BACKGROUND A membrane bioreactor and two hybrid moving bed biofilm reactor-membrane bioreactor systems were operated in parallel for the treatment of variable-salinity wastewater. Influent salinity was changed according to tidal-like cycles: 6 h of maximum salinity (4.5 or 8.5 mS cm(-1)) followed by 6 h of regular wastewater salinity (around 1 mS cm(-1)). RESULTS For the two salinity scenarios, the bioprocesses operated under different conditions of mixed liquor total suspended solids (2500 and 3500 mg L-1), and hydraulic retention time (6, 9.5 and 12 h). The results showed that the bioprocesses had better performance under 4.5 mS cm(-1) than under 8.5 mS cm(-1) in terms of removal of biological oxygen demand at day 5 (BOD5) (+6.07%), ammonium cation (NH4+) (+41.29%) and total nitrogen (+37.64%), the heterotrophic and autotrophic yield coefficients (+0.02777 mgVSS mgCOD(-1) and +0.13990 mgVSS mgN(-1)), and the autotrophic rate of substrate utilization (+3.39559 mgN L-1 h(-1)). CONCLUSIONS The results obtained would become of help for the modeling of membrane-based systems treating variable saline wastewater. (c) 2019 Society of Chemical Industry