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Water Talk

pH Adjustment Chemicals

Anyone have experience using potash (potassium hydroxide) for pH adjustment rather than caustic soda (sodium hydroxide). With our change to sodium hydroxide from Cl2 gas and continued use of sodium hydroxide for increasing our pH we have consistently gone over the 28 mg/L sodium notification level. Wondering if potash should be considered. Also will switching to 50% caustic from 25% help or would we still be adding the same amount of sodium. Thanks

 

4 Comments

  1. cheryl

    Apr. 4, 2016

    Household bleach is basically a solution containing 3–8% sodium hypochlorite and 0.01–0.05% sodium hydroxide. Our treatment hypo is two to two and a half times as strong as household bleach so there is a significant amount of ("caustic") sodium hydroxide in the solution. We were able to reduce our caustic feed because of this and keep our sodium level down while getting our desired pH. If your raw water has a low pH to begin with, then you will have to look at other pH adjusting chemicals like potash, but if your raw pH is around neutral and your treatment (coagulation) process is knocking your pH down, then maybe you could look at backing off of yourcoagulant while still maintaining good treatment and getting the organic removal you need without beating down your pH..try jar testing for coagulating at a 6.70 to 6.80 pH instead of lower. Maybe you've done this and are treating at your optimal dosages, resulting in a low pH that needs adjusting up. I'd try calcium hydroxide before I'd try potassium hydroxide. Yes, it will increase your plant effluent turbidity a little, but as a consumer, I'd rather have calcium in my water than sodium or potassium. I think its cheaper too. I've asked someone who, I think, has used potash to comment..so keep an eye out for it. Good luck.

    Reply
    1. cheryl

      Apr. 4, 2016

      Another comment from coworker "Your target pH would be best at 7.4 to 7.5. Ideal balance between corrosion control and the effectiveness of hypo. At 7 hypo is almost 100% acid form and much more powerful disinfectant than at pH 8 when it is almost all in the effective ion form."

  2. Dave

    Apr. 1, 2016

    Ooops...I meant our change to sodium hypochlorite from Cl2 gas. This had added more sodium to our treated water

    Reply
    1. Cheryl

      Apr. 5, 2016

      Contact: jsimpanen@aquarionwater.com That's Judy Simpanen. She manages Mystic Division and has used potash at her plants.

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