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 Fe super(3+) dosage of 15 mg/L. The results showed that the combination of Fe super(3+) and Ca super(2+) 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 Fe super(3+) and Ca super(2+) 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 floe size by enhancing biofloccula-tion of Ca super(2+) and Fe super(3+). 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 Ca super(2+).