Real-world assessment of a decentralized food waste anaerobic digestion system: A test-bedding case study application

Addressing the global challenge of food waste, this research delves into the assessment of an on-site food waste treatment solution through a full-scale decentralized anaerobic digester (AD) system, specifically deployed at a Singapore hawker centre. Demonstrating efficiency in Singapore's tropical climate (29 °C) without external heating, the 10.8 m³ digester exhibited resilience over 234 days, navigating through real-world fluctuations in average organic loading rates ranging from 0.07 ± 0.02 to 0.81 ± 0.38 kgVS/(m3d). The normalized specific biogas production averaged 0.70 ± 0.48 m3/kgVS, accompanied by a methane concentration of 56.9 ± 2.9%. During peak performance, with an organic loading rate of 1.1 kgVS/(m3d), the system achieved an impressive volumetric biogas production rate of 1.18 m3biogas/m3reactor, equivalent to 1.1 m3/kgVS of specific biogas production per day. The energy assessment revealed consumption rates of 0.57–0.97 m3/kWh, positioning it comparably with commercialized biogas technologies in China and Taiwan. In the realm of microbiome composition, the prevalence of hydrogenotrophic methanogens, including Methanomicrobia, Thermoplasmata, and Nanoarchaeia, is notable. These methanogens showcase a remarkable tolerance to acetate, surpassing common aceticlastic methanogens by 11 times, thereby playing a pivotal role in enhancing the stability of the AD system over extended periods. On the economic front, the present AD system yielded losses ranging from SG$552,434 to SG$742,919, primarily due to a low payback period and substantial investment costs. Profitability becomes a possibility if there are significant reductions in capital costs and operator salaries. The challenges encountered during the operation of this decentralized system, along with the corresponding mitigation measures, are thoroughly discussed. Positioned as a promising test-bedding model, this application underscores its technical feasibility potential for sustainable food waste management through AD technology in Singapore. It stands as a replicable prototype, contributing to closing the food waste loop and advancing the bioeconomy.