(710c) Fate and Removal Behaviour of Antibiotics in an Osmotic Membrane Bioreactor for Municipal Wastewater Treatment

Authors: 
Qiu, G., National University of Singapore
Ting, Y. P., National University of Singapore

Recently, there has been growing interest in the development of the osmotic membrane bioreactor (OMBR) process due to its low membrane fouling propensity, reduced energy demand and high rejection capability of various contaminants by the membrane. In this work, an OMBR was developed and operated with raw municipal wastewater as feed and seawater brine as draw solution (DS). The fate and removal behaviour of 21 types of antibiotics present in the municipal wastewater, including four β-Lactams, five fluoroquinolones, four macrolides, four tetracyclines, three sulphonamides and trimethoprim, were investigated in the OMBR system. With an influent concentration of 2.3-875.0 ng/L (the most prevalent antibiotics being enrofloxacin, sulfamethazine and cefalexin, followed by amoxicillin, lomefloxacin and ampicillin), the system showed 47%-99% overall removal of all the antibiotics. Almost all the antibiotics were efficiently rejected (87.3-99.7%) by the FO membrane, except sulphonamides (44.8-57.6%) due to their low molecular weights (250.1-278.1 g/mol). Relatively low biodegradation (10.7%-69.0%) was observed for all the antibiotics except macrolides (78.6-84.2%), which resulted in their accumulation (by 1.9-7.1 fold, with a maximum concentration of 2653.6, 2347.4 and 1081.1 ng/L for enrofloxacin, sulfamethazine and cefalexin, respectively) in the mixed liquor. Different antibiotics showed distinct sorption affinity to the activated sludge. The dominant antibiotics found in the activated sludge were ofloxacin (533.9 μg/gMLSS), amoxicillin (514.1 μg/gMLSS) and ciprofloxacin (476.7 μg/gMLSS) due to their high sorption constants (Kd). Ampicillin, lomefloxacin, enrofloxacin and oxytetracycline showed the poorest sorption to the activated sludge. All the antibiotics were detected in the DS (with an average concentration of 0.8-205.1 ng/L) except macrolides (with enrofloxacin, amoxicillin and sulfamethazine being the most predominant), which highlights the need for the enhancement of their biodegradation in the bioreactor. Accumulation of antibiotics in the bioreactor did not significantly affect pollutant removal efficiencies. High and constant removal of TOC (95%) and NH4+-N (99%) were achieved during the 98-day operation, with the DS TOC and NH4+–N concentrations being less than 5.0 mg/L and 0.1 mg/L, respectively.