Enhanced system performance by dosing ferroferric oxide during the anaerobic treatment of tryptone-based high-strength wastewater

Conductive materials can facilitate syntrophic methane (CH4) production by improving direct interspecies electron transfer. The effect of a conductive material, ferroferric oxide (Fe3O4), on the anaerobic treatment of tryptone-based high-strength wastewater was investigated in two anaerobic sequencing batch reactors (ASBRs). One was the control reactor without amendment of Fe3O4, and the other was the Fe3O4-amended reactor. In an ASBR reaction cycle, the dosage of Fe3O4 increased the CH4 production rate by 12.2%, shortened the methanogenic lag phase by 32.3%, and improved the COD removal rate by 8.1%. During anaerobic treatment, the dosage of Fe3O4 not only enhanced the CH4 production from acetate but also facilitated the hydrolysis/acidification process fed by tryptone. Maximum electron transport activities were increased by 40.4, 137.3, and 64.6% in the processes of the ASBR reaction cycle, the CH4 production from acetate, and the hydrolysis/acidification of tryptone, respectively. Among all tested quorum sensing signal substances, N-octanoyl-l-homoserine lactone was dominant in both ASBRs, with the highest concentration in the biomass and the lowest concentration in the water phase. In addition, the concentration of signal substance was high in the ASBR cycle and low in the CH4 production from acetate and the hydrolysis/acidification of tryptone. Proteiniclasticum and vadinCA02 were dominant acidogens, and their relative abundances increased during the long-term operation with Fe3O4 dosing. Methanosarcina was the predominant methanogen, contributing to interspecies electron transfer.