Effects of Magnetic Fe O Nanoparticles on the Characteristics of Anaerobic Granular Sludge and Its Interior Microbial Community

: In this study, the effects of magnetic Fe3O4 nanoparticles (Fe3O4 NPs) on soluble microbial products (SMP), loosely bound extracellular polymeric substances (LB-EPS), and tightly bound extracellular polymeric substances (TB-EPS) in anaerobic granular sludge were examined. In addition, the anaerobic granular sludge interior microbial community dynamics were investigated using high-throughput sequencing. The results demonstrated that the removal rate of COD was 83.6% after long-term exposure in the experimental reactor, namely, the anaerobic reactor containing Fe3O4 NPs. It was reduced by 5.7% in comparison with the removal rate in the control reactor. The total amount of TB-EPS in anaerobic granular sludge in the experimental and control reactors was 178.20 mg·g-1 and 138.24 mg·g-1, respectively, while the total amount of SMP in anaerobic granular sludge was 34.88 mg·L-1 and 27.44 mg·L-1, respectively. With regard to the LB-EPS in anaerobic granular sludge in the experimental reactor, the peak of humic acid disappeared and the peak intensity of coenzyme F420 decreased slightly using excitation-emission matrix (EEM) fluorescence spectra. In terms of the microbial community dynamics in the experimental reactor, the abundance of Methanobacterium was greatly augmented from 76.15% to 86.76%; whereas, the abundance of Methanothrix decreased from 17.1% to 7.51%. This indicated that Methanothrix was more sensitive to Fe3O4 NPs. Moreover, the changes in bacterial communities were evident:①the abundance of Proteobacteria dropped from 66.44% to 47.16%; ② the abundance of Actinobacteria grew from 8.97% to 17.33%; and ③ the abundance of Bacteroidetes increased from 8.07% to 17.74%. The increasing abundance of Actinobacteria and Bacteroidetes plays a positive role in the anaerobic hydrolysis of organic matter.