Removal behaviors of antibiotics in a hybrid microfiltration-forward osmotic membrane bioreactor for real municipal wastewater treatment

A hybrid microfiltration forward osmosis membrane bioreactor (MF-FOMBR) was operated with raw municipal wastewater as feed. The fate and removal behaviors of 20 commonly used antibiotics were investigated. With the influent concentration of 4.1-716.9 ng/L (the most prevalent antibiotics were enrofloxacin, sulfamethazine and cefalexin, followed by amoxicillin, lomefloxacin and ampicillin), the system showed 58.9-100% overall removal of all the antibiotics. Almost all the antibiotics was rejected efficiently (86.1-100%) by the FO membrane, except for sulfonamides and trimethoprim (as low as 71.0%) due to their low molecular weights (M.W., 250.1-278.1 g/mol). However, relatively low biological removal (8.7-45.7%) was observed for most antibiotics, except for macrolides (70.6-90.1%) which was effectively removed via biosorption, and beta-Lactams (up to 64.6%) which is readily biodegradable, resulting in their significant accumulation (up to 3.4 folds, with the maximum concentration of 1831.5, 1056.7 and 626.3 ng/L for sulfamethazine, enrofloxacin, and cefalexin, respectively) in the mixed liquor. Different antibiotics showed distinct affinities for sorption to the activated sludge. The solid/liquid partitioning of the antibiotics is governed by their hydrophobicity. All the antibiotics was detected in the draw solution (DS) (with average concentrations of 3.8-100.4 ng/L, and enrofloxacin, amoxicillin and sulfamethazine being the most predominant ones) except macrolides in certain cases, highlighting the need to improve their overall removal via the development and application of denser membranes or integration of necessary physiochemical treatment. The side-stream MF unit acted as a major exit (>50.1% of total mass) for the poorly biodegradable and poorly adsorbed antibiotics to leave the system, preventing their further contamination of the DS. The enrichment of the antibiotics in the MF effluent would also facilitate their final elimination via subsequent advanced treatments.