Electro-conditioning of activated sludge in a membrane electro-bioreactor for improved dewatering and reduced membrane fouling

Abstract

The impact of applying a direct current (DC) field on the morphology and structural composition of municipal wastewater flocs and their bound water content was investigated. The effects on sludge dewaterability and membrane fouling were assessed using batch electro-bioreactors and continuous flow submerged membrane electro-bioreactor (SMEBR). Series of batch electro-bioreactors were tested at current densities (CD) ranging between 5 and 35A/m2 for three concentrations of mixed liquor suspended solids (from 3000 to 15,000mg/l) and five electrical exposure modes (time-ON/time-OFF). Results of batch tests showed that CD of 15 to 35A/m2 enhanced sludge filterability, represented as specific resistance to filtration (SRF), up to 200 times compared to sludge in the control reactor. Electrically enhanced sludge under continuous flow (SMEBR) exhibited a reduction of SRF over the conventional activated sludge from 8 to 86 times, while membrane fouling rate decreased by 6 times. It was assumed that the removal of organic materials and soluble microbial products (SMP) through electro-coagulation (up to 90% for polysaccharides and up to 50% for protein), reduction of bound water by electroosmosis, increasing floc size through electro-bio-flocculation and the reduction of sludge organic/inorganic ratio were the major mechanisms contributed to SRF and membrane fouling reduction.