The study of organic removal efficiency and halophilic bacterial mixed liquor characteristics in a membrane bioreactor treating hypersaline produced water at varying organic loading rates

•>95% O&G removal from synthetic PW in MBR with halophilic consortium at high OLR.•O&G and SMP transient accumulation occurred but did not affect removal performance.•Bioflocculation and compressibility of flocs affected by EPS and surface charge.•At high OLR non-Newtonain rheology and EPS bulking in the mixed liquor was observed.•Membrane fouling mainly due to cake formation at highest OLR of 2.6kgCODm−3d−1. In this study the organic pollutant removal performance and the mixed liquor characteristics of a membrane bioreactor (MBR), employing a halophilic bacterial consortium, for the treatment of hypersaline synthetic produced water – at varying organic loading rates (OLR) from 0.3 to 2.6kgCODm−3d−1 – were considered. The oil and grease (O&G) and COD removal efficiency were 95–99% and 83–93%, respectively with only transient O&G (mainly polycyclic aromatic hydrocarbons) and soluble microbial products accumulation being observed. With increasing OLR, in the range 0.9–2.6kgCODm−3d−1, as a result of change in both extracellular polymeric substances (EPS) and zeta potential, bioflocculating ability improved but the compressibility of the flocs decreased resulting in the occurrence of EPS bulking at the highest OLR studied. The latter resulted in a change in the rheology of the mixed liquor from Newtonian to non-Newtonian and the occurrence of significant membrane fouling.