MBR Membrane Guideline: 2023 Key Research on MBR Operation and Maintenance

MBR membrane treatment system can efficiently carry out solid-liquid separation, the effect is far better than the traditional sedimentation tank, the effluent suspended solids and turbidity is close to zero and can retain bacteria and E. coli in the water, can directly enter the water reuse system, realize the effluent discharge resource, improve the comprehensive utilization rate of wastewater. MBR membrane technology brings high safety, environmental, and economic benefits to enterprises and has a wide range of application prospects.

In previous articles, we have also done a lot of discussion on MBR membrane technology. However, with the improvement of the water quality index, while using MBR membranes for water treatment, some operation and management problems have emerged, which have become the main factors limiting the stable operation of wastewater treatment systems. As a result, questions and discussions have arisen about using the MBR process for wastewater treatment today.

What is the whole process flow of MBR technology?

There are many process routes for MBR technology to treat sewage and wastewater. In most cases, MBR is combined with other processes, and the primary process route is as follows:

Grille

The coarse and fine screens remove the larger suspended solids in the wastewater.

Pretreatment

It mainly refers to oil separation, air flotation, and other equipment and facilities to control the oil concentration entering the MBR within a reasonable range.

Regulating tank

The water quality is homogenized and uniformly adjusted. The water quality is homogenized and uniformly adjusted. The submersible pump is installed in the pool. The water level control system controls the operation of the pump, which is convenient for the subsequent unit processing.

MBR reactor

It mainly includes an anaerobic zone, an anoxic zone, an aerobic zone, and a membrane module. Anaerobic and anoxic zones degrade and remove the hard-to-degrade organic matter in wastewater, improve the biochemical properties of wastewater, and provide a carbon source for part of the denitrification process. The aerobic zone further decomposes organic matter into small molecule organic or inorganic materials. At the same time, the combination of the phosphorus removal system and the biochemical system can effectively remove phosphorus, and finally, in the membrane section, solid-liquid separation by filtration of MBR membrane to further remove bacteria and pollutants, thus ensuring that the turbidity of the effluent is reduced to very low and meets the discharge standard.

Clear tank

Receives the effluent from the MBR reactor, discharges it to a nearby water body, or reuses it directly.

What are the factors affecting the operation of the MBR Membrane?

MBR membrane technology is still essentially physical filtration, so the biggest problems with MBR are still related to filtration. In other words, the most likely operational problem is the decrease in membrane flux, which leads to the inability to maintain sufficient water production capacity, resulting in a sharp reduction in effluent volume, and the failure of the system to pass enough water volume, resulting in a decrease in system processing capacity, stagnant, overflow, and other accidents. For this fundamental reason, MBR operation problems are mostly characterized by MBR clogging, mainly for the following reasons.

Causes of activated sludge

Clogging of MBR membrane due to insufficient concentration of microorganisms in activated sludge, more inorganic salts or inorganic substances, abnormal conditions in the microbial population (filamentous bacteria expansion and biological foam, etc.), and excessive EPS on the surface of microorganisms.

Feed water debris problem

Some wastewater treatment projects do not use or improperly use a fine grille of about 1mm to remove suspended solids in the water, while some use inoculated sludge directly into the MBR pre-bio tank to quickly increase the concentration of activated sludge in the bio tank during activated sludge cultivation. Not filtered by the grille, this sludge can cause membrane clogging, and even some sharp impurities can cause MBR membrane rupture and breakage.

Blower problem

Due to the improper design and selection of the membrane scrubbing blower, the process is over- or under-aerated, resulting in the blower clogging the MBR membrane. The over-aeration is also likely to cause the activated sludge to be over-oxygenated, which will impact phosphorus removal and denitrification, whether internal reflux or external reflux is used.

Raw water quality problem

The hardness or salt content in the wastewater or sewage is too high, which is deposited on the membrane surface and creates a hardness fouling situation, causing the membrane flux to decrease. After cleaning by acid immersion, the operation and maintenance personnel discharge this part of the effluent into the sewer network and back to the sump, which may still repeat the deposition fouling on the membrane.

