Physical-chemical treatment of landfill leachate for metals removal

A detailed treatability study investigating metals removal from leachates collected from a sanitary landfill is presented. Experiments investigated treatment of raw leachate from younger and older zones of the landfill and of a mixture of the two leachates (representing an average leachate from the landfill). The metal concentrations and COD in leachate from the older area were approximately one order of magnitude greater than in leachate from the active area. The leachates contained significant quantities of reduced iron and manganese that, upon aeration and base addition, were precipitated and served as sorbents for trace metals that were present at much lower concentrations. Most trace metals in the younger zone leachate and in the leachate mixture were removed by adjusting solution pH to 9.0, but in leachates collected from the older landfill area, even raising the pH to 11.0 did not remove all the trace metals efficiently. Various options for treating a blend of leachate from the older and younger areas (20%:80% by volume) were evaluated. One of the key design decisions was whether to aerate the leachate prior to pH adjustment. Trace metals could be removed efficiently from the leachate with or without aeration. Benefits of aeration include increased formation of iron oxide adsorbent and a significant reduction in the amount of base required to raise the pH, since aeration strips large amounts of CO2 from the leachates. Drawbacks include decreased sludge settleability and the cost of the aeration process itself. The settleability of the aerated sludge could be increased 5–10 fold by the addition of anionic polymer. Sludge produced was not toxic as determined by TCLP. Trade-offs implicit in these results are addressed both experimentally and theoretically.