High nitrate removal by autohydrogenotrophic bacteria in a biofilm-electrode reactor

Abstract

A biofilm-electrode reactor has been developed to effectively treat high nitrate-polluted wastewater. The novelty of this system is that the biological degradation of -N (electron acceptor) was enhanced by the generation of H₂ (electron donor) and direct immobilization of autohydrogenotrophic bacteria on the surface of the cathode. Nitrate degradation rate increased as current increased from 10 to 120 mA. When current was increased above 120 mA, the degradation rate was decreased. Meanwhile, nitrite accumulation decreased as current (below 120 mA) increased. If current was increased further to higher than 120 mA, nitrite was observed to accumulate again. Denitrification rate increased with initial nitrate loading below 350 mg -N L⁻¹. However, the denitrification was found to be inhibited at high nitrate loading (350–500 mg -N L⁻¹). Meanwhile, nitrite accumulation increased as nitrate loading increased and the highest accumulated nitrite level reached 16.07 mg -N L⁻¹ at nitrate loading of 500 mg -N L⁻¹. The reactor obtained optimum denitrification when C/N, temperature, and pH were 1.0, 25–30°C, and 6.0–7.0, respectively.

Keywords:

• Biofilm-electrode reactor
• High nitrate
• Autohydrogenotrophic bacteria
• Current
• Nitrite

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (NSFC) (No. 51008239 and 51378400), the Natural Science Foundation of Hubei Province, China (No. 2013CFB289 and 2013CFB308) and the opened fund of State Key Lab of Urban Water Resources and Environment (HIT) (No. QAK201014).