Wiley Wastewater Quality Monitoring and Treatment_12 doc

JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 198 Treatability Evaluation Table 3.2.5 N/COD ratios and calculations of the single fractions of TKN Values of N/COD ratios (g N/g COD) Symbol of Calculation N/COD ratio Typical value Range S ND = i NSS · S S i NSS 0.02 — X ND = i NXS · X S i NXS 0.04 0.02–0.06 S NI = i NSI · S I i NSI 0.01 0.01–0.02 X NI = i NXI · X I i NXI 0.03 0.01–0.06 N BH = i XB · X BH i XB 0.086 — 3.2.5 METALLIC COMPOUNDS The concentration of metals in raw wastewater can differ significantly depending on the domestic, commercial or industrial activities collected by the sewerage. The main interest is in metals characterized by potential toxic impact on health or the environment, such as Cd, Cr , Cu, Hg, Ni, Pb and Zn. The load of these components at the inlet of a WWTP can be several times greater in industrial sites than in residential areas far from industrial activities. Urban run-off during storm events is also a source of metals and other pollutants, and contributes to the total influent load into a WWTP. 3.2.5.1 Treatability of Metallic Compounds Metals inrawwastewater areremoved inWWTPs through twodifferent mechanisms: r Primary sedimentation: metals are separated as insoluble precipitates or adsorbed on settled particulate matter and then extracted with primary sludge. In contrast the removal of metals in soluble form is negligible. r Secondary treatment: during the biological process metals are integrated into acti- vated sludge or biofilm (adsorbed on flocs or in extracellular polymers). They are removed at the same efficiency as the sludge solids in the secondary settler and extracted together with the excess sludge. Some values for metal removal in primary and secondary treatments are summa- rized in Table 3.2.6 (European Union, 2001). Similar patterns of removal percentages are observed in primary and secondary treatments. Lower removal is observed in both cases for Ni due to its high solubility that limits the presence of Ni in the particulate matter and sludge. In contrast Pb, one JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 Metallic Compounds 199 Table 3.2.6 Percentage of metals removed in WWTPs, calculated with respect to the concentration in the influent raw wastewater Removal in primary Removal in primary + Metal treatment (%) secondary treatment (%) Ni 24 40 Cd 40 65–75 Cr 40 75–80 Zn 50 70–80 Cu 50 75–80 Hg 55 70–80 Pb 55 70–80 of the least soluble metals, shows higher removal in both the primary and secondary stages. For the majority of metals a significant percentage of the influent load, up to 70–80 %, is transferred into primary and secondary sludge. As a consequence the concentration of metals in dry sludge (measured as TSS) reaches levels of several thousand mg/kg TSS, about 1000 times higher than the concentration of metals in raw wastewater. In synthesis, the majority of metals entering the WWTPs with the raw waste- water is transferred to the sludge extracted from primary and secondary treatments. Depending on the metal solubility, a smaller amount, ranging from 20 to 40 % (60 % only for Ni), is however discharged in water bodies with the final effluent. With regards to the fate of sludge separated by settlers, the stabilization processes through aerobic or mesophilic anaerobic digestion cause the biological reduction of the volatile solids (30–50 %) and the specific metal content increases, metals being conserved during stabilization. Due to the presence of metals the final disposal of sludge may be problematic especially in the case of accumulation in soils interfering with the long-term sustainable use of sludge on land. For the prediction of the removal of metals from raw wastewater and the parti- tioning into final effluent and sludge, mechanistic approaches have been proposed (Monteith et al., 1993). On the basis of influent wastewater characterization (flow rate, metal concentrations) and the layout of the WWTP (unit volumes, operational conditions) the metal concentration in primary sludge, secondary sludge and final effluent can be predicted. The calculation is performed on the basis of mass balances by considering the main chemical and physical mechanisms (precipitation of soluble metals into a settleable form, sorption onto settleable solids, surface volatilization). In the model the mass of primary and biological sludge produced by primary sed- imentation and secondary treatment is calculated and partitioning coefficients are introduced in the model for the estimation of the metal concentrations in the soluble and solid phases. A similar approach can be applied also for estimating the fate of organic contaminants instead of metals in WWTP. Modelling can be performed both under steady-state or dynamic