Anaerobic stabilization and landscape utilization of rural sewage sludge from the enhanced membrane coagulation...

In this study, enhanced membrane coagulation (EMC) sludge was subjected to various alkaline (pH 7.2, 10, and 11), temperature (35 °C and 55 °C), and duration (0.5 h and 1 day) pretreatment conditions before being inoculated into biogas reactors operated for 176 days. Optimal pretreatment (pH 11, 55 °C, and 1 day) effectively hydrolyzed particulate COD to SCOD (8435 ± 121 mg/L). Higher pH levels also facilitated the dissolution of amphoteric aluminum-phosphorus (Al-P) compounds, enhancing phosphorus release (91.8 mg/L) from the sludge. This alkaline pretreatment, especially under optimal conditions, significantly increased biogas production and methane concentrations in long-term semi-continuous anaerobic digesters, with methane yields of 188.4 mL/gVS. The microbial community structure in all three reactors exhibited similar shifts, with saccharolytic and proteolytic fermentative bacteria dominating early stages and Thermovirga and an uncultured bacterium (Run-SP154) prevalent in later stages. Methanothrix, an acetotrophic methanogen, dominated the archaeal community in the inoculum (>91 %) and remained prominent (>40 %) throughout the experiment, while hydrogenotrophic methanogens from the genus Methanolinea increased over time, accounting for >24 % of the sequences in the final stages. Additionally, the feasibility of using EMC digestate as fertilizer for mulberry plants was tested, showing that digestate from optimally pretreated sludge promoted better growth than conventional chemical fertilizers. This suggests that this approach is a promising method for decentralized sewage treatment systems.