Enhanced tetracycline removal by bioelectro-Fenton through boosting Fe2+/Fe3+ cycle from microbial iron conversion

Abstract

Efficient microbial iron conversion was used to improve the iron cycle efficiency and reduce iron consumption in bioelectro-Fenton, and enhance the microbial activity through Fe2+/Fe3+ electron pair as electron medium. The bioelectro-Fenton with microbial iron cycle self-produced cathodic Fenton catalyst, which exhibited superior H2O2 production, pollutant removal and iron cycle rate. Compared with the conventional bioelectro-Fenton (the control reactor), the H2O2 production was increased by 22.2%, the tetracycline removal (70.3 ± 1.0% of 10 mg L−1, 84.0 ± 0.4% of 20 mg L−1 and 68.4 ± 0.1% of 50 mg L−1) was increased by 23.9%, 22.8% and 32.6%. The Fe2+ cycle rate (79.8–84.1%, based on self-produced Fe2+) was much higher than that of the control (14.6–16.1%), and the microbial Fe2+ cycle provided higher contribution of 78.1–83.0%. The relative abundance of the exoelectrogens and iron-reducing bacteria, and the gene copies of adenosine triphosphate synthase were increased by > 4.0 times, > 5.0 times and 24.3%. These results indicated that the microbial iron cycle improved the system performance by enhancing the microbial anode (electrons factory). The microbial iron cycle provided a new idea and energy-saving mode (produced electricity 0.0712 kW h m−3) to improve the efficiency of bioelectro-Fenton due to the self-produced catalyst, excellent Fe2+ regeneration and long-acting conversion.