Novel pilot-scale advanced liquefaction-anaerobic digestion (ALAD) process for food waste to biogas conversion

Traditional two-stage anaerobic digestion of food waste is hindered by long retention times and low digestion rates. To overcome these limitations, an advanced liquefaction-anaerobic digestion (ALAD) process was developed and verified at both the laboratory and pilot scales. The ALAD process first dissolved organic matter from the solid to the liquid phase by supplementing a microbial consortium, and then converted the liquefied organic matter into biogas in upflow anaerobic sludge blanket reactors. A eukaryote-prokaryote mixed microcosm enriched with Saccharomycetales and Clostridium for synergistic hydrolysis and acidogenic fermentation liquefied 52.3% of solid organic matter in 6 days. Subsequent methanogenesis of the liquefied organic matter achieved 94.0% COD removal at an organic loading rate of 11 kg COD/m³/d and a hydraulic retention time of 1 day. Methane generation was predominantly mediated by Methanobacterium and Methanosaeta, which together accounted for 34.7% of total microbial abundance and channeled 75.9% of organic carbon into biogas. Life cycle assessment of pilot-scale experimental data showed obvious advantages of ALAD for greenhouse gas mitigation and resource conservation. This study developed a scalable strategy for effective and sustainable resource recovery from food waste.