Enhanced nitrate removal in an Fe0-driven autotrophic denitrification system using hydrogen-rich waterElectronic supplementary information (ESI) available: Fig. S1 pH in the effluent of the control and DH reactors. See DOI: 10.1039/c9ew00423h

Autotrophic denitrification can be driven using zero valent iron (ZVI) as an electron donor. Balancing the competitive reactions of abiotic nitrate removal and biotic nitrate removal by H2is the key problem for iron-assisted autotrophic denitrification. Hence, H2production by ZVI corrosion plays an important role in the iron-assisted nitrate reduction process, which determines the nitrate reduction rate and the end product. However, few studies concentrate on the effect of soluble H2on ZVI corrosion and the performance of iron-assisted autotrophic denitrification. A hydrogen-rich solution is obtained by dual-chamber MFCs, which is usually directly discarded. The present study aimed to demonstrate that the dissolved hydrogen can be feasibly applied in iron-assisted autotrophic denitrification to accelerate nitrate reduction during ZVI corrosion. It was observed that a continuous dissolved hydrogen supply viaelectrolysis promoted and stabilized the performance of iron-assisted autotrophic denitrification. The average nitrate removal was 47.3% ± 0.2% in ZVI reactors with dissolved hydrogen-rich water (DH reactors), and 30.2% ± 0.3% in ZVI reactors without dissolved hydrogen-rich water (control reactors). Moreover, the concentration of nitrite was 0.04 mg L−1in the DH reactors compared with 0.50 mg L−1in the control reactors. No other intermediates (e.g.N2O) were found in both the autotrophic denitrification reactors. Finally, the hydrogen-rich water enriched the denitrifying bacteria and increased the abundance of specific functional genes, resulting in the promotion of hydrophobic denitrification during the iron-assisted nitrate removal.