What Is A Membrane Bioreactor And Why Use It For Treating Wastewater?

By Author: Rohan Mehra
Total Articles: 23
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The membrane bioreactor is used to treat municipal and industrial wastewater. It combines membrane processes like microfiltration or ultrafiltration with a biological wastewater treatment process or the active sludge process. A membrane is a material that allows the selective flow of certain substances. In the case of water purification, the aim is for the water to flow through the membrane, retaining any undesirable substances and particles on the other side. A membrane bioreactor is a version of the conventional activated sludge process (ASP). However, while the ASP uses a settlement tank or a secondary clarifier for solid/liquid separation, an MBR uses a membrane for this step. This gives a number of advantages to the MBR technology over the activated sludge process: high-quality effluent, higher volumetric loading rates, shorter hydraulic retention times [HRT], longer solid retention times [SRT], less sludge production and potential for simultaneous nitrification/ denitrification in long solid retention times.

Over the past two decades, MBR has increased in popularity due to its potential to produce high-quality ...
... effluent and is considered one of the best methods to treat wastewater. As a result of the growth in the human population, the number of various industries has also grown. This has given rise to two very basic and essential needs; First: the need for excess water supply; secondly: the need for technologies for the generation of high-quality effluent upon proper treatment. These needs can be fulfilled with the help of a membrane bioreactor (MBR) that has been proven to be helpful and effective in removing the organic and inorganic matters for biological wastewater treatment. When domestic wastewater is treated with the MBR process, it can produce effluent of high quality that can be discharged to the waterways or can also be reused for irrigation.

MBR process

The membranes used as a filter, removes the solids that are developed during the biological process, which gives out a clear and pathogen-free product. The wastewater first goes through a fine screen that removes big objects that might cause damage to the downstream equipment. Then it enters an Anoxic zone where the nitrogenous matter and phosphate are treated. This is followed by an Aerobic Zone where the microorganism along with the help of oxygen coming out of the Fine Bubble Diffusers (FBD), will digest the organic matter in the wastewater and clump together as they do so, resulting in a sludge. This sludge then enters the Immersed Membrane Bioreactor where the membrane separates the solids and the microorganisms from the water.

Advantages of MBR:

There are a number of advantages of membrane bioreactors over other wastewater technologies:

1. Independent control of HRT and SRT: As the biological solids are completely contained in the bioreactor, it allows for the SRT or solids retention time to be controlled independently from the HRT or hydraulic retention time. In the Activated Sludge Process or ASP, the flocculent solids are allowed to grow in size to the point where they can be settled out in the secondary clarifier. Thus, in ASP, the HRT and SRT are connected; which is not the case in membrane bioreactors.

2. High-quality effluent: As the membrane pores of the MBR are of small size (