Dechlorination is used to remove residual chlorine before effluent is dispersed into the receiving environment. The dechlorination approach currently available is the use of tablets made typically of sodium bisulfate. These tablets are stored in a stack tube and placed in the contact basin. Effluent passing through the contact basin is treated by the dissolving tablets in the same manner as described for tablet chlorination.

Chlorine residual is generally utilized as an indicator of appropriate disinfection. Chlorine residual is measured in the pump tank to determine if a sufficient quantity of chlorine is being dosed into the wastewater. Chlorine residual should be maintained at a level less than 0.2 mg/L. Growing awareness and understanding of the effects of chlorine on the environment are prompting many companies to optimize the performance, reliability, and safety of their chlorination products.

Chlorine residual tests can evaluate proper performance of the dechlorination system. When utilizing a dechlorination system, there should be no chlorine residual measurable in the effluent.