Application of a Ferric Chloride System to Simultaneously Control Biogas Sulfide and Enhance Activated Sludge Settling

The Thorn Creek Basin Sanitary District (TCBSD) provides wastewater treatment services in south suburban Chicago. The TCBSD operates a wastewater treatment facility comprised of preliminary treatment, primary settling, activated sludge treatment, sand filtration, chlorination, and dechlorination. Primary and waste activated sludges are anaerobically digested and land applied. The biogas produced in the digesters is currently used for heating of the anaerobic digesters. Rhodia Incorporated (Rhodia) is the largest discharger of industrial wastewater to the District.Rhodia would like to increase silica production at its facility, which would result in an increase in discharge of sodium sulfate, the waste product of silica production. Rhodia has requested that TCBSD increase its permitted discharge of sulfate by approximately 40 percent to 142,862 pounds per day corresponding to a total dissolved solids (TDS) discharge of 211,100 pounds per day. This paper provides a summary of the evaluation of potential impacts of increased TDS and sulfate discharge on the performance and operation of the District's plant, and describes the development of a ferric chloride delivery system to mitigate the impacts of sodium sulfate loading on the treatment plant