Principles and Functions of MBR Membrane Bioreactors

MBR membrane is the core component of Membrane Bio-Reactor (MBR) technology, a wastewater treatment device that organically integrates membrane separation technology and biological treatment technology. Detailed introduction to MBR membranes is as follows:

I. Working Principle of MBR Membranes

The core working principle of MBR membranes is wastewater filtration and separation via microporous membranes. Pre-treated wastewater is fed into the MBR system, carrying suspended solids, microorganisms and dissolved substances. Inside the MBR reactor tank, a water pump generates pressure to push wastewater through the membrane. Clean water permeates the micropores and flows out, while suspended solids, microorganisms and solutes are retained on the feed side to form concentrated retentate. Concentrates gradually build up on the membrane surface over time, lowering membrane flux. Therefore, regular cleaning is required to sustain stable membrane performance.

II. Classification of MBR Membranes

MBR membranes fall into three main categories:

Solid-Liquid Separation MBR

This is the most extensively researched type of membrane bioreactor in water treatment. It replaces the secondary sedimentation tank of conventional activated sludge processes via membrane separation. The membrane modules return solid organic matter to the reactor while discharging treated clean water. Based on the layout of membrane modules and bioreactors, solid-liquid separation MBRs are divided into submerged (integrated), side-stream (separate) and hybrid composite types.

Aeration Membrane Bioreactor (AMBR)

AMBR adopts dense gas-permeable membranes or microporous membranes. When the gas partial pressure is kept below the bubble point, bubble-free aeration can be realized inside the bioreactor. This process extends gas-liquid contact time and boosts oxygen mass transfer efficiency, facilitating precise aeration control.

Extractive Membrane Bioreactor (EMBR)

EMBR applies to wastewater featuring extreme acidity/alkalinity or biologically toxic pollutants. The membrane isolates wastewater from activated sludge: wastewater flows inside the membrane, while activated sludge containing specialized bacteria circulates outside. Organic contaminants pass through the selectively permeable membrane and get degraded by microorganisms on the other side.

In addition, MBR membranes are categorized by material and structure into hollow fiber membranes, flat sheet membranes, ceramic membranes and tubular membranes.

III. Application Fields of MBR Membranes

Thanks to its high-efficiency and stable water purification performance, MBR membrane technology is widely adopted across numerous industries, including:

Municipal Wastewater Treatment Plants: Treat domestic sewage to remove suspended solids, organics, ammonia nitrogen and other pollutants.

Building Reclaimed Water Reuse: Process toilet flushing wastewater and laundry drainage; treated water can be reused for non-potable purposes such as toilet flushing and green irrigation.

Food Industry Wastewater Treatment: Eliminate organics, suspended solids and oil contaminants in food processing wastewater.

Chemical Wastewater Treatment: Treat wastewater loaded with high-concentration organics, heavy metals and other refractory pollutants.

Pharmaceutical Wastewater Treatment: Remove antibiotic residues, organic pollutants and other hazardous substances from pharmaceutical wastewater.

Textile Wastewater Treatment: Filter out dyes and suspended solids in textile wastewater.

Beyond the above, MBR technology is also used in electronic wastewater treatment, mining wastewater treatment, micro-polluted drinking water purification, seawater desalination, rural domestic sewage treatment, hospital wastewater treatment, slaughterhouse wastewater treatment, aquaculture wastewater treatment and landfill leachate treatment.

IV. Design Requirements for MBR Membrane Modules

The following factors must be considered during the selection and design of MBR membrane modules:

Mechanical Support: Provide sufficient mechanical support for membranes with unobstructed flow channels, no dead zones or stagnant water areas.

Energy Consumption & Separation Efficiency: Maintain low energy consumption, minimize concentration polarization to improve separation efficiency and mitigate membrane fouling.

Packing Density & Operation Convenience: Maximize membrane packing density while enabling easy installation, cleaning and replacement.

Stability: Possess adequate mechanical strength, chemical stability and thermal stability.

V. Maintenance and Cleaning of MBR Membranes

Regular cleaning is essential to guarantee normal MBR operation. Two mainstream cleaning methods are chemical cleaning and physical cleaning. Chemical cleaning uses chemical reagents to dissolve or oxidize surface deposits, which are then flushed away by cleaning fluid. Physical cleaning removes concentrates accumulated on membranes through high-pressure flushing or air scouring with bubbles.

Conclusion

As a high-efficiency core component for wastewater treatment, MBR membranes play a vital role in multiple industrial sectors. Rational selection and design of MBR membrane modules combined with routine cleaning and maintenance ensure stable operation and outstanding treatment efficiency of the entire MBR system.