conditions. JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 200 Treatability Evaluation 3.2.6 FINAL CONSIDERATIONS WWTPs are effective in the reduction of most pollutants present in wastewater (such as organic matter, nutrients, potentially toxic elements or some micropollutants), be- fore the discharge of the treated effluents in surface waters. In WWTPs several biological and physico-chemical processes can be implemented, but the main path- ways for pollutants removal are: (1) the biological oxidation by activated sludge or biofilm systems; or (2) the accumulation of contaminants in excess sludge. In this chapter the main categories of pollutants present in influent wastewater and their fate in WWTPs has been discussed. The assessment of the treatability of a specific wastewater in WWTPs is strictly dependent on the fate of contaminants in the treatment stages. The amount of pollutants removed in conventional WWTPs or passing into the effluent has been indicated depending on the category of pollutants, separated into organic compounds, organic micropollutants, nutrients and metallic compounds. These main categories were identified in order to make an aggregation of the large number of individual pollutants; a much longer and detailed report would be required for the explanation of the fate of each single element. Therefore the present description is not exhaustive for understanding the fate of each single compound; the objective of this chapter is to explain the main pathways in WWTPs for macro-categories of pollutants. The wastewater characterization can be investigated more or less in depth de- pending on the particular needs in management of WWTPs, the requirement for discharge, and the practicalities of operators that make the measurements. The in- creasing detail in characterization and control of effluent wastewater from WWTPs coupled with the more stringent limits for discharge in receiving water bodies, ne- cessitates a more complex and sophisticated monitoring. This causes considerable additional effort and expense to obtain a high degree of knowledge about the type and the concentrations of pollutants and micropollutants in influent and effluent wastewaters. With regards to COD fractionation the routine measurement of all the parameters indicated in Section 3.2.2.1, according to the respirometric approach (described in Section 3.2.2.2), is extremely time-consuming because of the time required for the respirometric tests and the time need for data elaboration. Therefore, COD fraction- ation could be done only occasionally in a WWTP and the percentages obtained can be assumed as typical for a specific wastewater. Of course a periodic valida- tion of fractionation is required. Alternatively, the simplified procedure described in Section 3.2.2.3 can be applied, which is more approximate but is advantageously fast to use. A more detailed characterization, performed by using the respirometric approach, could be required in order to observe daily, weekly or seasonal variation or fluctuation occurring in the COD fractions. In the case of industrial sources, shock loadings are by their nature difficult to predict. In the case of N fractionation, the calculation described in Section 3.2.4.1 can be easily done thanks to its dependence on COD fractionation. JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 References 201 In general a good characterization of COD and N in the influent wastewater is very important to understand the fate of these components in WWTPs and to predict the quality of the effluent wastewater before discharge in receiving water bodies. With regards to metals or nutrients, they are routinely measured in wastewater and sludge and an extensive knowledge about these components is usually available in WWTP management. The measurement is done often routinely in influent and effluent wastewater due to the relative ease of the analysis and the moderate expense involved. In contrast, organic micropollutants, such as PAHs, PCBs, PCDD/PCDFs or phar- maceuticals, are rarely monitored because of the high cost of analysis and the need for specialized laboratories and, sometimes, the lack of unified and standardized methodologies. Furthermore, the limitation in the evaluation of the fate of organic micropollutants and potentially toxic elements is mainly related to the lack of studies on mass balance in WWTPs and with regards to partitioning in water and sludge. Further research is needed to improve knowledge in this field. REFERENCES APHA, AWWA and WPCF (1998) Standard Methods for the Examination of Water and Wastew- ater. American Public Health Association, American Water Works Association and Water Environment Federation, Washington DC, USA. Ekama, G.A., Dold, P.L. and Marais, G.v.R. (1986) Water Sci. Technol., 