Effects of Fe3O4 nanoparticles on anaerobic digestion enzymes and microbial community of sludge.

Fe₃O₄ nanoparticles (NPs) have potential effects on the anaerobic digestion of excess sludge. The effects of different concentrations of Fe₃O₄ NPs (0, 100, 200, 400 and 600 mg/L) on enzymes and microorganisms in anaerobic digestion were studied to explore the mechanism of the effect of Fe₃O₄ NPs on anaerobic digestion. The results showed that 100, 200 and 400 mg/L Fe₃O₄ NPs could promote anaerobic digestion, and 200 mg/L Fe₃O₄ NPs had the most obvious promoting effect. The activities of protease, cellulase, dehydrogenase, acetic kinase and coenzyme F420 in the 200 mg/L Fe₃O₄ NPs group reached 120 U/mg VS, 71.75 U/g VS, 135 U/mL, 94 mol/L, 1.37 umol/g VSS, respectively, which were 3.8, 1.5, 1.2, 1.2 and 1.6 times of the blank group, respectively. However, when the concentration of Fe₃O₄ NPs reached 600 mg/L, the activities of cellulase, dehydrogenase and acetic kinase were lower than those of the blank group, and anaerobic digestion was inhibited. The above conclusions can also be confirmed by high-throughput sequencing. The abundance of longilinea and ornatilina in the 200 mg/L Fe₃O₄ NPs group was 8.8% and 4.1% respectively, and methanthrix abundance was 69%, which was more conducive to decomposition acetic acid into CH₄. Highlights To explore the effects of Fe3O4 NPS on enzyme activity and microorganisms. 200mg/L Fe₃O₄ NPs could significantly promote the activity of enzyme. 200mg/L Fe₃O₄ NPs could promote the diversity of bacterial and archaeal communities. 600mg/L Fe₃O₄ NPs could inhibit some enzyme activities and microbial community diversity. [ABSTRACT FROM AUTHOR]