Recent advances in co-digestion conjugates for anaerobic digestion of food waste.

Anaerobic digestion (AD) is a biological process that breaks down organic waste materials, such as food waste (FW) that produces biogas and digestate. The biogas can be utilized as biofuel, and digestate could be applied as fertilizer. However, AD of FW alone has limitations on optimal degradation, digester stability and biogas yield. Co-digestion of FW along with other organic wastes such as animal manure, agricultural residue, sewage sludge and industrial organic waste, has shown substantial improvement in degradation process with increased biogas yield. The inadequacies in FW for optimum AD, like low carbon-to-nitrogen ratio (C/N ratio), lack of trace elements and irregular particle sizes, can be nullified by adding appropriate co-digestion conjugates. This review aims to describe the characteristic inadequacies of FW and examines the effect on mesophilic co-digestion of FW with animal manure, waste sludge and agricultural wastes for biogas production optimization. A critical review on the impact of pretreatment and co-digestion to enrich the methane (CH4) content in biogas has been performed. The review also examines the microbial community shift due to co-digestion, which is critical for the stability of an anaerobic digester. Finally, it discusses the prospects and challenges for the widespread application of the co-digestion technique as an effective organic waste management practice.

Load limit of a UASB fed septic tank-treated domestic wastewater.

Performance of a 250 L pilot-scale up-flow anaerobic sludge blanket (UASB) reactor, operated at ambient temperatures, fed septic tank effluents intermittently, was monitored for hydraulic retention time (HRT) from 18 h to 4 h. The total suspended solids (TSS), total chemical oxygen demand (CODT), dissolved chemical oxygen demand (CODdis) and suspended chemical oxygen demand (CODss) removal efficiencies ranged from 20 to 63%, 15 to 56%, 8 to 35% and 22 to 72%, respectively, for the HRT range tested. Above 60% TSS and 47% CODT removal were obtained in the combined septic tank and UASB process. The process established stable UASB treatment at HRT≥6 h, indicating a hydraulic load design limit. The tested septic tank-UASB combined system can be a low-cost and effective on-site sanitation solution.