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Leaching properties of thickened sludge suspensions and dewatered sludge cakes from an aluminum-anodizing and an electroplating plant were examined. Sludge specimens were examined before and after 27 to 207 days of storage under controlled conditions using the Environmental Protection Agency (EPA) extraction procedure (EP). Extracts were examined for silver, aluminum, cadmium, chromium, copper, mercury, nickel, lead, and zinc. Extract metal concentrations varied considerably with time of storage with no consistent pattern for all metals in either sludge.
The electroplating sludge was classified as hazardous using EPA standards for EP results. Cadmium levels in the sludge were initially 5 mg/L and increased to 13 mg/L following storage for 98 days for both the stored suspension and the stored dewatered cake specimens. Extract chromium and copper concentration decreased with storage time while those for lead decreased initially and then increased with storage time. Although extract metal concentrations for the aluminum-anodizing sludge varied with storage time, metal concentrations were well below levels designated as hazardous by EPA.
Filtrate metals were shown to have minimal impact on EP test results and the majority of extracted metals were from suspended metal precipitates in the sludges. Sludge storage was shown to have a significant effect on EP test results, indicating a need to recognize it as a test variable.
sludges, metal finishing, leaching, storage, electroplating, aluminum anodizing, EPA EP test, hazardous wastes
Associate professor, Environmental Engineering, School of Civil Engineering, Georgia Institute of Technology, Atlanta, GA
U.S. Army Sanitary Engineer, 10th Medical Laboratory, APO, NY
Environmental Engineer, Southwire Inc., Carrollton, GA