Membrane Bioreactors

What is a Membrane Bioreactor?

    - Membrane bioreactors are used during the filtration stages of water treatment.  Microfiltration and ultrafiltration are used with bioreactors to filter water. This operation has began to replace older systems as a cheaper more efficient source. It is essential to successful water treatment.
    -Membrane modules are submerged in the activated sludge to combine the biological step and the solid-liquid separation step into a single process.
    -Combines the use of an activated sludge bioreactor with a crossflow membrane filtration loop. It also provides a barrier to certain chlorine resistant pathogens such as Cryptosporidium and Giardia.
    -Sedimentation is usually incomplete, in getting rid of microorganisms.
    -Conventional plants will discharge 10000 to 100000 microbes per milliliter.
    -Since the membrane acts as a barrier to microorganisms, the quality is much better than that produced by a conventional plant. Also, the membrane barrier  allows the activated sludge to be more concentrated.  This reduces the capacity needed for biological tanks, saving space and money.

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The Process

    -Two MBR configurations exist: internal/submerged, where the membranes are immersed in and integral to the biological reactor; and external/sidestream, where membranes are a separate unit process requiring an intermediate pumping step.
    -External/sidestream-The filtration element is installed in either the main bioreactor vessel or in a separate tank. The membranes can be flat sheet or tubular, and can incorporate an online backwash system which reduces membrane surface fouling by pumping membrane permeate back through the membrane.
    -Internal/Submerged-The filtration elements are installed externally to the reactor, usually in a plant room. The biomass is either pumped directly through a number of membrane modules in 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.

Pollutants

The key pollutants that membrane bioreactors are intended to remove are microorganisms, water-bourne diseases, bacteria,etc.

Advantages

    -MBR system is that it effectively overcomes the limitations associated with poor settling of sludge in conventional sludge processes.
    - It is also a cheaper source of water filtration being more rapidly used today.
    -Filtering creates a disinfection barrier
    -Produces less waste.
    -Allows re-use.

Disadvantages

    -Membrane modules are expensive and have to be replaced every 5 to 10 years.
    -Cleaning solutions for the system can be considered hazardous waste.


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CITATIONS

                Chapman, Stephen. “Membrane Bioreactors (MBR) for Municipal Wastewater Treatment- An Australian Perspective.” --. N.p., n.d. Web. 7 Jan. 2011.                                     <http://www.membrane.unsw.edu.au/‌staff/‌papers/‌gleslie/‌mbr_for_reuse_awa.pdf

Crites, RW, et al. “Membrane Bioreactor (MBR) in Wastewater treatment.” Operators Notebook. N.p., n.d. Web. 6 Jan. 2011. <http://www.wrights-trainingsite.com/‌WWT%20MBR.htm>.

“Membrane Bioreactor.” Wikipedia. Wikipedia, 31 Dec. 2010. Web. 6 Jan. 2011. <http://en.wikipedia.org/‌wiki/‌Membrane_bioreactor>.

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