18(6), 91–114. European Union (2001) Pollutants in Urban Wastewater and Sewage Sludge. Office for Official Publications of the European Communities, Luxembourg. Field, J.A., Field, T.M., Poiger, T., Siegrist, H. and Giger, W. (1995) Water Res., 29(5), 1301–1307. Gujer, W., Henze, M., Mino, T. and van Loosdrecht, M.C.M. (1999) Water Sci. Technol., 39(1), 183–193. Halling-Sørensen, B., Nors Nielsen, S., Lanzky, P.F., Ingerslev, F., Holten L¨utzhøft, H.C. and Jørgensen, S.E. (1998) Chemosphere, 36(2), 357–393. Henze, M. (1992) Water Sci. Technol., 25(6), 1–15. Henze, M., Grady J., C.P.L., Gujer, W., Marais, G.v.R. and Matsuo, T. (1987) Activated Sludge Model No. 1. IAWQ Scientific and Technical Report No. 1, London, UK. Holt, M.S., Fox, K.K., Burford, M., Daniel, M. and Buckland, H. (1998) Sci. Total Environ., 210/211, 255–269. Kappeler, J. and Gujer, W. (1992) Water Sci. Technol., 25(6), 125–139. K¨orner, W., Bolz, U., S¨ußmuth, W., Hiller, G., Schuller, W., Volker, H. and Hagenmaier, H. (2000) Chemosphere, 40, 1131–1142. Mamais, D., Jenkins, D. and Pitt, P. (1993) Water Res., 27, 195–197. Manoli, E. and Samara, C. (1999) J. Environ. Qual., 28(1), 176–186. McNally, D.L., Mihelcic, J.R. and Lueking, D.R. (1998) Environ. Sci. Technol., 32, 2633–2639. Metcalf and Eddy. (2003) Wastewater Engineering. Treatment and Reuse,. 4th Edn. McGraw-Hill, New York. Monteith, H.D., Bell, J.P., Thompson, D.J., Kemp, J., Yendt, C.M., Melcer, H., (1993) Water Environ. Res., 65(2), 129–137. JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 202 Treatability Evaluation Orhon, D., Artan, N. and Cimsit, Y. (1989) Water Sci. Technol., 21(4–5), 339–350. Orhon, D., Ate¸s, E., S¨ozen, S. and Ubay C¸ okg¨or, E. (1997) Environ. Pollut., 95(2), 191–204. Pax´eus, N. (1996) Water Res., 30(5), 1115–1122. Prats, D., Ruiz, F., V´azquez, B. and Rodriguez-Pastor, M. (1997) Water Res., 31(8), 1925–1930. Roeleveld, P.J. and van Loosdrecht, M.C.M. (2002) Water Sci. Technol., 45(6), 77–87. Samara, C., Lintelmann, J. and Kettrup, A. (1995) Toxicol. Environ. Chem., 48(1–2), 89–102. Sinkkonen, S. and Paasivirta, J. (2000) Chemosphere, 40, 943–949. Sollfrank, U., Kappeler, J. and Gujer, W. (1992) Water Sci. Technol., 25(6), 33–41. Spanjers, H, Tak´acs, I. and Brouwer, H. (1999) Water Sci. Technol., 39(4), 137–145. Spanjers, H. and Vanrolleghem, P. (1995) Water Sci. Technol., 31(2), 105–114. STOWA. (1996) Methoden voor influentkarakterisering (in Dutch). STOWA Report 96–08, STOWA, Utrecht, The Netherlands. Vanrolleghem, P.A.,Spanjers,H.,Petersen,B., Ginestet, P.andTakacs, I. (1999) Water Sci. Technol., 39(1), 195 – 215. Weijers, S.R. (1999) Water Sci. Technol., 39(4), 177–184. Xu, S. and Hultman, B. (1996) Water Sci. Technol., 33(12), 89–98. Ziglio, G., Andreottola, G., Foladori, P. and Ragazzi, M. (2001) Water Sci. Technol., 43(11), 119–126. JWBK117-3.3 JWBK117-Quevauviller October 10, 2006 20:28 Char Count= 0 3.3 Toxicity Evaluation Martijn Devisscher, Chris Thoeye, Greet De Gueldre and Boudewijn Van De Steene 3.3.1 Introduction 3.3.2 Need for Toxicity Measurements 3.3.3 Influent vs Effluent Toxicity of Wastewater 3.3.3.1 Influent Toxicity Evaluation 3.3.3.2 Effluent Toxicity Evaluation 3.3.4 Units 3.3.5 Sources of Toxicity 3.3.6 Toxicity Testing 3.3.6.1 Influent Toxicity 3.3.6.2 Effluent Toxicity 3.3.7 Toxicity Mitigation References 3.3.1 INTRODUCTION Under the Urban Wastewater Treatment Directive 91/271/EEC, the quality of ef- fluents has been based on the monitoring of global chemical parameters, such as BOD (biological oxygen demand), COD (chemical oxygen demand) or TSS (total suspended solids). Wastewaters from various origins may contain compounds, toxic to the aquatic ecosystem, or even to the biocommunity responsible for the treatment of the wastewater. These toxic effects are insufficiently expressed in the currently practiced measurements. Wastewater Quality Monitoring and Treatment Edited by P. Quevauviller, O. Thomas and A. van der Beken C  2006 John Wiley & Sons, Ltd. ISBN: 0-471-49929-3 JWBK117-3.3 JWBK117-Quevauviller October 10, 2006 20:28 Char Count= 0 204 Toxicity Evaluation Although some countries impose toxicity tests on effluents, there is currently no general European legal framework that systematically prescribes toxicity tests on effluents. Nevertheless, it is expected that the role of toxicity tests will become more important in the near future. Indeed, the European Union Water Framework Directive 2000/60/EC places more emphasis on the reduction of discharges of toxic elements, and the Integrated Pollution Prevention and Control Directive (96/61/EC), coming into effect by October 2007, is based on a permit system requiring the use of best available technology (BAT). In this, toxicity measurements may play an important role. This chapterpresents