Welcome to Water Talk! This is a place where we offer to share ideas, and exchange information. But most importantly, this is where to come for help. Questions pertaining to water treatment can be posted so that fellow operators and other water industry professionals may respond with their experiences and recommendations. We encourage all to participate and weigh in on the conversations. There’s a lot of expertise and experience out there that needs to be shared. 

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Water Talk

Optimum pH for Coagulation

Now that my water is getting colder, should I target a lower pH (6.0 to 6.5) or a higher pH (6.5 to 7.0) for optimizing organics removal using alum? Thanks for your help.


  1. Stephen Olson

    Jan. 12, 2016

    Based on my experience, in cold water, alum typically works better for NOM removal in the pH range of 6.5 to 6.8, and for warm water a pH range of 6.2 to 6.5 is best. PACl is typically less sensitive to water temperature, but a pH from 6.5 to 6.8 works best. Since all waters are different, it's best to verify with a jar test.


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