The Ultimate FAQ Guide:Membrane Bioreactor (MBR) Wastewater Treatment

In recent years, more emphasis has been placed on wastewater treatment as environmentalists step up their attempts to cushion the ecosystem and its core inhabitants. Stringent rules to regulate the quality of effluent discharged into the environment and the manner in which it is disposed of have been enacted and are being actualized.

One of the ultra-modern technologies aiding municipalities, industries, and commercial enterprises to comply with the respective discharge regulations, is membrane bioreactor (MBR) treatment. By answering the internet’s frequently asked questions, our article today seeks to elevate your knowledge of MBR wastewater treatment and its varied applications.

Figure 1 Membrane bioreactor (MBR) plant.

What is MBR Wastewater Treatment?

Membrane bioreactor (MBR) wastewater treatment is a hybrid wastewater treatment process that intermarries biological and membrane treatment processes to stringently treat municipal, commercial, and industrial effluent. MBR wastewater treatment commenced in the 1960s and since then it has been significantly improved, making it more effective, dependable, and efficient. Perm-selective membranes, particularly ultrafiltration and microfiltration membranes, are specifically employed to filter out suspended solids.

A biological process, specifically, activated sludge treatment is then employed to extract biodegradable organics and nitrate. Membrane bioreactor is actually seen as a substitute for the traditional activated sludge treatment. Rather than deploying secondary clarifiers and pressure sand filters to expel suspended matter, membrane bioreactors for wastewater treatment rely on MF and UF filters, which are comparatively more efficient and productive. In the end, the quality of effluent generated through membrane bioreactor treatment tends to be of a significantly higher quality.

How does a Bioreactor Work?

MBR wastewater treatment essentially consolidates two renowned treatment processes; membrane filtration and biological treatment to effectively extract suspended matter and organics. However, the process is supplemented by effective preliminary and post-treatment processes to stringently treat the wastewater. Underneath, we will be looking at the process flow of a conventional MBR wastewater treatment plant.

●       Preliminary treatment.

Industrial, commercial, and municipal wastewater often harbors large solids such as plastics, wood, and glass. These solids are capable of clogging or fouling the perm-selective membranes hence they necessitate prior removal. Ordinarily, a bar screen is deployed to seize the relatively huge solid contaminants.

●       Bio-treatment.

Aeration plays a significant role in the biological treatment process. Essentially, oxygen is injected into the wastewater to stimulate the growth of bacteria. Aeration also helps convert ammonia into nitrate. The microorganisms subsequently extract oxygen from the nitrate resulting in the formation of nitrogen gas. Organic compounds in the wastewater are then degraded by the aerated bacteria consequently forming water and carbon dioxide (CO2). This process is essentially activated sludge treatment.

Figure 2 Membrane bioreactor process flow.

●       Membrane filtration.

Rather than driving the treated effluent into a secondary clarifier, the wastewater is subjected to membrane filtration. Only ultrafiltration or microfiltration membranes with a porosity size ranging from 0.05-0.4 µm are used to extract the remaining suspended solids. Ordinarily, three membrane configurations are employed in MBR water treatment.

●        Flat sheet membrane configuration.

This configuration is also known as the plate-and-frame configuration. In these membranes, the fluid flow permeates to the permeate side from the coated side of the membrane.

●        Hollow-fiber membrane configuration.

In this type of membrane configuration, the membrane flow originates from the lumen (outside), towards the shell side (inside).

●        Multi-tubular membrane configuration.

In multi-tubular membrane configurations, the fluid flow is the exact opposite of the hollow-fiber membrane configuration. That is, the fluid moves toward the lumen (inside) and away from the shell side (outside).

●       Disinfection.

MBR system is often concluded by sterilizing the effluent to shrink or completely exterminate the concentration of microbes. This is typically accomplished using UV water sterilization or chlorination. Chlorination is a chemical dosing process that uses chlorine to kill viruses, bacteria, and other pathogenic microbes. UV water sterilization on the flip side inactivates pathogenic microbes using germicidal rays at a wavelength of 253.7 nm. To understand how MBR wastewater treatment works, watch the following video.

What Are the Chief Pros of Membrane Bioreactor?

