1. What is MBR (Membrane Bioreactor)?
The MBR (Membrane Bioreactor) which was first used in the late 1960s made a revolution in the wastewater industry in the early 1990s by combining membrane filtration with a biological treatment solution to treat wastewater. It's been commonly used since then and can be seen widely practiced in the design of both new and old wastewater treatment facilities. MBRs are cutting-edge biological wastewater treatment technologies that combine membrane filtration with traditional suspended-growth activated sludge to separate and recycle suspended solids by filtration rather than sedimentation.
2. MBR vs. Conventional biological treatment method?
Traditional biological treatment methods include an aerobic process consisting of an aeration tank, a settling tank, and a sludge transfer facility. It is a method that relies exclusively on microorganisms. The aerobic bacteria oxidize/decompose BOD components in an aeration tank, and then active bacteria (sludge) differ in specific gravity in the settling tank. It is basically the method of sedimentation and separation. Whereas, in the MBR method, clean treated water can be directly discharged by immersing the separation membrane in the aeration tank without installing a sedimentation tank. The Filtered water is sucked through a fine filtration membrane and later transferred into an effluent tank. So, unlike the conventional biological method, the MBR approach treats water using a combination of membrane filtration and biological processes without the need for a sedimentation tank.
3. Advantages of MBRs over conventional biological treatment methods?
The conventional biological processes that rely solely on microbes appear to be simple and straightforward, but when operated in the field have several drawbacks in terms of operation, maintenance, footprint, effluent water quality, and construction costs. One of the most tenacious problems faced in the conventional wastewater treatment plant is sludge bulking. Sludge bulking can be caused by many different phenomena, but it is mostly said to be caused by the growth of filamentous bacteria that grows into long strands occupying greater volume and surface area. These bacteria naturally settle much more slowly than traditional flocs, affecting the quality of the treated water while making the process longer and costlier than the conventional biological treatment process.
MBR on the other hand complements the shortcomings of the existing biological method that relies only on these microorganisms, The advantage of the MBR method is that it combines the advantages of the biological treatment process and the membrane filtration process. With MBR the treated water quality is always stable as there is no effect of the sludge bulking phenomenon, which is the most problematic in the biological treatment process. Because the water is treated separately through decomposition and separation of the filter membrane, it doesn't depend on the sedimentation alone unlike the conventional biological method. Moreover, with MBR it is possible to maintain a high MLSS concentration as high as 3,000-10,000 mg/ℓ in the aeration tank, which is of course depending on the concentration of incoming organic matter. The advantage of maintaining a high concentration of microorganisms in the aeration tank is that it increases the stability against microbial shock, thus maintaining high stability of the treated water quality in large-capacity treatment. Furthermore, the need for larger reactor volumes for effective water treatment is eliminated and the cost of construction is also heavily reduced. So, the required site is small and the facility is compact compared to the existing conventional method. Also, the cost of sludge treatment is reduced and the treatment time for raw water is shorter.
<Summary of features and advantages of the MBR method>
Solves the problem of sludge bulking in the biological well process.
Perfect solid-liquid separation and high concentration MLSS can be maintained.
Separation and removal of contaminants through the separation membrane and decomposition and removal of organic waste through microorganisms are possible at the same time.
It is strong against impact load, and there is no change in treated water even under impact load.
Stable water quality can be produced even when the amount of incoming raw water fluctuates.
The treatment time for raw water is short and stable water quality can be secured even in large-capacity treatment.
Maintenance is easy, and maintenance costs such as chemical injection are low.
It has a comparatively smaller footprint than the conventional biological treatment process.
Due to the small construction site area, it is possible to save construction costs.
It is easier to retrofit in any existing biological treatment plant.