Membrane BioReactor (MBR)

Water scarcity implies the need to reuse it once it has been properly treated, thus guaranteeing environmental protection. Among the treatment technologies available to regenerate wastewater, those that use membranes stand out for their capacity to retain solids and salts and even disinfect water, thus producing water suitable for reuse in irrigation and other applications.

A membrane is a material that allows the selective flow of certain substances. In the case of water purification or regeneration, the aim is for the water to flow through the membrane, retaining undesirable particles on the other side. Depending on the type of membrane, it is possible to get better pollutant retention. Different types of materials can be used to manufacture the membrane. However, in the field of wastewater treatment and due to the several operational restrictions, the number of materials that used to construct a membrane is different than that in the other fields. Some of the required characteristics in a membrane for wastewater treatments are chemical and mechanical resistance for five years of operation, highly acidic or basic properties, or adaptability to operate in a wide range of pH.

There are two main types of membrane materials available on the market: organic-based polymeric membranes and ceramic membranes. Polymeric membranes are the most commonly used material in water and wastewater treatment.

Due to the growth in the human population globally, it is noted that various industries have also grown. The need for an excess supply of water and the generation of high effluent quality upon proper treatment technologies has become a necessity. These two crucial needs can be achieved with the aid of membrane bioreactor (MBR) that has been proven to be effective in removing organic and inorganic matters as a biological unit for wastewater treatment. MBR plants are created by integrating the biological process with membrane filtration which possesses numerous benefits if compared with conventional methods such as activated sludge; MBR is widely used for municipal and industrial wastewater treatment.  In order to tackle the existing limitation of MBRs to be practical on a larger scale, the existing challenges and future research efforts are proposed.

Membrane bioreactor (MBR) is a combination of membrane processes like microfiltration or ultrafiltration with a biological wastewater treatment process, the activated sludge process. It is now widely used for municipal and industrial wastewater treatment. In general, there are two different MBR configurations:

1. Submerged membrane bioreactor (SMBR)

2. Side stream membrane bioreactors.


In the first configuration, the membrane is located inside the biological reactor, submerged in the wastewater. In the latter configuration, the membrane is located outside the reactor, as an additional step after biological treatment.

MBRs differ from ‘polishing’ processes where the membrane is employed as a discrete tertiary treatment step with no return of the active biomass to the biological process.

Almost all commercial MBR processes available today use the membrane as a filter, rejecting the solid materials which are developed by the biological process, resulting in a clarified and disinfected product effluent.

When used with domestic wastewater, MBR processes can produce effluent of high enough quality for discharge into the sea, oceans, surfaces, brackish bodies, or waterways for usage in urban irrigation. Other advantages of MBRs over conventional processes include a small footprint, easy retrofit, and upgradation of old wastewater treatment plants.

It is possible to operate MBR processes at higher mixed liquor suspended solids (MLSS) concentrations compared to conventional settlement separation systems, thus reducing the reactor volume to achieve the same loading rate.

Two MBR configurations exist: internal/submerged, where the membranes are immersed in and integral to the biological reactor; and external/side stream, where membranes are a separate unit process requiring an intermediate pumping step.

Schematic of conventional activated sludge process (top) and external (side stream) membrane bioreactor (bottom)

Recent technical innovation and significant membrane cost reduction have enabled MBRs to become an established process option to treat waste waters. As a result, the MBR process has now become an attractive option for the treatment and reuse of industrial and municipal waste waters, as evidenced by their constantly rising numbers and capacity.

The global membrane bioreactor market is expected to grow in the near future, because of various driving forces, for instance, scarcity of water worldwide, which makes wastewater reclamation invariably necessary. This will be further aggravated by climate change. The growing environmental concerns over industrial wastewater disposal along with the declining freshwater resources across developing economies also account for the demand of MBR technology. Population growth, urbanization, and industrialization will further complicate the business outlook. Contingent on their composition, these changes can be demanding on natural resources and pose unsustainable challenges to the environment. Therefore, membrane bioreactor (MBR) technology is regarded as a key element of advanced wastewater treatment and reuse schemes and it is focused to grow towards sustainable water management across the municipal and industrial sectors.

However, high initial investments and operational expenditure may hamper the global membrane bioreactor market. In addition, technological restraints including the recurrence of fouling in the MBRs are likely to hinder production adoption. Ongoing R&D progressions toward increasing output and minimizing sludge formation are anticipated to fuel industry growth.

Membrane bioreactors can be used to reduce the footprint of an activated sludge sewage treatment system by removing some of the liquid components of the mixed liquor. This leaves a concentrated waste product that is then treated using the activated sludge process.