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JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 3.2 Treatability Evaluation Gianni Andreottola and Paola Foladori 3.2.1 Introduction 3.2.2 Organic Compounds as Aggregate Parameters 3.2.2.1 Fractions of Total COD in Wastewater and their Treatability 3.2.2.2 Respirometric Approach for COD Fractionation 3.2.2.3 COD Fractionation from Data of Conventional Analytical Monitoring in WWTPs 3.2.2.4 A Case Study at Regional Level 3.2.3 Organic Micropollutants 3.2.3.1 Categories of Organic Micropollutants 3.2.3.2 Treatability of Organic Micropollutants 3.2.4 Nutrients: Nitrogen and Phosphorus 3.2.4.1 Fractions of Nitrogen and their Treatability 3.2.5 Metallic Compounds 3.2.5.1 Treatability of Metallic Compounds 3.2.6 Final Considerations References 3.2.1 INTRODUCTION ‘To know treatability is to know the fate of contaminants in WWTPs’. The pollutantsintroducedinto thesewerage collectingsystem and reachingmunic- ipal wastewater treatment plants (WWTPs) derive principally from human activities 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 JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 180 Treatability Evaluation and in particular from domestic sources, industrial districts and urban run-off rain- water. A very large amount of different organic and inorganic compounds, estimated as several thousand, has been detected in raw wastewater. The treatability of these compounds in the conventional WWTPs can differ significantly depending on each considered contaminant. The importance of knowing the treatability of the differ- ent kinds of pollutants present in municipal wastewater is related to the prediction of the fate of these contaminants in WWTPs before the discharge in the receiving water bodies. The following principal categories of contaminants in municipal raw wastewater can be distinguished: r Organic compounds as aggregate parameters. The whole amount of organic matter is generally measured as aggregate organic parameters, such as chemical oxygen demand (COD), total organic carbon (TOC), or biological oxygen demand (BOD) in the case of the measurement of only biodegradable compounds. Aggregate or- ganic constituents are comprised of a number of individual compounds that cannot be distinguished separately. Eventually the fractionation of COD can be performed with the aim to discriminate biodegradable and nonbiodegradable fractions of or- ganic matter: r Organic micropollutants. The determination of these organic compounds is done as individual parameters; some of them are associated with a potential toxic risk to health and the environment. r Nutrients, such as nitrogen (N) and phosphorus (P). Among the inorganic non- metallic compounds, N and P in their different ionic or organic forms, represent the most important pollutants and are also, in most cases, the major nutrients of importance. r Metallic compounds. Some, including cadmium, chromium, copper, mercury, nickel, lead and zinc, are characterized by a potentially toxic action. The effectiveness of the removal of these categories in WWTPs depends on the plant configuration and not all WWTPs are able to remove all the pollutants present in the influent wastewater. Most WWTPs designed or upgraded in the last decades to European level are characterized by primary and secondary treatment (adopting activated sludge or biofilm configurations) able to achieve complete removal of biodegradable COD in influent wastewater. Furthermore, plants located in areas sensitive to eutrophication reach high efficiency in nitrification, denitrification and P removal, as directed by the European Directive promulgatedin1991 (91/271/CEE)thatimposed morerestrictive effluent limits for the discharge of treated wastewater in the receiving water bodies (see Chapter 1.1). In particular, the effluent concentration limit for total nitrogen is equal to 15 or 10 mg/l for a population equivalent (PE) lower or higher than 100 000, respectively. Analogously in the same Directive, the effluent limit for phosphorus is 2 and 1 mg/l for plant capacity below or above 100 000 PE, respectively. JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 Organic Compounds as Aggregate Parameters 181 Plants currently guaranteeing to meet the discharge limits for COD, biological oxygen demand for 5 days (BOD 5 ) and total suspended solids (TSS), could