Abstract
Direct interspecies electron transfer (DIET) among the cometabolism microbes plays a key role in the anaerobic degradation of persistent organic pollutants and stability of anaerobic bioreactor. In this study, the COD removal efficiency increased to 99.0% during the start-up stage in the combined bioelectrode-UASB system (R1) with magnetite nanoparticles addition, which was higher than those in the coupled bioelectrode-UASB (R2; 83.2%) and regular UASB (R3; 71.0%). During the stable stage, the increase of 2,4-dichloronitrobenzene (2,4-DClNB) concentration from 25 mg L−1 to 200 mg L−1 did not affect the COD removal efficiencies in R1 and R2, whereas the performance of R3 was deteriorated obviously. Further intermediates analysis indicated that magnetite nanoparticles enhanced the reductive dechlorination of 2,4-DClNB. High-throughput sequencing results showed that the functional microbes like Syntrophobacter and Syntrophomonas which have been reported to favor the DIET, were predominant on the cathode surface of R1 reactor. It is speculated that the addition of magnetite nanoparticles favors the cooperative metabolism of dechlorinating microbes and electricigens during 2,4-DClNB degradation process in the combined bioelectrode-UASB reactor. This study may provide a new strategy to improve the performance of microbial electrolysis cells and enhance the pollutant removal efficiency.
Highlights
Microbial electrolysis cells (MECs) as an emerging electricity-mediated microbial bioelectrochemical technology, are developed originally for high-efficiency biological hydrogen production from wastewater[1]
With the increase of chemical oxygen demand (COD) loading in the influent, the COD removal efficiencies of R2 and R3 were unstable during the first 45 days, whereas the COD removal efficiency in R1 increased from 41.8% to 99.0% (Fig. S1)
The COD removal efficiency in R2 increased to 83.2% while the corresponding value in R3 was 71.0%
Summary
Microbial electrolysis cells (MECs) as an emerging electricity-mediated microbial bioelectrochemical technology, are developed originally for high-efficiency biological hydrogen production from wastewater[1]. Several studies[20,21,22,23,24] have demonstrated that conductive iron oxides, e.g., goethite, hematite and magnetite, could promote the anaerobic biological treatment of wastewater by enhancing the direct interspecies electron transfer between functional microbial species. Carbon fiber brush and graphite felt were chose as the anode and cathode respectively in the combined bioelectrode-UASB due to their cost-effectiveness and good stability, and the anodic electrode was surrounded by the cathode electrode. The objectives are to 1) study the degradation of refractory pollutants such as 2,4-dichloronitrobenzene (2,4-DClNB), stability of combined system, and to 2) analyze the biofilm characteristic on electrodes surface and microbial community structure in combined system for revealing the possible mechanism for enhancement of DIET by magnetite addition
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