EFFECTS OF SEWAGE-SLUDGE AND REFUSE COMPOSITION ON THE RATE OF DEGRADATION AND LEACHATE QUALITY OF CO-DISPOSED WASTE IN A WATER-DEFICIENT ENVIRONMENT

At the Goudkoppies landfill to the south-west of Johannesburg co-dispo sal is part of the landfill operation. Laboratory and field tests were conducted to model the landfill processes and the effects of sewage s ludge addition. To test the hypothesis that the availability of nitrog en, phosphorus and moisture in the refuse and sewage sludge determine the effects of co-disposal, 19 lysimeters were monitored for 534 days. A factorial design approach was used to choose the lysimeter contents to simulate local landfill conditions. Degradation rates and ammonia concentrations in the leachate were found to depend on the interaction s between the nutrients and moisture, rather than on any individual va riable. Co-disposal led to a decrease in COD and nickel concentrations , while levels of ammonia and phosphorus in the leachate were elevated in comparison to the refuse only test. From field tests it was conclu ded that co-disposal can be practiced in the Highveld region without t he formation of leachate, while enhancing the rate of refuse stabilisa tion.