Mediated anaerobic system performance, co-metabolizing flora and electron transfer by graphene oxide supported zero-valent iron composite

To enhance the traditional anaerobic treatment process, zero-valent iron (Fe0) and graphene oxide (GO) have recently been used and studied. However, there are drawbacks in using GO and Fe0 alone. In this study, Fe0/GO composite was utilized in anaerobic treatment of high strength wastewater to compensate for the drawbacks, and the promoting effects and the mechanism were investigated. The results verified that Fe0/GO improved COD removal rate and gas production which reached 91.8 % and 511 mL/12 h, respectively, and a better sludge flocculation performance was obtained. Furthermore, the fermentation type was optimized due to alteration of pH and oxidation-reduction potential by Fe0/GO, resulting in increment of acetic acid production and reduction of propionic acid accumulation. A detailed microbial characterization indicated that Fe0/GO had a significant effect on hydrotrophic methanogens (Methanofastidiosum and Methanofastidiosales), increasing from 1.79 % to 24.11 %. The distribution of hydrolytic fermentation bacteria, acetogenic bacteria and methanogens was more balanced and more diverse in the Fe0/GO system, indicating that a stable co-metabolizing microbial community was maintained. Moreover, the highest electron transport system activity and Fe2+ and Fe3+ concentration demonstrated that Fe0/GO could improve the intracellular and interspecific electron transfer. The conductivity, current response, cyclic voltammetry area were the highest and the internal resistance was the lowest, indicating that Fe0/GO could improve the extracellular electron transfer. The stable co-metabolizing microbial community and efficiency intra/extracellular electron transfer promoted the anaerobic wastewater treatment. This study could provide theoretical support for the practical application of developing technologies for anaerobic wastewater treatment.