anoverviewof thecommon toxicity detectionmethods in use today. The discussion is limited to ‘conventional’ toxicity tests. In recent years, there has been increased concern over the release of pharmaceutically active compounds, personal care products and endocrine disrupting compounds into the environment. These compounds occur in low concentrations in the environment and are unlikely to cause acute toxicity. Highly sensitive bioassays have been developed to screen wastewater effluents on their (anti-)estrogenicity, (anti-)androgenicity, mutagenicity and cytotoxicity. Developments in these fields are extensive, evolve fast and deserve separate chapters in their own right. However, we have limited the discussion to tests that are most relevant to the operation of wastewater treatment plants (WWTPs): the detection of toxic influents that can disturb the treatment process, and of toxic compounds in the effluent, which may be an indication of diminished treatment efficiency. 3.3.2 NEED FOR TOXICITY MEASUREMENTS Toxic compounds are present in wastewater from various sources. In many countries in Europe, industrial plants are connected to the sewer. Industrial wastewaters can contain large amounts of toxic material, such as heavy metals, or synthetic chemicals and their waste products. These pollutants can even be present after conventional wastewater treatment (Paxeus, 1996). Also purely domestic wastewater can contain toxic elements. Domestic discharges can contribute toxins from consumer products (e.g. cleaning products) or liquid wastes. Urban run-off may contain leachates or organic pollutants deposited from the atmosphere onto paved surfaces. In combined sewer systems this run-offis also intro- duced into the sewer system. Other known sources of potentially toxic compounds include commercial premises such as health establishments, small manufacturing industries or catering/hotel enterprises. It is obvious that also illegal discharges to the sewer represent a potential source of toxicity. Chemical analyses alone are insufficient for assessing the toxicity of a wastewater. In the first place, the toxic compounds may be unknown. Indeed, the composition of wastewater is traditionally expressed in nonspecific terms such as BOD, COD or TOC (total organic carbon). These rather general measures reflect the general poor JWBK117-3.3 JWBK117-Quevauviller October 10, 2006 20:28 Char Count= 0 Influent VS Effluent Toxicity Of Wastewater 205 knowledge of the exact composition of wastewaters. Even if an exact composition of the wastewater is known, it is impossible to have a comprehensive overview on all compounds that are effectively present in the wastewater upon arrival at the treatment plant or in the environment. Several transformations may occur and create additional toxic content. Physico-chemical transformations may be occur, e.g. under the influence of sunlight UV, and toxic metabolites may originate via biodegradation, for example during storage in cesspits, during sewer transport or in activated sludge treatment. In addition to the presence of unknown compounds, the (eco)toxicity of the known components may not be well documented. Although databases of such data exist (e.g. ECOTOX:http://www.epa.gov/ecotox/), important gaps remain. The lack of this kind of information on thousands of chemicals on the market today has been acknowledged by the European Union, and has prompted the REACH (Registration, Evaluation, Authorisation and Restrictions of Chemicals) proposal (CEC, 2001). The goal of this proposal is to secure data on and regulate some 30 000 chemicals produced in excess of 1 ton for which there is limited information with regard to toxicity and environmental effects. These data will expand the knowledge on toxic effects of pure compounds. However, even when all toxic components in a wastewater have been identified, and detailed ecotoxicity information would be available for each of these compo- nents, an additional difficulty is the assessment of the effect of complex mixtures. Interaction of the compounds with each other, with the wastewater matrix or with the environment may result in synergistic or antagonistic effects, the matrix may render certain compounds biologically unavailable or may even increase toxicity (Hernando et al., 2005). A more direct measure of toxicity consists of submitting the whole complex mixture to a toxicity test. Although interactions with the final environment are not modelled precisely, it is a measure of the resultant toxicity of the complex wastewater mixture, integrating the combined effect of known and unknown toxic components and their interactions with the wastewater matrix. This type of testing is known in the USA as WET (whole effluent testing; US EPA, 1994). and in the UK as DTA (direct toxicity assessment; Tinsley et al., 2004). 