Synergistic effect of anaerobic co-digestion of South African food waste with cow manure: Role of low density-polyethylene in process modulation

Abstract The simultaneous digestion of two or more organic substrate in anoxic conditions is a proven strategy for optimizing anaerobic digestion (AD) efficiency, likewise, the maintenance of process temperature within the biocatalytic range of AD processes is critical for process stabilization. However, challenges with yield and process stability yet presents major bottlenecks for bio-digester designs specifically for low-income households due to characteristic limitations in feed profile and constant exposure to natural elements and fluctuations in weather conditions. In this study, knowledge of common advantages of co-digestion of kitchen wastes and animal manure; nutrient balancing for improved microbial growth and activity, augmentation of substrate characteristics, was combined with household digester design modification (with low-density polyethylene (LDPE) cover) for an improved, yet techno-feasible process. Low-cost, durable LDPE commonly used for its greenhouse heating function was explored here for sustaining bio-methane production from organic feeds in and at household digester conditions. Food wastes (KW) was co-digested with cow manure (CW) in a modular anaerobic digester with and without LDPE cover. Findings showed the optimum feed blend: KW to CW, 3:1 produced the highest amount of biogas over a hydraulic retention time of 30 days and organic loading rate of 4.41 kgVS/L/day. The co-digestion runs suggested significant synergy across runs while mono-digestion of KW failed due to acidification. Fed-batch codigestion of the substrates in the LDPE modified digester resulted in a significant increase in methane content of produced biogas with proof of slurry temperature within the mesophilic range (29–44 °C) across the 3-month study time.