value must actually be related to the P-content at the dosing point. In these cases higher values result than this normal operational definition. ρ Specific weight of the precipitant solution, e.g. in kg/m3
3
Introduction
Through legal regulations (§ 7a WHG; AbwV) the permitted phosphorus content in the effluent of municipal wastewater treatment plants is limited. With plants ≥ 10,000 PT up to 100,000 PT a monitoring value of 2 mg/l, with plants > 100,000 PT of 1 mg/l is to be maintained. More extensive requirements are possible in individual cases. Phosphates are removed through biological processes and through chemical precipitation. Aim of an automatic dosing of precipitant/flocculation agent is to achieve an extensive removal of phosphates from the wastewater with as small as possible employment of chemicals in order, in addition to the costs of precipitant, in particular to minimise the expenses for a disposal of the addition precipitation sludge produced. This should also be sought in order to keep the salting of the water low.
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4
Basic Elements and Process Description
Phosphorus is a wastewater content substance which can lead to eutrophication with discharge into a slowly moving or static body of water. In most water bodies the phosphorus content determines the degree of algae growth. In wastewater it usually originates from domestic discharges. Although a reduction of the specific total phosphorus production from ca. 5 to approximately 1.8 g/(I y d) through the very extensive reduction of the phosphate component in detergents, the normal concentrations in the influent of municipal wastewater treatment plants with 5 - 10 mg/l, however, lie as a rule still so high that an extensive removal is required. In individual cases, however, lower concentrations can also occur which can be traced back to either the dilution of the wastewater with infiltration water or to a higher component of industrial discharges. The latter usually only shows small phosphorus concentrations. A part of the phosphates contained in the influent is carried out both with the primary sludge (ca. 10 - 15 %) and also incorporated in the biomass and removed with the surplus sludge. Integration into the surplus sludge can, as a rule, can be estimated as 1 % of the added BOD5 or 0,005 y CCOD,InB (comp. ATV-DVWK A-131E). A small P/BOD5-ratio therefore requires less expense for extensive removal measures. A deliberately executed, increased biological Premoval can be achieved in the aeration stage through a special process technology (suitable switching in of anaerobic zones). The biological removal of P, however, does not always suffice in order to maintain safely the required monitoring value in the effluent. Therefore, as a rule, the possibility of dosing precipitant/flocculation chemicals is also planned for these cases. In general acidic iron salts as iron sulphate, iron chloride, iron chloride-sulphate, aluminium salts as aluminium chloride, the alkaline reacting sodium aluminate or, in special cases, also lime hydrate are applied as precipitants. For further basic information attention is drawn to the appropriate literature (ATV-DVWK-A 202E and the ATV Manual “Biological and advanced treatment of wastewater” [Not available in English]). The dosing of precipitant must be capable of being matched to the fluctuating influent and/or effluent values. With this, due to competing reactions, dosing has to be more or less hyperstoichiometric. Every overdosing, however, leads to a formation of
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hydroxides or carbonates which, due to increased sludge formation, are unwanted. For the adjustment of the dosing with plants with exclusively chemical phosphate removal a ß-value of 1.5 is set. As, however, usually phosphate is increasingly removed biologically, in practice the ß-value, elated to the P-content in the influent to the precipitation reactor (as a rule the aeration stage) very frequently lies under 1.0. With the addition of lime hydrate the precipitation of phosphates takes place through the raising of the pH value. With this, insoluble calcium phosphates are formed using the calcium ions contained in the wastewater. With the exception of very soft water there are sufficient calcium ions available. The correct selection of the pH value at the dosing point is dependent on the local conditions. With preprecipitation pH values up to 9.3 are permitted. With a dosing of lime hydrate into the aeration stage a pH value of 9.0 may normally not be exceeded in the effluent of the plant, as ammoniac, toxic to fish, can result due to the high pH value in the bodies of water. The chemical P-removal takes place in two steps, the rapid chemical reaction (precipitation) and the subsequent agglomeration of the small flocs into larger, easily separable floc formations (flocculation). Here, for the chemical reaction, a rapid, energy-intensive admixture of the precipitant into the wastewater is required. The flocculation itself on the other hand requires only a very small input of energy. Frequently points can be found in a wastewater treatment plant at which the admixture is ensured without additional input of energy. For example, overflows can be used for this. If necessary the required turbulence can also be created through the incorporation of chicanes or input of additional energy (e.g. employment of pumps). An alternative is also to improve the utilisation of precipitants by dosing the precipitant at several points of the aeration tank or over the complete width of the channel. In larger plants the production of a separate precipitation and flocculation reactor can be sensible with new construction measures. Depending on the place of dosing one differentiates the dosing into pre-precipitation, simultaneous precipitation and post-precipitation. With pre-precipitation the precipitant dosing takes place in the grit chamber or in the inlet to the primary settling with separation of the flocs in the primary settling tank. Due to the negative effects on the denitrification (reduction of the BOD5 load) it is, however, rarely employed. With a high component of industrial wastewater with high BOD5 and phosphorus concentrations or a downstream fixed bed plant, this process can, however, be employed
ATV-DVWK-M 206E thoroughly practically for the relief of the biological stage. In any case attention is to be paid that for the subsequent biological process still sufficient phosphorus remains in the wastewater. Simultaneous precipitation is currently the most widely employed process with which the addition of precipitant takes place directly into the activated sludge stage; the separation of the flocs takes place in the secondary settling tank. In addition to a good utilisation of the precipitant an improvement of the sludge index often presents itself as a positive side effect of simultaneous precipitation. The low Pconcentrations normal today in the wastewater usually allow the maintenance of the monitoring values of 2 mg/l and 1 mg/l respectively using this simple to operate method with sufficient efficiency of the secondary settling stage. If, with regard to an especially weak performance receiving water an even lower P-concentration is required usually additional measures have to be taken. Such measures are: – –
–
filtration, sieving or similar for separation of suspensa; polishing ponds can also support this. post-precipitation in the form of flocculation filtration: in order not to load the filter with too high a quantity of precipitation sludge, flocculation filtration, depending on the required effluent value, assumes a previous partial removal to 1 to 2 mg/l P. conventional post-precipitation: this takes place in a separate stage following the secondary settling tank. It consists of precipitation and flocculation tanks as well as the separation stage with a further secondary settling tank or a flotation plant.
