I am working on an industrial water treatment project. In my study I have found that the industry is using NaClO(sodium hypochlorite), HCl(hydrochloric acid), SMBS(sodium metabisulfite) and antiscalant to treat water before reverse osmosis is carried out. My question is, what is the actual use of HCl in the process and its effect on the treatment?
Hello.
It is used to remove alkaline scales and metal oxide deposits from membranes and pipes, and to control the pH of the feed water eliminating (or reducing the risk) of deposition of some salts (such as sulfates). This is basically it.
Cheers
Mário Silva thanks a lot. I would also like to know what are the ill effects of over dosing the water with HCl?
If the dose is too small, then you will not get the desired effect.
If the dose is too big, then you can get corrosion and even destruction of piping, membranes, valves, etc...
Industry do this is to control pH. When NaOCl dissolves in water it is alkali. HCl is used to control the pH to make the disinfectiong property favourable.
https://www.tpomag.com/editorial/2013/12/understanding_sodium_hypochlorite_wso
A big factor for membrane fouling is biological fouling, physical fouling and chemical fouling. Biological fouling could be controlled by adding disinfectants. (In this case a blend of HCl and NaClO) however noting that the NaClO when dissolved in water becomes alkaline in n
NaOCl + H2O = OCl¯ + OH¯
Industry do not use Chlorine as a disinfectant, as it chlorine has been known to attack the membrane surface. Plus chlorine gas being volatile and requires chemical safety handling makes it a less ideal disinfectant. Which brings to point 2. When NaClO reacts with HCl it produces chlorine gas. Thus the control of HCL is very crucial to prevent membrane damage.
As for the control of chemic fouling, like what @mario mentioned the addition of HCl also fulfils this purpose. It is for control of alkline scales.
The higher the dose the more the corrosive effect and chlorine gas production. The lesser the dose the least effective the disinfectant will be. So It is important to control the dosage properly. Hope this helps.
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