5 Misunderstandings About MBR

Nowadays, the MBR(membrane bio-reactor) is widely used in the water treatment industry, such as the water reuse, the dispersion treatment and the sewage emission updated. Compare with the traditional water treatment method. The advantages of MBR are obviously – supports a higher load, longer SRT, higher-efficiency interception & so on…

However, there are some misunderstandings in the MBR application.

Misunderstanding 1 - Bigger flux is better.

Not true. The flux of the membrane is determined by the membrane material and structure. There is a maximum limit to the porosity rate and flux of a unit. Filtration is essentially a physical process. The membrane material must sacrifice the flux while reducing the pore size, at the same time, need to balance the strength and ensuring long-term operation. So, those reason leads to constant flux. Therefore, in the design and application process, the design should be based on the recommended parameters from the manufacturer.

Misunderstanding 2 - If we use the MBR, the water quality will be 100% guaranteed.

Essentially, the MBR process is a combination of activated sludge process and membrane filtration, replacing the secondary settling tank with membrane filtration on the basis of the traditional activated sludge process.

The MBR process brings advantages, such as high sludge concentration. But this doesn’t mean that the MBR process can deal with all problems. For the removal of pollutants, membrane filtration has a very obvious effect on SS. But the removal of organic matter still depends on the biodegradability of activated sludge and organic matter. For the biodegradable sewage or the previous treatment, which not so good or not meet the standard, MBR has a limited effect.

Misunderstanding 3 - The MBR process doesn’t need to dispose of the sludge.

Due to the excellent retention effect of MBR, the activated sludge in the MBR process can reach a higher concentration, achieving the separation of HRT and SRT, without considering the influence of sludge concentration on the effluent. However, this advantage only enhances the space for biochemistry. It does not affect the product-water. But it couldn’t support it. The problem of that should be returned to the activated sludge. If the sludge is not disposal, the activated sludge will have many problems, which will affect the biochemical performance and affect the aeration. The MBR process in the project can indeed reduce sludge discharge, but it not means non-discharge.

Misunderstanding 4 - Decrease the concentration of the sludge to prevent the membrane get polluted.

Not true. Plugging is a common problem in MBR applications, especially when the sludge concentration is too high. So, there is a misunderstanding that reduces the sludge concentration to avoid be polluted. In fact, the low concentrations and high concentrations of sludge can all cause the membrane polluted quickly. The correct way is to keep the concentration within a suitable range. In addition, the effect of aeration on the surface of the scouring membrane should also be maintained at the corresponding holding amount.

Misunderstanding 5 - The membrane determines the quality of product water.

The principle of the membrane is filtration. It is a physical process. SS is the main pollutant in removing. Its significance for MBR is to improve biochemical performance, but it couldn’t filter soluble organic matter. So it isn’t responsible for COD and other indicators. The removal of organic matter still depends on the design and operation management of the entire process chain.