not meet the limits for N and P as imposed by 91/271/CEE for sensitive areas, requiring further upgrading. Discharge limits areindicatedalsoforotherconstituents, such as metals or organic micropollutants; due to their wide heterogeneity and their different treatability not all the WWTPs are suitable for the complete removal of these contaminants, but many of them can be removed only partially. For example, organic micropollutants can be biodegraded only in part, but often are removed physically from water and accumulated in excess sludge, transferring the pollution problem from water to sludge. This occurs also in the case of metals. For evaluating the wastewater treatability, two key aspects have to be considered: the compositionof theinfluentwastewater; andthetreatment capacityin theWWTPs. In particular, the treatment capacity is related to the physico-chemical processes performed in the plant and the biodegradation capacity of activated sludge or biofilm processes in the secondary treatment. The wastewater composition in combination with the plant treatment capacity constitutes the basis of the ‘treatability’ concept. The knowledge of these aspects is fundamental in order to evaluate the entity of pollutants removal in the plant and to predict the quality of the treated effluents aimed to respect the imposed limits and to reduce the impact in receiving water bodies. In the following paragraphs the fate through WWTPs of the categories of pol- lutants cited above are described and the repartition of contaminants in sludge or effluent water is indicated. In particular, the influence of the various treatment pro- cesses (physico-chemical primary treatment, biological secondary treatment and eventually tertiary treatment) is considered for each category of contaminants. 3.2.2 ORGANIC COMPOUNDS AS AGGREGATE PARAMETERS The quantification of the total organic matter in wastewater and its characterization is of primary importance for the correct design, management and optimization of a WWTP. Carbonaceous substrates are generally quantified by using aggregate pa- rameters such as BOD 5 or COD, but only the analysis of COD is able to represent the whole amount of organic matter, while BOD 5 is representative of the biodegradable fraction only. As far as the BOD 5 parameter is concerned, it has been widely applied in the field of receiving water bodies and for wastewater characterization. Due to the 5-day duration of the BOD test (BOD 5 ), the measurement of oxygen consump- tion (index of biodegradability) is relative to 5 days and therefore very different from wastewater retention time in WWTPs where the biodegradation occurs. The problems related to the interpretation of the BOD 5 test for the measurement of biodegradable compounds in wastewater and its use in the design and management JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 182 Treatability Evaluation of treatment processes gave increasing interest to new characterization proposals. In particular, interest in biodegradability characterization has been increased from the simulation models for the activated sludge process that do not use traditional pa- rameters [for example, the Activated Sludge Model, from ASM No. 1 (Henze et al., 1987) to ASM No. 3 (Gujer et al., 1999)]. In the literature, proposals for the charac- terization of the biodegradability of carbonaceous substrates are available, especially based on respirometry (Henze, 1992; Spanjers and Vanrolleghem, 1995; Orhon et al., 1997; Spanjers et al., 1999). Respirometry is defined as the measurement and the interpretation of the rate of oxygen consumption (oxygen uptake rate,OUR) by activated sludge or wastewater under different load conditions. The consumption of oxygen is due to two different factors: (1) Endogenous respiration (OUR endo ) measured for a biomass in the absence of external substrate and due to cellular maintenance and oxidation of dead cells. (2) Exogenous respiration (OUR exo ) measured during the oxidation of biodegrad- able COD present in wastewater added to a biomass. The quantification of biodegradable COD in wastewater can be assessed through respirometric tests carried out on activated sludge after the addition of an adequate amount of wastewater. The dynamics of OUR exo are monitored for a period of about 10–20 h and the data are interpreted as described in more detail in Section 3.2.2.2. Alternatively, in the absence of respirometric measurements, a rapid estimation of COD fractions (less precise than the results obtainable by respirometry) can be done in existing WWTPs, according to an easy calculation based on BOD 5 and COD analyses in influent and effluent wastewater, as indicated in Section 3.2.2.3. 