quire a certain maintenance expense and the employment of chemicals. As comprehensive information for the employment and operation of process analysis equipment including the systems for the pre-treatment of samples are contained in ATVDVWK Advisory Leaflet M 269 [Not available in English], the essential analysis processes for the determination of phosphorus compounds are only gone into briefly in the following sections. Using process analysis equipment both orthophosphate (SPO4) and also Ptot (CP) can be determined. With measuring equipment for the determination of Ptot at most a coarse filtration may be placed upstream for the protection of the equipment, as an extensive separation of suspended solids which contain phosphorus leads to considerably reduced findings. The determination of the precipitable orthophosphate compounds, on the other hand, takes place as a rule following a sample pre-treatment, in order to be able to analyse reliably the then extensively solid matter-free wastewater. The sample pretreatment systems which come into question are described in detail in ATV-DVWK-M 269.
5.2
In the continuous analytics of orthophosphate up to now two photometric processes have gained in significance. With both processes polyphosphate and organic phosphorus compounds are not recorded. Depending on the application purpose there are, at the forefront, requirements for higher accuracy, DIN conformity or economic efficiency. The measuring process is to be selected accordingly.
5.2.1
5
Continuous Measurement of the Phosphate or Phosphorus Concentration
5.1
General
The continuous measuring facilities with process analysis equipment today employed for monitoring, control and regulation of the removal process operate according to expensive physical-chemical measuring processes. For this reason and due to the content substances in the wastewater, they re-
Measurement of Orthophosphate (SPO4)
Molybdenum Blue Process
With the molybdenum blue process (EN 1189) orthophosphate with ammonium molybdate in an acid medium converts into complex phosphorus molybic acid. This is subsequently converted using reduction agent into phosphorus molybdenum blue. The light attenuation brought about by the colouring is determined photometrically and is a measure for the orthophosphate concentration. The process covers the range from 0.01 to 5 mg/l SPO4 and is therefore particularly suitable for precise measurement with low concentrations. With higher concentrations the process has to be appropriately adjusted (e.g. through dilution of the wastewater sample). The chemicals used are, however, relatively expensive and are of only limited use.
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ATV-DVWK-M 206E 5.2.2
Vanadate Molybdate Process
With the vanadate molybdate process (yellow process), orthophosphates react in the acid medium with ammonium molybdate and ammonium vanadate into yellow ammonium phosphorus vanado-molybdate. The light attenuation brought about by the colouring is determined photometrically and is a measure for the orthophosphate concentration. Yellow wastewater content substances influence the measured value. This effect, as a rule, can be compensated through special automatic calibration procedures. The process covers a range from 0.1 to 20 mg/l SPO4. In comparison to the molybdenum blue process the chemicals are inexpensive and last longer.
5.3
Measurement of Total Phosphorus (CP)
Total phosphorus measuring equipment, as a rule, functions in accordance with the molybdenum blue process, but following previous digestion. Some equipment also allows the separate determination of the orthophosphate content. Digestion, as a rule, takes place through the heating with peroxodisulphate and sulphuric acid (modelled on EN 1189), partially under pressure, in order to shorten the degradation times. A degradation though UV radiation can only be applied for samples free of solid matter. The measurement of the total phosphorus content requires the inclusion of all solid matter in the digestion, as the greatest part of the phosphates are bonded to solid matter. Therefore it must be guaranteed that an unfiltered sample is analysed. In addition care is to be taken with sampling and preparation that a homogenous sample is produced. The lower limit of the measurement range of total phosphorus measuring equipment with the molybdenum blue process lies between 0.01 mg/l and 0.1 mg/l P. The upper limit of the measurement range varies between 5 mg/l and 15 mg/l P.
5.4
Operation and Maintenance
Process analysis equipment for the determination of phosphorus compounds requires a significantly higher maintenance expense than normal process measurement equipment such as, for example, for temperature or pH-value. Information on the gen-
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eral equipment requirements, for measures of quality assurance, for maintenance and servicing as well as the necessary training measures are to be found in Advisory Leaflet ATV-DVWK-M 269.
6
Automation Concept involving Metal Salts and Sodium Aluminates
6.1
Preamble
Although only the dissolved phosphates can be determined with precipitation the actual objective is the observation of the monitoring value for the total phosphorus concentration in the plant effluent with the lowest possible costs. With the choice of whether to integrate in a regulation/control of the Ptot (CP) or only to record the dissolved orthophosphate compounds (SPO4), the selected measuring site and dosing point as well as the intended control or regulation strategy are by all means to be taken into account. More detailed information is given by Table 1 in the following section. As, with precipitation, as far as possible phosphate loads should be taken into account, an integration of the wastewater flow into the automated concept is fundamentally to be recommended.
6.2
Measuring Sites and Dosing Points
In principle, for regulation and control tasks, various procedures come into consideration. Fig. 1 reflects schematically the possible measurement sites and dosing points in wastewater treatment plants as well as their suitability for this. The actual arrangement of measurement sites and dosing points is, inter alia, dependent on: – – – –
the local conditions (arrangement of tanks and pipeline layout), the selected automation concept (comp. Chap. 6.3), the process technology (chemical or combined biological-chemical phosphate removal, precipitation process) and the precipitant used.
