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Frequent CIP

Frequent CIP

Frequent CIP

(OP)
Dears,

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

Regards

RE: Frequent CIP

If that is the case, then you probably need more pretreatment of the incoming water.

RE: Frequent CIP

(OP)
Thank you GHartmann

what kind of pretreatment shall i use because SDI now more than 5 and i already use sand filter with Coagulant

Thanks

RE: Frequent CIP

I have seen installations where filters are used in series. The first filter is operated at a higher throughput and coagulant is used. The second filter is a polishing filter and is operated at 3 gpm/sq ft.

You should be using a multimedia filter instead of sand filter.

I have also seen installations where sodium cation water softeners are used as pretreatment. These are more appropriate if you have a high sodium water.

RE: Frequent CIP

One more thought. Have you considered that the coagulant may be causing the fouling?

RE: Frequent CIP

(OP)

I have Online oxidation of H2S by injection of air before sand filters Coagulating injection after the air injection

Thanks

RE: Frequent CIP

Hydrogen sulfide is difficult to remove and typically takes several hours to air oxidize. Would suspect that the hydrogen sulfide is not fully oxidized prior to the RO system.

RE: Frequent CIP

(OP)
I think you are right so what is your suggestion to use chlorine oxidation or to change the location of Air injection with using static mixer to improve contact between the air and the water and for coagulant do you think we should stop inject it or to change another brand to avoid fouling ( because SDI still more than 5 with coagulant injection )

Thanks

RE: Frequent CIP

Air oxidation might take more than 2 hours while chlorine oxidation takes 10 minutes.

If the hydrogen sulfide is not too high, chlorination would work. You may have to remove the any excess chlorine depending on the RO manufacturer requirements.

Hydrogen sulfide is difficult to remove. If the level is high, then chlorination will be expensive. It takes up to 8 atoms of chlorine to oxidize 1 molecule of hydrogen sulfide.

RE: Frequent CIP

(OP)
Dear bimr
thank you for your answers. what about if we stop inject air before sand filters and we backwash sand filters with high dosage of chlorine

Thank you

RE: Frequent CIP

You will need an online continuous addition of chlorine, not just with the backwash.

RE: Frequent CIP

The oparameters of concern are iron and phosphate. The iron should be oxidized with air and removed by the filter. That does not seem to be happening. Phosphate is more difficult to remove and may cause problems with the RO.

RE: Frequent CIP

Bonjour wwtp2014

It seems your are on brackish well water, probably not too far from the sea ?
I'm wondering at your finding of iron in the permeate.....leaking or damaged membrane maybe.
Are you using ferric chloride as a coagulant ?
High SDI could come from the iron, what is the look of the SDI filter and where do you sample it ?

regards

RE: Frequent CIP

Hi

it would seem the coagulant you use uis a bit underrated for the NTU you have. 14 NTU is quite high and the spec sheet says only 2 NTU max.....
The high level iron seems to be a problem (linked to corrosion by chloride?), but you have no free chlorine. Anyway considering the pH, the iron should be oxydised (ferric) and so should be captured on the sand filter (if the filtration velocity is small enough) or on the cartridge filter.
A question : what causes according to you the frequent cleaning need? Is it biofouling or scaling ? There could be some scaling because the permeate conductivity for RO 1 is higher than for RO 2.
also you seem to be running the 2 units at different conversion rate.

the best thing to do would be to describe the totality of your installation (flowrates, diameter of the sand filter, type of cartridge filtration, hydraulic settings, antiscalant used and the like).

I suspect some scaling or membrane leak (higher conductivity of the permeate on RO1). Probably also some particulate fouling due to the high NTU.
what is your cleaning sequence and are the results good ?

regards

RE: Frequent CIP

(OP)
Good Day All,

please let me know your comments about the results of Iron analysis which have been done on 07 Jan 2015 .

Process (sample taken before process tank) ----- 0.12mg/l
Filtrate water (Sample before filtrate tank) ----- 0.04mg/l
Raw water (sample after raw water tank) ------ 0.04mg/l
Well water (sample after well tank) ------ 0.06mg/l

I think our problem is H2S or Becteria
also i like your comment about Ryznar index of the water which is 3.48 and Larson index of the water is 6.869


Thank you

RE: Frequent CIP

The picture seems to be corrupted, can you repost?

RE: Frequent CIP

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.

RE: Frequent CIP

(OP)
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

RE: Frequent CIP

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.

RE: Frequent CIP

(OP)
Good Day All,

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

Thank you

RE: Frequent CIP

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.

RE: Frequent CIP

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
www.water-eg.com

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