Water and Wastewater Terms Beginning F

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free chlorine

Forms of chlorine that are not combined with any other compounds and are the most effective disinfectants. Three components make up the free chlorine concentration: chlorine gas, hypochlorous acid, hypochlorite ions. Chlorine gas combines with water to form hypochlorous acid, which partially dissociates into hypochlorite ions. Unreacted chlorine gas is usually a very small component. In wastewater, free chlorine reacts with ammonia and organic substances to form combined chlorine.