Includes bibliographical references (p. 86-88). "September 1981." "EPA-600/2-81-169." "PB82-102336." "Contract Nos. 14-12-150 and 68-03-2745." "Project Officers Albert D. Venosa, Irwin J. Kugelman, Wastewater Research Division, Municipal Environmental Research Laboratory."

A study of dechlorination was conducted in the County Sanitation Districts of Los Angeles County to determine the utility and efficiency of the sulfur dioxide method and to provide a cost-effectiveness comparison of sulfur dioxide and two other methods of dechlorination, namely, activated carbon and holding tank processes. Study objectives were accomplished through three main phases of work: literature review, pilot-scale testing, and full-scale evaluation in the field. The pilot-scale testing indicated that no degradation of physical and chemical water quality occurred in the dechlorinated effluents from any of the three dechlorination processes investigated. However, a one to two order of magnitude increase in total coliform density in the 10-minute samples following dechlorination was commonly observed among the three dechlorination processes. The increase seemed to originate from contamination by the existing microorganism communities in the dechlorinated effluent rather than from the reactivation of injured bacterial cells. The field survey involved the canvassing of 55 operating plants in California by mail, telephone, and site visits to selected facilities. Although overdosing of sulfur dioxide was frequently necessary to meet the residual chlorine discharge standards, most installations found pH adjustment and reaeration of the dechlorinated effluent unnecessary. Process cost estimates indicated that sulfur dioxide process is the most cost-effective method for dechlorination.