Membrane Bioreactor Process
What is the MBR Process in Wastewater Treatment?
Membrane Bioreactor (MBR) is generally a term used to define a wastewater treatment process where a perm-selective membrane, e.g. microfiltration or ultrafiltration, is integrated with a biological process - specifically as suspended growth bio reactor. An MBR, or Membrane Zone, can best be described as the initial step in a biological process where microbes are used to degrade pollutants that are then filtered by a series of submerged membranes (or membrane elements). The individual membranes are housed in units known as modules, cassettes, or racks and a combined series of these modules are referred to as a working membrane unit. Air is introduced through integral diffusers to continually scour membrane surfaces during filtration, facilitate mixing and in some cases, to contribute oxygen to the biological process.
How is the MBR Process Being Used?
The MBR process being used in the wastewater treatment industry is a method to produce high quality effluent from a raw waste stream being discharged from the site facilities. This effluent will be of a quality high enough to be permitted to be re-used as grey water or discharged to coastal water, surface waterways or to be reclaimed for irrigation. The advantage of MBR process over conventional processes would include a small footprint and ease of upgrade or retrofit of existing wastewater treatment systems. MBR will allow the wastewater treatment system to be operated at a higher mixed liquid concentration of the suspended solids (MLSS)
Nutrient Removal- Another advantage of the MBR process
In the wastewater treatment industry, nutrient removal is one of the main effluent quality concerns, especially in areas that are sensitive to eutrophication. The definition of eutrophicatiois is the process by which a body of water becomes enriched in dissolved nutrients (such as phosphates) that stimulate the growth of aquatic plant life usually resulting in the depletion of the dissolved oxygen in the water.
As in the conventional extended aeration wastewater treatment process, nitrification is currently the most widely used technology for N-removal from domestic wastewater. The nitrification process requires both an in combination of de-nitrification to achieve the removal of the nutrients being discharged from the effluent. This takes more tankage volume, which requires more space, and therefore is more expensive.
How MBR Treatment Process Works
MBR Tank Types
Side Stream MBR Tank
The membrane filtration unit shall be installed externally to the bio-reactor, often in a plant room. The biomass is either pumped directly through a number of membrane in a series and back to the bioreactor, or the biomass is pumped to a bank of modules, from which a second pump circulates the biomass through the modules in series. Cleaning and soaking of the membranes can be undertaken in place with use of an installed cleaning tank, pump, and pipework.
Submerged MBR Tank
The integral tank membrane system type will be installed within the bioreactor chamber directly. The membranes can be either flat sheet or tubular, or combination of both. The membrane system is equipped with a backwash system. Its purpose is to clean the surface fouling of the membrane by water washing using the membrane permeate, pumping it back through the membrane. For membranes requiring extreme cleaning, a soak procedure will be required. This will require the membrane to be removed from the bio chamber and transferred to the cleaning tank. In addition, the membrane will have to be exposed to air washing to provide air scour reducing fouling.