ATV-DVWK-M 206E
Fig. 1:
Measurement sites and dosing points
With pre-precipitation using acidic metal salts or sodium aluminate, the phosphate or Ptot concentration is measured conveniently in the influent to the primary settling tank (B). Using this measurement a regulation of the input of precipitant into the grit chamber (A) or a control with input into the influent of the primary settling tank (B) is possible. The problem of a continuous measurement at this measurement site corresponds with that in the influent to the biological reactor (comp. Table 1). With simultaneous precipitation the dosing of precipitant can take place at various points in the system. A regulated input into a possibly available anaerobic stage or into its effluent (E) is basically not practical as the process of biological phosphate removal is not finished here and the take up of redissolved phosphate takes place first in the aerated stage. Frequently the precipitant is dosed into the return sludge circuit (C) and the phosphate content measured in the effluent of the aeration tank (F or G). This process has disadvantages due to the delay and dead times existing here. In addition there is only a little phosphate in the return sludge available for the reaction with the precipitant. The precipitant is used for the formation of metal hydroxide so that it has only limited availability for P-removal in the activated sludge stage. Through this, as a rule, an overdosing must take place. With input into the in-
fluent of the aeration tank (D) a certain overdosing must also take place, because the removal through incorporation of phosphorus into the surplus sludge has to be estimated. With a measurement in the effluent to the biological reactor the influence of the time delay on the regulation behaviour is to be taken into account. Furthermore attention is to be paid that the measured value in the effluent of the biological reactor does not correspond with the actual value in the plant effluent as subsequent influences such as, for example, balancing of concentrations or redissolving events in the downstream treatment stages (in particular with systems with biological phosphate removal) are not recorded. The best control reaction is to be expected if the precipitant is dosed into the effluent of the aeration tank or possibly into the last tank of a cascade (F). Measurement takes place conveniently in the influent to the secondary settling stage (G). With this variant a particularly careful mixing of the precipitant in the wastewater is to be ensured so that at the not far removed measuring site the precipitation reaction is extensively completed. Dosing in the influent to the secondary settling stage G) has also shown itself to be favourable. With unfavourable conditions here, however, only a control can be realised, measurement then takes place before the dosing point.
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ATV-DVWK-M 206E The dosing into the effluent of the aeration tank (F) with a measurement in the effluent of the secondary settling stage (H), due to the long retention time of the wastewater in the secondary settling tank leads to large dead times. Therefore a rapid reaction of changes of the P-load, which occurs particularly with combined wastewater influents, is impossible. With a post-precipitation the precipitant dosing takes place before the downstream stage (H). For Table 1:
regulation measurement is carried out in the effluent of this stage (I), with control in (H). The flocculation filtration with both concepts can be realised. In addition to the measuring site the measurement parameter for the control and regulation tasks is of particular significance. As an example Table 1 shows an overview of possible combinations of measurement sites and measurement parameters with the mainly applied simultaneous precipitation.
Combinations of measurement sites and measurement parameters with simultaneous precipitation Measurement parameter
CP
SPO4
Measurement site Influent biological reacPossible The incorporation of P in the surplus sludge is to be tor taken into account by estimation. A continuous sampling must take place so that the sample is not influenced by a pre-treatment which, possibly, can lead to a separation of particularly bonded phosphorus. This can, however, be guaranteed with difficulty at this measurement site. Effluent biological reacImpractical The phosphate bonded in the sludge flocs but which tor is not precipitable is also recorded therefore is not suitable for inclusion in the regulation of the precipitation. Effluent secondary settling stage
*
Impractical for an inclusion in the regulation* The monitoring parameter is recorded completely. The delay time is, however, too large for an inclusion in the regulation.
Possible At this measurement site only 60-75 % of the phosphorus compounds are already available as orthophosphate. The phosphate component which can be removed chemically has to be estimated. In this case the incorporation of P in the surplus sludge is also to be taken into account. Preparation of the sample at this measurement site can be expensive. Practical Direct recording of the precipitable P-component, through short delay times suitable for inclusion in the regulation (with suitable dosing site). Disadvantage: no complete recording of the monitoring parameters. Impractical As for the effluent of the biological reactor but, due to long delay time not suitable for inclusion in the regulation.
Although an input (proportional regulation) of the precipitant depending on the phosphorus concentration in the effluent of the secondary settling stage (both SPO4 as well as CP) is not to be recommended, such a measurement can, however, provide information on the effectiveness of the precipitant input and, under certain circumstances, enables an iterative adjustment of the precipitant input. Taking into account the real wastewater flow the regulation of the Ptot concentration in the effluent of the wastewater treatment plant in combination with a subordinate regulation of the PO4-P concentration in the effluent of the biological reactor (cascade regulation within the sense of control engineering) can increase the certainty of maintaining the monitoring values.
6.3
Control and Regulation Concept for Phosphate Removal
6.3.1 Control according to Timeplan With constant precipitant dosing in general a considerable overdosing of precipitant has to be undertaken as otherwise load peaks cannot be covered with certainty. With regard to the costs of precipitant and with the higher sludge yield associated with the input of precipitant, this strategy is not to be recommended for large plants. The quantity of precipitant can already be reduced effectively through the specification of different day and night dosing quantities. A further improvement is also possible through the dosing according to a specified load hydrographic curve. With hydrograph control one is concerned in principle with the replacement of a measured quantity with an empirical value. Representative daily
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hydrographs of the phosphate load are determined through measurements and placed in automation systems for control. Here, it has shown itself to be sensible to record hydrographs working days as well as for both weekends and holidays separately. Industrial discharges must, under certain circumstances, also be recorded separately. For practical purposes the hydrographs are determined in the effluent of the activated sludge stage as, through this, the influence of the biological phosphorus removal is taken into account. In principle control according to a hydrograph is, however, not in a position to react to unforeseen variations of the phosphate load. As, for example, the efficiency of the biological phosphorus removal can also vary, a safety reserve must always be created with this concept through overdosing. The hydrograph should be capable of being amended simply by operating personnel and thus matched to the changing requirements.
