What are the Types and Characteristics of MBR Membranes?

The most widely used membrane in municipal wastewater or large-scale sewage treatment projects is the MBR membrane. MBR membranes are excellent regarding treated water quality and quantity compared to other treatment methods. Today, we would like to give you a detailed introduction to the types and characteristics of MBR membranes.

What is MBR?

MBR is the abbreviation of Membrane Bio-Reactor, a new water treatment technology combining membrane separation and biological treatment technology. It combines the advantages of membrane and biological treatment technology, replacing the traditional secondary sedimentation tank with a microfiltration membrane module as the mud-water separation unit. The microfiltration membrane retains microbial flocs and suspended solids in the activated sludge mixture, maintaining high biological concentration and extending the residence time of organic solids in the bioreactor, significantly improving the oxidation efficiency of microorganisms on organic matter and thus obtaining high-quality effluent water quality.

According to the combination of MBR membrane module and bio-reactor, membrane bio-reactors can be divided into three basic types: recirculated membrane bio-reactor, submerged membrane bio-reactor, and hybrid membrane bio-reactor.

1. What is recirculated membrane bio-reactor?

The MBR membrane module is separated from the bio-reactor as an independent unit, the mixed liquid is pressurized by the circulation pump and enters the filtration end of the membrane module, and the permeate of the membrane module is the effluent of the system. The MBR membrane retains solids and macromolecules and flows back to the bio-reactor with the concentrate.

Recirculated membrane bio-reactors use cross-flow membrane modules, where the mixture flows parallel to the membrane surface and perpendicular to the filtrate flow direction. Cross-flow filtration generates significant shear, which limits the thickness of the filter cake layer and is highly effective in mitigating MBR membrane fouling.

To maintain a stable water permeability, the cross-flow rate at the membrane surface is generally required to be greater than 2m/s, which requires more water circulation, resulting in higher energy consumption per unit of production water, but the stable operation, high membrane flux, and easy cleaning and replacement of membrane modules. Below is the process flow for reference.

2. What is a submerged membrane bio-reactor?

Also known as an integrated membrane bio-reactor, the MBR membrane module is submerged in the reactor without needing solid-liquid separation and return flow. The permeate of the membrane module is used as the effluent of the system through head pressure difference or pumping, while the retained activated sludge remains in the reactor. Due to the aeration device being installed directly below the membrane module, the aeration makes the mixture flow upward with the airflow, which generates a shear force on the membrane surface and realizes the cross-flow on the membrane surface. The sludge particles are forced to leave the membrane surface under this cross-flow, which delays membrane fouling.

The energy consumption of the submerged membrane bio-reactor is lower. However, the stability of operation, the cleaning effect of the membrane, and the convenience of replacement are not as good as those of the recirculated membrane bio-reactor. The below figure shows the process flow.

3. What is a hybrid membrane bio-reactor?

It also belongs to the submerged membrane bio-reactor. Still, the difference is that the biofilm carrier is added to the bio-reactor, thus forming a hybrid membrane bio-reactor, which changes some reactor properties.

There are two purposes for adding biofilm carriers in the hybrid membrane bio-reactor. One is to improve the shock load resistance of the water treatment system and ensure the treatment effect of the system; the other is to reduce the concentration of suspended activated sludge in the reactor, reduce the pressure of membrane purification, and ensure a high membrane flux.

In the hybrid membrane bio-reactor, due to the large number of microorganisms growing on the biofilm carriers, it can ensure the system has a high treatment effect and the ability to resist the shock load while not making the concentration of suspended sludge in the reactor too high, which affects the membrane flux. The below figure shows the process flow.

What is an MBR membrane?

MBR membrane is a microporous filtration membrane (microfiltration membrane and ultrafiltration membrane) with uniform pore size and a rated pore size range of 0.001~0.4μm, usually used in membrane bio-reactor wastewater treatment. There are many types of them; the common ones are hollow fiber membranes, flat sheet membranes, ceramic membranes, tubular membranes, etc.

The most prominent role of the MBR membrane is to replace the traditional secondary sedimentation tank and replace it with a membrane tank, which also takes on the task of biochemical treatment and secondary tank simultaneously. The conventional secondary tank is used to precipitate impurities by gravity. This process may result in many other situations, such as the upward expansion of sludge and the appearance of foam. On the other hand, membrane filtration is much more thorough, and the wastewater is much easier to treat.

Currently, MBR membranes are mainly divided into PVDF and PTFE, with PVDF being relatively inexpensive but less resistant to membrane fouling and blocking than PTFE and having a shorter life span. As for which material is more cost-effective, it depends on the specific wastewater type and composition. However, for wastewater with high pollution levels, such as garbage permeate and some industrial wastewater, a PTFE MBR membrane is highly recommended.

What are the types of MBR membranes?

Many types of MBR membranes can be classified according to different conditions, and the common ones are as follows.

MBR membranes are classified into microfiltration (MF) membranes and ultrafiltration (UF) membranes according to pore size. Microfiltration membranes mainly adopt 0.1~0.4μm membrane pore size, while ultrafiltration membranes are generally 0.01~0.03μm.

