Remediation of nitrate contamination by membrane hydrogenotrophic denitrifying biofilm integrated in microbial electrolysis cell

Complete biological denitrification is usually restricted in electron donor lacking waters. Hydrogenotrophic denitrification attracts attention for its clean and cost-efficiency advantages. Therein, the hydrogen could be effectively generated by microbial electrolysis cells (MECs) from organic wastes. In this study, a gas diffusion membrane (GDM) integrated MEC (MMEC) was constructed and provided a novel non-polluting approach for nitrate contaminated water remediation, in which the hydrogen was recovered from substrate degradation in anode and diffused across GDM as electron donor for denitrification. The high overall nitrogen removal of 91 +/- 0.1%-95 +/- 1.9% and 90 +/- 1.6%-94 +/- 2.2% were respectively achieved in Ti-MMEC and SS-MMEC with titanium and stainless-steel mesh as cathode at all applied voltages (0.4-0.8 V). Decreasing applied voltage from 0.8 to 0.4 V significantly improved the electron utilization efficiency for denitrification from 26 +/- 3.6% to 73 +/- 0.1% in Ti-MMEC. Integrating MEC with GDM greatly improved TN removal by 40% under applied voltage of 0.8 V. The hydrogenotrophic denitrifiers of Rhodocyclaceae, Paracoccus, and Dethiobacter, dominated in MMECs facilitating TN removal. Functional denitrification related genes including napAB, nirKS, norBC and nosZ predicted by PICRUSt2 based on 16S rRNA gene data demonstrated higher abundance in MMECs. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Biological denitrification in water lacking electron donors is usually limited, but can be effectively improved by using gas diffusion membrane integrated microbial electrolysis cells (MECs) to generate hydrogen from organic wastes for cost-efficient denitrification. Different materials of MECs achieved high overall nitrogen removal rates of 90%-95% at all applied voltages, with decreasing voltage significantly improving electron utilization efficiency. Integration of MEC with gas diffusion membrane greatly improved total nitrogen removal by 40%, with dominant hydrogenotrophic denitrifiers facilitating nitrogen removal and higher abundance of functional denitrification related genes predicted by PICRUSt2 based on 16S rRNA gene data.