ATV-DVWK-M 206E
Fig. 2:
Control according to P-load
6.3.2 Control according to P-Load With this process the product from the wastewater flow at the site of the P measurement and the phosphorus concentration for the control of the dosing facility is used (comp. Fig. 2). The precipitant flow QFM here results as
QPF = k •. Q •. CP (Eqn. 1) with: QPF k Q CP
precipitant flow, e.g. in m3/h proportionality factor, e.g. in l/mg wastewater flow at the site of the measurement of the P-concentration, e.g. m3/h = measured phosphorus concentration, z. B. mg/l
= = =
The proportionality factor k (here for example for precipitant containing iron) is
k = f •. ß •. 55.8/30.9•. 1/ρ •. 1/mMe (Eqn. 2) Here the following is taken into account: f ß ρ
= = =
safety factor ß-value, e.g. 1.1 mol Fe/mol P specific weight of the precipitant solution, e.g. 1200 kg/m3 = effective metal content, e.g. 87 kg mMe Fe/1000 kg precipitant solution 55.8/30.9 = ratio of the mol masses of iron and phosphorus The safety factor f is to be set according to operating experience and normally lies between 1.0 and 1.5. This concept can be realised with simultaneous precipitation basically in two process engineering variants (comp. Fig. 1):
Variant a: Measurement site for CP and dosing point in the influent to the aeration tank (D) Variant b: Measurement site for SPO4 and dosing point in the effluent of the aeration tank (F or G) With Variant a the proportionality factor k must also take into account the estimated incorporation of phosphorus in the surplus sludge. The concept therefore contains a large uncertainty which has to be balanced through higher precipitant dosing. With Variant b the biological P-removal - both planned and unplanned – is completed and therefore no longer requires to be taken into account in the proportionality factor. Using this concept changes of the phosphorus concentration can be reacted to very rapidly and accurately. The load-controlled dosing can be applied particularly where other concepts, for example due to large delay and dead times or control engineering unfavourable arrangement of the reactors, cannot be applied. With this process, however, no direct control of the effectiveness of the precipitation is possible.
6.3.3 Control according to Wastewater Flow The control of the precipitant dosing according to the wastewater flow is a simplified variant in comparison with control of the P load. This concept is suitable when the P-concentrations in the influent vary only slightly. With combined wastewater flows, which cause a reduction of the P-concentration, such a procedure, however, leads to a significant overdosing.
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Fig. 3:
Control according to wastewater flow
Fig. 3 shows a typical characteristic curve for the control of the precipitant dosing according to the wastewater flow. With the undercutting of the value b) for the quantity of wastewater the proportionality factor k between wastewater flow and precipitant no longer applies, rather the dosing remains at a constant level. With a long-term undercutting of a “limiting quantity of water” c), which is to be determined empirically, a dosing of precipitant can possibly be dispensed with. If the wastewater flow exceeds the restart limit d), the dosing of precipitant is restarted. If the “limiting quantity of water” c), with the lowering of the water flow, is not achieved or is undercut, the dosing of precipitant remains up to the achievement of the value b) at a constant level. The selection of the limiting value must be in such a way that stable dosing conditions are set, that means no too frequent changing between switching in and out. In particular it must be checked in normal plant operation whether the restart limit d) can be set smaller or larger than b).
In smaller and more medium sized plants this strategy, an effective and economic application of precipitant can be realised without additional technical measuring expense.
6.3.4 Regulation of SPO4 The most favourable solution for technical regulation is an addition of precipitant into the effluent or the outlet area of the aeration tank, whereby the dosing of the precipitant is undertaken dependent on the orthophosphate concentration. Through a locking in of the wastewater flow (or the load) this regulation can be improved further. In both cases a continuous measuring of the SPO4 is necessary which, with thorough mixing, can take place several metres, otherwise up to 20 m or more behind the dosing point.
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Fig. 4:
Control of the orthophosphate concentration
In order to guarantee the maintenance of the monitoring value for the phosphate concentration (CP) in the effluent of the wastewater treatment plant the design value for SPO4 at the measuring site must be smaller than the monitoring value. That is necessary in order to take into account the P-load which is contained in the residual suspended matter which is contained in the effluent. The Pconcentration, which is contained in the solid matter, results from the percentage by mass of the phosphorus of filterable solids and their concentration in the effluent of the plant: CP,Part =
mP,SS • CXSS
SPO4,des with: SPO4,des CP,MV CP,Part F
= CP,MV – CP,Part – F
(Eqn. 4)
= orthophosphate design value in mg/l = monitoring value for the Ptot concentration in the effluent in mg/l = P-concentration through negative lift in mg/l = increased factor of safety as empirical value in mg/l
Fig. 4 shows the regulation concept for simple regulation of the phosphate concentration.
(Eqn. 3)
with: CP,Part = P-concentration due to residual suspended (in mg/l) mP,SS = P-contents of dry matter in the sludge (in mg P/g SS). This value is normally 25 – 35 mg P/g SS CXSS = concentration of the filterable solids (in g/l) Furthermore an “increased factor of safety” F to take into account the resolution effects in the downstream treatment stages of non-precipitable phosphate compounds as well as uncertainties in measurement of the process analysis equipment is required which, on the basis of operational experience, is to be set at about 0.2 mg/l SPO4. Thus there results as PO4-P design value for the regulation of the P-dosing a concentration SPO4,Spec of:
The quality of regulation can be improved still further through the locking in of the wastewater flow as influence quantity (comp. Fig. 5). This is particularly interesting with plants with combined biological–chemical phosphate removal. Here, with hydraulic peaks, resolved phosphate is often displaced in surges from the anaerobic zone into the aerobic zone. With too short retention times for an extensive take up of phosphate or with short-circuit flow, the phosphate concentration in the effluent of the activated sludge stage can increase very rapidly. This effect can be countered through a disturbance variable compensation depending on the quantity of water as this affects a timely increase of the dosing quantity. Attention is to be paid that the locking in of influencing quantities is so arranged that, following the start up of a combined wastewater inflow, it remains effective for a certain time only.
