Pre filter for RO Membrane

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Is there any prefilter available in the market for RO (other than Micron cartridge filter)? 

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8 Answers

  1. The primary goal of water entering an RO is to have an SDI of less than 5, but much better if it is less than 3 for various reasons that I don't talk about here. Now, what counts is therefore to reduce the suspended solids to the minimum possible, in particular the colloids present in the water. Putting cartridge filters reduces SDI but must therefore be measured! And also if the water is dirty there is the risk of having to change the cartridge filters too frequently ...
    Also do not underestimate that there are several dissolved salts that can quickly go into over-saturation concentrating in the permeate (an example is Barium which, if present even in small quantities, can generate a precipitate of barium sulphate, clogging the membranes).
    That said, returning to what was said at the beginning, a solution could be to insert MF or UF membranes before the ROs if you can't get a good SDI before the RO. Both UF and MF technologies rely on size as the primary factor determining which suspended solids and high molecular-weight dissolved organics are retained by the respective membranes.
    Due to the microporous nature of MF and UF membranes, the
    pressure required to drive water through them is significantly lower than for RO membranes, typically less than 100 psi.

    1 Comment

    1. Obviously you will also need to dose an excellent antifoulant before entering the membrane since with a Recovery of 75% the brine water concentrates 4 times and this also implies massive precipitation phenomena of various inorganic salts, in particular calcium carbonate. , but also Iron, Sulphates, Strontium, Phosphates etc represent threats to be controlled

  2. Dear Sir

    A lots if Products you need in the market...we have supply water then go to softener...then go to RO....For me right now which still be the big problem is brine water from RO which contains high salt...may be more than 40 g/l...How to solve this...I have found the Crystalliization method...Hopefully it will be work...because in Thailand we don't concern in this point but it is coming up to be the big problem in near future...

    2 Comments

    1. Hi Aggasit, there is lot of evaporation methods are available (multi effect evaporator, Mechanical vapor re-compressor followed by dryer like Agitated Thin Film dryer etc,.) to treat the RO reject water. 

    2. It is normal for RO reject water to have high salts which are rejected salts by RO operation.You can make a solar pond to dry up the salts.Or you can mix it with other effluent from other plants and use it for deep well injection after carrying out proper compatibility study.There is also option of mixing it with municipal sewage in calculated manner.

  3. Hi Sunil, I am happy to discuss your application needs yuri@baleen.com Supporting information at www.baleen.com Rgs, Yuri

    1 Comment

    1. Hi, Yuri. we are having two stage RO (9 m3/hr & 3 m3/hr) in our ETP. Recently we replaced the RO membranes, hence i am looking for some kind of pre filter in addition to Micron cartridge filter which can give additional safety to the RO membrane.

      1 Comment reply

      1. Thank You Sunil, for such low flows you could use just one of our small to mid size units at between 25 to 50um (for near absolute algae/grit removal) as a 'non-replaceable' prefilter/barrier to your finer 'replaceable' cartridge filtration. Does your application involve seawater or other process water stream? Regards, Yuri

  4. The most important aspect of RO operation is pretreatment, which includes pre-filtration (normally micron and or submicron) filtration, chlorine removal and polymer precipitant control. Skip these steps and you will likely be replacing membranes,   

  5. There are quite a few manufacturers of various types of RO "pre-filters".  The two most important considerations are the desire final feed water quality to the RO and the flow rates.  Most manufacturers recommend a minimum change-out period of six months.

  6. Micron cartridge filters are required to reduce SDI. Self cleaning filters are available but they  are not suitable to reduce SDI.

  7. The membrane manufacturer quite often specifies the filter immediately prior to the membranes regardless of the pretreatment upstream as a requisite of the membrane warranty.  It is more commonly considered a safety filter or filter of last resort in case there is a huge breakthrough of something that would absolutely finish the membranes.  It is a bit of a holdover from the very first RO systems.  Bag filters have been used and at least one plant employs diatomaceous earth but even then cartridges were stuck in front of the membranes.   Several plants, i.e. Malta and the Caribbean had to change out the cartridges before they became rotten and so the material of the cartridge became a factor.   At least one large plant employed their own cartridge winding machine on site.   One site in KSA employing very enterprising Phillipino operators, designed a "backwashing" machine to reuse cartridges--not good.  Another plant in Iran found the operators "knitting" with the strands.    Suggest negotiating with the membrane supplier and based on the pretreatment system employed, perhaps going to a "looser" cartridge such as 25 or 50 micro instead of the usual 10 micron.