Free available chlorine in wastewater treatment consists of which components?

Free available chlorine in wastewater treatment is a critical parameter as it represents the amount of chlorine present in a form that can effectively disinfect water. The correct answer identifies free available chlorine as consisting of chlorine gas, hypochlorous acid, and hypochlorite ion.

Chlorine gas is the elemental form of chlorine that is often used for disinfection. When chlorine gas is dissolved in water, it forms hypochlorous acid, which is a powerful disinfectant. Hypochlorous acid can also dissociate to form the hypochlorite ion. Both of these components, hypochlorous acid and hypochlorite ion, are responsible for the antimicrobial properties of chlorine in wastewater treatment processes.

The presence of these three components helps in achieving effective disinfection and maintaining the necessary chlorine residual in the treatment process, making it vital for controlling pathogens and ensuring effluent standards are met.

In contrast, other options include substances that do not contribute to the free available chlorine measurement in the same manner. For instance, phosphoric acid and phosphorus compounds are not forms of chlorine but rather additives that might modify other chemical properties in treatment processes. Chlorine dioxide and chloramines, while also used in disinfection, represent different chemical forms and are