High-solid thermophilic methanogenic degradation of alcohol fermentation waste: Biogas production, operation stability and energy recovery potential.

Alcohol fermentation waste (AFW) is a by-product of the alcohol manufacturing process with a rich carbohydrate and protein, serving as a suitable substrate for biomethane production via anaerobic digestion (AD). This study investigated the methanogenesis feasibility of AD treating AFW (total solids of 100.0 ± 1.0 g/L) in a thermophilic continuous stirred-tank reactor and explored the optimal operational conditions by regulating the hydraulic retention time (HRT) from 100 to 60, 30, and 20 days, based on system stability, CH4 yield, and organic matter degradation efficiency. The results revealed that a higher CH4 yield of 0.51 ± 0.03 L/g-VSdegraded was achieved sustainably at an HRT of 30 days. System stability was disrupted at an HRT of 20 days, which was primarily attributable to the accumulation of propionic acid (2.47 ± 0.11 g-HAc/L). The modified first-order kinetic model accurately simulated the CH4 yield and organic matter degradation efficiency under varying HRTs (all R2 > 0.92). Mass flow analysis and critical parameter correlation analysis are beneficial for reducing operational costs and streamlining operational procedures. The combination of syntrophic acetate oxidation bacteria (SAOB) and hydrogenotrophic methanogen (HM) is the dominant metabolic pathway in the system. As the HRT adjusted from higher (100 and 60 days) to lower (30 and 20 days) levels, the dominant SAOB and HM shifted from p_Firmicutes_MBA03 to Coprothermobacter and from Methanothermobacter to Methanobacterium, respectively. The energetics evaluation results revealed that a lower HRT (from 100 to 30 days) was conducive to achieving higher net energy (from 17.43 to 46.06 kJ/d).