5 replies to this topic

[modianurag]

Can anyone please list down the reasons for increase in turbidity of cooling water?

Filtration is an effective method to keep the turbidity in check, but is there any approach by which we can attack the root cause of increase in turbidity?

[P.K.Rao]

If you are dozing Sodium Hexametaphosphate to prevent scale  formation, turbidity may appear in the long run because sodium hexa metaphosphate hydrolyzes to sodium ortho phosphate which reacts with calcium salts present in water and gives calcium ortho phosphate which is not soluble in water and gives turbidity when in small quantities and precipitates out in the basin or circulates. Filtration does improve.

[shvet]

 but is there any approach by which we can attack the root cause of increase in turbidity?

 

A root cause in turbidity is makeup water quality. At first you should find out what is the nature of turbidity then choose appropriate method. You can control turbidity via makeup water or side-stream treatment.

 

1. Clarification by coagulation, flocculation and sedimentation in sludge-contact clarifiers or tilted-plate (or parallel plate) clarifiers. The first one is prefrered because thay are more forgiving to fluctuations in water quality and flowrate but second one requires less space. If you have no limitations on sludge contaminants you can use alum (Al2(SO4)3) or iron salts. If you have - contact aluminate and organic polymer coagulant vendors.

 

2. Cold or hot lime softening (can be combined with clarification) can remove turbidity by removing SiO2 via adsorbtion on precipitate (sludge) up to 5 NTU

 

3. Filtration on in-depth filters (antracite coal + sand) can remove turbinity up to 0.5 NTU. Cartridge filters (usually polymer) can control turbidity but replaceable cartridges can be expensive. Microfiltration with backwashing can remove turbidity up to 0.1 micron but you should contact vendor to find out how much backwashing and chemicals consumption are required.

Edited by shvet, 14 August 2016 - 12:52 AM.

[modianurag]

If you are dozing Sodium Hexametaphosphate to prevent scale  formation, turbidity may appear in the long run because sodium hexa metaphosphate hydrolyzes to sodium ortho phosphate which reacts with calcium salts present in water and gives calcium ortho phosphate which is not soluble in water and gives turbidity when in small quantities and precipitates out in the basin or circulates. Filtration does improve.

sir, how do we check for if this phenomena is happening as Ca hardness is within limits(<300). Is there any other parameter which can help identify root cause? Or is it an industrial practice to go for filtration if NTU is high without actually eliminating the root cause?

[P.K.Rao]

Even if the calcium hardness is within the limit, trisodium phosphate will react to form calcium phosphate.  

 

2Na3(PO4) + 3CaCO3 = 3Na2CO3 + Ca3(PO4)2

 

When in small quantities, Ca3(PO4)2 gives turbidity and in large quantities it precipitates.

 

Check cooling water basin bottom for any sludge of Calcium Phosphate.

 

Or, take adequate quantity of cooling water and coagulate the turbidity by dozing Alum in suitable quantity. Filter off the coagulated precipitate and analyze for calcium and phosphate.

[breizh]

Hi ,

Take a look at Langelier and Riznar indexes , this will help you to understand the quality of your water ( Corrosive , ability for deposit )

 

http://www.lenntech....ndex/ryznar.htm

 

Hope this helps .

Breizh