An In-Depth Assessment of Membrane Bioreactor (MBR) Treatment

Membrane bioreactor (MBR) technology is now essential for wastewater treatment, as it detoxifies water to an impeccable standard and guarantees its suitability for reuse. By studying this article, you will understand the advantages of MBR, what it can do in terms of treating wastewater, and its limitations.

Figure 1 MBR treatment.(1)

Membrane Bioreactor (MBR) Wastewater Treatment

The combination of filtration technology with biological treatment referred to as membrane bioreactors (MBRs) offers a highly effective form of wastewater treatment solution. Microorganisms are utilized in an MBR system to decompose and remove organic material, nutrients, and other contaminants from the wastewater. In a biological reactor, the microorganisms live and eat the pollutants, transforming them into the water and carbon dioxide, two harmless byproducts.

Membrane filtration stands out among other wastewater treatments as it is used to distinctly separate the treated water from its microorganisms. This sets Membrane Bio Reactor (MBR) apart and makes it a revolutionary option for wastewater treatment. The membranes used in MBR are typically made of materials like polyethylene or polypropylene. They have tiny pores that allow only clean water to pass through while retaining microorganisms and solids.

The Membrane Bioreactor Process

Through competent, efficient processes, MBR water treatment creates the highest-quality effluent that can be reused or released by completely eliminating contaminants from wastewater. The steps in the MBR process are as follows:

● Preliminary Treatment

The first step is to screen out any large solids and debris using a mechanical screen or grit chamber. This prevents clogging and damage to downstream equipment.

● Biological Treatment

The wastewater is then introduced to a biological reactor where it is treated by microorganisms such as bacteria, and protozoa. These microorganisms break down organic matter and nutrients in the wastewater, converting them into carbon dioxide, water, and microbial biomass.

● Membrane Filtration

The wastewater is routed to a membrane filtration machine for microfiltration or ultrafiltration to remove any leftover suspended particles and other impurities after biological treatment. The membrane can be made of various materials such as polymeric or ceramic and can be in the form of flat sheets or hollow fibers.

● Membrane Cleaning

Over time, the membrane can become fouled with organic and inorganic matter, reducing its filtration capacity. To avoid this, it is important to do routine membrane cleaning. This is typically done using chemical cleaning agents or backwashing with water.

● Disinfection

After membrane filtration, the treated wastewater is disinfected to remove any remaining pathogens. This can be done using various methods such as ultraviolet (UV) radiation, chlorination, or ozone treatment.

● Effluent Discharge or Reuse

Finally, the treated wastewater can be discharged into a receiving water body, such as a river or ocean, or reused for non-potable applications such as irrigation, industrial processes, or toilet flushing.

Membrane Bioreactor (MBR) Configurations

There are various MBR configurations that can be broadly divided into two types:

● Submerged MBR Configuration

In this setup, the biological treatment is carried out in an aeration tank with the membrane modules submerged. The membranes may be tubular, hollow fibers, or flat sheets. A vacuum or a pump is used to draw the mixed liquor—a mixture of wastewater and biomass—through the membranes. Through the membranes, we are able to collect the purified water before it is removed from its holding tank.

Figure 2 Side-stream Vs Submerged MBR Configuration.(1)

Side-Stream MBR Configuration

In this configuration, the membrane modules are located outside the aeration tank, and the mixed liquor is pumped to the membranes for filtration. The permeate is collected outside the membrane modules and withdrawn for further treatment or discharge. The external configuration can be further divided into two types:

  • Cross-flow external MBR: In this configuration, the mixed liquor flows tangentially across the membrane surface, which helps prevent fouling of the membranes.
  • Dead-end external MBR: In this configuration, the mixed liquor is pushed through the membranes, and the fouling can be a problem if the flow rate is not controlled.

Types of Membranes Used in MBR Treatment

As a physical barrier, the membranes used in MBRs enable the separation of suspended particles and bacteria from the treated water. Two membrane types are typically used in MBRs:

● Microfiltration (MF) Membranes

Suspended solids, germs, and other particles can be removed from wastewater using MF membranes, which contain pores that range in size from 0.1 to 1.0 microns. These membranes are relatively low-cost and require low operating pressures, making them suitable for use in MBRs.

● Ultrafiltration (UF) Membranes

The pores on UF membranes range in size from 0.01 to 0.1 microns, which can separate smaller particles such as viruses, colloids, and macromolecules from the wastewater. UF membranes are more expensive than MF membranes but offer better filtration performance and require less space.

The Application of Membrane Bioreactor (MBR) in the Wastewater Treatment.

Membrane bioreactor technology is a highly versatile solution for a variety of wastewater treatment needs. Its flexibility and effectiveness make it an ideal choice for many applications. MBR systems have a high level of treatment efficiency and are compactly designed making them an attractive option for many different industries and applications.

● Municipal Wastewater Treatment

Urban regions have employed MBRs to treat municipal wastewater because they produce high-quality, reusable effluent. MBRs can be built to be compact and modular, which makes them particularly useful in locations where there isn’t enough room for conventional wastewater treatment plants.

● Industrial Wastewater Treatment

High amounts of various organic and inorganic contaminants, including heavy metals, oils, and chemicals, can be found in effluent from a variety of industrial activities. MBRs can be used to treat these wastewaters to remove the toxins before they are released into the environment.

● Agricultural Wastewater Treatment

Moreover, MBRs can be utilized to treat wastewater produced in agricultural facilities including livestock farms and food processing facilities. These wastewaters often contain high levels of nutrients and organic matter, which can be effectively removed using MBR technology.

● Landfill Leachate Treatment

Landfill leachate is the term used to describe the liquid formed when water permeates through waste in a landfill. Before releasing this leachate into the environment, pollutants can be removed using MBRs.

● Greywater Treatment

Greywater is the wastewater produced by tasks like cleaning dishes, doing laundry, and taking a shower. This water can be treated by MBRs so that it can be used for non-potable tasks like irrigation or toilet flushing.

Figure 3 MBR for treatment of wastewater.(1)

The Pros of Using Membrane Bioreactor for Wastewater Treatment

MBR treatment is superior to traditional wastewater treatment methods in a number of ways. The following are some of the primary rewards of employing MBR treatment:

● Superior Effluent

High-quality discharge that is free of bacteria, viruses, and suspended particulates is produced via MBR treatment. With pore diameters as fine as 0.1 microns, the MBR membranes utilized in the process can completely extract all suspended debris from the wastewater. The wastewater can then be recycled for non-potable uses including industrial processes and irrigation.

● Small Footprint

MBR treatment uses less space than conventional wastewater treatment techniques. The technology combines the biological treatment process and membrane filtration in a single tank, which makes it more compact and efficient. The small footprint also makes it suitable for installation in areas with limited space.

● Energy Efficiency

MBR water treatment is energy-efficient because it requires less energy for aeration and pumping compared to traditional treatment methods. The process also produces biogas as a by-product, which can be used to generate electricity and heat. This reduces the overall energy consumption of the treatment plant.

● Easy to Operate and Maintain

MBR treatment is easy to operate and maintain because the process is automated and requires less manual intervention. Besides self-cleaning, the membranes utilized in the procedure lessen the frequency of cleaning and maintenance.

● Flexibility

MBR treatment is adaptable and may be tailored to meet particular requirements for wastewater treatment. Municipal, commercial, and agricultural wastewater, among others, can all be treated using this method. It can also be used to treat wastewater with high levels of nutrients, such as nitrogen and phosphorus.

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