BIOREACTOR LANDFILL APPLICATION FOR SEQUENTIAL AEROBIC-ANAEROBIC TREATMENT OF MUNICIPAL SOLID WASTE

Solid waste disposal in landfills remains the most economical route in the majority of case studies. In Greece, the main destination for municipal solid waste (MSW) is landfilling, although, over the past decade special attention has been given to other MSW strategies like minimization and recycling. Nevertheless, even when minimization and recycling potentials are fully exploited, there is still a residual fraction which has to be disposed of. Bioreactor landfill represents a beneficial technique for waste stabilization under controlled operational conditions. A lab scale bioreactor landfill was operated for 184 days. The bioreactor had a 343L volume capacity and was filled with 120kg of the organic fraction of MSW. Both aerobic (110 days) and anaerobic (65 days) degradation were applied, with leachate recirculation. The leachate parameters that were monitored included: pH, redox, BOD5, COD, SO4, NH4-N, NO3-N, NO2-N, Cl- and DOC. The experimental process included also measurements of landfill gas and mass settlement. The main objectives of this research were to simultaneously achieve a high level of organic matter and ammonia nitrogen removal, to evaluate the leachate eco-toxicity and to produce a stabilized waste mass. During the initial phase, the pH values started to increase due to aeration. After 3 weeks of treatment the pH was 8 and then was stabilized between 7.5 and 8.5. During the anaerobic period, a slight decline of pH was observed. Redox potential was reverted from strongly negative to positive, after two months of aerobic treatment. Redox decreased rapidly during the early stages of anaerobic phase, indicating anaerobic microbial activity. The initial COD and BOD5 values were 46500mg/L and 45000mg/L, respectively. At the end of the first month the values were 9000 and 6000mg/L, respectively, indicating the fast degradation aerobic process. During the anaerobic period no significant changes were observed, since most of the easily biodegradable organic matter had removed. The mass settlement follows the trend of COD and BOD5 removal. After the first month the settlement was 7cm, over a total value of 14cm after 184 days. Finally, the leachate toxicity was evaluated and according to the results ecotoxicity followed a decreasing trend but at the end of the experiment the toxicity levels were quite high, indicating the need for further treatment.