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ATV-DVWK-M 206E
Fig. 5:
Control of the PO4-P concentration with locking in of the influencing quantity of the wastewater flow
6.3.5 Other Control Concepts
6.3.6 Substitutional Value Strategies
The control concepts described can be expanded or combined taking into account the existing process technical conditions in the practical case. For example the regulation of the PO4-P concentration with a locking in of the wastewater flow shown as an example in Fig.5 can be so expanded that, in accordance with the model of Fig. 2, not the wastewater flow but rather the P-load is locked in as influencing quantity. Furthermore it can be practical or necessary to carry out the locking in not as a static locking in but rather that this is done via dynamic elements, for example as “moderating locking in” (comp. Section 6.3.4).
The above presented automated concepts assume that the actual phosphorus concentrations present are available reliably and as far as possible continuously as measured values. In order that a failure of the measurement signal, for example during a calibration or with an equipment fault is not associated with negative consequences for the process control, substitutional values must therefore be secured for the automation which, in place of the real process values, ensure emergency operation. Furthermore, it is to be defined when the measured value is to be considered as faulty and, instead of this, a substitute value is to be applied.
In individual cases so-called “knowledge based regulation systems” are also employed of which fuzzy controls have achieved the highest degree of familiarity. With these approaches, control is defined in the form of verbally formulated, blurred rules. Assuming a clear number of these rules, control solutions result which are characterised in general through transparency and good reproducibility. The necessary process knowledge for the design of such control systems corresponds with that for the design of the simple conventional control and regulation described in Sections 6.3.1 to 6.3.4. The dynamic systems behaviour of a fuzzy control system can be interpreted as non-linear characteristic diagram. Due to the few plants managed by this type of regulation a detailed handling of this area is not included in the scope of this Advisory Leaflet.
Within the scope of the substitute value strategy it is determined which of the following processes are to be applied for the creation of substitute values: – – – – –
declaration of a fixed value as default value, specification of characteristic curves, adoption of measured values from a train operated in parallel, employment of the last undisturbed value with or without extrapolation in time, employment of auxiliary parameters.
The following can be viewed as criteria for a “measured value fault” with the activation of a substitute value strategy:
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ATV-DVWK-M 206E – – – –
fore place particular requirements on the dosing facilities.
so called “live zero” – monitoring of the 4 – 20 mA signal of the measuring transducer, status report (self-monitoring) of the analysis equipment, deviation from the plausible range of measured values through monitoring of the upper and lower boundary values, operation of a “maintenance switch” with calibration procedures.
7
Storage and Dosing Technology
7.1
General
The precipitants containing iron and aluminium as well as milk of lime are classified as weak water hazarding substances (WHC 1). The facilities for the storage and dosing of chemicals are to be established and operated in accordance with the requirements of the respective [German] Federal State (e.g. Ordnance on the Handling of Water Hazarding Substances and on Specialist Operation [In Germany = VAwS]). The aqueous solution of acidic precipitants based on iron and aluminium salts is, as a result of the low pH-value and the high salt concentration, extremely corrosive. All parts in contact with the solution must therefore be made resistant to acid, for example covered in plastic or with a suitable coating. With the employment of GRP, attention should be paid that the plastic coating is acid- and alkali-resistant, in order that acidic or alkaline precipitants can be stored as desired.
Common precipitants are summarised with their important physical and chemical data in Table 2. Solubility, density and viscosity depend strongly on the temperature and the substance contents and thereTable 2:
Physical and chemical data on the most common precipitants Product supplied
Precipitant (main component))
Examples for normal solution
Typical form of delivery
WHC
Percentage by Prec
Active subst.
Density or bulk density 3
Viscosity
Operating temperature
Iron(III) chloride Iron(II) chloride Iron(III) chloridesulphate Iron(II) sulphate
FeCl3 FeCl2 FeClSO4
Solution (32-42 %) Solution (20 – 30 %) Solution (ca. 40 %)
1 1 1
% 40 20 41
% 13.8 8.7 12.3
g/cm 1.43 (20 °C) 1.36 1.52
mPa y s 10 (20 °C) 3 (20 °C) 42 (15 °C)
°C > - 12 > - 15 > - 10
FeSO4 . 7H2O
1
-
3 (20 °C)
>-2
AlCl3
1
30
17.8 – 19.6 6
1.2 (20 °C)
Aluminium chloride Polyaluminium chloride Aluminium sulphate Sodium aluminate
Crystalline bulk material Solution (30-40 %)
1.3 (20 °C)
10 (20 °C)
> - 20
Al(OH)3-xClx
Solution (5-10 %)
1
-
5.9 – 7.5
1.3
10 (20 °C)
> -15
Al2(SO4)3
Solution
1
24
4
1.27
10 (20 °C)
> -15
NaAl(OH)4
Solution (5-12 %)
1
-
7.3 – 11
1.3 (20 °C)
20 (20 °C) * to 200 ** (20 °C)
> - 20
White fine lime CaO White lime hy- Ca(OH)2 drate Milk of lime Ca(OH)2 * ** ***, ****
Powder Powder
1 1
-
-
0.8 –1.0 0.4
Suspension (20-40 %)
1
20
-
1.1 (20 °C)
> 200 (20 °C) ** 100-150 *** 800-1200 ****
>0
5 % Al content 11 % Al content 10 % solution; different values through different grain size distribution
Table 3 contains information on the resistance of various material compared with aqueous solutions of the precipitant.
