CHLORIDE REMOVAL FROM LANDFILL LEACHATE BY THE ULTRA-HIGH LIME WITH ALUMINUM PROCESS

Abstract

Besides organic contaminants, nutrients and heavy metals, high concentrations of chloride have also been observed in landfills accepting ash deposition from waste-to-energy applications, which is difficult be removed in wastewater treatment processes. Chloride may percolate and cause surface salt formation and soil alkalinity increase, thereby resulting in loss of soil. In plants, chloride tends to accumulate in the tissues, especially the leaves. Conventional removal techniques are not feasible from the cost perspective. In this research, the ultra-high lime with aluminum process was evaluated for chloride removal from landfill leachate by precipitation as calcium chloroaluminate (Ca4Al2Cl2(OH)12) in the presence of calcium and aluminum at high pH. Chloride removal was found to be a function of both aluminum concentration and pH. Chloride removal increased with the increase of alum addition until 20 mg/L, after which the chloride removal became moderate. With the increase of pH, obviously more chloride was removed. At pH of 10, the removal reached 90%. To save the chemical costs, alum sludge from a drinking water treatment plant was tested for the removal of chloride from the landfill leachate. The results showed that the supernatant of the alum sludge was more efficient than that of alum sludge suspension in chloride removal. The usage of alum sludge can dramatically save the chemical costs.