Emissions of pollutant loads from combined sewer systems and ...

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11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008 separate sewer system paved area (roof, streets etc.) surface runoff storm sewer storm sewer flow treatment devices (if necessary) storm sewer outlets (SSO) receiving water households, commerce, industry dry weather flow combined sewer combined sewer flow CSO devices (e.g. stormtank) combined sewer overflow (CSO) combined sewer system water supply rainfall water supply rainfall households, commerce, industry dry weather flow sanitary sewer inflow wwtp (dw) WWTP effluent WWTP (dw) inflow WWTP (dw, ww) paved area (roof, streets etc.) surface runoff WWTP effluent WWTP (dw, ww) Figure 1. Pathways and emissions from separate sewer systems and combined sewer systems; WWTP: waster water treatment plant; ww: wet weather, dw: dry weather A second frequently discussed issue is the question, what are the right substance parameters to assess possible impacts of discharges from sewer systems? Up to now, often common wastewater parameters (e.g. suspended solids (SS) and chemical oxygen demand (COD)) are regarded (de Toffol et al., 2007). The recently released European Community Water Framework Directive (WFD) considers further specific pollutants (e.g. heavy metals, pesticides, polycyclic aromatic hydrocarbons (PAHs)) as priority substances for classifying the chemical status of receiving waters (EC, 2006). In Germany, emissions out of sewer systems (SSS and CSS) have already been identified to be a significant source of receiving water pollution (Irmer, 2006). As a consequence, it becomes essential to extend the list of considered parameters in sewer system discharges. Therefore, in this study five substance parameters were selected covering a representative range of individual substance properties. These properties are significant for occurrence and fate of the substances at relevant emission points out of sewer systems (Welker, 2006). In order to assess which sewer system has minor pollution emissions to receiving waters it is important to decide which is the right decisive criterion. In this field two possibilities are under discussion: (a) long term criteria like annual emitted pollutant loads, which is the common procedure in Germany and (b) short term criteria like substance concentration values. The focal points of this paper are the relevant emitted pollution loads that are calculated with pollution load simulations. 2 Welker
11 th International Conference on Urban Drainage, Edinburgh, Scotland, UK, 2008 METHODS Selection of pollutant parameters In a first step representative substance concentration ranges in dry weather flow, surface runoff and effluent of WWTP were stated summarizing reported field data (for details see Welker, 2004 and 2007). These values were used as input for pollution load simulations described below. The chosen parameters are two classical wastewater parameters (COD and ammonium) supplemented by three pollutants (copper (Cu), carbamazepine and estradiol (E2)) (see Table 1). Copper is a typical surface runoff derived compound that is efficiently removed in WWTPs. Carbamazepine is a human pharmaceutical, estradiol is a natural hormone. Both compounds derive exclusively from dry weather flows. Still, they have completely different elimination rates in the WWTP (estradiol: nearly 95 %; carbamazepine: nearly 0 %). Table 1. Substance concentrations in important flow types of the combined sewer system and the separate sewer system value COD NH4-N Cu carbamazepine E2 [mg/l] [mg/l] [µg/l] [µg/l] [ng/l] dry weather flow 441 22 66 0.73 15 surface runoff 107 1.0 116 < 0.02 * < 0.02 * effluent WWTP (dw) 66 2.0 13 0.73 0.8 effluent WWTP (ww) ** 31 0.7 21 0.21 0.2 references 1 2-4 2-5 2, 6-13 13-20 dw: dry weather; ww: wet weather; COD: chemical oxygen demand; NH 4-N: ammonium; E2: 17-β-estradiol; * calculation with 50 % of the lowest reported detection limit; ** calculated by a balance references: 1: House et al., 1993; 2: Welker, 2004; 3: Brombach et al., 2005; 4: Smullen et al., 1999; 5: Makepeace et al., 1995; 6: Thornton et al., 2001; 7: Reinhard et al., 2003; 8: Gross et al., 2004; 9: Webb, 2001; 10: Heberer, 2002; 11: Clara et al., 2005; 12: Joss et al., 2006; 13: Ternes et al., 2007; 14: Miege et al., 2007; 15: Birkett and Lester, 2003; 16: Spengler et al., 2001; 17: ATV-DVWK IG-5.4, 2002; 18: Schlüsener and Bester, 2005; 19: Svenson et al., 2007; 20: Johnson et al., 2005 Pollution load simulations A representative and hypothetical catchment (187 ha) which was previously used for various theoretical studies in Germany was chosen for the simulation study (Welker et al., 1999). The catchment (9,900 inhabitants) has a total paved area of 98 ha and is drained by a combined sewer system including two CSOs and two stormwater tanks (SWT) (for details see Welker, 2006). Calculations for the separate sewer system were obtained by transferring the chosen catchment into a separate sewer system. For pollution load simulation the software KOSMO (Kontinuierliche Schmutzfrachtmodellierung) has been used (Schmitt, 1993). KOSMO includes models for all relevant processes like surface pollution with an exponential accumulation and wash off equation. Surface runoff and the corresponding sewer flow were computed with a hydrological method. The calculated annual water volumes are illustrated in Table 2. Welker 3
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