Membrane bioreactor MBR membranes integrate biological treatment with advanced filtration, providing an innovative solution for wastewater treatment that ensures high-quality effluent and promotes sustainable water management practices.

What is a membrane bioreactor?

Nowadays, a MEMBRANE BIOREACTOR (MBR) is a common technique in both industrial and municipal WasteWater Treatment Plants (WWTPs) that combines a suspended growth bioreactor with a microfiltration or ultrafiltration membrane unit.

Bioreactor

A bioreactor is a specially made chamber used in wastewater treatment processes to provide a biologically active environment. This environment allows bacteria and protozoa, sometimes known as biomass, to grow and consume part or all of the compounds present in the raw wastewater.

Depending on whether oxygen and nitrates are present or not, they can be aerobic (to remove organic matter and oxidize ammonia to nitrate), anoxic (to remove nitrogen from nitrates to nitrogen gas), or anaerobic (to remove organic matter). Membranes are usually erected following either anaerobic or aerobic bioreactors (the MBR and An MBR procedures, respectively).

Types of bioreactors

Suspended growth bioreactors, where the biomass grows into flocs.
Attached growth (or biofilm) bioreactors, where the biomass grows attached to carriers.
Hybrid bioreactors, which combines suspended and attached growth.
For MBR procedures, these bioreactors are usually suspended growth bioreactors. Hybrid bioreactors can also be employed if they are designed properly.

Membranes

Membranes serve as a solid-liquid separation tool in the MBR process, retaining biomass inside the bioreactor before releasing the treated wastewater into the environment. In essence, they replace the clarifiers that are utilized in the traditional activated sludge (CAS) process.

MBR applications can make use of both ultrafiltration (UF) and microfiltration (MF) membranes. Because of their superior separation properties (which allow them to remove certain colloids and viruses as well) and lower fouling tendency (because to their smaller pore size, they are less likely to clog pores), UF membranes are usually the recommended option.

Types of membrane geometries used for MBRs

Hollow fibre (HF)
Flat sheet (FS)
Tubular (or multi-tubular, MT)

Treatment Process and Basic Design Principles

Membrane bioreactor (MBR) membranes offer a higher degree of organic and suspended particles removal by combining membrane filtration with traditional biological treatment techniques (such as activated sludge). These systems can also offer a higher degree of nutrient removal when appropriately constructed. The membranes of an MBR system are immersed in an aerated biological reactor. Depending on the manufacturer, the membranes’ porosities range from 0.035 microns to 0.4 microns, which falls between micro and ultrafiltration.

This degree of filtration removes the sedimentation and filtration procedures commonly employed in wastewater treatment, allowing high-quality effluent to pass through the membranes. The biological process may function at a significantly greater mixed liquor concentration since sedimentation is no longer necessary. As a result, far less process tankage is needed, and many existing plants can be updated without acquiring additional tanks. The mixed fluid is normally maintained at the 1.0–1.2% solids range, which is four times that of a standard plant, to offer the best aeration and scour around the membranes.

Advantages of MBR Membranes

Smaller footprint (new WWTPs) or higher hydraulic throughput (existing WWTPs)

It is no longer necessary to use large clarifiers. The size of the secondary clarifier, which is controlled by solids loading and hydraulics, is replaced by a smaller, frequently rectangular chamber equipped with membrane cassettes. Furthermore, a lower footprint of up to 50% is achieved by storing the same total amount of solids in a smaller tank due to the greater biomass concentrations that can be maintained within the bioreactors.

High-quality effluent, free of bacteria and pathogens

The effluent has less bacteria and virus content and is free of suspended particles as compared to the activated sludge (CAS) process. As a result, minimal disinfection is necessary.

As a result, the MBR process makes it simple to release the treated wastewater to vulnerable receiving bodies or to recover it for use in utilities, urban irrigation, or toilet flushing. Additionally, it is of excellent quality for direct feeding into a reverse osmosis (RO) process.

Given the stringent effluent quality standards enforced by municipal legislation that have gone into effect in recent years and will soon go into effect, this is becoming more and more important.

Higher automation capabilities

The MBR system’s operation can be completely automated, reducing the need for operator intervention that is usually necessary for traditional treatment facilities. This indicates that decentralized sites can also simply adopt the MBR method.

Applications of MBR Membranes

Municipal wastewater treatment

MBR systems were initially created with an emphasis on water reuse and recycling for municipal wastewater treatment applications. The MBR’s small size, capacity to generate reusable water, and trouble-free operation make it the perfect method for recycling municipal wastewater in areas with limited water and space.

Industrial wastewater treatment

Alternative treatments like (MBR) membranes are preferred because industrial waste streams may contain large organic loadings and chemicals that are particularly challenging to handle or decompose.

In actuality, MBRs retain all of the biomass, which promotes the biodegradation of resistant materials (such pesticides and herbicides) and increases the diversification of the bacterial and protozoan populations.

Landfill leachate treatment

MBRs have been used in a variety of other fields outside the treatment of industrial and municipal wastewater. One example is the handling of leachates from landfills. Both organic and inorganic chemicals are typically found in high amounts in landfill leachates. For the removal of heavy metals and inorganics, MBR systems have been effectively employed in conjunction with additional treatment procedures including reverse osmosis and nanofiltration.

Conclusion

MBR membranes represent a significant advancement in wastewater treatment technology, offering efficient organic and nutrient removal while minimizing the footprint of treatment facilities. Their ability to produce high-quality effluent with reduced pathogen content makes them ideal for both municipal and industrial applications. As water scarcity becomes an increasingly pressing issue, the versatility and effectiveness of MBR systems will play a crucial role in sustainable water management and recycling efforts worldwide.

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