Combined anaerobic treatment of domestic wastewater and landfill leachate at psychrophilic temperatures

The aim of this study was to investigate the influence of low temperature on a lab-scale continuous-flow Upflow Anaerobic Sludge Bed (UASB) reactor performance treating pre-settled raw sewage and leachate (1.0% by volume) mixture, without any additional heating. The mesophilic seed was acclimatized to low temperatures with synthetic wastewater characterizing raw sewage (HRT =12 h). The reactor was then fed with raw domestic wastewater (aver-age COD _tot ≅ 235 mg/L) at the same HRT. Results indicated average COD_tot, and COD_sol removals of 59% and 32%, respectively (OLR=0.5 kg COD/m³.day), only with raw sewage feeding. During pre-settled sewage feeding, average COD_tot, and COD_sol removals were observed as 14% and 37%, respectively (OLR= 0.3 kg COD/m ³.day) at a HRT of 8 h. Low organic removals could be attributed to very dilute influent (weak strength) characteristics of both raw and pre-settled sewage. In the study, raw sewage and young landfill leachate (with 1.0% by volume) were mixed and pre-settled in order to increase the initial COD _tot, to around 550 mg/L. Since raw sewage reflected a very weak strength character, the aim was to increase the influent organic concentration to a relatively medium strength character by leachate addition, before the psychrophilic UASB reactor was fed. Average COD_tot, and COD _sol removals improved and were obtained as 60% and 67% (OLR=1.3 kg COD/m³.day; HRT=10 h) respectively at room temperatures (15±3°C). Besides, average biogas production was calculated to be 0.25 m³/kg COD_removed.day with leachate addition, whereas almost no biogas productions were observed in the cases of either pre-settled or raw domestic sewage treatment. Apparently, low influent COD resulted in low substrate levels inside the reactor, and also in a low biogas production rate. Thus, anaerobic treatability performance based on COD removals was significantly affected by influent COD concentration rather than operational temperature.