3.3.3 INFLUENT VS EFFLUENT TOXICITY OF WASTEWATER The first major distinction to be made is whether the wastewater is monitored before or after treatment. We will refer to these techniques as influent toxicity monitoring and effluent toxicity monitoring, respectively. This distinction is different because both the goal and requirements, and therefore the adopted methods differ whether the wastewater is monitored before or after treatment. JWBK117-3.3 JWBK117-Quevauviller October 10, 2006 20:28 Char Count= 0 206 Toxicity Evaluation 3.3.3.1 Influent Toxicity Evaluation These tests have the intention to protect the biological wastewater treatment process from the effect of toxic influents. Although Annex 1 of the Urban Wastewater Treat- ment Directive already states that ‘Industrial wastewater entering collecting systems and urban wastewater treatment plants shall be subject to such pretreatment as is re- quired in order to ensure that the operation of the wastewater treatment plant and the treatment of sludge are not impeded’, these tests are not commonly imposed by regulators. The tests used are sometimes referred to as upset early warning devices (UEWDs; Love and Bott, 2000). The sensitivity of these tests should be representa- tive for the biocommunity of the wastewater treatment process. This sensitivity can differ greatly from that of the receiving ecosystem. 3.3.3.2 Effluent Toxicity Evaluation The purpose of effluent toxicity evaluation is to assess the effect of a certain wastewa- ter on the receiving waters. The methods used are essentially the same as those used for ecotoxicity testing of pure compounds. Effluent toxicity tests are imposed by some discharge consents and have been extensively studied and standardized. The conventional approach is the use of bioassays. In these tests, the biological response of a certain bioindicator species is monitored in response to the wastewater to be tested. These bioassays can be further subdivided according to the species involved, the duration (acute/chronic toxicity test) or to the effect on the indicator organ- ism (mortality, reproduction, motility). The requirements of these tests are a high sensitivity and representativity for the receiving ecosystem. Although the distinction between influent and effluent toxicity is clear, it is evident that there is a strong link between the two. The effluent of an industrial treatment plant may be part of the influent to a municipal plant, and highly toxic substances in the influent may inhibit the treatment process in such an amount, that the toxic compounds break through to the effluent to cause effluent toxicity. 3.3.4 UNITS Central to (eco)toxicity evaluation is a dose–effect relationship. Since bioavail- ability of a compound introduced in wastewater differs greatly for each individ- ual compound, test species and wastewater matrix, the exact dose imposed on the test organism is difficult to quantify. Therefore, in aquatic toxicity testing, a concentration–effect relationship is considered, relating the concentration in the wastewater to the effect on the test organism. This relationship becomes evident in JWBK117-3.3 JWBK117-Quevauviller October 10, 2006 20:28 Char Count= 0 Sources Of Toxicity 207 100 75 50 25 0 0246 LC 50 810 Concentration (e.g. mg/l) Cumulative response (%) NOEC LOEC Figure 3.3.1 Sigmoidal response curve. (Adapted from Connell et al., 1999 with permission from Blackwell Publishing) the commonly used units for ecotoxicity: r EC 50 : The concentration at which 50% of the effect is observed. r LOEC: Lowest observable effect concentration, i.e. the lowest concentration at which an effect can be observed. r NOEC: No observable effect concentration, i.e. the highest concentration at which no effect can be observed. The term concentration, in the context of whole effluent testing, refers to dilution series of the original wastewater, ranging from 0 to 100 % of the wastewater. These measures are graphically represented in Figure. 3.3.1. (Eco)toxicity is determined by studying quantifiable effects. The effects studied are specific to each toxicity test. A commonly observed effect is mortality (lethal effect). In this case, the term LC 50 is used rather than EC 50 . This determines the concentration at which 50 % mortality is observed. Another commonly used measure is IC 50 which is the concentration at which 50 % inhibition of a certain activity (e.g. light emission) is observed. There is no such thing as a EC 50 of a certain compound. Toxicity is a measurement of aneffect to a certain organism or community of organisms. It is therefore important that the test method is specified together with the EC values. 