METAL ADSORPTION AND TURBIDITY REMOVAL BY SELECTED POWDER ACTIVATED CARBONS COMPARED TO METAL SALT COAGULANTS, AND AN EVALUATION OF CARBON REGENERATION
Abstract
The research was designed to evaluate the removal of heavy metals and turbidity from water by powder activated charcoals (PAC). Eleven PACs were first evaluated to choose the most efficient. Preliminary results indicate that Hydro Darco B (HD-B) and Hydro Darco C (HD-C) were the most efficient PACs. HD-B and HC-C were then compared to ferric chloride, ferrous sulfate, alum, and ferric sulfate for metal adsorption and turbidity removal. Also evaluated was the regenerative capacity of the selected PACs in order to assess whether it was feasible to reuse the PAC to reduce water facility operating costs. Heavy metal adsorption and desorption was assessed by measuring the concentration of Cd, Ni, Pb and Zn in water, using atomic adsorption spectrophotometry (AA). Turbidity removal was evaluated using a Hellige turbidimeter. The jar test procedure was employed to simulate water treatment facilities for the removal of metals and turbidity. The adsorption of metals (Cd, Ni, Pb and Zn) by four PACs (HD-B, HD-C, Pittsburg and bone charcoal) at pH values ranging from about pH 2.5 to about pH 14.0, was studied using a modified procedure reported by Rubin and Mercer (1981). The procedure consisted of slowly increasing the pH of the system while measuring the soluble metal concentration by AA. Metal salt coagulants were found to be more efficient than PACs in removing Cd, Ni, Pb and Zn, and turbidity when used in equal amounts at pH 7.0 and pH 8.5. The mean metal removal by ferrous sulfate, ferric chloride, ferric sulfate, alum, HD-B, and HD-C were 84.14, 84.08, 79.60, 79.39, 65.91, and 67.59 percent, respectively. The metals were generally removed in the order Pb > Zn > Ni > Cd, but this order varied slightly with different coagulants and experimental conditions. Desorption studies indicate that the adsorbed metals could not be desorbed from HD-B to a significant degree. Desorption was never above 0.5 percent of the adsorbed metal. The usefulness of PACs would be somewhat limited to cases where the pH of the system is at or near 8.5 and when PAC doses are equal or larger than 0.1 g per liter.
Degree
Ph.D.
Subject Area
Public health
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