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Particulate, colloidal, and some organic foulants contained in water can be removed successfully using microfiltration (MF) or ultrafiltration (UF) pretreatment. MF/UF is a membrane used to treat water with about a 10,000-300,000 molecular weight cutoff. The membrane rejects organic macromolecules, viruses, and asbestos. The membrane operates by sieving.

Depending on the force (pressure or vacuum) driving the filtration process, membrane pretreatment systems are classified as pressurized (pressure driven) or submerged (vacuum driven). Depending on the size of the membrane pores, the membrane systems used for pretreatment are classified as microfiltration (pores of 0.04 μm) or ultrafiltration (pores of 0.02 μm). While earlier generations of MF elements had pore sizes of 0.1 to 0.2 µm, at present the difference between MF and UF element pores is only a factor of 2 to 3.

For these systems coagulation is typically applied when the saline source water contains particles of natural organic matter with a high negative charge that can be coagulated easily and removed via filtration, when heavy algal blooms or oil spill events occur.

There are some of the large seawater desalination plants in the world with membrane pretreatment in operation at present. The application of membrane filtration for saline water pretreatment is gaining a wider acceptance. The number of medium and large desalination plants with membrane pretreatment increased from less than half a dozen in 2002 to over 40 in 2011.

Practical experience has shown that membrane pretreatment alone may not always provide a competitive solution, especially for challenging source saline waters of high organic content and biofouling potential. A number of desalination plants with relatively shallow intakes and source water of high turbidity and organic loads (e.g., Shuwaikh, Beckton, Kindasa) have an additional pretreatment step prior to the membrane filtration system in order to cope with these source water quality challenges. However, in most installations worldwide, membrane filtration is the only pretreatment system prior to reverse osmosis desalination.

 


 
 

This product support by Avin Palayesh Niroo (Fan Niroo Subsidiary)