Membrane bioreactors can combine various functions of membrane separations and biocatalyst characteristics of enzymes, microbial cells, organelles, animal and plant tissues. The cell is retained by the membrane whereas inhibitory by products are selectively removed. This paves the way for high cell density culture and thus helps in higher productivity of bioreactors. Other reactions like enzyme reactions utilizing cofactors, macromolecule hydrolysis, Anaerobic cell culture, are also effectively carried out in membrane bioreactors. The industrial application of this bioreactor is still in infancy.
Membrane bioreactors combine with both microfiltration and ultrafiltration for biological treatment of water from the following sources:
- Municipal
- Commercial
- Industrial wastewater treatment
- Water reuse applications.
Preliminary or primary Treatment. In some units fine screens are used before the MBR reactors in order to remove small suspended solid particles. This system is designed for preventing the membrane from fouling. The BOD like sugars, starches, carbohydrates, etc are consumed by the microbes in the aeration basin. This result in the conversion of BOD into additional microorganisms, or they attached to the biological floc.
Conventional activated sludge facilities uses secondary clarifier(s) after the aeration basin. This results in the settling of the microbes to the tanks's bottom. The effluent is provided in the clarifier through which the microbes flush out. In MBR process there is no secondary clarifier because the membranes produced effluents that are even more cleaner Than that which would be produced by a secondary clarifier. The effluents produced by the membrane filtration process produces an effluent which have low suspended solids concentration and turbidity units.
Main outcomes of R&D on MBR processes in the last decade
Although the MBR process is a recent technology, much public and private R&D has been undertaken worldwide in the past years, leading to very significant progress. These levels of investment on R&D, very high in comparison with the current market, reflect not only the relative youth of the technology, but also the great expectations and promises hold by the process in terms of applications and future commercial revenues. The salient outcomes of the international R&D undertakings are summarised below:
Treatment performance of MBR processes. This aspect has been extremely well investigated since the first lab studies up to recently the large full-scale MBR plants.
Advantages of Membrane Bioreactors
There are different advantages of membrane bioreactors:
- It requires less space for operation however for module-based design its capacity can be expanded if the situation demanded.
- It is a sustainable technology and is cost effective.
- It provides good alternative for municipal wastewater treatment.
- Quality of the effluent is good.
- As this bioreactors use membrane hence it does not require any settling tank.
- Using MBR, hydraulic retention time (HRT) and suspended solids retention time (SRT) can be separated thereby controlling the biological reactions.
- Water so treated contains no suspended solids and micro-organisms.
- Process operation is stable.
- Wastewater treatment having salt concentrations up to 120 g/l can be treated easily.
In 2005 the world market for MBR was estimated to be $216.6 million. The average annual growth rate of the market is 10.9% and is expected to touch $363 million in 2010. This system is growing faster than other membrane separation technology. The government regulations worldwide and the continuous use by municipalities are the key drivers of this industry.
