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

 

[GHartmann]

Please refer to this link:

http://www.eng-tips.com/viewthread.cfm?qid=375669

 

[bimr]

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

 

[wwtp2014]

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

 

[bimr]

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.

 

[bimr]

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

 

[wwtp2014]

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

Thanks

 

[bimr]

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.

 

[wwtp2014]

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

 

[bimr]

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.

 

[wwtp2014]

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

 

[bimr]

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

 

[wwtp2014]

please see attached our water analysis and kindly let me know your comments & recommendation

Thank you

 

[bimr]

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.

 

[dfmorvan]

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

 

[wwtp2014]

we use RoQuest3000 from Avista as coagulant (please see attached file)
and i think the iron maybe comes from the tanks because we found them very corroded

Thanks & Regards

 

[dfmorvan]

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

 

[wwtp2014]

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

 

[wwtp2014]

Attached 5 micron cartridge filters pictures after sand filter and before membranes

Regards

 

[bimr]

The picture seems to be corrupted, can you repost?