Behaviour of the main nonsteroidal anti-inflammatory drugs in a membrane bioreactor treating urban wastewater at high hydraulic- and sludge-retention time

[Display omitted] •Aerobic transformation of NSAIDs is predominant in MBR working with high SRT and HRT.•Anoxic transformation of NSAIDs in MBR working with high SRT and HRT is irrelevant.•Diclofenac accumulates in activated sludge of MBR working with high SRT and HRT.•MBR diclofenac accumulation working with high SRT and HRT results in negative removal. The behaviour and removal efficiency of ibuprofen (IBU), diclofenac (DCF), ketoprofen (KPF), and naproxen (NPX) during the real urban wastewater treatment by an experimental full-scale MBR working at high sludge and hydraulic retention time (SRT, HRT) were determined. The MBR worked in denitrification/nitrification conformation at 35.4h of HRT (Q=0.45m3/h), 37 d of SRT and a recirculation flow rate of 4Q. The experiments were made under steady-state conditions, reaching a biodegradable organic matter removal higher than 99.5%. The MBR system showed similar removal capacity for IBU, NPX, and KTP (>95%), whose main transformation occurred in the aerobic reactor with a low contribution from the anoxic reactor. The system worked with complete nitrification, also achieving an effective retention of the unbiodegradable organic matter due to recirculation. DCF removal was low with negative removal yields for several samplings. Both removal and increase transformation of DCF also occurred in the aerobic reactor, this not being observed in the anoxic one. DCF tends to accumulate in the system and to be recirculated. Thus, during the sampling in which DCF influent concentration decreases, removal yields turn negative. The increase of DCF concentration in the aerobic bioreactor also contributes to the negative removal yields.