Unlocking biomethane and biohydrogen potential of lipid-rich wastewater using anaerobic granular sludge

The recovery of biofuels from lipid-rich industrial waste, such as confectionery wastewater, offers a promising path toward sustainable energy. This study investigates confectionery wastewater's methane and hydrogen production potential using anaerobic granular sludge (AnGS) under varying inoculum-to-substrate ratios (ISRs). Methane yields were evaluated at ISRs of 3, 4, and 5, with the highest specific production (313.5 ± 4.3 mL CH₄/g CODinf) observed with an ISR of 5. Methane production followed first-order kinetics with no lag phase, indicating rapid microbial activity and uninhibited degradation of long-chain and volatile fatty acids, particularly caproic acid. Hydrogen production was assessed at ISRs of 0.25, 0.5, and 1. No hydrogen was observed with the ISR set at 0.25, likely due to excessive VFA accumulation (mainly lactic acid) and a significant pH drop (i.e., down to 3.1 ± 0.1). At ISR of 1, a specific hydrogen yield of 44.7 ± 7.2 mL H₂/g CODinf was achieved in two days. AnGS demonstrated strong resilience to lipid-induced inhibition, ensuring stable methane production and manageable VFA levels. These results highlight AnGS as a robust inoculum for treating high-lipid waste, offering new insights into optimising biofuel recovery from industrial wastewater.