3. General features of MBR systems

Membranes have been used for many years as biological treatment (aerobic and anaerobic) and solid–liquid separation methods in physical applications. Nowadays, these methods are increasingly attracted to the name of membrane bioreactors combined with biological wastewater treatment [28]. Membrane bioreactor technology is emerging as a mature technology around the world with many full-scale installations for municipal and different wastewater treatments [29–31]. The reactor is operated in a similar manner to a conventional activated sludge process, and there is no need for tertiary stages such as secondary purification and sand filtration. Low-pressure membrane filters such as microfiltration (MF) or ultrafiltration (UF) are used to separate wastewater from the activated sludge [32].

Several factors have been reported that may affect contamination in MBR membrane properties such as floc size, mixed liquid viscosity, mixed liquid viscosity, pH, solubility, associated polymeric compounds (EPS), pore size, porosity, surface charge, roughness, and hydrophilicity/hydrophobicity. Operating parameters such as hydraulic retention time (HRT), solid retention time (SRT), and food/mass (F/M) ratio do not have a direct effect on membrane contamination [33, 34]. They affect more sludge properties and therefore sludge filtration properties. Organic contamination is caused by contamination of the membrane during active sludge filtration compared to inorganic pollution [35].
