A half-submerged integrated two-phase anaerobic reactor for agricultural solid waste codigestion

• An innovative half-submerged integrated two-phase anaerobic reactor is developed.
• Acidogenic and methanogenic units were combined together but separated spatially.
• Methanogenic community, pH, VFAs are different in acidogenic and methanogenic units.
• Co-digestion of wheat straw and fruit/vegetable waste in the reactor is proved.
• Digestion efficiency is affected by ratio of feedstocks and loading rate.

Anaerobic digestion is widely used in bioenergy recovery from waste. In this study, a half-submerged, integrated, two-phase anaerobic reactor consisting of a top roller acting as an acidogenic unit and a recycling bottom reactor acting as a methanogenic unit was developed for the codigestion of wheat straw (WS) and fruit/vegetable waste (FVW). The reactor was operated for 21 batches (nearly 300 d). Anaerobic granular sludge was inoculated into the methanogenic unit. The residence time for the mixed waste was maintained as 10 d when the operation stabilized, and the temperature was kept at 35 °C. The highest organic loading rate was 1.37 kg VS/(m3 d), and the maximum daily biogas production was 328 L/d. Volatile solid removal efficiencies exceeded 85%. WS digestion could be confirmed, and efficiency was affected by both the ratio of WS to FVW and the loading rate. The dominant bacteria were Bacteroides-like species, which are involved in glycan and cellulose decomposition. Methanogenic community structures, pH levels, and volatile fatty acid concentrations in the acidogenic and methanogenic units differed, indicating successful phase separation. This novel reactor can improve the mass transfer and microbial cooperation between acidogenic and methanogenic units and can efficiently and steady codigest solid waste.