3.2.2.1 Fractions of Total COD in Wastewater and their Treatability While some organic compounds are easily biodegradable in WWTPs, others are persistent and refractory and they are found in the treated effluents or in the excess sludge. Thecompletefractionation of CODinraw wastewater isshownschematically in Figure 3.2.1, in which symbols are adopted according to ASM models. The total COD concentration is subdivided into two biodegradable and nonbiodegradable fractions and into an active biomass fraction. A soluble part (S) and a particulate part (X) are distinguished for both biodegradable COD (indicated by subscript S) and nonbiodegradable COD (indicated by subscript I). In COD fractionation the following terms are introduced and defined: (1) Total COD: determined experimentally by chemical analysis without any pre- treatment of the wastewater (APHA, AWWA and WPCF, 1998). (2) Soluble COD (S): determined experimentally by means of the chemical anal- ysis of COD after a pretreatment of wastewater with coagulation, flocculation JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 Organic Compounds as Aggregate Parameters 183 Total COD biodegradable nonbiodegradable active biomass X BH , X BA Soluble S S Particulate X S Soluble S I Particulate X I Figure 3.2.1 Scheme of total COD fractionation in wastewater and 0.45-μm-filtration, according to the procedure proposed by Mamais et al. (Mamais et al., 1993). Alternatively, the determination of soluble COD can be carried out by the direct filtration of wastewater at 0.1 μm, in order to minimize the occurrence of colloidal solids. The results obtained from the two kinds of measurements are similar with a difference of about 1 % (Roeleveld and van Loosdrecht, 2002); (3) Particulate COD (X): determined as the difference between total COD and soluble COD. (4) Soluble biodegradable COD (S S ): made up of simple molecules ready to be as- similated through the cellular membrane (readily biodegradable COD) or easy to be hydrolysed (rapidly hydrolysable COD); it can be measured by respirometry. (5) Particulate biodegradable COD (X S ): made up of suspended and colloidal solids and compounds with high molecular weight that require enzymatic hydrolysis before being metabolized. It is also called ‘slowly biodegradable COD’ and can be measured by respirometry; the biodegradation rate of X S is about 10 times smaller than the rate of S S . (6) Soluble inert COD (S I ): made up of dissolved nonbiodegradable molecules. It is calculated as the difference between S and S S . (7) Particulate inert COD (X I ): made up of nonbiodegradable compounds, both in suspended and colloidal forms. It is calculated as the difference between X and X S . (8) Heterotrophic and autotrophic active biomass (X BH and X BA , respectively): made up of the cellular active biomass present in wastewater and represents an inoculum for the biological process in the WWTP. The value of X BH can be quantified by respirometry, while the amount of X BA is often neglected in the COD fractionation. The total COD is given by: total COD = S S + X S + S I + X I + X BH + X BA JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 184 Treatability Evaluation Table 3.2.1 Fractionation of COD in raw and presettled wastewater (percentages are referred to total COD) Fraction Raw wastewater (%) Presettled wastewater (%) S S 10–30 20–40 X S 40–60 30–50 S I 5–10 5–15 X I 10–20 7–15 Typical percentages of the COD fractions for raw wastewater and presettled wastewater (after primary sedimentation) are indicated in Table 3.2.1. This fractionation allows understanding of the composition of organic matter in wastewater and to predict its fate during treatment in WWTPs. The fate of each individual fraction is: r S S is rapidly biodegraded in the biological stage of the WWTP, requiring a short time (generally less than 1–2 h). r S I is transferred in the effluent without any modification, being not biodegradable and not settleable; for its reduction a tertiary treatment is eventually required. r X S is mostly biodegraded during the biological treatment and eventually part is transferred in primary or secondary sludge. The amount of X S discharged in the final effluent is negligible. r X I is transferred in primary and secondary sludge, without any significant modi- fication, being nonbiodegradable. r X BH is an inoculum in the biological process in WWTP (and subjected to growth and death) and it is separated with the primary and secondary sludge. 