Enhanced tetracycline removal by iron sustained-release in a Fe2+ self-produced Bioelectro-Fenton

The iron cycle was a key link in bioelectro-Fenton, the cycle rate and catalyst concentration played an important role in pollutant degradation. The sustained-release ball contained Fe3+ prepared by polymer encapsulation was added to the anodic chamber of bioelectro-Fenton, in which sustained-release Fe3+ was reduced to Fe2+ by microorganism and then transferred to the cathodic chamber through exchange membrane to catalyze the in-situ generated H2O2. The Fe3+ release could be adjusted by the pore-forming agent with an optimal content of 15 wt%. Compared to the case without pore-forming agent (i.e., 0 wt%), the generated •OH, power generation and tetracycline removal (90.2 ± 0.6%, increased by 19.5%) were all significantly improved. The cathodic Fe2+ was maintained among 0.65–0.87 mg L−1, which significantly increased the cathodic Fe2+/total iron proportion (82.4–84.7%), and thus promoted the Fe2+ cycle and the bioelectro-Fenton efficiency. The content of the microbial electron transport enzymes was found to increase >1.18 times, possessing higher and more active microbial process for stable Fe2+ production and iron cycle. The tetracycline removal in river background confirmed that it was suitable for treating antibiotics in natural water background. Further, the tetracycline removal and iron source loss amount (reduced within 92.3%) was much better than that of the conventional bioelectro-Fenton (cathodic Fe2+ direct adding mode), supporting this anodic sustained-release and Fe2+ self-produced bioelectro-Fenton maintained better pollutant removal and iron source utilization thus had greater practical application potential.