GERMAN ATV-DVWK RULES AND STANDARDS

Standard ATV-DVWK-A 198EStandardisation 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 D-53773 Hennef Tel. ++49-22 42 / 8 72-120 Fax:++49 22 42 / 8 72-100 E-Mail: vertrieb@atv.de Internet: www.atv-dvwk.de

ATV-DVWK-A 198E

User NotesThis 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: 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: vertrieb@atv.de Internet: www.atv-dvwk.de

Setting-up and printing: DCM, Meckenheim

ISBN: 3-924063-63-X Printed on 100 % recycled paper

ATV-DVWK Deutsche Vereinigung fr 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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ATV-DVWK-A 198E

AuthorsThis 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. Meiner, Mnchen Dipl.-Ing. H. Schmidt, Erkrath Prof. Dr.-Ing. Th. Schmitt, Kaiserslautern Dr.-Ing. M. Schrder, Aachen Bauass. Dipl.-Ing. G. Willems, Essen

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ATV-DVWK-A 198E

ContentsUser Notes ............................................................................................................................................... 2 Authors .............................................................................................................................................................3 1 1.1 1.2 1.3 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 3 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 4 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 Area of Application ...........................................................................................................................6 Preamble ................................................................................................................................... 6 Objective.................................................................................................................................... 6 Scope ........................................................................................................................................ 6 Symbols..............................................................................................................................................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 Preparatory Work for the Derivation of Dimensioning Values ...................................................12 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 Determination of Data about the Actual Condition ......................................................................16 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 198E4.3.1.5 4.3.1.6 4.3.1.7 4.3.1.8 4.3.2 5 6 7 8 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 Forecast Data.....................................................................................................................................28 Costs and Environmental Effects ...................................................................................................28 Relevant Regulations, Standards and Standard Specifications ................................................28 Literature [Translators 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

1.2 ObjectiveThis 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.

1.1 PreambleIn 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.

1.3 ScopeThe here summarised terms and bases for the determination of catchment areas, flows/discharges, loads and concentrations

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ATV-DVWK-A 198Econcern 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). 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-

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Symbols

2.1 GeneralA 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]. Translators 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. For the main meanings below the indices are specified in the following order:

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

Catchment areas (AC) [AE], further subdivision, for example:

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ATV-DVWK-A 198E2.2 Surface Parameters and Runoff CoefficientsAs 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 assignableSymbol English AC AC,s AC,ns AC,p AC,np AC,Ind Aimp A_C A_C,s A_C,ns A_C,p A_C,np A_C,ind A_imp AE AE,k AE,nk AE,b AE,nb AE,G Au German A_E A_E,k A_E,nk A_E,b A_E,nb A_E,G A_u ha ha ha ha ha ha ha Catchment area; e.g. of a wastewater disposal region 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 Commercial and/or industrial catchment area Impermeable surface area, application-related numerical value: Aimp = AC,s or Aimp = AC,p [Au = AE,k or Au = AE,b ] (dependent on terms of reference), if required also sum of several flow-effective surface components: Aimp = (AC,i i) [Au = (AE,i i)] 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, = AC,p/AC [ = AE,b/AE] 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 m, peak [m, s] 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-DVWKM 177 (2001) for the determination of the numerical value Aimp from the size of the paved surface AC,p [AE,b] Unit

from the locality, others first result through multiplication using a runoff coefficient and represent numerical values. In Appendix A further explanatory notes can be found on surface parameters and the values derived from these.Designation

PD IG I_G ED IG I_G

I/ha E/ha % -

m

_m

m

_m

-

s

_s

s

_s

-

A128

_A128

A128

_A128

-

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ATV-DVWK-A 198E2.3 Flow/Discharge ParametersSymbol English fWW,QCW QD QInd QWW QWW,max,85 f_WW,QCW Q_D Q_Ind Q_WW Q_WW,max,85 fS,QM QH QG QS QS,max,85 German f_S,QM Q_H Q_G Q_S Q_S,max,85 l/s l/s l/s l/s 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 Unit Designation

QInf QDW QR QComb QR,Sep QThr Qa Qd QDW,d QDW,d,aM

Q_Inf Q_DW Q_R Q_Comb Q_R,Sep Q_Thr Q_a Q_d Q_DW,d Q_DW,d,aM

QF QT QR QM QR,Tr QDr Qa Qd QT,d QT,d,aM

Q_F Q_T Q_R Q_M Q_R,Tr Q_Dr Q_a Q_d Q_T,d Q_T,d,aM

l/s l/s l/s l/s l/s l/s l/s l/s l/s l/s

QDW,aM Qd,Conc Qh Q2h QWW,x QDW,max QDW,h,max QDW,2h,max qInf qR qInd wd wWW,d

Q_DW,aM Q_d,Conc Q_h Q_2h Q_WW,x Q_DW,max Q_DW,h,max Q_DW,2h,max q_Inf q_R q_Ind w_d w_WW,d

