PHYSICAL-CHEMICAL TREATMENT OF LANDFILL LEACHATE FOR METALS REMOVAL

A detailed treatability study investigating metals removal from leacha tes collected from a sanitary landfill is presented, Experiments inves tigated treatment of raw leachate from younger and older zones of the landfill and of a mixture of the two leachates (representing an averag e leachate from the landfill). The metal concentrations and COD in lea chate from the older area were approximately one order of magnitude gr eater than in leachate from the active area. The leachates contained s ignificant quantities of reduced iron and manganese that, upon aeratio n and base addition, were precipitated and served as sorbents for trac e metals that were present at much lower concentrations. Most trace me tals in the younger zone leachate and in the leachate mixture were rem oved 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 al l the trace metals efficiently. Various options for treating a blend o f 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 poor to pH adjustment. Trace metals could be removed efficien tly from the leachate with or without aeration. Benefits of aeration i nclude increased formation of iron oxide adsorbent and a significant r eduction in the amount of base required to raise the pH, since aeratio n strips large amounts of CO2 from the leachates. Drawbacks include de creased sludge settleability and the cost of the aeration process itse lf. The settleability of the aerated sludge could be increased 5-10 fo ld by the addition of anionic polymer. Sludge produced was not toxic a s determined by TCLP. Trade-offs implicit in these results are address ed both experimentally and theoretically.