Assessment of dissolved and non-dissolved metals in aerated landfill leachate

Landfill leachate was sampled from eight municipal solid waste landfills, with the object of determining the dissolved and non-dissolved portion of selected metals in the leachate after aeration treatment. After 24 hours treatment, Zn, Cd, Cu. Pb and Fe were present mainly (70-90 %) as colloidal/particulate matter (> 0.45 mu m). On average, 4050 % of the Cr and Co were also in particulate form, whilst Ni was present mostly (on average 80%) in the dissolved fraction (<0.45 mu m). A clear correlation between the suspended matter content and the Fe, Cd, Zn and Cr content in the aerated samples was observed. With the exception of Fe, the metal distribution in the aerated samples did not differ much from the distribution in freshly sampled leachate. It was therefore concluded that, where the removal of heavy metals is concerned, aeration of the leachate is not particularly useful as a method of pre-treatment before sedimentation. The fact that a large portion of the heavy metals were present as particulate matter in the leachate showed that sedimentation treatment can be very efficient for removing these metals from leachate.