Energy recovery from organic matter in municipal wastewater using a two-stage system with high-rate contact stabilization and activated sludge processes under seasonal water temperature variations

To maximize energy recovery in municipal wastewater treatment plants, the high-rate contact stabilization and activated sludge (HiCS-AS) process-consisting of a two-stage sequencing batch reactor-represents a promising technology for the efficient recovery of organic matter from wastewater as sludge that can be readily converted to methane. The HiCS-AS process was studied under practical conditions using actual wastewater to determine the effect of seasonal water temperature fluctuations (15.9-26.5 degrees C) in the reaction tank on the methane gas production of sludge recovered from the entire system, compared with the simple activated sludge (SAS) process. The methane recovery rates were in the ranges of 0.13-0.17 g COD CH4 per g COD (produced methane as g COD per g COD of influent) for the HiCS-AS process and 0.08-0.15 g COD CH4 per g COD for the SAS process across all periods, with the HiCS-AS process consistently having higher methane recovery rates. Methane production from HiCS sludge ranged from 0.41 to 0.45 NL CH4 per g volatile solid (VS), surpassing the range of 0.27-0.28 NL CH4 per g VS for the SAS sludge across all periods. Furthermore, the quality of the effluent was verified, and the concentration of residual organic matter in the effluent of the HiCS-AS process was equivalent to that of the SAS process.