Aerobic biostabilization of a high-strength landfill leachate

One particularly undesirable aspect of solid waste disposal on land is the contamination of water passing through the landfill site. The potential adverse environmental effects of these "leachates" have been recognized to the extent that their control and treatment is the subject of a great deal of current research in water pollution control. This study was initiated to investigate the possibility of reducing the amounts of oxygen demanding material in a high-strength landfill leachate by aerobic biological methods, without any prior removal of the heavy metals contained in that leachate. The effect of varying solids detention time was also investigated and the distribution of the heavy metals in the effluents was examined. Using very high mixed liquor volatile suspended solids concentrations, 8,000 to 16,000 mg/l, and a combination of air and mechanical mixing, anticipated foaming problems were controlled and stable digester operation was maintained at solids detention times as low as 10 days. For influent COD concentrations between 44,000 and 52,000 mg/l, settled effluent COD removal increased marginally from 96.8 to 99.2 percent, as the solids detention time increased from 10 to 60 days. Mixed liquor COD removal similarly increased from 51.5 to 75.7 percent. Increasing the solids detention time from 10 to 20 days, significantly improved the quality of the settled effluent with respect to oxygen demanding material. At solids detention times greater than 20 days, and with influent BOD₅ between 32,000 and 38,000 mg/l, settled effluent B0D₅ averaged 58.1 mg/1, as opposed to settled effluent BOD₅ greater than 125 mg/l when the solids detention time was 10 days or less. The leachate feed used in these studies contained a variety of heavy metals including aluminum (41.8 mg/l), cadmium (0.39 mg/l), chromium (1.9 mg/l), copper (0.24. mg/l), lead (1.44 mg/l), nickel (0.65 mg/l), and zinc (223 mg/l). Most of these metals including aluminum, cadmium, chromium, nickel and zinc were almost completely removed by the settling biological floe. Others were associated with the sludge solids to a lesser extent. Analysis of the kinetic parameters associated with the biostabilization process indicated that the high heavy metal concentrations in the mixed liquors inhibited the actual biological removal of oxygen demanding material in the digesters tested. The settling biological floe was found, however, to remove greater than 97 percent of the mixed liquor BOD₅ and greater than 96 percent of the mixed liquor COD when solids detention times were maintained greater than 20 days. Therefore, for best treatment results a solids detention time of at least 20 days is recommended and the food to micro-organism ratio should be kept below 0.15 lb.BOD₅/lb.MLVSS/ day.Applied Science, Faculty ofCivil Engineering, Department ofGraduat