Treatment of landfill leachates

Abstract Landfill leachate, which resembles concentrated mixed industrial waste water, threatens national groundwater supplies. Several processes drawn from industrial water treatment have been considered for renovating landfill leachate: biodegradation, chemical and thermal degradation, adsorption, reverse osmosis, and coagulation/precipitation. Since transporting leachate off-site entails considerable risk and expense, these technologies must be evaluated for their applicability to on-site treatment. Biodegradation has the greatest potential for removing the varied organic compounds found in leachate streams due to its flexibility and relatively wide application in waste-water treatment. Use of combinations of biological processes, such as sequential aerobic and anaerobic treatment, or of biological and physical processes, such as biologically activated carbon, may improve performance. Alternative chemical or thermal destruction processes are more energy intensive and require finer control than biological processes. Coagulation/precipitation, adsorption, and membrane processes have been studied for treating leachates to remove organic compounds, heavy metals, entrained oil, and colloidal material. Because these processes partition the leachate and, thus, concentrate toxic substances, further treatment of their residues is necessary. They are particularly suited for pretreating influent to a biological process or for polishing a biological effluent. Much work remains in applying these treatment processes to actual landfill leachates. Design of leachate treatment processes must be tailored to the site and will depend on the quantity and characteristics of treatment residues allowed under the prevailing regulatory environment. The variability of landfill leachates both from site to site and temporally within a site makes leachate treatment a challenging problem.