3.2.2.2 Respirometric Approach for COD Fractionation Many authors have proposed methods based on respirometry for the assessment of the COD fractions in wastewater (Ekama et al., 1986; Kappeler and Gujer, 1992). In depth contributions about wastewater characterization have been published by Henze (Henze, 1992) and Vanrolleghem et al. (Vanrolleghem et al., 1999). Further- more, methods have been proposed to obtain the complete fractionation of COD in wastewater and other kinetic parameters by modelling the respirometric data ac- quired during a single batch respirometric test. This opportunity requires however the availability and the implementation of a simulation model and the extraction of accurate data requires specific competences (Spanjers et al., 1999). In this section an approach is described for the complete fractionation of COD based on the measurement of OUR and without the need of modelling. This 10-step procedure is summarized in Table 3.2.2. JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 Organic Compounds as Aggregate Parameters 185 Table 3.2.2 Synthesis of the respirometric approach for the complete fractionation of total COD Step Parameter Method 1 Total COD Lab. analysis (APHA, AWWA and WPCF, 1998) 2 Soluble COD (S) Lab. analysis of soluble COD 3 Particulate COD (X) As difference of 1 and 2: X = total COD − S 4 Biodegradable COD (S S + X S ) Respirometry 5 Soluble biodegradable COD (S S ) Respirometry 6 Particulate biodegradable COD (X S ) As difference of 4 and 5 7 Heterotrophic active biomass (X BH ) Respirometry 8 Autotrophic active biomass (X BA ) Considered as negligible 9 Soluble nonbiodegradable COD (S I ) As difference of 2 and 5: S I = S − S S 10 Particulate nonbiodegradable COD (X I ) As difference of 3, 6 and 7: X I = X − X S − X BH The biodegradable COD, subdivided into the readily (S S ) and slowly (X S ) biodegradable fractions, can be quantified by using respirometric tests, while the remaining inert fractions, X I and S I , are calculated as the difference of known val- ues. Also the content of heterotrophic active biomass (X BH ) can be measured by respirometry. The proposed respirometric methods and the laboratory instrumenta- tion used for tests are described below. Description of instrumentation for respirometric tests The OUR tests were carried out using a series of closed respirometers. A closed respirometer is made up of a temperature controlled 2 l reactor. Aeration and mixing are guaranteed by compressed air and magnetic stirrer. The revolution speed of the magnetic stirrer must avoid spontaneous reoxygenation of the mixed liquor. Dis- solved oxygen was monitored by an oxymeter (OXI 340, WTW GmbH, Germany) connected to a data acquisition system. A scheme of the instrumentation used is shown in Figure 3.2.2. OUR is measured during programmed phases without aeration. Evaluation of biodegradable COD by respirometry (step 4 of Table 3.2.2) For the estimation of biodegradable COD (S S +X S ) the respirometric test is carried out with 1–1.5 l of activated sludge in which an adequate amount of wastewater (about 0.5 l) and allylthiourea (ATU) are added. An example of the dynamics of OUR(t) versus time (respirogram) obtained after the addition of raw wastewater is shown in Figure 3.2.3. JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 186 Treatability Evaluation Magnetic stirrer Feeding Cryostat Air pump DO probe Oxymeter DO control Automatic aeration control Figure 3.2.2 Scheme of the instrumentation utilized for the respirometric runs At the beginning of the test the higher OUR values are due to the oxidation of readily biodegradable substrates, while successively, after the complete depletion of S S , a gradual decrease of OUR is observed due to the consumption of slowly biodegradable compounds limited by hydrolysis. When all the biodegradable sub- strates are completely oxidized, the OUR values reach the endogenous respiration. ΔO 2 0 5 10 15 20 25 