Enhanced system performance by dosing ferroferric oxide during the anaerobic treatment of tryptone-based...

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.