Co-digestion of primary sewage sludge with drinking water treatment sludge: A comprehensive evaluation of benefits.

Anaerobic co-digestion of primary sludge with two types of drinking water treatment sludge (DWTS), namely iron- or aluminum-rich DWTS (Fe- or Al-DWTS) were systematically evaluated by biochemical methane potential tests, kinetic modelling, downstream process parameters and microbial community analysis. Specific methane yields decreased approximately 19% to 123 mL·g VS, while the hydrolysis constant k decreased from 0.21 d to 0.18 d for Fe-DWTS at 10% to 40% dosages. On the contrary, specific methane yields decreased 45-55% for Al-DWTS, and k decreased to 0.14 d at 40% dosage. Significant removals (>95%) of phosphate and hydrogen sulfide were observed for Fe- and Al-DWTS additions at 40% dosage. Microbial community analysis revealed that Al-DWTS increased the abundance of most hydrogenotrophic methanogens, while Fe-DWTS increased the abundance of acetoclastic methanogens. Kinetic modelling further revealed that Fe- and Al-DWTS additions affected the hydrolysis and methanogenesis process kinetics and the methane yield differently.