Water and Wastewater.com Help Forums - Variation in SDI of Treated water after storage.

Gururaj YaBB Newbies Offline I love Water and Wastewater.com Posts: 23 Company or Organization: GIPL Bangalore	Variation in SDI of Treated water after storage. Jul 03^rd, 2012, 5:22am Dear All, i am having one query regarding SDI value of RO plant, One of Waste water treatment plant having pre treatment ,UF followed by RO. Online SDI of UF PERMEATE is < 5 and after 1hr storage SDI more than 5 after 12 hrs SDI of sample not countable. Let me know reasons of variation in SDI after storage. GURURAJ.
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grrun God Member Offline WaterandWastewa ter.Com is the best! Posts: 3525 Pekin, IL Gender: Company or Organization: Freelance Environmental Engine	Re: Variation in SDI of Treated water after storage. Reply #1 - Jul 3^rd, 2012, 11:19am My guess is that the UF does not remove water soluble substances and that exopsure to air (possibly CO₂) may cause some precipitation resulting in an increase in SDI. grrun
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Gururaj YaBB Newbies Offline I love Water and Wastewater.com Posts: 23 Company or Organization: GIPL Bangalore	Re: Variation in SDI of Treated water after storage. Reply #2 - Jul 4^th, 2012, 6:47am Thanks sir, I could not get your point water soluble substance removal from UF. sir please explain this suspect in detail or any other parameters to be checked.
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grrun

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Re: Variation in SDI of Treated water after storage.
Reply #3 - Jul 4^th, 2012, 9:06pm

Water soluble substances means anything that dissolves in water. Souble salts such as sodium chloride, calcium and magnesium salts, etc. etc. These substances will readily pass through the UF membrane. Now some of the ions that pass through the UF membreane can react with CO₂ (absorbed from the air) and can precipitate out of solution to raise the SDI. If your RO system cannot tolerate the increased SDI, then you may have to do something to prevent the absorption of air during storage.

grrun

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Gururaj

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Re: Variation in SDI of Treated water after storage.
Reply #4 - Jul 4^th, 2012, 10:54pm

Dear sir,

Thanks for valuable inputs. In our system there is no any chance of air absorption only 15 min RT vessel for permeate storage. But slime layer being observed on membranes and Cartridge filter after every 20hrs operation. I agree with you soluble salts reacts with CO2 and make ppt. i am facing problem of sticy ppt layer on cartridge filters before RO and part of RO membranes and Circular cuts of membranes in short period. kindly give me suggestions on this observation.

Gururaj

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grrun

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Re: Variation in SDI of Treated water after storage.
Reply #5 - Jul 5^th, 2012, 4:03pm

While UF generally prevents the passage of bacteria, bacteria, and other bioorganisms can either be introduced or grow from low concentrations in the permeate. There are some "dipsticks" that can identify some of these microorganisms and approximately determine their concentrations. Now, unless you disinfect the permeate tank periodically, my guess is that you may have a fungus clinging to the walls of the permeate tank that is continuously reinoculating the permeate. Perhaps Victor Santa Cruz can assist you in solving this problem.

Sorry that I couldn't have been of more assistance.

grrun

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JB

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Re: Variation in SDI of Treated water after storage.
Reply #6 - Jul 6^th, 2012, 11:45am

Dear Gururaj

Helo

SDI is a measure of how much silt is present in the feed or effluent. Dissolved solids do not contribute to SDI. Moreover you do use 45 micron filter paper during SDI which does not hold dissolved ions.

The higher values of SDI may be due to the use of sub standard micron filters or it could be due to the erosion of walls of treatment plant plaster etc. By the way how old is the plant you are operating. Take a sharp MS rod and poke it at all civil structures next to the treated water line and see if any of the walls have got damaged. If you find any black color oozing out from any of the walls that could be the culprit. This is one of many other reasons of high SDI values in the treated water.

regards

JB

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Jeff Naumann God Member Offline I love Water and Wastewater.com Posts: 1133 Torrance, California Gender: Company or Organization: Jeff Naumann & Associates	Re: Variation in SDI of Treated water after storage. Reply #7 - Jul 6^th, 2012, 6:04pm I always thought that SDI referred to Reagan's "Strategic Defense Initiative?"
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Gururaj YaBB Newbies Offline I love Water and Wastewater.com Posts: 23 Company or Organization: GIPL Bangalore	Re: Variation in SDI of Treated water after storage. Reply #8 - Jul 8^th, 2012, 10:38pm Thanks for response JB, Plant is only one year old, there is not Civil tank in between UF and RO.This type of fouling we observed from very early stage of observations. Gururaj.
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grrun God Member Offline WaterandWastewa ter.Com is the best! Posts: 3525 Pekin, IL Gender: Company or Organization: Freelance Environmental Engine	Re: Variation in SDI of Treated water after storage. Reply #9 - Jul 9^th, 2012, 2:46pm Your description of the filter and membrane plugging led be to believe that the problem was primarily the result of biological growth rather than a crystaline precipitate such as silt. I'd check some of the slime in a laboratory for carbon content. grrun
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