Insight into the effects and mechanism of cellulose and hemicellulose on anaerobic digestion in a CSTR-AnMBR system during swine wastewater treatment.

The cellulose and hemicellulose content in swine wastewater significantly affected the performance of a continuous stirred tank reactor-anaerobic membrane bioreactor (CSTR-AnMBR). When the influent content of cellulose and hemicellulose was controlled at 3.88 ± 0.89 and 9.72 ± 2.05 g/L, respectively, the CSTR-AnMBR showed a low methane yield (0.04-0.06 L CH4/g COD) at both HRT of 12 d and HRT 30 d. The functional microbes preferred to use the freshly added degradable COD, and the decomposition of refractory COD was paused. Meanwhile, the AnMBR unit was troubled by rapidly growing membrane fouling. The trans-membrane pressure increased with a rate of 1.63 kPa/d (HRT = 12d), and 0.99 kPa/d (HRT = 30 d) exacerbated the reactor performance. In high cellulose and hemicellulose-containing environments, the cellulolytic and hemicellulolytic microbes, including Bacteroidetes and Proteobacteria, were stimulated to a certain extent. In addition, cellulose and hemicellulose up-regulated the gene expression for sugar and amino acid metabolism, decreasing the abundance of metabolism related to methane production. When the influent content of cellulose and hemicellulose decreased to 0.62 ± 0.12 and 0.77 ± 0.30 g/L, respectively, the system's performance was significantly improved, microorganisms produced less low-molecular-weight soluble microbial products, which also reduced membrane fouling risk. This study provides significant guidance for treating livestock manure with the CSTR-AnMBR system.