Anaerobic digestion of aqueous product of co-hydrothermal liquefaction of beverage waste and sewage sludge: Reduction of toxicity and energy assessment

Beverage waste and sewage sludge are two of the most generated waste-based biomasses. Recently, the production of biocrude through the hydrothermal liquefaction (HTL) of both wastes independently or jointly resulted in the generation of an aqueous byproduct (ACP) of high dissolved organic carbon. The high dissolved organic carbon means that ACP can be digested anaerobically to recover more bioenergy products like methane. This study investigated the anaerobic digestion (AD) of ACP produced from co-HTL of beverage waste [winery rose lees (RL)/brewery trub (BT)] and primary sludge (PS) with reference to the quantity and energy content of methane produced as well as the suitability of digestate as an organic fertilizer. Results indicated that ACP generated from the HTL of combined RL and PS (RLPS) produced the highest specific methane yield of 317 mL/gCOD and energy recovery of 80.64% while ACP generated from PS produced the lowest specific methane yield of 26 mL/gCOD and energy recovery of 6.62%. Results also indicated the N/P ratio of the anaerobic digestate makes it suitable for fertilizer application although it needs to be supplemented by K, Ca, and Mg. The results of this study proved that ACP produced during the HTL processing of mixed sewage sludge and beverage waste generates higher methane yield than what could be generated if both wastes are not mixed. This study emphasized that efficient process optimization and energy recovery can be obtained in AD of HTL ACP using a mixed feedstock rather than single feedstocks.