CHARACTERISTICS AND ENVIRONMENTAL SIGNIFICANCE OF COLLOIDS IN LANDFILL LEACHATE

Landfill leachate samples were collected from a municipal landfill and treated by microfiltration and ultrafiltration to separate their colloidal materials into specific size fractions. Each of these size fractions was then analyzed to quantify and characterize the colloidal materials and identify associated contaminants. The major component of the isolated colloids was organic matter, which probably existed on the surface of the colloids and kept them in a stable suspension. Equilibrium calculations suggest that the inorganic component of the colloids was predominantly carbonate and phosphate precipitates. Significant fractions of Zn, Pb, and Cr were associated with the colloids or complexed with dissolved organic ligands. Hydrophobic organic pollutants were found to be strongly associated with colloids larger than 0.1 mum. Results of this study suggest that treatment processes for landfill leachate are likely to be affected by the associations between leachate pollutants and colloids. It is unlikely, however, that those associations can significantly enhance the movement of pollutants in contaminated aquifers.