According to the physical form of the membrane, it can be divided into the hollow fiber, flat sheet, and tubular. Hollow fiber membranes are membranes with a fibrous-like shape and self-supporting role, which are asymmetric membranes with a dense layer located on the fiber’s outer and inner surfaces. Hollow fiber membranes can be divided into curtain-type membranes and cylindrical-type membranes, as well as hollow fiber membranes with liner and hollow fiber membranes without liner.

MBR membranes can be divided into submerged and external membranes according to the state of use, with submerged membranes mainly hollow fiber curtain membranes and flat sheet membranes, and external membranes mostly tubular membranes and column hollow fiber membranes.

Due to the different properties of membrane modules, MBR membranes can be divided into internal and external pressure membranes. The direction of water permeation in the internal pressure membrane is from the inside to the outside, while the external pressure type is just the opposite. In practice, the external pressure membrane is more popular because the internal pressure type is prone to clogging, resulting in decreased membrane flux and, thus, reduced membrane treatment effectiveness.

What are the characteristics of MBR membranes?

MBR membrane separation technology replaces the secondary sedimentation tank in the activated sludge method for solid-liquid separation, which effectively achieves the purpose of mud-water separation and has incomparable advantages of the traditional process.

Efficient solid-liquid separation, the effect is much better than the traditional sedimentation tank, the effluent quality is good, the suspended solids and turbidity of the effluent are close to zero, and can be directly reused, realizing the resource of sewage.
The high-efficiency retention effect of the membrane makes microorganisms wholly retained in the bioreactor, realizing complete separation of reactor hydraulic retention time (HRT) and sludge retention time (SRT) and flexible and stable operation control.
MBR membrane tank combines a traditional wastewater treatment aeration and secondary sedimentation tank. It replaces all the processes and facilities of tertiary treatment, so it can significantly reduce the footprint and save the civil construction investment.
It is conducive to the retention and reproduction of nitrifying bacteria, and the nitrification efficiency of the system is high. Changing the operation mode can also have the functions of ammonia and phosphorus removal.
Sludge age can be very long, significantly improving the degradation efficiency of hardly soluble organic matter.
The reactor operates under a high volume load, low sludge load, long sludge age, and extremely low residual sludge production. The sludge age can be infinitely long, theoretically realizing zero sludge discharge.
The system can be controlled by PLC, which is convenient for operation and management.

What are the advantages of MBR technology?

MBR technology has been widely and maturely applied in sewage & wastewater treatment, which strengthens bioreactor performance by membrane separation technology, improves the activated sludge concentration, and enhances the efficiency of wastewater treatment. In addition, MBR has the following advantages compared to traditional biochemical water treatment technology.

Hydraulic retention time is separated from sludge age. MBR membrane technology can retain all microorganisms in water and realize the separation of hydraulic retention time and sludge retention time, which can maintain a very short hydraulic retention time and simultaneously ensure a very long sludge retention time.
The effluent quality is higher than the traditional biochemical process. Membrane technology can not only retain microorganisms in the water but also retain some large insoluble pollutants, prolong the residence time of pollutants in the reactor, and increase the removal rate of hard-to-degrade pollutants. The effluent quality of MBR is better than that of the traditional process because of the long sludge age and good denitrification effect. In addition, the effluent does not contain suspended solids.
With strong impact resistance, MBR sludge load is generally 0.05~0.15kgBOD5/(kgMLSS.D) or 0.1~0.2kgCOD/(kgVSS.D), while the volume load can be several kilograms.
Effectively reducing the concentration of pollutants, MBR membrane technology, as a biochemical treatment process, can convert organic matter into carbon dioxide and water and nitrogen pollutants into nitrogen but also reduce the raw water conductivity, which makes the subsequent membrane treatment load significantly reduced, extending the membrane life, improve the water yield, reduce the concentration of concentrated liquid.
Small footprint. Due to the high retention rate of the membrane system, it is possible to maintain a high sludge concentration in the reactor, which is usually 3~5 times that of the traditional activated sludge method, and the reactor volume is much smaller than that of the conventional technology. Plus, with the high-efficiency bottomless water oxygen supply, the biochemical part area is much smaller than the traditional process.
Low residual sludge production and zero sludge discharge can be achieved, reducing sludge treatment costs.
Wide range of applications. Such as urban sewage treatment and water reuse in buildings, industrial wastewater treatment, micro-polluted drinking water purification, landfill, fertilizer leachate treatment, manure sewage treatment, etc. At the same time, the operation and management are convenient and easy to realize automatic control.

Where to order MBR membranes?

Finding a trustworthy and reliable manufacturer & supplier is critical for the success of your sewage & wastewater treatment project. Turn to EcoLan^TMMBR membrane. We are a professional manufacturer of MBR membranes with about 20 years of experience and provide cost-effective one-stop solutions for sewage & wastewater treatment.

We bid on various products, supplying technical support and custom solutions to meet your requirements. If you need high-quality MBR membranes for your new cases, contact our sales team today, and we will revert to you within 24 hours.