Treating Metal Finishing Wastewater

Sultan I. Amer, Ph.D. AQUACHEM INC. Environmental Technology • March/April 1998 Wastewater from metal finishing industries contains high concentrations of contaminants which are hazardous to the environment and pose potential health risks to the public. With increasingly stringent regulations governing wastewater discharge and greater quantities of wastewater being produced, there is a growing need for more efficient and cost effective methods to remove heavy metals. In accordance with the National Pollutant Discharge Elimination System (NPDES), as required by the Clean Water Act, metal finishers are required to pretreat their wastewater prior to releasing it to municipal sewers or surface waters. As the regulations governing the discharge of wastewater become more stringent, publicly owned treatment works have set lower discharge limits on heavy metals and other contaminants of concern. With the greater quantities of wastewater being produced and discharge limits being lowered, there is a need for more efficient processes to remove heavy metals. Wastewater from metal finishing industries contains contaminants such as heavy metals, organic substances, cyanides, and suspended solids, at levels which are hazardous to the environment and pose potential health risks to the public. Heavy metals, in particular, are of great concern because of their toxicity to human and other biological life. Heavy metals typically present in metal finishing wastewater are cadmium, chromium, copper, lead, nickel, silver, tin, and zinc. Table 1 shows the EPA best practical control technology, BPT, limits for metal finishing effluent. Table 1: BPT Limits for Metal Finishing Effluent