Establishment of direct interspecies electron transfer through ethanol supply during azo dye Reactive Red 2 anaerobic degradation

Abstract

Abstract Azo dye, for example reactive red 2, threatened the environment and human health when directly discharging into waters, and appropriate treatment methods are urgently required for such contaminants. In this study, ethanol was added to the digesters to promote azo dye Reactive Red 2 (RR2) anaerobic digestion efficiency. Results showed that the COD removal and RR2 removal efficiency were 37.0% and 63.2% in cycle 6 (only RR2 used as the substrates) in ethanol co-digested reactor, which was 16.0% and 54.5% higher than that in control reactor, and 14.5% and 52.0% higher than that in acetate co-digested reactor, respectively. Mechanisms exploration found that the electron transfer system (ETS) activity, specific methanogenic activity (SMA) and Coenzyme F420 of the sludge were effectively improved in ethanol co-digested reactor, which indicated that the addition of ethanol to anaerobic digester could enhance the activity of the microbial. Microbial community analysis showed that the electroactive microbial (Geobacter and Methanothrix) were more enriched in ethanol co-digested reactor. It was speculated that the direct interspecies electron transfer (DIET) process was possible established between Geobacter and Methanothrix, which played an important role for the improvement of RR2 removal efficiency in ethanol co-digested reactor.