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ATV-DVWK-M 206E Tab. 3: Resistance of various materials to aqueous solutions of precipitants at 20 °C (1 = good resistance, 2 = limited resistance, 3 = non-resistant) Material: Aqueous solution of: Iron(II) chloride Iron(III) chloride Iron(III) chloride-sulphate Iron(II) sulphate Sodium aluminate Aluminium chloride Aluminium sulphate Aluminium hydroxide chloride Milk of lime * **
St 35, St 37
1.4301 (V2A)
1.4571 (V4A)
GCI*, NGI**
Titanium
PVCU
HD PE
GRP
3 3 3 3 1 3 3 3 1
3 3 3 2 1 3 2 2 1
3 3 2 1 1 2 1 2 1
3 3 3 3 1 3 3 3 1
1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1
2 2 2 1 1 1 1 1 1
GCI = grey cast iron NGI = nodular graphite iron
Precipitants based on iron and aluminium salts and sodium aluminate are yielded as by-product in the metal and chemical industries. They can contain residues and foreign material which complicate the employment in wastewater treatment. Type and share of these substances as well as the observation of the permitted limiting values are to be given or guaranteed by the producer. Maximum values are, inter alia, contained in ATV-A 202E. Pour able precipitants tend, with longer storage to material compacting and hardening (bridge building). Therefore special measures for storage are necessary in particular with hygroscopic products. (see Chap. 7.3.3). Sodium aluminates are as a rule also not stable for longer than six months. Here precipitation and hardening can take place.
7.2
Dosing Facilities
The dosing facilities and the pipelines associated with these must satisfy the requirements of the VAwS. Also with regard to the material used the same requirements are to be applied as for facilities for disposal (so-called produce – treat – use plants [in German: HBV plants: Herstellen Behandeln Verwenden]) and for warehousing (so-called store – fill – tranship plants [in German: LAU plants: Lagern Abfüllen Umschlagen] ). As the dosing facility functions as final control element its delivery range is to be agreed with the required delivery performance in the actual and design condition (expansion status). A too high dosing performance is frequently applied, whereby the dosing accuracy in the lower operation range is affected adversely or too high quantities of precipitant are always applied. The highest dosing performance per hour should therefore be no more
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than 15 % of the daily performance. In case the pump is dimensioned too large an intermittent dosing can in emergency further reduce the consumption of precipitant. Exceptions here are formed by plants with deliberate biological phosphate removal. Here, if required, even a separate pump to cover peak loads can be practical. The precipitants in general are dosed through dosing pumps or under gravity, e.g. from a levelling bulb, through a fitting. With plants with several dosing points it is recommended to carry out dosing from a ring circuit in order to ensure an even distribution and to avoid incrustation. Ring circuits should also be employed with suspensions which tend towards depositing. As dosing pumps mainly reciprocating and rotary pumps are used, such as diaphragm pumps, piston diaphragm pumps and eccentric screw pumps as well as, less often, hose pumps. Due to their form reciprocating and rotary pumps maintain with higher accuracy the dosing quantities (design values) specified by the control or regulation facility. For circulation mainly centrifugal and eccentric screw pumps are employed. Connections for flushing, air removal and emptying are to be supplied in sufficient numbers for running up and running down. They should be installed at points where depositing and precipitation takes place. Externally laid pipelines are to be insulated and equipped with concomitant heating. With frost-free laying in the ground this can be dispensed with. They are basically to be produced as pipe-in-pipe systems which have a gradient to a visible outlet or manhole. They are to be checked before commissioning and subsequently according to the provisions of the applicable VawS. The output with reciprocating and rotary pumps, depending on the system, is influenced by the
ATV-DVWK-M 206E number of revolutions per minute, piston stroke or number strokes per minute, with eccentric screw pumps by the revolutions per minute, with shut-off devices by the duration of the opening time and with regulator devices by the degree of opening. The dosing and circulation pumps should as far as possible be set up in the vicinity of the storage tanks, in order to keep the suction lines short. Fundamentally the suction line should be a nominal width larger than the pressure line. With piston and piston diaphragm pumps operating behaviour is improved by pulsation dampers. With dosing using pumps care is to be taken to provide a sufficient back pressure on the delivery side. With several dosing points and different delivery heads the pressure drop is to be taken into account. Therefore appropriate measures, such as pressuriser valves or separate dosing pumps, are to be planned. For the layout it is to be noted that the performance data of the dosing facilities are
Fig. 6:
related to clean water, but precipitants have a higher viscosity and density. In particular, the different viscosity of the precipitant depending on temperature and metal content is often not taken into account. The high - in comparison with iron salts – viscosity of sodium aluminate with higher Al contents (ca. 10 %) and low precipitant temperatures is to be noted particularly in this case.
7.3
Storage and Dosing
7.3.1 Liquid Precipitants The necessary equipping of a plant for the storage and dosing of liquid precipitant is shown in Fig. 6. Here the storage tank (1) is represented with double walls. Single-wall tanks are to be placed in collecting troughs without outlet which have the same capacity.
Storage and dosing station for liquid precipitants
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ATV-DVWK-M 206E The following details are pointed out: – – – –
–
start-up facilities (10,14), which can be replaced by a filling connection for process water as an alternative (17). flap trap with strainer basket (16). overflow valve (22) for the security of the pump membrane and the pressure side pipeline system. the delivery flow can be determined using suspended solid particle flowmeters or MIF (24). with larger plants the continuous registration of the precipitant flow using MIF is sensible for operating reasons. At least one container should be firmly installed for the gauging of capacity in litres in order thus to be able to check the dosing simply at certain time intervals. leakage monitoring (29), which indicates leaks in the dosing station and the pipeline system and which possibly automatically activates a
Fig. 7:
18
– – –
ventilation valve on the suction line in order to avoid a siphoning of the tank. expansion fittings are to be provided for the maintenance intensive systems. in order to avoid overfilling with certainty, a second, independent measuring systems (digital limit selector) should be installed. with a change of precipitant the system – in particular the tank – is to be washed out carefully as precipitant residues can react with the new product (precipitation). Furthermore the plant must be approved for the new precipitant.
