INTEGRATED EFFECTS OF CALCIUM AND IRON CATIONS ON THE PERFORMANCE OF SUBMERGED MEMBRANE BIOREACTORS FOR TREATING SYNTHETIC MUNICIPAL WASTEWATER

The performances of membrane bioreactors (MBRs) were investigated in bench-scale submerged MBRs for treating synthetic municipal wastewater at three Fe:Ca concentration ratios of 1:2, 1:6 and 1:10 with constant Fe3+ dosage of 15 mg/L. The results showed that the combination of Fe3+ and Ca2+ had a slight impact on effluent quality, while its effect on membrane fouling was significant. The fouling rate decreased with the decline of Fe:Ca ratio from 1:2 to 1:6, while it increased when Fe:Ca ratio further decreased to 1:10, suggesting that there was an optimum concentration combination of Fe3+ and Ca2+ in reducing membrane fouling. When the Fe:Ca ratio declined from 1:2 to 1:6, the reduction of total resistance was due to the decline of fouling layer resistance, which could be attributed to the reduction of soluble microbial products (SMP) and increase of floc size by enhancing bioflocculation of Ca2+ and Fe3+. As the Fe:Ca ratio decreased from 1:6 to 1:10, the increase of total resistance could be attributed to the rise of irreversible adsorption and pore plugging mainly due to the precipitation and physical adsorption of Ca2+.