Date: July 27, 2014
MBR technoloty belongs to the group of so called “Green Technologies”. MBR (Membrance Bio Reactor) is
a technology belonging to the group of separation processes combined with a separation of the biological sludge by micro-or ultra filtration membrances with pore size of typically 10 mn to 0.5um to produce the particle free effluent. The latter step replaces the final clarifiers used in conventional activated sludge treatment which achieve solid separation by gravity only. The physical barrier imposed by the membrane system provides complete disinfection of the treated effluent. MBR technology effectively overcomes the problems associated with poor setting of sludge in conventional activated sludge processes. It also enables operation at higher sludge concentrations and therefore permits to reduce the required footprint and/ or sludge production. The need to recycle wastewater and stricter environmental regulations make a membrane bioreactor (MBR) system a viable solution for current and future wastewater treatment.
MBR technology offers several advantages over conventional activated sludge process.
Advantages of MBR technology
- Compactness and small layout size of the plant.
- Small quantity of excess sludge and therewith connected costs
- Constant effluent quality, regardless of the influent
- Operation Costs are lower than in classical biological plant
- Complete bacteria removal, no risk of biomass loss, no odors emission or noise
- Possibility of reuse of treated waste water for irrigation purposes or as process water.
- Fast construction, because of relatively small size of the plant
- Reduced quantity of chemicals needed for phosphorus reduction.
- Flexibility on maximal and minimal inflows, within the given parameters.
- Simple management of the plant, as a result of high degree of automation(loe dependence human factor).
- MBR plants enable Total Waste Water Management.
After initial development started in the late 60’s, the MBR technology for wastewater treatment experienced rapid development from the early 1990’s onwards. The first systems commericialized in the 70’s and 80’s were based on what have come to be known as sidestream configurations, i.e. the memberane4 seperation step was employed in an external sludge recirculation loop, mainly with in –to-out flow through organic or ceramic tubular membranes. Due to the high energy demand, these technologies targeted only small and niche market applications such as treatment of ship-board sewage, landfill leachate or industrial effluents.
In the early 90’s, the Japanese Government Launched an ambitious 6- year R&D project which led to a major technological and industrial breakthrough of the MBR process: the conception of submerged membrane modules, working with low negative pressure (out-to-in-permeate suction) and membrane aeration to reduce fouling. This paved the way towards a significant reduction of capital and operations costs, due to reduction and simplification of equipment and the abandonment of the energy demanding sludge recirculation loop.
Membranes are usually made from different plastic and ceramic materials, but metallic membranes also exit. The most widely used materials are celluloses, polyamides, polysulphone, charged polysulphone and other polymeric materials such as polyacrylonitrile(PAN),polyvinylidene difluoride (PVDF),polyethylsulphone (PES),polyethylene (PE), and polypropylene (PP). All of these polymeric materials have a desirable chemical and physical resistance. They are also hydrophobic, and it is known that hydrophobic membranes are more prone to fouling are of hydrophobic nature. All commercially available membranes are therefore modified by chemical oxidation , organic chemical reaction, plasma treatment, or by grafting to achieve more hydrophilic surface. This modification process usually differs one membrane from another together with the method of fabrication of the membrane module .
Technologies of submerged membrane modules are predominant on the MBR market . both the features out-to-in permeate filtration and comprise the flat-sheet (or plate &frame) membrane module and the hollow fibre membrane module.
MBR technology has played a pivotal role in establishing submerged MBR technology as a preffered wastewater treatment solution for many applications, in both municipal and industrial markets, throughout the world. In submerged MBR system micro or ultra-filtration membranes are immersed in an aeration tank, in direct contact with mixed liquor. Through the use of a permeate pump , a vaccum is applied to a header connected to the membranes. The vaccum draws the treated water through the hollow fiber/flat sheet filtration membranes.Permeate is then directed to disinfection or discharge facilities. Intermittent airflow is introduced to the bottom of the membrane module,producing turbulence that scours the external surface of the hollow fibres. This scouring action transfers rejected solids away from the membrane surface. The cleaning of the separation system (ultra filtration membrane) is performed by backwashing in short time period without interrupting the treatment process.
Although MBR capital and operational costs exceed the costs of conventional process, it seems that the upgrade of conventional process ocurrs even in cases when conventional treatment works well.it can be related with increase of water price and need for water reuse as well as with more stringent regulations on the effluent quality. along with better understanding of emerging contaminants in wastewater, their biodegradability, and with their inclusion in new regulations,MBR may become a necessary upgrade of existing technology in order to fulfill the legal requirements in wastewater treatment plants (WWTPs). Membrane bioreactor systems may be used in such applications as water reuse, new housing developments, parks and resorts ,retrofits, and turnkey projects. Novel and alternative MBR filtration systems have recently appeared in the market and we can expect that the most innovative products will raise commercial interest in the coming years.
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