Use of Fly Ash for the Stabilization of Heavy Metals Derived from Sewage Sludge�

Abstract

The land disposal of sewage sludge from a sewage treatment plant in north Tulsa, Oklahoma has created environmentally hazardous levels of heavy metals in the upper horizon of a soil profile. A DTPA extract and subsequent ICAP analysis revealed concentrations of available zinc, copper and nickel to be 348ppm, 104ppm and 33.9ppm respectively. In-situ stabilization of the site is desired. Increasing the soil pH to 6.5 or above has historically been effective to limit mobility and toxicity of heavy metals. Upper and lower horizons were extracted for a pilot greenhouse study, since permission to conduct on-site investigat1ons was denied. The pH of the sludgedsoil was 6.4. Using fly ash as a liming material, the pH was adjusted to 6.8 and 7.0. Plant uptake movement was investigated for copper, nickel and zinc for the pH ranges of 6.4 (check), 6.8, 7.0, and recommendations for use of fly ash as a stabilizing agent, based upon the experimental results, are discussed.