Methane Production from Sludge of High-Rate Contact Stabilization Process Through Anaerobic Digestion for Maximizing Energy Recovery

For maximizing energy recovery in municipal wastewater treatment plants, the recovery of organic matter from raw wastewater using a primary settling tank (PST) and the recovery of organic matter from the PST effluent using the HiCS–AS process, which combines high-rate contact stabilization (HiCS) and activated sludge (AS) processes, are both promising methods. In this study, to investigate energy recovery as methane from PST effluent of municipal wastewater, the HiCS–AS process was operated using a two-stage sequencing batch reactor, and the conventional AS process (CAS) was operated in parallel. As a result, 18%, and 14% of the influent COD mass was recovered as sludge in the HiCS–AS and CAS processes, respectively. The specific methane yields of the HiCS, AS, and CAS processes were 449, 266, and 281 NmL g−1 VS added, respectively. Consequently, the methane recovery rates of the HiCS–AS and CAS processes were 13% and 8.1% of the influent COD mass, respectively. A meaningful increase can be expected by adopting the HiCS–AS method in WWTPs.