7.3.2 Non-Pourable Precipitants Fig. 7 shows the system setup of a facility for the dosing of iron(II) sulphate, in which the installations for storage, dissolving of the salts and the storage of the solution (1) are combined in one structural unit.
Storage and dosing station for non-pourable precipitants
November 2001
ATV-DVWK-M 206E Attention is drawn particularly to the following:
7.3.3 Pourable Precipitants
–
Fig. 8 shows the necessary equipping for the storage, preparation and dosing of milk of lime as lime hydrate. In general lime hydrate is delivered in silo vehicles and transferred into the storage silo (6). The delivery of precipitant is supported pneumatically via air cushions (5). The blower (2) should, as far as possible, be mounted directly on the silo. An automatic monitoring of the cleaning intervals and a monitoring of the pressure difference of the exhaust air filters (12) is recommended. The filling level is monitored using mechanical detectors (7, 8), for example rotating blades, pivoting forks, or monitored via the silo weight through continuous measurement equipment (15), for example: pressure pickup. Cellular wheel sluices prevent the “shooting” of the silo content material and serves as initial distributors for the downstream spiral conveyer (14) or container scales. The material is transported via the spiral conveyor (14) by charge into the batching and storage tanks (16). The addition of dilution water (13) is controlled via the filling level (19). Normally the silo material, as no high demands have for accuracy have to be placed on the mass flow, is added via metering screws proportional to volume. By means of special structural design, for example as hollow screw, opposed double-lead screws or as metering screw with superimposed rotational and axial movement, a self-cleaning effect is achieved and encrustation prevented.
– – –
–
it is recommended that the cover of the filling opening (6) is equipped with load-relieving weights or springs for easy handling. As faulty filling cannot be avoided the tank should be provided with openings, safeguarded by sieves (5) for the introduction of flushing water. With the planning of the structure and the access routes attention is to be paid that vehicles can approach and dump their cargo without problem. in order to avoid a spilling of crystalline salt during filling, the dissolving bunker must be extensively emptied before charging (19). the consumption of precipitant solution is completed automatically through the addition of solution water (7). dosing takes place in Fig. 7 from the levelling tank (11). Attention is to be paid to the careful retention of undissolved salt in the dissolving chamber. for improved dissolving it is expedient to pump over the solution (17, 18).
In addition the last five bullet points in Section 7.3.1 are to be taken into account.
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ATV-DVWK-M 206E
Fig. 8:
Storage and dosing station for pourable precipitants
The milk of lime is dosed, from the storage tank, from a ring circuit (23), for example via rubber pinch valves (24). The dosing of milk of lime, in addition, sets special requirements: – –
–
– –
concentration of the suspension: 5-10 %, maximum 15 %. with several dosing points as well as with long transport paths it is practical to dose from a ring circuit. The suspension is pumped around this in order to avoid sedimentation. ring circuits and dosing pipelines are for practical purposes made from fabric reinforced plastic hose (∅ > 1″, radius of curvature > 5 times ∅). Baffles and changes of cross-section are to be avoided; flow rate > 1.5 m/s. dosing pipeline outlets from the ring circuit may branch upwards only in order to avoid sedimentation of the milk of lime. rubber pinch valves have proved to be successful as dosing fixtures.
– – –
dosing lines, as far as possible, should discharge below the water level. ring circuits should always be filled, when idle with water. Longer pipelines should be flushed with water on completion of dosing. connections for the acidulation of the pipeline system are to be provided.
In addition the requirements from the last three bullet points in Section 7.3.1 are to be considered analogously. Below some peculiarities with pourable precipitants are additionally pointed out: –
–
with the storage of pourable iron(II) sulphate and iron(III) chloride it is necessary to protect the silos from the sun as the products upwards from ca. 40 °C tend to form lumps. with hygroscopic precipitants the exit opening of the dry material screw conveyor (14), the screw mouth, is particularly sensitive to backing-up, as the moist air rising from the solution tank below condenses here. In this case an asNovember 2001
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ATV-DVWK-M 206E sociated heating and an automatic gate valve below the screw outlet opening should be provided. However, basically, the screw mouth should be easily accessible in order to be able to carry out possible necessary cleaning tasks.
7.4
Measurement of the Precipitation Concentration
The density and concentration of the precipitant are linearly dependent on each other. Thus the density can be used in order to determine the salt content of the precipitant solution. This can take place manually discontinuously by means of spindle measurement according to Beaumé, continuously using a differential pressure measurement or a using a mass flowmeter in accordance with the Coriolis principle. The concentration of the working substance is to be taken from the data sheet of the respective supplier.
7.5
P-Removal by Raising the pH-Value
With a precipitation using hydrated lime, the dosing system must be so designed that, despite variations of the flow of wastewater, the desired pH value can be maintained at +/- 0.1 pH precisely, as the pH value to be maintained in the effluent lies very close to the operating point of simultaneous precipitation (pH = 8.6 – 9.0). Gel electrodes with short reaction times have shown themselves to be suitable for pH measurement. The manufacturers offer electrodes which are especially suitable for the dosing of milk of lime (e.g. electrodes with Teflon diaphragms). The electrode brackets should have large flow openings so that they cannot clog. In addition they must be mounted in such a way that the electrodes are easily accessible for maintenance and can be wetted at every water level. In addition, it is an advantage for regular mechanical cleaning to employ an automatic electrode cleaner with which the electrode(s) can be washed or acidated at short intervals. The acid flushing facility must be designed in such a way that no tangles can form on the spray elements. Systems which clean the electrodes in a separate tank can be an advantage here. During cleaning the control facility (automatic) must be interrupted and the last dosed quantity of lime kept constant until the pH electrode is again ready for operation. It is recommended that, in addition to the control electrode an additional further electrode is applied for the monitoring of the system.
