ABSTRACT
Communities have often placed additional restrictions on cadmium discharges in an effort to protect sewage treatment system performance and to extend the usable life of sludge land application sites. The wastewater treatment plant is one of the largest in the United States utilizing the calcium sulfide process to remove cadmium. The treatment plant utilizes two-stage alkaline chlorination for cyanide destruction, sulphur dioxide for hexavalent chrome reduction, sodium hydroxide precipitation, calcium sulfide, precipitation and effluent filtration. The calcium sulfide system is a safe, easy-to-operate means of treating electroplating wastewaters containing cadmium. Emergency holding tank can receive treated cyanide and chrome waste and general rinse water in the event of a power failure or influent pump shutdown. Chrome and cadmium would be removed as hydroxide with the remaining cadmium being removed as a sulfide. Laboratory scale bench tests confirmed the suitability of the two stage process design.
