Long-term operation of cathode-enhanced ecological floating bed coupled with microbial electrochemical system for urban surface water remediation: From lab-scale research to engineering application

Ecological floating bed coupled with microbial electrochemical system (ECOFB-MES) has great application potential in micro-polluted water remediation yet limited by low electron transfer efficiency on the microbial/electrode interface. Here, an innovative cathode-enhanced EOCFB-MES was constructed with nano-Fe3O4 modification and applied for in-situ remediation both at lab scale (6 L, 62-day operation) and demonstration scale (2300 m2, 1-year operation). The cathode-enhanced ECOFB-MES exhibited superior removal in TOC (81.43 ± 2.05%), TN (85.12% ± 1.46%) and TP (59.80 ± 2.27%), much better than those of original ECOFB-MES and anode-enhanced ECOFB-MES in the laboratory test. Meanwhile, cathode-enhanced ECOFB-MES boosted current output by 33% than that of original ECOFB-MES, which made a great contribution to the improvement of ectopic electronic compensation for pollutant decontamination. Notably, cathode-enhanced ECOFB-MES presented high efficiency, stability and durability in the demonstration test, and fulfilled the average concentration of COD (9.5 ± 2.81 mg/L), TN (1.00 ± 0.21 mg/L) and TP (0.10 ± 0.04 mg/L) of effluent water to meet the Grade III (GB 3838-2002) with stable operation stage. Based on the KOSIM calculation, the removal loads of cathode-enhanced ECOFB-MES in carbon, nitrogen and phosphorus could reach 37.14 g COD/(d·m2), 2.62 g TN/(d·m2) and 0.55 g TP/(d·m2), respectively. According to the analysis of microbial communities and functional genes, the cathode modified by Fe3O4 made a sensible enrichment in electroactive bacteria (EAB) and nitrogen-converting bacteria (NCB) as well as facilitated the functional genes expression in electron transfer and nitrogen metabolism, resulting in the synergistic removal of carbon in sediment and nitrite in water. This study provided a brandnew technique reference for in-situ remediation of surface water in practical application.