QT,aM Qd,Konz Qh Q2h QS,x QT,max QT,h,max QT,2h,max qF qR qG wd wWW,d

Q_T,aM Q_d,Konz Q_h Q_2h Q_S,x Q_T,max Q_T,h,max Q_T,2h,max q_F q_R q_G w_d w_WW,d

l/s m3/h m3/h m3/h m3/h, l/s l/s m3/h, l/s m3/h, l/s l/(sha) l/(sha) l/(sha) l/(Id) l/(Id)

2.4 Concentration ParametersConcentrations without additional details apply for 24-h composite samples, with index, for example, 2h is defined as the average concentration in a

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 198ESymbol English CXXX C_XXX CXXX German C_XXX mg/l Concentration of the parameter XXX, in the homogenised sample Concentration of the parameter XXX, in the homogenised grab sample Concentration of the parameter XXX, in the filtered sample (0.45 m membrane filter) Concentration of the filter residue, XXXX = CXXX - SXXX Average concentration in a 2-h interval Annual average value of a concentration Concentration of BOD5 in the homogenised sample Concentration of BOD5 in the sample filtered with 0.45 m membrane filter Concentration of COD in the homogenised sample Concentration of COD in the sample filtered with 0.45 m membrane filter Concentration of total nitrogen in the homogenised sample as N (CN = CorgN + SNH4 + SNO3 + SNO2) Concentration of Kjeldahl nitrogen in the homogenised sample (CTKN = CorgN + SNH4) Concentration of organic nitrogen in the homogenised sample as N (CorgN = CTKN SNH4 or CorgN = CN SNH4 SNO3 SNO2) Concentration of inorganic nitrogen as N (SinorgN = SNH4 + SNO3 + SNO2) Concentration of ammonia nitrogen in the filtered sample as N Concentration of nitrate nitrogen in the filtered sample as N Concentration of nitrite nitrogen in the filtered sample as N Concentration of phosphorus in the homogenised sample as P Concentration of phosphate in the filtered sample as P Unit Designation

CXXX,GS SXXX XXXX CXXX,2h CXXX,aM CBOD SBOD CCOD SCOD CN CTKN CorgN SinorgN SNH4 SNO3 SNO2 CP SPO4 SALK XSS XorgSS XinorgSS

C_XXX,GS CXXX,SP S_XXX X_XXX SXXX XXXX

C_XXX,SP S_XXX X_XXX C_XXX,2h C_XXX,aM C_BOD S_BOD C_COD S_COD C_N C_TKN C_orgN S_anorgN S_NH4 S_NO3 S_NO2 C_P S_PO4 S_KS X_TS X_orgTS

mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l mg/l

C_XXX,2h CXXX,2h C_XXX,aM CXXX,aM C_BOD S_BOD C_COD S_COD C_N C_TKN C_orgN S_inorgN S_NH4 S_NO3 S_NO2 C_P S_PO4 S_ALK X_SS X_orgSS CBOD SBOD CCOD SCOD CN CTKN CorgN SanorgN SNH4 SNO3 SNO2 CP SPO4 SKS XTS XorgTS

mmol/l Alkalinity mg/l mg/l Concentration of suspended solids (0.45 m membrane filter, drying at 105 C) Concentration of organic suspended solids Concentration of inorganic suspended solids

X_inorgSS XanorgTS

X_anorgSS mg/l

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ATV-DVWK-A 198E2.5 Sludge ParametersSymbol English QSl,d QWS,d SVI DRSl oDRSl DSWS Q_Sl,d Q_WS,d SVI DR_Sl oDR_Sl DS_WS QSchl,d QS,d SVI TRSchl TRSchl TSS German Q_Schl,d Q_S,d SVI R_Schl oTR_Schl S_S 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 Unit Designation

2.6 Load ParametersTraditionally, with loads, the period of time is the first index before the index for parameter.Symbol English Bd,XXX,2wM B_d,XXX,2wM Bh,XXX B2h,XXX B_h,XXX B_2h,XXX Bd,XXX,2wM Bh,XXX B2h,XXX B2h,XXX,max German B_d,XXX,2wM B_h,XXX B_2h,XXX B_2h,XXX,max kg/d kg/h kg/h kg/h 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 Unit Designation

B2h,XXX,max B_2h,XXX,max

Numbers of inhabitants or population equivalents [see EN 1085] P EZ PEXXX,ZZ PE_XXX,ZZ EGWXXX,ZZ EGW_XXX,ZZ I [E] I [E] 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

PT EW

I [E]

2.7 Other Characteristic ValuesIndices 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

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.

