Biohythane production from tofu processing residue via two-stage anaerobic digestion: operational conditions and microbial community dynamics

Two-stage anaerobic digestion (TAD) of tofu processing residue (TPR) was investigated, considering the impacts of operational conditions on microbial community diversity and biohythane production. The results showed that the optimal conditions of TAD were dark fermentation (DF) operated at a substrate-to-inoculum ratio (SIR) of 8, 5% solid content, and 37 degrees C for 36 h, followed by methanogenic fermentation (MF) performed at a SIR of 1 and 37 degrees C for 13 days, which produced 324.4 mUg-VSfed of biohythane along with 103 mM acetic acid and 38 mM propionic acid. Compared to one-stage anaerobic digestion, TAD improved specific energy recovery by 45.3%, producing a biogas yield of 189.6 mL/g-VSfed. SIR and temperature affected microbial community diversity of DF system, where high-SIR speciated hydrogen producers such as Mobilitalea and Clostridium sensu stricto/at thermophilic and mesophilic temperatures, respectively, whereas low-SIR stimulated methane generation by the speciation of Methanoculleus thermophilus. Likewise, hydrogenotrophic methanogens (Methanomassiliicoccus) enriched MF reactors operated at low-SIR. Overall, this study demonstrated TAD as an efficient technology for producing clean energy and value-added products using TPR.