3.3.5 SOURCES OF TOXICITY Influents of industrial WWTPs may contain a large variety of toxic compounds. It is practically impossible, and certainly beyond the scope of this chapter, to give a [...]... thorough maintenance and control scheme is implemented and respected 3.3.6.2 Effluent Toxicity Effluent toxicity tests attempt to quantify the toxic effect of the effluent on the receiving ecosystem Bioassays consist of monitoring a quantifiable effect on an indicator organism These tests have been used for this purpose for a long time, and extensive documentation, toxicity data and standard procedures are... (FMN) and a long chain fatty acid (RCOOH), along with the emission of blue-green light Since FMNH2 production depends on functional electron transport, only viable cells produce light This relationship between light emission and cellular viability forms the basis of the assay and it forms the link between toxicity and the observed response These bioluminescence tests are standardised (International Standardization... monitored and compared with the response to a reference influent The experiment is usually performed in a short time span, and can therefore be automated and included in the on-line supervision and control systems of the plant All respirometry-based methods in some way refer the measurements to a reference influent, known not to be toxic to the biomass By careful selection of this reference influent and the... representative, yield complementary results (Ren and Frymier, 2004) An additional difficulty is the fact that adaptation mechanisms can reduce the sensitivity of the sludge community to certain compounds For example, phenolics, cyanides and thiocyanates are known to be toxic for biological treatment systems (Blum and Speece, 1991) Grau and Da-Rin (Grau and Da-Rin, 1997) reported serious municipal plant... of the wastewater Immobilisation is recorded at 24 and 48 h and the data are then used for calculating the EC50 Other tests exist, such as the 21-day reproduction test, and many other invertebrates have been proposed, such as mayflies (Baetis spp.) amphipods (e.g Gammarus lacustris) or stoneflies (Pteronarcys spp.) Several invertebrate bioassays are being marketed in user-friendly kits Plant and algae... evaluate treatability of a wastewater before introduction, or for confirmation of the results of on-line testing An extensive overview on influent toxicity detection methods has been given in Love and Bott (Love and Bott, 2000), and an update in Ren (Ren, 2004) We will restrict the discussion to the most commonly used methods: bacterial luminescence, nitrification inhibition and respirometry Bacterial... Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), establishing a European Chemicals Agency and amending Directive 1999/45/EC and Regulation (EC) (on Persistent Organic Pollutants) Brussels, 29.10.2003, COM(2003) 644 final Connell, D.W., Lam, P., Richardson, B and Wu, R (1999) Introduction to Ecotoxicology Blackwell, Oxford, UK Copp, J.B., Spanjers, H and Vanrolleghem, P.A (Eds) (2002)... additives used in wastewater and sludge treatment such as coagulants, flocculant aids, or disinfectants or chemicals for phosphorus precipitation, when not dosed in an adequate manner, can form serious threats to the health of the biocommunity and the receiving ecosystem When persistent toxicity is observed, identification of the source is necessary Toxicity tests on strategic locations in the wastewater transport... realise that, even with these precautions, considerable differences may exist between the predicted effect and the actual in-situ effect of the studied effluent to the receiving water (La Point and Waller, 2000) An overview of effluent toxicity measurements can be found in Farr´ and Barcel´ e o (Farr´ and Barcel´ , 2003) These authors classified the toxicity detection methods e o according to the test species... proposed, and besides lethality, other fish bioassays are based on larval growth, larval survival and adenosine triphosphate (ATP) measurements Recent developments are ongoing to replace fish tests by direct measurements on cultured cells Fish bioassays are quite laborious They require specialised equipment and staff Invertebrate bioassays Popular species for invertebrate toxicity testing include Daphnia and . collecting systems and urban wastewater treatment plants shall be subject to such pretreatment as is re- quired in order to ensure that the operation of the wastewater treatment plant and the treatment. the wastewater. These toxic effects are insufficiently expressed in the currently practiced measurements. Wastewater Quality Monitoring and Treatment Edited by P. Quevauviller, O. Thomas and A characterization of COD and N in the influent wastewater is very important to understand the fate of these components in WWTPs and to predict the quality of the effluent wastewater before discharge