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For calibration purposes, an intensive sampling program was performed for 7 days at the WWTP to perform accurate wastewater characterization. Because this study focussed on the biological stage only, the WWTP performance was monitored for settled sewage (inlet to the biological process) and biologically treated effluent. The temperature was optimum during the sampling program (sewage temperature approximately 29 °C). The analyses were performed according to Standard Methods for the Examination of Water and Wastewater (APHA 2005). Mass and hydraulic balances at the plant were performed based on hydrometer readings and flow rates of pumps for the inflow, outflow, waste and return sludge, TSS and COD measurements. The information obtained through the sampling program was combined with the historical daily routine measurements of the plant. Wastewater characterization was performed based on the STOWA method (Roeleveld & van Loosdrecht 2002). Tables 3 and 4 show the averaged measurements and wastewater characterization during the sampling program, respectively.

Table 3

Averaged measurements during the sampling program

TestSettled sewageBiologically treated effluent
Flow (m3/d) 49416.7 ± 276 – 
Temp. (°C) 28.93 ± 0.6 – 
pH 8.92 ± 0.2 8.77 ± 0.07 
Total alkalinity 290 ± 81.6 – 
TSS (mg/l) 349 ± 38 33.7 ± 7 
VSS (mg/l) 287 ± 39 26.8 ± 7.7 
BOD5 (mg/l) 207 ± 19 33.7 ± 6 
COD (mg/l) 483 ± 58 81.3 ± 8 
Filtered COD (mg/l) 234 ± 28 32 ± 3 
DO (mg/l) 0.13 ± 0.1 – 
TKN (mg/l) 34.2 ± 1 – 
NH4-N (mg/l) – 26.2 ± 0.5 
NO2-N (mg/l) 0.05 ± 0.03 0.24 ± 0.09 
NO3-N (mg/l) 1 ± 0.8 7.4 ± 4 
TestSettled sewageBiologically treated effluent
Flow (m3/d) 49416.7 ± 276 – 
Temp. (°C) 28.93 ± 0.6 – 
pH 8.92 ± 0.2 8.77 ± 0.07 
Total alkalinity 290 ± 81.6 – 
TSS (mg/l) 349 ± 38 33.7 ± 7 
VSS (mg/l) 287 ± 39 26.8 ± 7.7 
BOD5 (mg/l) 207 ± 19 33.7 ± 6 
COD (mg/l) 483 ± 58 81.3 ± 8 
Filtered COD (mg/l) 234 ± 28 32 ± 3 
DO (mg/l) 0.13 ± 0.1 – 
TKN (mg/l) 34.2 ± 1 – 
NH4-N (mg/l) – 26.2 ± 0.5 
NO2-N (mg/l) 0.05 ± 0.03 0.24 ± 0.09 
NO3-N (mg/l) 1 ± 0.8 7.4 ± 4 
Table 4

COD fractions for settled sewage

ParameterNameValue gCOD/m3Ratio to total COD
SI Soluble inert organic matter 14.6 3% 
SS Soluble substrates 219.1 45% 
XI Particulate inert organic matter 144.3 30% 
XS Slowly biodegradable substrate 105.1 22% 
ParameterNameValue gCOD/m3Ratio to total COD
SI Soluble inert organic matter 14.6 3% 
SS Soluble substrates 219.1 45% 
XI Particulate inert organic matter 144.3 30% 
XS Slowly biodegradable substrate 105.1 22% 

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