The influence of lower temperature, influent fluctuations and long retention time on the performance of an upflow mode laboratory-scale septic tank

AbstractThe influence of temperature in a range of 15–5°C, fluctuations in soluble chemical oxygen demand (sCOD) and suspended solids (SS) of the influent and also long hydraulic retention times (HRT) of 36 or 50 d on the performance of a laboratory septic tank were studied. A laboratory-scale septic tank with a volume of 20 L, started up at 15°C was fed with domestic wastewater from two settlements with sCOD up to 450 and up to 2,000 mg/L, respectively. The efficiency of the septic tank was assessed based on pollutant removal and biogas production. A stepwise decrease in temperature by 5°C in the range of 15–5°C halved the daily emission of biogas. Removal efficiencies for sCOD and SS were in the range of 74–86 and 86–88%, respectively. An increase in sCOD of influent from 450 to 4,000 mg/L resulted in a decreased performance of the septic tank (to ~25% less). The highest biogas emission was observed at 10°C and at retention time (36 d), owing to increased consumption of CO2 and CH4 by autotrophic microo...