Filter Membrane Blockage Prevention

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In a treatment package plant attached with a reverse osmosis machine, how can one resolve the issue of membrane filter blockage prematurely and how long does it take before a filter needs replacement?

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8 Answers

  2. I presume that you are meaning that the pre-treatment filters are blocking prematurely rather than the membranes becoming fouled. If that is the case it sounds like the raw water quality is rather worse than the system was designed for and that could be due to a lot of reasons such as others have mentioned silt, iron, biofouling etc.

    What you need to do is to identify this and then put in additional treatment steps such as self washing filters and/or chemical treatment to reduce the load going onto the protection filters.

       

  3. We have a self cleaning filtration technology that works very well to remove TSS down to 20 um. This would be installed ahead of your membrane filter. We also have an environmentally friendly flocculent that works well to capture fines down to 3um.

     

  4. Fouling remediation can be done through pre-treatment the feed to limit its fouling propensity, improving the antifouling properties of the membrane, membrane cleaning and backwash conditions and optimization of the operating conditions.Membranes are susceptible to fouling; therefore, pretreatment of the feed is required to control colloidal, organic, and biological fouling as well as scaling. The pre treatment scheme must be capable of controlling membrane fouling to such an extent that a practical cleaning frequency can be achieved. For low-pressure membranes, a number of pre-treatment methods are currently used.

    Coagulation involves the addition of chemicals coagulants, such as: FeCl3 , FeSO4 , alum, polyaluminum chloride, etc.., to increase the size of suspended and colloidal particles in the feed prior to filtration. It was found that reversible fouling was reduced with coagulation pre-treatment, but the extent of irreversible fouling was unchanged. This can be attributed to the fact that large particles are formed from small particles, and hence, reversible fouling decreases with the use of coagulation. However, smaller particles, which are not coagulated, still remain in the feed and causes irreversible fouling. Factors affecting membrane fouling includes coagulant dosage, pH, nature of dissolved organic matters as well as Ca2+ content of the feed water. 

  5. Hi Hakeem,

    Membrane scaling and biofouling is a major operational concern, and adequate pre treatment is a necessary common practice. However one approach I know of that actually increases recovery and prevents scaling is Flow Reversal RO. Ronit@adedgetechnologies.com

  6. Ensure your pre-treatment processes produce a final water with a low Silt Density Index - don't only rely on the membrane filter, which is a final polishing step.

    The filter needs replacement when the pressure drop reaches the limit permitted for the filter (unless you can wash it separately and replace it for another service - just ensure it is not damaged by the washing process)

  7.   Dear Hakeem, You have proposed a rather vague question with no additional information. What are you filtering out, sand, iron, other? The pre-filters are there to protect the membrane from damage or fouling. The kind of debris the filters remove, the volume of debris, and the volume of water passing through those filters are all variables. You should be able to define a filter change schedule to meet your particular needs, as every system and its supply water are different!  There are different types of filter medias, mesh, and micron sized cartridges, bags, and spin down filters available. But more information is needed to make any recommendations!

  8. The answer depends a lot on the quality of the raw water going to the treatment plant and what quality you are trying to achieve at the discharge. Ground water with calcium hardness should be softened before going to an RO system, and highly turbid water should definitely be pre-filtered.  If your system doesn't have bag or cartridge pre-filters that may be the cheapest and quickest fix to extend RO membrane life.

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