Which test is used to determine the optimum chemical dosage in water treatment?

• A. BOD test
• B. Alkalinity test
• C. Jar test
• D. Titration

Answer: (C)

Finding the right amount of chemical to add in water treatment is about using a jar test to optimize coagulation and flocculation. In this test, you place water samples in several jars and add varying doses of coagulant (and sometimes a polymer). Each jar undergoes a rapid-mix stage to break up particles, followed by slower mixing to encourage floc formation, and then settling. You compare the results—usually looking at how clear the water becomes and how much sludge is produced—to identify the dose that gives the best contaminant removal with acceptable sludge and cost. This approach accounts for the specific water quality and helps set the optimal chemical dosage for full-scale operation. The other tests don’t serve this purpose: a BOD test measures how much oxygen microbes will demand from organic matter, not dosing; an alkalinity test assesses buffering capacity; and titration determines concentration or acidity, not the optimal dose of treatment chemicals.