Membrane bioreactor treatment plants have exponentially grown in prominence in the past decade. This can partly be attributed to their diverse benefits, which often supersede those of other wastewater treatment plants. Here are some of their guaranteed pros.

●       Outstanding discharge.

MBR wastewater treatment extracts huge chunks of suspended matter, organic compounds as well as microorganisms. This results in high-quality effluent characterized by high clarity. The effluent’s quality permits its disposal in water bodies and reuse in applications such as irrigation.

●       Independent control of Solid retention time (SRT) and hydraulic retention time (HRT).

In MBR water treatment, sludge or mixed liquor is accommodated in a bioreactor. This means you can regulate the solid retention time without particularly having to regulate the hydraulic retention time at the same time. In conventional CAS treatment, both the hydraulic retention time and the solids retention time are interlinked.

●       Smaller footprint.

MBR operates at a relatively shorter hydraulic retention time (HRT) and does not necessitate secondary clarifiers. This means the plants are relatively smaller and compact hence they occupy smaller footprints.

●       Elevated bio-treatment.

The solid retention time (SRT) of membrane bioreactor wastewater treatment is comparatively higher. This stimulates the flourishing of bacteria, particularly nitrifiers whose growth is pretty slow. As such, MBR water treatment is quite proficient at biologically treating wastewater.

Figure 3 MBR wastewater treatment filter.

What Are the Main Process Configurations of MBR Technology?

Primarily, there are two process configurations for membrane bioreactor (MBR) wastewater treatment; side-stream and immersed MBR configurations. Beneath, we are going to look at the two distinct configurations, their disparities, and consequential rewards.

●       Side-stream MBR (sMBR).

Side-stream membrane bioreactor configuration is also referred to as cross-flow MBR. This process configuration is characterized by a membrane module located just outside of the aeration tank. Ordinarily, this configuration uses tubular membranes. The permeate generated after the mixed liquor has been filtered by the membranes is discharged while the resulting retentate is driven into the aeration tank. Thanks to the addition of a suction pump to supplement the recirculation pumps, the sMBR configuration is presently flexible and energy-efficient.

●       Immersed MBR (iMBR).

Immersed membrane bioreactor process configuration is also known as submerged configuration. In immersed MBR configurations, the respective membrane modules are installed inside the aeration tanks. The energy demands of iMBR treatment are relatively higher compared to those of side-stream MBR configuration.

How Much Does a Membrane Bioreactor Cost?

Membrane bioreactors for wastewater treatment are generally economical. Despite undergoing significant modifications that have left them more efficient and productive, the cost of investing in MBR wastewater plants (CAPEX) has gradually shrunk. The resulting efficiency has similarly lessened the operating costs (OPEX) of MBR plants. The CAPEX however differs depending on the plant’s size, the membrane characterization, and the construction cost.

Compared to the investment cost of other wastewater treatment plants, MBR plants have relatively higher investment costs. They however make up for this by efficiently utilizing land space and necessitating smaller tanks. The operational costs incurred when rolling out membrane bioreactor treatment cover power, maintenance, chemicals, and manpower. All these cost categories are subject to change based on the operational conditions.

An economical study of distinct wastewater treatment plants with capacities of 30,000 m3 per day, showed that MBR wastewater treatment costs $0.43 per unit volume ($0.43/m3). Activated sludge treatment, on the other hand, costs approximately $0.2/m3. Although conventional CAS is relatively cheaper, MBR treatment is more revered for its high-quality effluent.

Figure 4 Activated sludge vs membrane bioreactor treatment.

How is MBR Wastewater Treatment Different from Activated Sludge Treatment?

Activated sludge treatment is a wastewater treatment process that extracts organic compounds by degrading them using bacterial microorganisms. Membrane bioreactor treatment on the other hand treats wastewater by integrating biological treatment and membrane filtration. As such, MBR treatment produces effluent with higher clarity compared to conventional activated sludge (CAS) treatment.

In CAS wastewater treatment, secondary clarifiers are mandatory and they are tasked with extracting suspended matter. However, MBR treatment plants do not rely on clarifiers. Instead, they employ microfiltration or ultrafiltration membrane filters to seize suspended solids. The absence of secondary clarifiers makes MBR plants quite smaller and compact compared to activated sludge plants.