The role of phosphorus removal agents

A large amount of chemical phosphorus remover also makes part of the inorganic salts deposited on the surface of the MBR membrane, causing chemical fouling and clogging of the MBR, which requires acid immersion cleaning.

The effect of leakage on the effluent quality

Membrane filament after a period of use and improper operation during offline cleaning may tear the membrane filament or crack the product water pipe connection. As a result, the mixture will enter the production water pump through these channels, affecting the effluent quality, equivalent to the filtration leakage problem.

How to install the MBR membrane in packaged MBR system?

The installation of the MBR membrane will directly affect the operation of the MBR membrane module and the excellent water effect, so the installation and commissioning must be carried out according to the installation standards.

When installing the membrane, the first thing to do is to organize the installation environment to make sure that the MBR membrane pool is clean and tidy, and free of particles, the membrane module holder is fixed and reliable, and sharp instruments that may touch the membrane surface during the installation process should be wrapped to prevent damage to the membrane.
The membrane elements should be disassembled and reassembled with a smooth, soft material as a bedding layer, not placed on the ground without protective measures or stacked indiscriminately. When handling the membrane sheet, both hands should hold the skeleton part on both sides and keep a certain distance from the human body, and the membrane surface should not be bent strongly.
Before installing, carefully check each membrane sheet to see any traces of scratches on the membrane surface, check if there are any empty spaces at the adhesive joints, and replace the membrane sheet in time if any problems are found.
When installing the membrane sheets, move slowly to ensure each sheet is placed in the corresponding partition, do not forcefully pull or push. The membrane sheets are put into the membrane module in order. Please pay attention to the direction of the water outlet of each one, whether it corresponds to the main suction pipe, to prevent the wrong direction.
After the installation of the membrane sheet is completed, the rubber limiting strips should be placed, compacted with stainless steel strips, and tightened until the membrane element is not bent and deformed. Finally, connect the membrane module outlet piping and the aeration piping.

How to maintain the performance of the MBR membrane?

MBR bioreactor in actual operation will encounter all kinds of problems because MBR is a submerged membrane filter. It is closely related to the activated sludge system of the biochemical treatment process in operation. MBR operation abnormalities will also significantly impact the activated sludge, so it is necessary to fully consider the operating conditions of the MBR membrane process and carry out proper membrane cleaning and maintenance work.

Ensure the removal of feed water impurities. Raw water impurities, exceptionally sharp small stones, and tangled impurities should be effectively removed before entering the biological tank to ensure that the MBR membrane does not produce tangled bundles and that the internal membrane filaments play an appropriate processing capacity.
Select the appropriate aeration volume. Adequate air volume and sufficient aeration strength can produce enough vibration force to the membrane filaments. So, it can effectively clean the surface impurities and remove the internal storage sludge of multi-stranded membrane filaments.
Regularly use disinfectant to remove the biofilm on the surface of the MBR membrane. The biofilm accumulates on the surface of the MBR membrane under the negative pressure generated by the pump. Therefore, disinfectants must kill it to make the biofilm fall off and keep the MBR membrane clean.
Set a reasonable online and offline cleaning cycle, use acid for soaking and cleaning to determine the cycle in combination with the change of membrane flux, and perform acid dissolution cleaning for hardness accumulation and chemical residue on the membrane surface.
Reduce the expected value of membrane flux in actual use, adjust the set value appropriately, and do not blindly adopt high flux. Higher flux may be due to incomplete consideration of the complex working conditions of the site, and various unfavorable factors may occur in operation, resulting in membrane flux not reaching the design requirements and taking reasonable process preparation measures to ensure stable operation of the treated water quality and quantity.

Conclusion

The application of MBR membrane bioreactors in wastewater treatment projects is becoming increasingly widespread. However, operational problems are also gradually coming to the fore. Therefore, the operation and maintenance personnel who adopt MBR technology should combine the actual working conditions of activated sludge, have an in-depth understanding and mastery of MBR membrane bioreactor, and take good process, operation, and maintenance management measures to ensure excellent and stable operation of MBR process.