Elimination Of Micro-organic Pollutants In An Anaerobic/anoxic/aerobic-membrane Bioreactor

Research on elimination and fate of micro-organic pollutants in wastewater reclamation process is essential to ensure the safety of water reuse and optimize the removal of these emerging chemicals in existing wastewater treatment process. This study focused on the removal and behavior of 8 typical endocrine disrupting chemicals (EDCs) and 11 typical pharmaceuticals and personal care products (PPCPs) in an anaerobic/anoxic/aerobic-membrane bioreactor (A~2/O-MBR) process, which is considered as a representative of wastewater reclamation technology. Additionally, batch experiments were carried out to get an insight into the contribution of biodegradation, adsorption by activated sludge, and the indirect retention by membrane in MBR to the removal of micro-organic pollutants.A long period of detection on the concentration of target compounds in both sludge phase and aqueous phase in every units of a full-scale A~2/O-MBR showed that most of the targets were eliminated at ratios above 50%, with biodegradation and/or adsorption on activated sludge as the primary removal means. In which, hydrophobic ones such as bisphenol A (BPA), 17α-ethinylestradiol (EE2), galaxolide (HHCB) and tonalide (AHTN) could be removed at 50% by activated sludge adsorption. However, the concentration of several compounds such as carbamazepine, diclofenac and sulpiride could not be decreased sufficiently during the process, and most of their residues were discharged with the effluent. A series of batch tests were carried out as supplementary to prove that the rapid adsorption on sludge of targets was the main reason why anaerobic tank plays an essential role in the removal of most targets in the A~2/O-MBR process.As the removal contribution of target compounds by membrane was observed in the A~2/O-MBR plant, the indirect rejection of targets by membrane in MBR was further investigated in this study, focusing on the adsorption of membrane and gel layer, as well as the adsorption of soluble and colloid organic molecules in the supernatant of MBR. The results presented that the adsorption by membrane was relatively weak for the removal of most targets except for the hydrophobic ones like 4-NP. The formation of gel layer could enhance the adsorption of targets to a certain degree, and the adsorption capacity closely related to the hydrophobicity and structure of the gel layer. On the other hand, model adsorbents such as alginic acid Na, humic acid and bovine serum albumin were employed to simulate the soluble and colloid organic molecules. As the equilibrium showed that the adsorption of target compounds on model adsorbents was consistent with linear adsorption characteristics, and the competitive adsorption among different targets was little enough to be ignored. Furthermore, the adsorption of targets on soluble and colloid organics was considered to be affected by the hydrophobicity and structures of target molecules, as well as the hydrophobicity and size distribution of adsorbents.