Nutrient requirements for aerobic biostabilization of landfill leachate

When solid wastes are disposed of in a sanitary landfill, contaminated seepage, known as leachate can become a problem. High strength leachate can be successfully treated using an aerated biostablization lagoon, as long as the sludge age is maintained at greater than 20 days. The object of this study was to determine the nitrogen and phosphorus requirements of aerobic micro-organisms treating high strength leachate, by itself and in combination with domestic sewage. Special emphasis was placed on determining the efficiency of metal removal, as a function of nutrient loading. In the first experiment, the nutrient loading was varied in a series of biological reactors with a 20 day detention time. The input feed was high strength leachate. The BOD₅/N/P ratio was varied from 100/3.19/0.12 to 100/5/1.1. The most effective treatment was achieved with a nutrient loading of 100/3.19/1.11. When the nutrient loading was increased or decreased from 100/3.19/1.11, there was an increase in BOD₅, suspended solids and metal concentrations in the treated effluent. At nutrient loadings below 100/3.19/1.11, the mixed liquor sludge bulked, with the volume of sludge generated doubling from 0.022 to 0.050 ml of settled sludge per mg of BOD₅ destroyed. In the second experiment, the high strength leachate was combined with domestic sewage in proportions varying from 0 to 20% (vol. leachate)/ (vol. leachate & sewage). No nutrients were added to the reactors but the BOD₅/N/P/ ratio varied from 100/24/4.3 to 100/3.62/0.12. The biostabilization system effectively treated all the variations of wastewaters. There was no corresponding increase in BOD₅ or metal concentration in the treated effluent when a higher proportion of leachate was added to the reactors. The sludge did not bulk even though the BOD₅/N/P ratio dropped to 100/3.62/0.12. When treating leachate in an aerated biostabilization lagoon with a 20 day sludge age, the required nutrient loading can be significantly reduced below the recommended BOD₅/N/P ratio of 100/5/1. At low volumetric BOD loadings of approximately 0.16 kg BOD₅ applied per cubic meter, a low nutrient loading of 100/3.62/0.12 does not adversely effect treatment efficiency. However, at a relatively high volumetric loading of 1.0 kg BOD₅/cubic meter, the minimum nutrient loading needed was 100/3.19/0.5. The increase in volumetric loading required a corresponding increase in phosphorus input. When the nutrient loading was sufficiently reduced, the mixed liquor sludge bulked and settled poorly. This resulted in a high level of suspended solids in the final effluent. Since the metals were bound to the suspended solids, the metal concentration in the final effluent also increased.Applied Science, Faculty ofCivil Engineering, Department ofGraduat