8
Economic Efficiency
The economic efficiency of the measures for the automation of chemical phosphate removal is to be checked carefully in every case. As a rule, savings with the required quantity of precipitant as well as with sludge treatment and disposal counter the expenditure for measurement and control technology. Advantageous, but barely appraisable, is the stable maintenance of the monitoring value. Already the installation of simple controls (input of precipitant dependent on specified characteristic curves or dependent on flow of wastewater) is worthwhile even for smaller plants. Upwards from a certain design capacity the employment of process analysis equipment in combination with the previously described regulation and control concepts is, however, more economic. The total system of the measurement system is always to be considered for the assessment of the costs. In addition to investment costs for the analyst, a possible necessary space for the accommodation of the system, the pre-treatment of samples and the continuous transfer of samples, in particular also the running costs for reagents, replacement parts and expendable items, servicing and maintenance and other incidentals are to be included (comp. ATV-DVWK M-269). To be added to these are the costs for automation. Cost considerations according to the Cost Comparison Calculation (KVR) Directive of the LAWA [German Federal State Working Group Water] show that the employment of process analysis equipment, depending on local conditions, as a rule is economical upwards from a connection capacity of some 40,000 PT. Frequently such equipment is already present for other reasons (e.g. monitoring of documentation and operation). Then it is possible to combine these also into the regulation and control concept, if necessary the equipment for this can be transferred to suitable positions (comp. Chapter 6). The economic efficiency of process control with solely chemical P-removal is substantially dependent on the variations of the P-concentration at the dosing point. Thus, with relatively constant Pconcentration, only a limited amount of precipitant can be saved and the precipitation sludge yield reduced. If the chemical P-removal is employed to supplement biological P-removal, although the Pconcentrations at the dosing point in the outflow of the biological stage overall are significantly smaller than without biological P-removal, the variations in
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ATV-DVWK-M 206E concentration can, in certain cases, be large due the varying process behaviour of the biological Premoval. Here, through process control, there is the possibility of stabilising the biological P-removal through prevention of a large input of precipitant and thus indirectly reduction of the requirement for precipitant and the sludge yield. Furthermore, it is pointed out that an adaption of the storage and dosing facilities also contributes to the economical efficiency of phosphate removal. In particular with very small plants it is not practical to install very large storage tanks as here, with complete filling, the precipitant has to be stored too long. This is to be noted particularly with sodium aluminate and pourable precipitants. Although higher costs result with smaller storage tanks and smaller delivery quantities, the investment costs of smaller tanks are lower and the operation simpler.
9
Ordinances, Standard Specifications and Standards [Translator’s note: References available in English are shown as such. For those references with no known official translation a courtesy translation is provided in square brackets]
EN 879 EN 881
EN 882 EN 883
EN 887 EN 888 EN 889 EN 890
22
Aluminium sulphate, iron-free, for treatment of water intended for human consumption: 1992 Aluminium chloride, aluminium hydroxide chloride and aluminium hydroxide chloride sulphate (monomer), for treatment of water intended for human consumption: 1997 Sodium aluminate, for treatment of water intended for human consumption: 1997 Polyaluminium chloride hydroxide and –chloride hydroxide sulphate, for treatment of water intended for human consumption: 1997 Aluminium iron sulphate, for treatment of water intended for human consumption: 1992 Iron(III) chloride, for treatment of water intended for human consumption: 1998 Iron(II) sulphate, for treatment of water intended for human consumption: 1998 Iron(III) sulphate, for treatment of water intended for human consumption: 1998
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EN 891 EN 935
EN 1189
EN 12255-13 DIN 19 611
DVGW W 622
Iron(III) chloride sulphate, for treatment of water intended for human consumption: 1998 Aluminium iron chloride and aluminium iron hydroxide chloride (monomer), for treatment of water intended for human consumption: 1992 Water quality – determination of phosphorus – by the ammonium molybdate spectrometric method: 1996 Wastewater treatment plants, Part 13: Wastewater treatment through addition of chemicals Weißkalk zur Wasseraufbereitung – Technische Lieferbedingungen [White lime for the processing of water – Technical delivery conditions], Issue 1983-04 Dosieranlagen für Flockungsmittel und Flockungshilfsmittel [Dosing facilities for flocculants agents and flocculation aids.
ATV-DVWK-A 131E Dimensioning of Single-Stage Activated Sludge Plants, (2000) ATV-A 202 Verfahren zur Elimination von Phosphor aus Abwasser [Processes for the Removal of Phosphorus from Wastewater] (1992) ATV-DVWK-M 269 Prozessanalysengeräte zur Bestimmung von N, P und C in Abwasseranlagen [Process Analysis Equipment for the Determination of N, P and C in Wastewater Systems] (2000) KVR-Richtlinie [CCC Directive] Leitlinie zur Durchführung dynamischer Kostenvergleichsrechnungen [Guideline for the carrying out of dynamic cost comparison calculations], Publ.: LAWA, Kulturbuchverlag Berlin GmbH, ISBN 3-88961-228-8 NN Verordnung über Anlagen zum Umgang mit wassergefährdenden Stoffen und über Fachbetriebe (VAwS), länderspezifisch [German Ordinance for plants on the handling of water-hazardous substances and on specialist operation (VAwS), specific for each German Federal State] NN Herstellung, Lagerung und Dosierung von Kalkprodukten [Production, storage and dosing of lime products];
ATV-DVWK-M 206E Bundesverband der Deutschen Kalkindustrie e.V., Köln (1992), pH-gesteuerte Dosierung von Kalkmilch zur simultanen Phosphorelimination auf Kläranlagen [pH controlled dosing of milk of lime for simultaneous phosphorus removal in wastewater treatment plants]
NN Herstellung und Dosierung von Kalkmilch [Production and dosing of milk of lime]; Bundesverband der Deutschen Kalkindustrie e.V., Köln (1986)
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