Elimination and fate of selected micro-organic pollutants in a full-scale anaerobic/anoxic/aerobic process combined with membrane bioreactor for municipal wastewater reclamation

Abstract

The occurrence and elimination of 19 micro-organic pollutants including endocrine disrupting chemicals (EDCs) and pharmaceuticals and personal care products (PPCPs) in a full-scale anaerobic/anoxic/aerobic-membrane bioreactor process was investigated. The investigated process achieved over 70% removal of the target EDCs and 50%-100% removal of most of the PPCPs, with influent concentration ranging from ng/L to μg/L. Three PPCPs, carbamazepine, diclofenac and sulpiride were not well removed, with the removal efficiency below 20%. A rough mass balance suggests that the targets were eliminated through sludge-adsorption and/or biodegradation, the former of which was particularly significant for the removal of hydrophobic compounds. The two-phase fate model was employed to describe the kinetics of sludge-adsorption and biodegradation. It was found that the fast sludge adsorption (indicated by mass-transfer rates greater than 10 for most compounds) is responsible for the rapid decline of the aqueous concentration of the targets in the first compartment of the treatment process (i.e. in the anaerobic tank). In contrast, the slow biodegradation proved to be the rate-determining step for the entire degradation process, and the rates are generally positively related to the dissolved oxygen level. On the other hand, this study showed that the removal rates of most targets can reach a quasi-plateau in 5 h under aerobic conditions, indicating that hydraulic retention time of ca. 5 h in aerobic tanks should be sufficient for the elimination of most targets.