Solid-state anaerobic co-digestion of food waste, rice straw, and rice husk supplemented with cattle digesta under thermophilic conditions

Improving the solid-state digestion of food waste (FW) is important for recovering energy and utilizing the digested residue as fertilizer. Herein, solid-state anaerobic co-digestion was conducted using thermophilic digesters. The inhibitory effects of ammonium were controlled using seasonal rice straw (RS) and perennial rice husk (RH). Furthermore, to accelerate lignocellulosic biomass digestion, cattle rumen digesta was supplemented as an alternative microbial source. When only restaurant FW (average C/N ratio = 13) was used as feed, ammonium accumulation decreased methane production. Methane was successfully produced when RS and RH were mixed with FW, wherein the total solid (TS) ratio of RS and RH to FW was 2.0 (TS = 30–40%; volatile solids (VS) loading rate = 5.08 kg m˗3.day). The FW and RS methane yields were 0.573 m3 kg˗1 VS and 0.259 m3 kg˗1 VS, respectively, similar to the biomethane potential (BMP) of each biomass, whereas the methane yield of RH (0.115 m3 kg˗1 VS) was higher than the BMP. Microbial community analysis revealed that hydrogenotrophic methanogens Methanoculleus and Methanothermobacter were dominant in the digested sludge and cattle digest could be used as a supplement of rumen microorganisms.