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How does antiscalant work in RO?

What's the difference between Antiscalant  and Coagulant?

Can Excessive Antiscalant Foul the Membranes?

Is there a chemical reaction between Antiscalant & AM-88?

Is there a chemical reaction between Flocon260 and a cationic coagulant?

 


How does antiscalant work for a reverse osmosis water treatment application?


An antiscalant is a pretreatment injected into the feedwater before the feedwater enters the RO membranes. Its presence delays the reaction between calcium magnesium and bicarbonate. This results is scale not forming as the water is being purified by the RO. As the duration of the water in the membrane system is relatively short during the treatment, scale formation is prevented.

* Click here for more details and ordering information on Antiscalant 



What is the difference between Flocon 260 Antiscalant/Dispersant and Coagulant?


Flocon 260 Antiscalant is used to keep water hardness from precipitating during reverse osmosis treatment of water.  The antiscalant also contains a dispersant which prevents iron or aluminum in water from reacting with the antiscalant and making it ineffective.

Coagulant, on the other hand, works just the opposite.  It is used to cause the suspended solids that may be present in water to coagulate and settle out.  By coagulation we mean that the very fine particles of suspended matter come together to become a larger cluster which will settle more easily than the smaller suspended particles.  The fine suspended particles in the water normally have an electrical charge.  The coagulate facilitates the removal of the charge, allowing the particles to coagulate and settle.   In short, coagulant is used to remove suspended solids.

In membrane process, coagulants are used only in rare situations.  Many coagulants can be harmful for the membranes.  Coagulants are commonly used in municipal water treatment systems.

In short:  Antiscalant is used for hardness, which is dissolved in the water, and coagulant is used for suspended solids.

* Click here for more details and ordering information on Flocon 260 Antiscalant/Dispersant 



Can excessive Antiscalant foul the membranes?


Excessive antiscalant can cause fouling of the membrane.  This fouling can be cleaned by flushing the membranes with water at a pH of 2-3.



Antiscalant (organo-posphonate) and AM-88 (sodium meta-bisulphite for dechlorination) are sometimes both used for pretreatment.  In this case, is there any chemical reactions which would cause fouling of the membrane?

There is no chemical reaction between the two chemicals.


We are dosing a cationic coagulant before sand filter in our seawater desalination RO pretreatment system. Meanwhile, Flocon 260 (anionic) is dosed after sand filter. I wonder whether these two chemicals may react and result in fouling on RO membrane.

Flocon 260 is typically not compatible with cationic polymers.  If we knew the exact polymer you are using, we would be able to give a definite answer.  There are alternative Antiscalants that may be used (FLOCON 40), but in order to determine whether this will work, we will need a complete water analysis.  The FLOCON 40 does not offer much scale control for most of the 'sulfite' scales.


What is the dose rate and method of injection for Flocon antiscalant?

Dose Rate

The amount of Flocon required to inhibit scale formation depends on the degree of supersaturation of the insoluble salts at the point of highest concentration in the system.  The degree of supersaturation in turn depends on the concentration of the ionic species in the feedwater, the overall salinity of the feed, the temperature of the feedwater, the percentage of the feedwater recovered as permeate and the type of membrane used for the application.

 

FLOCON Solution Concentration* %

Amount of Solution to be Injected per 1,000 Gallons of Feed Water, In Gallons

3 ppm

5 ppm

100

0.003

0.005

50

0.006

0.010

20

0.015

0.025

10

0.030

0.050

* Use soft water or RO permeate to mix with Flocon.

Dose Method

Flocon should be added to a membrane system prior to the final cartridge filter.  If media filtration or activated carbon is used, Flocon should be applied after these treatment stages.

 

Flocon should be delivered by dosing pump from a dilution tank, direct from the drum or from a bulk storage facility, into the feedwater at a rate that is determined by the size of the membrane system, the recommended dose rate and the delivery range of the dosing pump.  It is recommended that the dosing pump be adjusted by the stroke length, while maintaining stroke frequency at a high level as possible to achieve even distribution of the Flocon in the membrane system feedwater.

 

CAUTION  - Biological Activity:

Flocon contains a preservative that is effective up to a dilution of 1 part Flocon to 15 parts of system permeate water.  General periodic cleaning of the dosing system is recommended as part of the planned maintenance program.

   

 
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All Content on this site is  intended for informational purposes for experienced water treatment professionals only.  Applied Membranes, Inc. does not assume any liability for any damages caused by the misapplication or misinterpretation of any of the information contained on this website.
Applied Membranes, Inc. 2007