What Are the Main Design Points of the MBR Membrane Bioreactor

MBR membrane bioreactor is a standard water treatment equipment used in various industries and has contributed significantly to wastewater treatment. MBR membrane bioreactor is a collection device that combines biochemical and membrane separation technologies, and today we will explain its design points in detail.

How to determine if raw water can be treated by MBR technology?

MBR technology is not a panacea. MBR membranes are microfiltration membranes, which are defined by the particle size that can pass through the membrane pores, so the clogging problem is the key for it, and some raw water that is prone to scaling, contains more oil materials and viscous materials is recommended not to use MBR membrane method.

Generally speaking, the wastewaters unsuitable for MBR technology are emulsion, grinding fluid, quenching fluid and cooling fluid wastewaters, surfactant wastewaters, petroleum wastewaters, lipid wastewaters, and so on. But, of course, if these wastewaters have been pre-treated, it is possible to use the MBR membrane process.

How to determine the brand and quantity of MBR membrane?

It is determined that the MBR membrane process will be used to treat the wastewater, and the next step is to decide which brand of MBR membrane to use. Before 2010, international manufacturers dominated the market; after 2010, the rise of local Chinese brands has led to a significant increase in market share, a gradual substitution effect, and higher cost performance.

MBR engineering designers should do an excellent job of in-depth technical communication with suppliers, especially regarding design flux. The design flux has generally been reserved for a margin by membrane manufacturers. However, in practice, designers must manage it carefully according to site conditions and not rule out increasing the margin again.

It is important to note that the quality of MBR membranes on the market varies. Therefore, whether you use international or Chinese brands of MBR membranes, you need to choose a reliable membrane manufacturer and strictly control the quality and technology of the product to take full advantage of the MBR process.

What are the design points of MBR membrane modules?

Generally speaking, the design points of membrane modules are mainly considered from the following perspectives.

The membrane sheet is assembled to form a membrane module, paying particular attention to the distance between the membrane sheet and the membrane sheet should be sufficient, and the valuable space should be greater than 100mm ( the axial distance is greater than 140mm ). If the filament density of the membrane itself is large, then the effective space should be appropriately relaxed. The purpose of doing so is to keep the flushing air flow smoothly to the top of the membrane. It can also reduce the hardening and retention between the membrane and decrease the cleaning frequency of the membrane module. If the flat membrane is used, the distance is only 60 ~ 80 mm, which can save more space.
We can install the membrane horizontally or vertically, depending on the installation space. When installed horizontally, the membrane filaments are kept slightly sagging, and the sagging range is maintained at 10mm. However, ensuring that the membrane filaments are not pulled should be as straight as possible so that not much debris is left between the membrane filaments and the filaments. Therefore, it is recommended to use the vertical installation method.
We cannot make the membrane module very large because too large a membrane module, its installation density will be large, and the same amount of mixing air for it is not enough. When accumulating many wrappings on the membrane, we need to spray wash the membrane. Installation is too dense for a high-pressure water gun, or tap water is difficult to flush to the inner membrane. It is recommended that a single membrane module processing capacity should be at most 1.5m³/h.

What are the design points of MBR aeration?

The design points of MBR aeration are generally considered from the following points.

We can fix the aeration device to the bottom of the tank (make a membrane module support frame and sliding rail) or do it together with the membrane module. Each has its advantages and disadvantages. We should carefully consider the location of the aeration pipe. Using DN20 perforated pipe, each membrane sheet gap corresponds to a perforated pipe, perforation size Φ2.0mm, perforation spacing 100mm, two adjacent pipe perforation location staggered interpolation, and the orifice do single row vertical up, and the settled sludge will not block the orifice.
The amount of aeration can be roughly estimated, according to practical experience, according to the steam-to-water ratio of 24:1 (based on the manual, the conventional pool depth of 3.5m), and the blower exhaust head selection is 0.01 MPa higher than the highest liquid level. Blower outlet set relief valve, the complete opening of the relief pipe can remove 70% of the air volume. The relief port is equipped with a silencer, which controls the DO level in the biochemical tank and protects the blower.
Each membrane module aeration is equipped with a separate control valve. In contrast, the oxygenation aeration of the entire biochemical tank should be separately controlled by a separate control valve, with a microporous oxygenated aeration system to ensure we can flexibly adjust the mixing air and oxygenated air.
The best DO value of the MBR tank is between 2.5~5, and the expected level is about 3ppm. While the level varies, the DO value will also change but should not exceed 5.0ppm for a long time.

