Enhancing Food Waste Anaerobic Digestion Efficiency with Biochar as a Sustainable Technology in Decentralized Real-World Systems

Long-term anaerobic digestion (AD) of food waste often faces challenges, with volatile fatty acid inhibition being a common issue that hinders optimal performance. This research explores the effect of biochar supplementation on long-term AD of food waste characterized by volatile fatty acid inhibition. The findings demonstrate that adding a modest amount of biochar (0.055 g/L) effectively enhances AD under ambient conditions at 29 °C. This biochar supplementation reduced volatile fatty acids to a safe level of 1195 mg/L after 36 days, well within the generally accepted safe threshold of 1500 mg/L. This safe threshold is supported by other studies, which indicate that maintaining VFA concentrations below 1500 mg/L minimizes the risk of process inhibition and ensures stable AD operation. Additionally, the normalized specific biogas yield averaged 1.33 ± 0.45 m3/kg VS, representing a 47.4% improvement over the control AD conducted under identical conditions. After stabilization, the study assessed whether AD could maintain functionality and stability under mesophilic conditions (35 °C) without further biochar supplementation, simulating a real-world scenario to test long-term efficacy in industrial-like conditions. This mesophilic postbiochar AD resulted in an additional 31.8% increase in the normalized average specific biogas yield, reaching 1.95 ± 0.25 m3/kg VS. Biochar increased Methanosaeta methanogens by 30%, enhancing direct interspecies electron transfer and strengthening syntrophic interactions. This shift made aceticlastic methanogens 9 times more prominent, improving acetate oxidation, biogas yield, and overall AD stability. These findings highlight biochar’s potential to enhance decentralized biogas facilities, promote sustainable food waste management, and advance the bioeconomy by providing a replicable model for closing the food waste loop.