30 35 40 0.0 0.2 0.4 0.6 0.8 Time (days) OUR (mgO 2 /L/h) OUR after the addition of wastewater in activated sludge (OUR exo +OUR endo ) endogenous OUR (OUR endo ) t final Figure 3.2.3 Respirogram obtained for activated sludge after the addition of municipal raw wastewater. The contributions from both OUR endo and OUR exo are indicated JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 Organic Compounds as Aggregate Parameters 187 The area between OUR exo and OUR endo (O 2 ) represents the total oxygen con- sumed for the oxidation of biodegradable COD present in the added wastewater. The conversion from oxygen into the equivalent amount of COD is calculated by applying the following expression, in which the contribution of the biomass yield is subtracted (Ekama et al., 1986): O 2 = t final  0 OUR exo (t)dt (mg O 2 /l) S S + X S = 1 1 − Y H · V ww + V as V ww t final  0 OUR exo (t)dt (mg COD/l) where V as is activated sludge volume (l), V ww is wastewater volume (l), Y H is the yield coefficient, assumed equal to 0.67 mg COD/mg COD and t final is the time corresponding to the complete oxidation of biodegradable COD in wastewater. Evaluation of soluble biodegradable COD by respirometry (step 5 of Table 3.2.2) A method for the estimation of S S has been proposed by Xu and Hultman (Xu and Hultman, 1996), who put forward a method based on a calibration curve between a readily biodegradable substrate having a known COD (acetic acid or sodium acetate) and the oxygen demand for its removal. S S in wastewater can be assessed from the measurement of the oxygen consumption and the conversion into COD by using the calibration curve. In particular, this technique allows the assessment of S S concen- tration through a so-called ‘single-OUR’ method, because only an oxygen depletion curve is necessary and therefore the time required for the test is very short (Ziglio et al., 2001). Calculation of particulate biodegradable COD (step 6 of Table 3.2.2) Knowing the value of S S the concentration of X S in wastewater is obtained immedi- ately as: X S = ⎛ ⎝ 1 1 − Y H · V ww + V as V ww . t final  0 OUR exo (t)dt ⎞ ⎠ − S S (mg COD/l) Evaluation of heterotrophic active biomass by respirometry (step 7 of Table 3.2.2) For evaluating X BH in wastewater the respirometric test has to be carried out only in the presence of wastewater, without any addition of activated sludge, according JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 188 Treatability Evaluation y = 6.21 x + 1.29 R 2 = 0.98 0.0 0.5 1.0 1.5 2.0 2.5 3.0 0.00 0.05 0.10 0.15 0.20 0.25 Time (days) ln OUR (mgO 2 /L/h) Figure 3.2.4 Results of the respirometric test for the estimation of X BH in wastewater. The y-intercept is 1.29 mg O 2 1L/h and the OUR slope is μ H,max − b H = 6.21/day [where μ H,max is the specific maximum growth rate (/day) and b H is the decay rate (/day)]. X BH = 27.1 mg COD/l to the method proposed by Kappeler and Gujer (Kappeler and Gujer, 1992). At the beginning of the test the ratio S 0 /X 0 (substrate/biomass) must be higher than 4 in order to reproduce the optimal organic load for nonlimiting bacterial growth. The value of X BH is derived easily from the OUR dynamic during the exponential growth phase. By plotting ln OUR values versus time (Figure 3.2.4) the linear interpolation of the data allows to calculate the slope (μ H,max − b H ) and the y-intercept on the vertical axis. The specific decay rate (b H ) is assumed equal to 0.24 day −1 . Finally the active heterotrophic biomass in wastewater is obtained by the follow- ing relationship: X BH = e ( y−intercept) · 24 1−Y H Y H · (slope +b H ) (mg COD/l) whereY H is theyieldcoefficientforheterotrophic biomass, assumedequalto 0.67mg COD/mg COD. Calculation of inert COD (steps 9 and 10 of Table 3.2.2) Finally, after the experimental determination of S S ,X S and X BH , the two remaining inert fractions of COD can be calculated immediately as difference. In particular the value of S I is obtained as the difference from the soluble COD in wastewater and the value of S S : S I = S − S S (mg COD/l) [...]