Frequent CIP

[wwtp2014]

Dears,

we do frequent CIP to our RO's due to Delta p high please i need your advice ( SDI > 5)

Regards

 

[wwtp2014]

Thank you bimr

please see Attached 5 micron cartridge filters picture after sand filter and before membranes. And these filters we change them Frequently


Regards

 

[wwtp2014]

Attached 5 micron cartridge filters picture after sand filter and before membranes. And these filters we change them Frequently

 

[bimr]

It looks like the crud is iron.

What is the capacity of your system? Is this well water? What type of filter? How long in service?

As I mentioned earlier, your pretreatment system needs to be more robust. It is optimistic to expect an online oxidation/filter to remove the hydrogen sulfide. The filter may be allowing the iron to pass through as well. Perhaps the iron is not being completely oxidized prior to the filter or the filter media is in bad condition.

 

[wwtp2014]

45 m3/hr. well water.
40.5 m3/hr to reverse osmosis with recovery 74%, 30 m3/hr treated water

please what do you mean by type of filter

kindly did you see Iron analysis in previous post

How Do I pretreat H2S on feed water before R.O. System ?


Thank you

 

[bimr]

Based on what you have posted so far, your best option is to chlorinate at a pH of less than 6.4. This pH will ensure that the sulfides are completely oxidized to sulfate. The sulfides will not oxidize at higher pH's

You will probably have to remove the excess chlorine with sulfite since the membranes can not tolerate the chlorine.

You should feed the chlorine as far upstream as practical since the reaction time to oxidize the sulfides to sulfates is 10 minutes or less. The iron should also be completely oxidized at that point.

Regarding the filter, I was just wondering if the material is passing through the filter or being oxidized after it goes through the filter. You need a quality filter to remove the oxidized material.

You can prove the reactions with some simple lab tests.

 

[wwtp2014]

Good Day All,

Does Cartridge filter reduce SDI and please which type or brand i should use to minimize membrane fouling

Thank you

 

[bimr]

Anything that removes particulate including a cartridge filter will give you a lower SDI.

Depending on the raw water quality, the pretreatment process may consists of all
or some of the following treatment steps:
• Removal of large particles using a coarse strainer.
• Water disinfection with chlorine.
• Clarification with or without flocculation.
• Clarification and hardness reduction using lime treatment.
• Media filtration.
• Reduction of alkalinity by pH adjustment.
• Addition of scale inhibitor.
• Reduction of free chlorine using sodium bisulfite or activated carbon filters.
• Water sterilization using UV radiation.
• Final removal of suspended particles using cartridge filters.

Cartridge filters, almost universally used in all RO systems prior to the high pressure pump, serve as the final barrier to water born particles. The nominal rating commonly used in RO applications is in the range of 5 - 15 microns. Some systems use cartridges with micron ratings as low as 1 micron. There seems to be little benefit from lower micron rated filters as such filters require a high replacement rate with relatively small improvement in the final feed water quality.

 

[sbush]

Silt density index is a measurement of the colloidal suspended matter in the water supply. Colloidal matter is not filterable by sand filter alone or cartridge filter or softener or carbon filter. Some coagulants can be effective in some cases, but not every, when used in conjunction with sand filter.

WWTP 2014 is on the right track, in my opinion, with his suspicions that hydrogen sulphide or bacteria or both could be the culprit. Hydrogen sulfide is very often colloidal and partially ionized. When hydrogen sulfide is present, it very likely to find Sulfate reducing bacteria also. Both can affect higher SDI readings.

Aeration will only remove hydrogen sulfide gas, but will not remove any colloidal or ionic sulfur which in turn bacteria feed on. Until you can substantially reduce the hydrogen sulfide and bacteria, you will continue to experience heavy loading on the filters and plugging of the membranes.

In some cases, the sulfur bacteria resides within the well casing and intake. This condition may require shock treatment with a strong disinfectant, typically recirculating for several hours. When the well is clean, you might consider using a strong dose of chlorine ahead of a carbon filter to remove hydrogen sulfide and control bacteria. However, there may need to be frequent replacement of the carbon media. There are other options.

If you're still having a problem, I would contact the membrane manufacturer and request their input regarding hydrogen sulfide reduction and sulfate-reducing bacteria control with respect to their membranes. The membrane manufacturer is the best suited professional to advise you on a course of action, in this particular case.

S. Bush

http://www.water-eg.com