Performance of up-flow thermophilic septic tank treating blackwater

“Up-flow thermophilic septic tank” (UTST) has been recently developed as an innovative on-site treatment technology to improve the treatment performance of existing sanitation technologies such as septic tanks and cesspools by promoting the growth of thermophilic microorganisms and enhancing the contact between these microorganisms and blackwater. The UTST is an improved version of the conventional solar septic tanks by integrating an up-flow hydraulic mode in the septic tank. The aims of this study were to investigate the effects of hydraulic retention times (HRTs) on the performance of UTST treating blackwater, identify dominant microbial clusters in the UTST and develop a platform for design and operation of the UTST. The experiments were conducted with a laboratory-scale UTST (27 L in size) fed with blackwater collected from public toilets of an academic building. After acclimatization, the laboratory-scale UTST was operated at the HRTs of 8, 16, 24 and 32 h with continuous blackwater feeding for 4 months. The average chemical oxygen demand (COD) removal efficiencies of the laboratory-scale UTST operating at 8, 16, 24 and 32 h at the temperature of 50 °C were 53, 67, 77 and 75%, respectively, while similar trend was observed for the 5-day biochemical oxygen demand (BOD 5 ). Because there were no significant differences ( p > 0.05) in COD and BOD 5 removal efficiencies between 24- and 32-h HRTs operation, the HRT of 24 h was selected to be optimum. The average CH 4 yield by the laboratory-scale UTST operating at 50 °C and HRT of 24 h was found to be 0.037 L/gCOD input . The abundance and dominance of microbial clusters in both liquid and sludge layers in the UTST analyzed by high-sequencing 16S rRNA revealed the abundance and dominance of Methanosaeta and Methanothermobacter responsible for organic degradation and CH 4 production. The results of this laboratory-scale experiment on UTST suggested its applicability for blackwater treatment which should lead to better pollution control and public health protection.