Anaerobic offsite Fe²⁺ releasing for electrocoagulation in ABMBR: Membrane fouling mitigation, nutrients removal and anodes protection

To solve the problems of pollutants removal and membrane fouling in membrane bioreactor (MBR) and plate passivation in the process of electrocoagulation (EC), anaerobic baffled membrane bioreactor (ABMBR, 4 cells for anaerobic process and 1 cell for membrane separation) was proposed for anaerobic offsite release of Fe²⁺ in the process of EC. The iron plates were placed in the anaerobic unit and the membrane module was placed outside the electric field. The results showed that the operation time could be extended from 5 to 8 days to 63 days when 3 V intermittent voltage (5 min on and 5 min off) was adapted. As the result of EC, protein and polysaccharide contents of soluble microbial products (SMP) and extracellular polymeric substances (EPS) from sludge and filter cake layer were decreased obviously. The sludge particle size was increased from 400 nm to 80 μm and zeta potential was decreased from −11 mV to −20 mV. The water quality results showed that almost 100 % of ammonia nitrogen (NH₄⁺-N) and 87 % of total phosphorus (TP) were removed under the action of EC without excess sludge discharge. By placing the iron plate in the anaerobic unit, plate passivation was very slow during 195 days of operation, which solved the problem of plate passivation in EC.