Although systematic reuse of treated water has not been commonly adopted by the municipalities and industries in the recent years, there is still a significant interest from the government and industrial sector to explore its potential to avoid any future water scarcity problems. Recycling and reuse of water should become the rule wherever the resource is limited, with drinking water taking the priority followed by industry and finally irrigation where the water is used.
Membrane Bioreactors (MBR) combine conventional biological treatment processes with membrane separation. In a conventional activated sludge plant, biodegradation occurs in a bioreactor, followed by a secondary settling tank to separate water from the solids. However, due to economic and physical constraints, the effectiveness of such options is often limited and an alternative method for better solid/liquid separation becomes attractive.
Since suspended solid are totally eliminated through membrane separation, the settleability of the sludge, which is a problem in conventional activated sludge, has absolutely no effect on the quality of the treated effluent. Sludge retention time (SRT) is independent of hydraulic retention time (HRT). Therefore a very long SRT can be maintained resulting in complete retention of slowly growing microorganisms, such as nitrifying bacteria, in the system. The overall activity level can be raised since it is possible to maintain high concentrations in bioreactors while keeping the microorganisms dispersed as long as desired and as a result, reactor volume will be reduced. In addition, the system requires neither sedimentation nor any post-treatment equipment to achieve reusable quality water, so the space saving is enormous.
While centralized wastewater treatment systems are an economically attractive solution for a large scale wastewater treatment plant, membrane based systems, become an attractive for small to medium size decentralized wastewater treatment units. Thus, currently MBR systems are considered the most attractive alternative decentralized wastewater treatment and reuse system.
The review of the membrane bioreactors for the application of wastewater treatment has proven that this emerging technology has developed a niche in the wastewater treatment sector. While, research efforts of late have been directed towards application of membrane separation bioreactors to various wastewaters, the challenge continues for the researchers in its development of a membrane bioreactor process that is both robust and efficient for various wastewater applications and to realize the goal of decentralized wastewater management.