Enhancement of nitrate removal under limited organic carbon with hydrogen‐driven autotrophic denitrification in low‐cost electrode bio‐electrochemical reactors

Abstract

AbstractBACKGROUNDNitrate‐contaminated water is a concerning environmental and health problem in agricultural areas. Due to its low organic carbon content, such water cannot be purified using a conventional bioreactor with heterotrophic denitrification. Low‐cost bio‐electrochemical reactors were established with the aim of enhancing denitrification performance by cooperation of heterotrophic and hydrogenotrophic denitrification.RESULTSAt the lowest C/N ratio of 1.0, the bioreactor reached only 67.4% for NO3‐N removal and 47.5% for total N removal (total N removal rate of ca 1.2 mg L−1 h−1), whereas the Cu reactor (bio‐electrochemical reactor using copper wire as cathode) achieved the best efficiencies of 73.7% and 53.8% for NO3‐N and total N removal (total N removal rate of ca 1.3 mg L−1 h−1), and followed by the SS reactor (bio‐electrochemical reactor using stainless steel wire as cathode). On the other hand, the greatest total organic carbon (TOC) removal efficiency was observed for the bioreactor and followed by the SS reactor and the Cu reactor. The low TOC consumption of 1.2–1.4 mg‐TOC (mg‐N)−1 in the Cu reactor and the SS reactor indicated the enhanced denitrification from coexisting hydrogenotrophic denitrification. In addition, the performance of hydrogenotrophic denitrification was improved by increasing the applied current from 10 to 30 mA.CONCLUSIONSThe abundance of autotrophic denitrifying bacteria (identified as hydrogenotrophs) was higher than that of heterotrophic denitrifying bacteria in both the Cu reactor and the SS reactor. Archromobacter and Flavobacterium were the most dominant genera in the biofilm of the Cu reactor cathode and in the suspended sludge, respectively. Hydrogenophaga were detected in both biomass samples, but were absent from the biomass samples of the conventional bioreactor. © 2021 Society of Chemical Industry (SCI).