Incompleteness of wastewater dechlorination

Article abstract of DOI:10.1021/es00004a023

Dechlorination by sulfur dioxide or other S(IV) compounds is employed to protect aquatic wildlife from toxic residual chlorine in wastewater treatment plant effluents. Tests at two wastewater treatment plants show that dechlorination removes 87-98% of residual chlorine but that a remainder, which exceeds regulatory limits, is very slowly reduced. Judging from kinetic evidence, chlorinated secondary organic amines and peptides probably contribute to S(IV)-resistant residual chlorine. Most of the S(IV)-resistant fraction is extractable into octanol. Its hydrophobic character suggests that this fraction may be harmful to organisms in receiving streams. S(IV)-resistant residual chlorine has been overlooked previously because the dechlorinating agent interferes with standard analytical methods for total chlorine. (Authors)