Enhancing electron transfer by ferroferric oxide during the anaerobic treatment of synthetic wastewater with mixed organic carbon

- The effect of ferroferric oxide on anaerobic treatment was investigated.
- Ferroferric oxide increased the maximum CH4 production rate and shortened the lag phase.
- Methanosarcina was the predominant methanogen contributing to DIET.
- Proteiniclasticum and Kosmotoga were responsible for protein degradation.

Conductive materials can enhance direct interspecies electron transfer (DIET) during the anaerobic treatment of wastewater and provide ecological advantages for syntrophic methane (CH4) production. The effects of ferroferric oxide (Fe3O4) on the system performance and microbial communities were examined during the anaerobic treatment of synthetic wastewater with mixed organic carbon. The addition of Fe3O4 did not enhance the relative abundance of methanogens, but increased the maximum CH4 production rate by 15.4% and shortened the lag phase by 13.9%. Methanosarcina was the predominant methanogen contributing to DIET. Proteiniclasticum and Kosmotoga were dominant upon the addition of Fe3O4 and were responsible for protein degradation. More extracellular proteins were produced and a filamentous morphology was observed upon the addition of Fe3O4. Short-term Fe3O4 addition also improved the performance of the anaerobic treatment in the control reactor, and the Fe3O4 rather than the microbial morphology was the more important factor enhancing DIET.