3.1 Initial SituationAs 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. As every evaluation has a very definite aim it must first be determined which values are required, see Chap. 3.3. Then, inter alia, it is to be examined , 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.

3.2

Data Gathering

3.2.1 Flow MeasurementFor 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. In the ideal case, in addition to the daily flow Qd in m/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.

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ATV-DVWK-A 198E3.2.2 Sampling for the Derivation of LoadsA 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 m/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 m/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 DataFor 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 m/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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ATV-DVWK-A 198Esioning 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 m/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 m/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 PlantsThe 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 OverflowsFor 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 198Econcentration 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. 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-

3.3.2.3 For the Dimensioning of Wastewater Treatment PlantsFor 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

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ATV-DVWK-A 198Etions 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]. 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. 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

Determination of Discharge Data

4.2.1 Data on Water ConsumptionThe 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

4

Determination of Data about the Actual Condition

4.1 General Documents and DataFor 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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ATV-DVWK-A 198Eof 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/(Id). 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/(Id), the reasons are to be explored. 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).

4.2.2

Data on Sewage Flow

4.2.2.1 Determination of Essential Flow DataAs 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 [Authors afternote: For the emptying of stormwater reservoirs]. Days with melting snow and days

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ATV-DVWK-A 198EThe 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. 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.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.

4.2.2.2 Determination of the Annual Mean Dry Weather FlowThe 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

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 w WW ,d ,aM 86400 + AC ,Ind q Ind

[l/s]

(1)

[l/s] (4)

4.2.2.3 Determination of the Wastewater FlowFor 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.QWW ,aM = QDW ,aM QInf ,aM

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 FlowThe 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].

[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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ATV-DVWK-A 198EThe 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. An ATV-DVWK Advisory Leaflet, which deals with the determination of the infiltration water flow is in preparation. 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 valuesQDW ,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:

xQ max =

24 QDW ,h ,max QInf ,pM QDW ,d QInf ,pM pM

[h/d]

(7)

4.2.2.5 Determination of Daily Peaks and Nightly MinimaMaximum and minimum wastewater flow 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:

Maximum and minimum flow with dry weather as 2-hourly mean

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 m/h is produced from all dry weather days.

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ATV-DVWK-A 198EIf 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

Schleypen and Meiner [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.

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 PlantThe 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 m/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

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

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ATV-DVWK-A 198Ecombined 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/(Id). The area-specific industrial respectively commercial wastewater discharge rate qInd in l/(sha) 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 ValuesThe annual wastewater flow QWW,aM in l/s can be estimated on the basis of the inhabitant-specific wastewater yield wWW,d in l/(Id) as well as the area-specific commercial and/or industrial wastewater discharge rate qInd in l/(sha) 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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ATV-DVWK-A 198EFurther suitable estimated values for dimensioning or for plausibility checks are to be found, application specific, in the relevant ATV-DVWK Standards and Advisory Leaflets. 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.

4.3 4.3.1

Determination of Loads and Concentrations Determination through Evaluation of Measured Values

4.3.1.1 Sampling Frequency and Necessary ParametersAs 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-

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.

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ATV-DVWK-A 198E4.3.1.2 Examination of Available InformationUsing 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 SamplingIn 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

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ATV-DVWK-A 198Eloaded 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.

4.3.1.4 Summary of Measured Data and Calculation of the Daily Load as well as the Values of the Concentration RatioThe 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

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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 MeansThe following load cases can be differentiated for the dimensioning of activated sludge plants: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. 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. 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.

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: 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. 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 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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ATV-DVWK-A 198E4.3.1.6 Determination of the Relevant Loads as 85 % ValuesThe 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. 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 NitrogenIn accordance with ATV-DVWK-A 131E (2000) the peak factorfN = 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.

4.3.1.7 Determination of the Relevant ConcentrationsIf 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-

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ATV-DVWK-A 198E4.3.2 Estimation of Pollutant Loads and Concentrations on the Basis of Empirical ValuesIf 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/(sha) 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/(Id), which are undercut on 85% of the days, see also ATV-DVWK StandardATV-DVWK-A 131E (2000)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

Parameter BOD5 COD SS TKN P

Rawwastewater 60 120 70 11 1.8

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 Tab