Removal of bisphenol-A from spiked synthetic effluents using an immersed membrane activated sludge process

Abstract

With the recent emergence of estrogenic contaminants as reclaimed wastewater quality issue, our study has investigated the removal of bisphenol-A (BPA) using a submerged membrane bioreactor. Experiments were performed at initial BPA concentrations ranging from 1.0 to 15mg/L. A very low sludge mineralization occurred in the bioreactor (with a VSS/TSS ratio around 0.8–0.9), irrespective of the variation of biomass concentration and a long retention time of solids. The specific oxygen uptake rate values recorded did not reveal any significant change in the microbial respiratory activity in the absence (2.00mgO2/gVSSh) and in the presence (1.4mgO2/gVSSh) of BPA in the synthetic effluent. The performance of the bioreactor in terms of COD removal remained constant and reached 99% irrespective of the hydraulic retention time imposed (3–6h), whereas 66–99% of COD removal was recorded while using conventional activated sludge system. The limit of the toxicity (21.6g BPA/m3/d) determined for the bioreactor membrane system was higher than that recorded for the conventional activated sludge (2.5g BPA/m3/d). BPA was effectively removed in the membrane bioreactor (abatement ⩾98% was reached) due to adsorption and biodegradation/transformation processes. Residual BPA concentrations recorded in the mixed liquor remained low (0.017–0.004mg/L), when the raw wastewater contained a concentration of 1.0mg BPA/L. This indicates that BPA was not accumulated in the membrane bioreactor, but bacteria oxidized it. Likewise, the membrane bioreactor was found to be effective in removing ammonia–nitrogen (>99% of N–NH4 removed), whereas 61% of phosphate (P–PO4) could be simultaneously removed. The membrane bioreactor was a total barrier for total suspended solid and turbidity was effectively removed (residual turbidity was lower than 1.0 NTU).