Dear Nikolay,

Desalination of sea water - deep SWRO.Z filters provide effective protection of water reverse osmosis membranes sea, for greater efficiency of the membranes and a long service life.

With my best regards

Prof. Bachir ACHOUR

Dear Mr. Nikolay

In most of the desalination plant, Pressurized Sand filter is used as final filter media in Pretreatment, Sand filter may remove particles from 10-25 microns. Remaining small suspended particles removed by Cartridge filters( conventional Cartridge filter removes up to 5 micron in Desalination Plant), therefore it has benefit to use Cartridge Filter for Desalination RO Plant.

Hi NIkolay  It is my experience that you need to have several pre-treatment steps for Sea Water Desalination. The first can be heavy sand filtration, followed by tight Ultrafiltration.  I would avoid actual cartridge filtration and any other  form of Microfiltration.   Ceramic cross flow filters (wrongfully called membranes) in particular are notorious for leakage that cause frequent washing requirements of the RO modules.

Your original question is in error.  There is no need to treat RO water with filters, but there may be a need for Ozone disinfection when the water is stored for some time.

Hi Nikolay! As you probably already know there are no large seawater facilities that use cartridge filters downstream of an ultrafiltration process (and I will assume it is a coagulation or softening combined UF pretreatment process); at least to my knowledge none exist.  I do know (and most likely you also knew this as well)  that there are large brackish surface water facilities in the USA that do employ a coagulation or softening-UF-Cartridge Filter pretreatment combination ahead of the RO process (e.g. Granbury TX), but not at any of the large seawater facilities I am aware of on the planet. If you do find any such case please let me know, as I also would be interested as to why one would do this (assuming at worst case you have 0.1 NTU entering the membrane feed channel downstream of the UF process-more likely 0.03 NTU if its a well designed and operated coagulation-UF process). Steve.

Example of SWRO plant with membrane pretreatment which uses CF after pretreatment is the Perth II SWRO (Southern) plant is Australia.  In this case CFs are found beneficial when solids are released into the filtrate as a result of occasional fiber breaks, which are typically caused by pressure surges related to power interruptions. 

Thanks Nikolay - interesting to note but perhaps an expensive way of dealing with a UF operational issue related to fiber breakage. Not sure what vendor supplied the fibers but its seems like overkill. How much turbidity can one expect from "occasional" fiber breaks? I am not sure how beneficial this would be; perhaps there are proven economics to show this value? I remain skeptical as to why you need CF's downstream of UF. Maybe for insurance only? I personally have a hard time believing a few broken fibers result in massive damage to SWRO elements. Thanks for the information!

Yes, they do an it is a big mess...it depends on the membrane strength and how many breakages you end up having - which depends on the strength of the membrane fibers.  I cannot name names but some of the most popular membrane elements used for seawater pretreatment has caused significant fouling problems in full-scale plants.

Next time I see you we can discuss this in person. Remain very surprised about this.... certainly would support the case for conventional surface water pretreatment for SWRO then, perhaps?. Thanks Nikolay.