MINI-REVIEW Membrane bioreactors and their uses in wastewater treatments Pierre Le-Clech Received: 1 August 2010 / Revised: 31 August 2010 / Accepted: 2 September 2010 / Published online: 24 September 2010 # Springer-Verlag 2010 Abstract With the current need for more efficient and reliable processes for municipal and industrial wastewaters treatment, membrane bioreactor (MBR) technology has received considerable attention. After just a couple of decades of existence, MBR can now be considered as an established wastewater treatment system, competing direct- ly with conventional processes like activated sludge treatment plant. However, MBR processes still suffer from major drawbacks, including high operational costs due to the use of anti-fouling strategies applied to the system to maintain sustainable filtration conditions. Moreover, this specific use of membranes has not reached full maturity yet, as MBR suppliers and users still lack experience regarding the long-term performances of the system. Still, major improvements of the MBR design and operation have been witnessed over the recent years, making MBR an option of choice for wastewater treatment and reuse. This mini- review reports recent developments and current research trends in the field. Keywords Membrane bioreactor . Wastewater . Recycling . Fouling . Aerobic . Anaerobic Introduction The membrane bioreactor (MBR) process is generally described as the combination of biodegradation treatment by activated sludge with liquid/solid separation by porous membranes. The presence of the micro- or ultra-filtration membrane (i.e., physical barrier rejecting particles larger than its pore size, ranging from 0.05 to 0.4 μm) leads to significant improvements and advantages when MBR is compared to conventional activated sludge processes (CASP; Fig. 1): & As the secondary clarifiers are replaced by the more compact membrane modules, the footprint for the overall treatment system is largely reduced. & The use of membrane filtration as separation process also improves the quality of the produced effluent. MBR allows the complete physical retention of bacte- rial flocs and most of the suspended solids, and therefore can offer good disinfection capacity. As a result, the total coliforms reduction can reach an average of log 7 (Hirani et al. 2010). & The total retention of activated sludge in the bioreactor also allows operation under high mixed liquor- suspended solids (MLSS) concentrations and elevated solid retention time (SRT). Higher volumetric loading could therefore be applied to MBR systems. Long SRT allows the development of slow-growing microorgan- isms responsible for the degradation of specific organic pollutants (especially nitrogen-based compounds). The high MLSS concentration also allows the reduction of the size of the bioreactor. & Operation at elevated SRT can also lead to low-sludge yield, resulting in sludge minimization. In addition to these advantages, many other drivers have boosted the recent development of MBR technology. They include the limited available footprint for the construction of new treatment systems, the more stringent regulations imposed for environmental discharge experienced world- wide, the reduction in membrane cost, the continuous P. Le-Clech (*) UNESCO Centre for Membrane Science and Technology, School of Chemical Engineering, The University of New South Wales, Sydney, Australia e-mail: p.le-clech@unsw.edu.au Appl Microbiol Biotechnol (2010) 88:1253–1260 DOI 10.1007/s00253-010-2885-8