In CAS plants, the solid retention time and hydraulic retention time are interlinked while in membrane bioreactor treatment, they are controlled independently. The investment and operational costs of the two technologies also differ with MBR wastewater treatment being relatively higher. In addition, MBR water treatment plants are more susceptible to fouling than activated sludge plants. If you compare the outputs of the two technologies, MBR technology edges out CAS treatment.

What Are Some of the Application Fields of Membrane Bioreactor?

Numerous market studies undertaken across the globe show that the adoption of membrane bioreactors for wastewater treatment grows at 15% annually. At present, membrane bioreactor for wastewater treatment is being exploited in over 200 countries. This is primarily a consequence of the dwindling investment and operational costs (CAPEX & OPEX). Their effectiveness, compared to other wastewater treatment technologies is also unrivaled and this explains their ever-growing utilization.

Technically, MBR technology is perfectly suited for industries, municipalities, and commercial entities with constrained land space and high-quality effluent demands. Their diversity and ability to extract a range of contaminants make them stand out from other wastewater treatment systems. The plants are often customized in size and design to ensure maximum feasibility with the imminent application. Underneath are some of the application fields presently exploiting MBR technology.

  • Landfill leachate treatment.
  • Municipal wastewater treatment.
  • Food and beverage effluent treatment.
  • Pharmaceutical waste treatment.
  • Petroleum wastewater treatment.
  • Pulp and paper industrial waste treatment.
  • Textile wastewater treatment.

Figure 5 Containerized MBR plant.

MBR Wastewater Treatment Plants Maintenance

Wastewater typically harbors aggressive contaminants such as large suspended solids, and if proper maintenance is not undertaken, they can lead to membrane clogging and/or fouling. Servicing your MBR plant significantly mitigates the untimely damage of key components such as the membrane modules. In addition, the optimal filtration rate of the membranes is upheld thereby preventing the generation of low-quality effluent.

One way to stop membrane clogging or fouling is by installing preliminary screening equipment to filter out the aggressive solids. Secondly, you can regularly clean the membrane modules to flush out the trapped foulants. Ordinarily, membrane cleaning is accomplished using physical or chemical processes.

●       Physical cleaning.

Physical cleaning is mainly undertaken to flush out gross solids trapped on the surface of the membranes. It is a remedy for reversible fouling. The process of physical cleaning is undertaken by simply flushing clean water in a backward flow. To attain the best possible results, you can enhance the backwash water with air bubbles.

●       Chemical cleaning.

Unlike physical cleaning, chemical cleaning is more suited to extracting tenacious constituents. It is primarily used as a remedy for irreversible fouling. The process is often undertaken using sodium hypochlorite, which is blended with organic or mineral acids like citric acid.

Cleaning can also be carried out as clean-in-place or intensive cleaning.

●       Clean-in-place (CIP).

Clean-in-place cleaning is often undertaken annually for residential MBR plants and twice a year for commercial MBR plants. The membrane’s operations are first halted before a solution of Clorox and water is injected into the membrane modules. The chemical solution is allowed at least 4 hours to allow optimal reaction with the modules. After completion, the membranes are put to task again.

●       Intensive cleaning.

Intensive cleaning is often undertaken after CIP cleaning has been undertaken for several years. First, the membranes are drawn from the aeration tank and cleaned with semi-pressurized water. This dislodges the built-up sludge. Subsequently, the membrane modules are immersed in chlorinated water for at least 4 hours. After completion, the membranes are taken back into the aeration tank and normal operations resumed.

NEWater MBR System

NEWater manufactures products that meet worldwide standards, allowing it to deliver MBR Industrial Wastewater Treatment solutions. Our MBR technology for wastewater treatment includes a membrane bioreactor for home wastewater treatment, a complex technology developed at the end of the twentieth century that achieved an effective combination of membrane separation technology and biological technology.

The membrane separation technology substitutes the old active sludge technique and the standard filter unit, and its high separation ability may reduce turbidity to near zero. The hydraulic retention time (HRT) and sludge age (SRT) have been entirely separated, the outlet water is of high and stable quality, and it may be reused without the third stage treatment. It considerably widens the spectrum of application of wastewater recycling due to the high security and affordable and effective water.

Our courteous customer service experts are available every day to assist you with your queries. Please contact us at info@newater.com for the most reliable MBR Plant.

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