9 Common Misconceptions About MBR Technology in 2023

As we all know, the wide application of MBR technology is mainly due to its outstanding advantages, such as high load, long sludge age, high-efficiency retention, and small land occupation. However, in practical application, many companies recommend and use MBR technology indiscriminately, which makes the MBR membrane clogging and even damage serious, reduces membrane life significantly, leaving a terrible impression on customers, and even questions the product.

Here, we summarize the common MBR process misconceptions and explain them individually to facilitate a better and more accurate understanding of the MBR wastewater treatment process.

High MBR membrane flux design will be better?

The membrane material and structure determine the flux of the membrane, and there is an upper limit to the porosity and flux of a given membrane treatment unit. Filtration is a physical process; membrane materials must sacrifice throughput while reducing pore size. At the same time, it also considers strength and ensures long-term operation, which results in constant flux.

Therefore, in the design and application process, it should be designed according to the recommended parameters of MBR membrane manufacturers. The EcoLan^TM range of membranes is of high quality and stable flux, configured with detailed product parameters and recommendations for best results.

The membrane fluxes are carefully selected because different water quality has other effects on the membrane filaments. Therefore, the design considers all possible influencing factors, and the values tend to be conservative. EcoLan^TM provides fluxes based on empirical values derived from a wide range of data, such as pure water experiments, pilot tests, and actual usage, always with a responsible attitude to the customer.

MBR technology must guarantee the effluent quality?

Many people think an MBR membrane system can significantly improve the effluent quality and even 100% ensure discharge standards. In fact, the MBR process is essentially a combination of the activated sludge process and membrane filtration, replacing the secondary sedimentation tank with membrane filtration based on the traditional activated sludge method, which has the advantages of a good retention effect and high sludge concentration. However, this does not mean the MBR process can cure all “diseases.”

For the removal of pollutants, membrane filtration has a pronounced effect on suspended solids. In contrast, organic matter removal still depends on the activated sludge and the biochemical properties of organic matter. Therefore, in the previous section, the MBR process effect is limited to poorly biochemical wastewater or sewage with adequate biochemical treatment.

No sludge discharge in MBR technology?

Due to membrane filtration’s excellent retention effect, the MBR technology’s activated sludge can reach a higher concentration and achieve the separation of hydraulic retention time and sludge age without considering the influence of sludge concentration on the effluent.

However, this advantage only enhances the space for biochemical properties, and not affecting the effluent is not a reason to support the non-discharge of sludge. The issue of discharging or not discharging sludge will still come to the activated sludge. If the sludge is not released, the activated sludge will become dead sludge, with reduced activity and aging, which will affect the biochemical performance and impact the aeration. In practice, the MBR process can reduce sludge discharge, but it is not without sludge discharge, and regular sludge discharge from the MBR membrane tank is necessary.

Minimize sludge concentration (MLSS) to avoid membrane fouling?

One of the biggest headaches in using MBR is the fouling of the membrane, and most of the reasons for this are from the sludge. Especially in water with excessive sludge concentration, the MBR membrane suffers. Therefore, there is a misconception of minimizing sludge concentration to avoid membrane fouling, which is precisely caught in another misunderstanding.

Too-low and too-high sludge concentrations can quickly clog the membrane, and the correct approach is to keep the concentration in an appropriate range. In addition, aeration has the effect of scouring the membrane surface and should also be maintained at the proper level. EcoLan’s MBR membrane products have detailed recommendations and reference values, and customers can operate accordingly.

MBR technology is only applicable to domestic sewage?

The MBR technology combines the activated sludge method and membrane filtration and is derived from the combination of the traditional activated sludge process and secondary sedimentation tanks. In this sense, the MBR process applies to scenarios where the activated sludge method is used, so MBR is not only used to treat domestic sewage.

However, pretreatment must meet the requirements for some sewage or difficult-to-degrade wastewater prone to membrane fouling, and it is unrealistic to expect a simple MBR to solve the problem. For example, one of our customers’ pharmaceutical wastewater treatment project adopts the combined treatment process of “grille + pretreatment + UASB + AO + MBR + ozone oxidation” so that the hard-to-degrade industrial wastewater can be treated well and meet the discharge standard. Therefore, users should design the overall process flow according to the characteristics of the wastewater to obtain the ideal treatment effect.

MBR membrane is responsible for effluent quality?

The principle of the membrane itself is filtration, a physical process, and the removal of pollutants is mainly suspended solids. Therefore, its significance for MBR is to improve biochemical performance. Still, it does not filter soluble organic matter, so it cannot be responsible for COD and other indicators. Therefore, removing organic matter still depends on the design and operation management of the entire process chain.

This point can also refer to the abovementioned explanation of whether the MBR technology can guarantee effluent quality.

MBR membrane fouling (scaling) is a quality problem?

MBR membrane fouling is a common problem for all users, and many people’s first reaction will be whether the quality of this batch of membranes needs to be qualified. In fact, this view is one-sided. Apart from the quality problem, many factors affect membrane fouling, such as uneven aeration, high sludge concentration, and large changes in feed water quality. Therefore, it is recommended that when customers encounter membrane fouling, they should assign professional technicians to visit the site, analyze the causes from multiple angles, identify the problems, and solve them.

We have written a separate article on How to Control and Clean MBR Membrane Fouling (Scaling) in 2023 with a more detailed explanation and maintenance solutions.

MBR technology will replace the traditional activated sludge process?

It is not possible unless there is a revolutionary breakthrough in technology. The MBR technology is mainly suitable for medium-sized wastewater treatment plants with a scale of about 1000 tons/day to 20000 tons/day, and the purpose is to require reuse or to reduce the footprint.

No single technology can completely overturn other technologies. Still, there is no denying that MBR does bring the best effluent quality in replacing secondary sedimentation tanks and provides a viable solution to the environmental problem of water pollution. Therefore, we only have to evaluate the balance of pros and cons.

Energy consumption of the MBR process is less than 1kWh/ton of water?

For large-scale wastewater treatment projects, after superb design and highly optimized operation can be achieved, for small wastewater treatment projects are not, and for wastewater plants that are not operating at total capacity, it is impossible to achieve.

MBR technology cannot be viewed one-sidedly, regardless of any process; as long as it does not run at full load, it will cause the problem of high operating energy consumption. But if the modular design, according to the different water volumes for effective modular operation, will not reduce operating costs? Therefore, from a technical point of view, MBR technology is more suitable for a modular design.

Conclusion

There are far more problems like this in engineering applications, and MBR technology is so widely used that practitioners need to learn relevant knowledge and skills.

In fact, the beauty of MBR lies in replacing the traditional process of secondary sedimentation tanks with highly efficient retention membrane filtration, which in turn achieves better sludge concentration and enhances biochemical treatment.

MBR operation and maintenance is to keep the membrane in good condition on the one hand and to regulate the activated sludge well on the other hand. Not understanding biochemistry and letting the membrane do everything is the root cause of many MBR project problems.