... acquired during the conventional monitoring of WWTPs The need to measure data in influent and effluent wastewater is the main limitation of this procedure, that is applicable only in the case of existing and fully monitored plants In particular the following analytical parameters are required: COD, soluble COD and BOD5 in influent wastewater and soluble COD in effluent wastewater, collected after secondary... emulsifier and it is found widely in municipal raw wastewater Because of its lipophilic properties it is removed from water and concentrated in excess sludge produced in secondary treatment (5) Surfactants and detergent residues Surfactants are used in washing and cleaning products and are always present in municipal raw wastewater Linear alkylbenzene sulfonates (LASs) are commonly used in detergents and. .. their regular monitoring requires a high number of parameters to be analysed with complex and expensive laboratory procedures The analytical measurement for the quantification of PAHs, PCBs, PCDDs and PCDFs in wastewater or sludge is very expensive and it is the reason for the scarce availability of these data in wastewater Recently, the importance of these contaminants in urban wastewater and sludge has... the mechanism of absorption on solids and sludge JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 194 Treatability Evaluation (3) Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs and PCDFs) PCDDs and PCDFs are produced by thermal processes or incomplete combustion and released into the atmosphere and reach WWTPs due to deposition and runoff Analogously to PCBs the degradation... influent raw wastewater The fate and the effective treatability of organic micropollutants is not easy to predict, because of the very large number of different organic species that may be present in municipal raw wastewater and the complex aspects of the physico-chemical sorption mechanisms onto sludge solids 3.2.4 NUTRIENTS: NITROGEN AND PHOSPHORUS The removal of nutrients, N and P, from wastewaters... analysis (APHA, AWWA and WPCF, 1998) Lab analysis of soluble COD As difference of 1 and 2: X = total COD − S Lab analysis (APHA, AWWA and WPCF, 1998) Conversion of the BOD5 value Lab analysis of soluble COD in the final effluent after treatment As difference of 2 and 6: SS = S − SI As difference of 5 and 7 As difference of 3 and 8: XI = X − XS Considered as negligible Considered as negligible JWBK117-3.2... adsorbable and contain halogens (usually chlorine but also fluoride, bromine and iodine) that can envelop organic substances These substances are often not easily degradable in WWTPs and highly toxic in the environment Moreover, some AOX are known to have endocrine effects 3.2.3.2 Treatability of Organic Micropollutants The first three categories (PAHs, PCBs and PCDDs/PCDFs) are present in municipal wastewater. .. the municipalities and the consequent capacity of the WWTP affects the COD fractionation of raw wastewater, as shown in Figure 3.2.5 In particular, wastewaters of larger plants are characterized by a lower percentage of readily Table 3.2.4 Results of COD fractionation of influent wastewater of 70 WWTPs (percentages are referred to total COD) SS Average (%) Maximum (%) Minimum (%) Standard deviation (%)... Scheme of TKN fractionation in wastewater On the basis of this fractionation the TKN concentration in wastewater is made up of the following: TKN = SNH + SND + XND + SNI + XNI + NBH + NBA The terms and the fate in WWTPs of these seven fractions are: r Ammonia (SNH ): determined by conventional chemical analysis (APHA, AWWA and WPCF, 1998); it is nitrified in low-loaded WWTPs and when the volume of the biological... conversion of the BOD5 value This conversion has been recently evaluated in depth by Weijers (Weijers, 1999) and Roeleveld and van Loosdrecht (Roeleveld and van Loosdrecht, 2002), with the aim to apply a simplified procedure for the advanced fractionation of COD in numerous WWTPs in The Netherlands Firstly, the BOD5 value is converted to the corresponding BOD∞ value (that is, the oxygen consumption for . collectingsystem and reachingmunic- ipal wastewater treatment plants (WWTPs) derive principally from human activities Wastewater Quality Monitoring and Treatment Edited by P. Quevauviller, O. Thomas and A parameters are re- quired: COD, soluble COD and BOD 5 in influent wastewater and soluble COD in effluent wastewater, collected after secondary treatment. The 11- step procedure is summarized in Table. dibenzo-p-dioxins and dibenzofurans (PCDDs and PCDFs). PCDDs andPCDFs areproducedby thermal processesor incompletecombustion and released into the atmosphere and reach WWTPs due to deposition and run- off.