Insights on the Use of Activated Sewage Sludge for Microalgae Harvesting and Improved Biogas Production

The present study explored the use of activated sewage sludge for microalgae harvesting and improving biogas production. Among the various sewage sludge to microalgae (S/A on % TS basis), 100% biomass harvesting was achieved at a 1:4 ratio within 8.5 h. The process, when validated in a benchtop photobioreactor (4 L), also showed complete harvesting of microalgae within 8.5 h, which indicated its potential applications for mass scale microalgae harvesting. Interaction studies revealed that pH-induced flocculation and metabolically active microorganisms were involved in sewage sludge mediated microalgae settling. The anaerobic digestion of microalgae-sewage sludge (MASS) biomass showed a higher biomethane yield (382.35 ± 6 mL/g VSS) compared to both sewage sludge (100.32 ± 2.5 mL/g VSS) and microalgae (304.48 ± 3 mL/g VSS), highlighting the synergistic benefits of co-digestion. In essence, sewage sludge-based microalgae harvesting represents a unique process with significant potential for biofuel production.