Enhancing anaerobic digestion performance of food-waste solid residue through alkali-thermal pretreatment

Abstract

The resource utilization of food-waste solid residue has received much attention, but the high organic content has resulted in poor hydrolysis performance during anaerobic digestion. In this study, pretreated food-waste solid residues through alkali, thermal and alkali-thermal were mixed with excess sludge for anaerobic digestion. Results indicated that pretreatments significantly alleviated the inhibitory effect of NH₄⁺-N and stabilized the pH of the digestive environment. Under the condition of alkali-thermal group, the concentrations of soluble chemical oxygen demand (SCOD), soluble protein, soluble polysaccharide and Volatile fatty acids (VFAs) were degraded by 81.00 %, 53.02 %, 42.87 % and 99.99 %, respectively, compared to the condition of control group. The absolute abundance advantage of Dojkabacteria significantly reduced the risk of ammonia inhibition and the relative abundance of Methanobacterium archaea was nearly 90 % under the condition of alkali-thermal group. It was observed that substrate was fragmented and enriched with bacilli and cocci in the crevices after the reaction under the condition of alkali-thermal group. The pretreatment was effective in utilizing more DOM, thereby increasing the efficiency of methane production. The condition of alkali-thermal group had the highest methanogenic potential, which was 16.78 % and 34.04 % more than alkali group and thermal group, respectively, and the maximum methane production rate was at its highest (R_max =522.70 mL/d). Compared to the condition of control group, the cumulative methane productions increased by 685.90 %, 593.71 % and 847.07 % under the conditions of alkali group, thermal group and alkali-thermal group, respectively. This founding provided an effective way for resource utilization of food-waste solid residue.