Regulation of interspecies metabolic balance by pseudocapacitance/ conductance mechanisms to enhance anaerobic treatment of high-concentration wastewater

Interspecies electron transfer (IET) is vital for ensuring efficient and stable anaerobic digestion. However, IET was generally unsatisfactory and inefficient when dealing with high-concentration organic wastewater, resulting in acidification and metabolic imbalance. In this study, a Fe3O4-incorporated carbon fiber (Fe@CF) possessing both pseudocapacitance (2.5 F/g) and conductivity (6.3 mu S/cm) was proposed for regulating the flux of electrons and H+ between acetogens and methanogens. The conductive Fe3O4, serving as an electron "expressway", accelerated the speed of direct interspecies electron transfer, while the pseudocapacitive carbon fiber, acting as an electron "reservoir", buffered the system's pH by storing/releasing excess electrons. Experiments demonstrated that under the influent COD concentrations of 7.5 and 15.0 g/L, the Fe@CF reactor maintained a COD removal efficiency of 85 % while the pH remained stable at 7.5. In contrast, the Control reactor failed to withstand the organic load shock, resulting in a decrease in COD removal efficiency from 72 % to 42 %, accompanied by severe acidification. Key enzymes involved in organic decomposition and electron transfer were increased by 20 %-72 % with Fe@CF supplement and remained active even as the influent COD concentration increased to a relatively high level. Metagenomics analysis revealed an up-regulation in the expression of genes pertinent to electron transfer and energy synthesis within Fe@CF reactor, indicating the potential mechanism for promoting the synthesis of NADH/NAD+, F420H2/F420, and ATP. This study provides a novel strategy to address the accumulation of H+ and electrons resulting from the imbalance between acetogens and methanogens, contributing to the efficient treatment of high-concentration organic wastewater.