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Assessing MBR efficiency for industrial wastewater treatment: a cost-benefit analysis

MBR system
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The membrane biological reactor system, as we have seen on several occasions, is a biological water purification system that consists of a combination of the traditional activated sludge purification process and a membrane filter separation system that replaces the normal secondary sedimentator.

MBR has become increasingly popular due to its superior effluent quality and small footprint. Yet although the advantages are unequivocal, it may not be the best choice in all cases.

When is it an efficient choice, and when is it better to implement an alternative technology? In this new article, I want to clearly explain the advantages and disadvantages of the MBR.


How the MBR wastewater treatment plant works

As you may know, an industrial Membrane Biological Reactor (MBR) integrates biological treatment with membrane filtration.

Wastewater undergoes biological degradation by microorganisms in an aeration tank.
The mixed liquor then passes through submerged or external membranes, separating solid waste from the treated water.
The membranes’ fine pores retain biomass and suspended solids, allowing only clean water to pass through.

Let’s make a real example. In the food industry, a dairy processing plant uses MBR to treat high-strength wastewater, effectively reducing organic load and producing high-quality effluent suitable for reuse in non-potable applications, such as equipment cleaning and irrigation. This ensures regulatory compliance and reduces environmental impact.

How a membrane bioreactor (MBR) works - Infographics
How a membrane bioreactor (MBR) works – Infographics


8 advantages of the MBR wastewater treatment plant

The advantages of MBR can be summarized in the following points:

  1. considerable reduction in the volume required for wastewater treatment, when compared to conventional technologies;
  2. elimination of the risk of sludge spillage, which in conventional plants can occur from the secondary settler as a result of foam formation, excess or poor settling of sludge, and excess oil and grease;
  3. high performance and excellent quality of the purified effluent. In particular, suspended solids are absent, and disinfection of the effluent is also achieved because the membranes have sufficient porosity to achieve very high removals for all categories of coliforms;
  4. consistent benefits with regard to management and disposal operations. The MBR technology has a high degree of modularity, which allows wide ranges of treatment potential to be covered;
  5. MBR is indispensable and preparatory for the subsequent successful operation of reverse osmosis. By having a very good pre-treatment beforehand, it is possible to push the R.O. to a recovery of up to 95%, the so-called ZLD (zero liquid discharge);
  6. it saves on the construction of civil works, as the installation of the MBR means that the secondary sedimentator (i.e., the final part of the Biological treatment) is no longer necessary;
  7. MBR is fully automated and therefore does not require constant staffing;
  8. MBR is efficient in disinfecting water to remove disease transmission, which usually are only inactivated through physical/chemical methods.
Installing an MBR
Installing an MBR


Disadvantages of the membrane bioreactor

A membrane bioreactor may be the right choice for your wastewater treatment plant, but the CAPEX sometimes may not be affordable for all industries.

In summary, we can say:
– volume reduction: biological oxidation requires less space due to the elimination of sedimentator and other intermediary phases when required to implement the recovery/re-use of water;
– elimination of the risk of sludge spillage: there is no risk of sludge spillage, which can occur in traditional plants for various reasons;
– high effluent performance and quality: the purified effluent contains no suspended solids and is disinfected as the membranes effectively remove coliforms;
– management and disposal benefits: the modularity of the MBR covers wide treatment ranges.
– support for reverse osmosis: the MBR is essential for the effective operation of reverse osmosis, allowing up to 95% recovery.

A membrane bioreactor plant
A membrane bioreactor plant


But are operating CAPEX really that high?

At a first very superficial analysis, it may seem that the capex of an MBR installation is very high, but obviously it is necessary to understand when it is the right choice.
For a company that is about to implement a water recovery system, and therefore a reverse osmosis system, the alternatives to MBR would be a set of technologies which would still lead to a considerable investment and would not guarantee the same reliability as MBR.

We would return to what is the now outdated process of having:

  • a secondary settler
  • multimedia filtering
  • an external ultra-filtration
  • and finally the reverse osmosis, which however would hardly be able to push the recovery % beyond certain limits as it is not sufficiently preserved by the pre-treatment.

So we can say that if a company intends to implement water recovery with reverse osmosis, the installation of an MBR system cannot be bypassed, under penalty of a reduction in recovery efficiency, but above all it would entail an enormous risk for the integrity of the same reverse osmosis plant.

Disclaimer: This article is based on published scientific research and actual case studies. The sources used are available upon request.
This article provides general information and does not constitute professional advice. It is always advisable to consult with qualified experts for specific water treatment needs.

Picture of Pranay Behl
Pranay Behl
Indian entrepreneur with over 20 years of experience in normatives applied to water treatment sector. His work has had a significant impact on the water treatment industry in India and around the world.

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