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

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 Fe 2+ /Fe 3+ electron pair as electron medium. The bioelectro-Fenton with microbial iron cycle self-produced cathodic Fenton catalyst, which exhibited superior H 2 O 2 production, pollutant removal and iron cycle rate. Compared with the conventional bioelectro-Fenton (the control reactor), the H 2 O 2 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 Fe 2+ cycle rate (79.8–84.1%, based on self-produced Fe 2+ ) was much higher than that of the control (14.6–16.1%), and the microbial Fe 2+ 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 Fe 2+ regeneration and long-acting conversion. • Microbial iron conversion improved tetracycline removal and Fe 2+ /Fe 3+ cycle. • H 2 O 2 production and tetracycline removal was increased by 1.6 times and 22.8%. • Fe 2+ cycle was increased from 16.1% to 79.9% by microbial iron cycle. • Microbial Fe 2+ cycle and contribution was 64.1–80.8% and 78.1–83.0%. • Energy recovery (0.0712 kW h m −3 ) was increased by 31.1%.