What are the design points of the MBR suction pump?

The design points of the MBR suction pump are as follows.

Try to have one MBR suction pump for each membrane module, and install transparent flow meters on the suction pipe of each membrane module so that it is easy to observe and determine each membrane module’s status (pressure and flux). One MBR suction pump for multiple membrane modules is also possible.
We should install the MBR suction pump below the liquid level as much as possible; the lower, the better. In the normal state of the membrane module, the water can be discharged by siphoning. If the MBR tank is underground, make an underground machine room to ensure the suction pump has enough suction range.
We must install the MBR suction pump below the MBR liquid level, and the primary consideration is the influence of the transmembrane pressure difference. Although each brand’s regulations are slightly different, they generally should not be higher than 0.03Mpa = 3m, where the transmembrane pressure difference is not necessarily equal to the vacuum meter reading but also depends on the height difference between the inlet height of the pump and the liquid level of the biochemical tank, if the vacuum meter reading is 0.03Mpa = 3m, the liquid level of the biochemical tank is 1m higher than the pump inlet. The transmembrane pressure difference at this time is 0.04Mpa = 4m.
Suppose the pump installation position is 1m higher than the biochemical tank liquid level, the MBR suction pump is suction-mounted, and the suction height is 1m. Currently, the transmembrane pressure difference is only 0.02Mpa = 2m. The calculation formula is transmembrane pressure difference = vacuum table reading (take positive) + (biochemical tank liquid level height – suction pump inlet height).
It is recommended that the MBR suction pump outlet pipeline is equipped with a transparent flowmeter and a sampling valve. The water quality status can be visually seen through the transparent flowmeter. In addition, a regulating valve is added in front or behind each flowmeter to adjust the water output of the membrane module.
Electric control. Generally, the MBR suction pump (self-priming pump) is set up to start for 13 min and stop for 2 min. That is, a running cycle of the pump T = 13 + 2 = 15 min—the specific start-stop time to consult the manufacturer’s advice. The pump can be stopped and alarmed if the electric contact pressure gauge pressure exceeds the limit. And the suction pump should be able to be linked to the blower. When the blower stops, the suction pump does not work.

What are the control points of the MBR biochemical process?

MBR technology in the biochemical process, there will be some control points, as follows.

When the influent water temperature is lower than 8℃, the activated sludge activity will be affected to some extent, so we should reduce the effluent volume appropriately to ensure that the organic matter in the wastewater is fully degraded in the reaction tank to ensure the effluent quality and slow down the membrane clogging.
In winter or other cases, when the temperature changes suddenly, pay special attention to observing the effluent water quality, such as the effluent water quality changes obviously, we should appropriately reduce the effluent volume and increase the aeration time.
In regular operation, disinfectants that inhibit the metabolism of microorganisms should be strongly avoided from being mixed into the biological reaction tank to prevent the standard biological mechanism of microorganisms in the equipment from being destroyed, resulting in the deterioration of the effluent.
When the sewage contains a large amount of synthetic detergent or other foaming substances, the MBR membrane reaction tank will have a large amount of foam, which can be solved by spraying water, but do not add defoamer containing oily substances to the reaction tank to remove the bubbles and do not use silica gel series defoamer, which will be adsorbed to the membrane surface and accelerate the pressure difference between the membranes and make the membranes clogged. At this time, it is difficult to restore the differential pressure even with the chemical cleaning solution, and the MBR membrane needs to be replaced.
MBR process system should discharge a certain amount of residual sludge regularly. The amount of discharged sludge can be determined according to the sludge settling ratio, sludge concentration of mixed liquid, organic load of activated sludge, or sludge age.

The above is the design points and precautions of the common MBR membrane bioreactor. In the application process, if you have other new problems or are challenging to understand, you are welcome to discuss them with us.