Stabilization of a Mixed Waste Sludge for Land Disposal

ABSTRACT

A solidification and stabilization technique was developed for a chemically complex mixed waste sludge containing nitrate processing wastes, sewage sludge and electroplating wastewaters, among other wastes. The sludge is originally from a solar evaporation pond and has high concentrations of nitrate salts; cadmium, chromium, and nickel concentrations of concern; and low levels of organic constituents and alpha and beta emitters. Sulfide reduction of nitrate and precipitation of metallic species, followed by evaporation to dryness and solidification of the dry sludge in recycled high density polyethylene with added lime was determined to be a satisfactory preparation for land disposal in a mixed waste repository. The application of post-consumer polyethylene has the added benefit of utilizing another problem-causing waste product. A modified Toxicity Characteristic Leaching Procedure was used to determine required treatment chemical dosages and treatment effectiveness.

The waste complexity prohibited use of standard chemical equilibrium methods for prediction of reaction products during treatment. Waste characterization followed by determination of thermodynamic feasibility of oxidation and reduction reactions allowed estimation of reactants required and possible reaction products. These calculations were shown to be accurate in laboratory testing.