Optimization of dry anaerobic co-fermentation of sludge and corn straw with magnetite (Fe3O4)

In this study, an Optimized addition amount of magnetite (Fe3O4) and the combination of Pall ring with Fe3O4 were investigated to scrutinize the concentration of short-chain fatty acids during the dry anaerobic co-fermentation of corn straw and waste sludge for the first time. Experimental results revealed that the produc-tion of SCFAs was significantly promoted in the presence of 0.16 g/g TS magnetite. Under these conditions, the maximum SCFA concentration was 283.4 +/- 11.1 mg COD center dot L-1, which was 1.35 times that without magnetite (Fe3O4) (210.1 +/- 4.8 mg COD center dot L-1) and 1.23 times that with 0.08 g/g TS (229.6 +/- 24.5 mg COD center dot L-1). Meanwhile, 0.16 g/g TS Fe3O4 could significantly enhance the release of soluble organic matter, and NH4+-N removal effi-ciency was considerably accelerated. Consequently, the removal rate of TS and VS were significantly enhanced to 1.01 +/- 0.10 g center dot d-1 and 0.84 +/- 0.04 g center dot d-1 with the addition of 0.16 g/g TS Fe3O4, which were 1.53-folds and 1.31-folds than that of the control. Microbial community analysis revealed that 0.16 g/g TS Fe3O4 improved microbial activity, microbial community richness and the relative abundance of hydrolyzed acid-producing microbes such as Firmicutes, Synergistota, Bacteroidetes and Chloroflexi. The relative abundance of Proteobacteria (SCFA consumer) was highly enriched and reached 41.39% in the control group. The combination of Pall ring with 0.16 g/g TS Fe3O4 had no obvious synergistic effect on promoting acid production, but exhibited high microbial activity and lower concentration of NH4+-N. Collectively, this work will provide suggestions to boost SCFA yield from corn straw and waste sludge via anaerobic co-digestion.