ENHANCING LANDFILL GAS RECOVERY IN TROPICAL ENVIRONMENT

Many landfills in Malaysia are being operated under saturated conditions due to high rainfall or swampy site conditions. This condition is favorable for high leachate and landfill gas production. The gas particularly methane is one of the greenhouse gases which contribute to global warming. The aim of this paper is to evaluate leachate treatability by in-situ degradation in sand layer below the landfill and landfill gas production in a simulated landfill reactor. The reactor was 0.2 m in diameter and 4 m in height. One meter sand layer was packed at the bottom of the reactor followed by 2.5 m solid waste layer and 0.4 m sand layer as cover soil. The reactor was operated under fully saturated condition. Degradation of waste in the solid waste layer was mainly at acidification stage as indicated by the leachate quality with average pH, ammonia and COD of 5.3, 2075 and 36994 mg/L respectively. There was no gas production observed in the middle of the solid waste layer probably due to methanogenic inhibition from low pH and high ammonia. However a methanogenic environment was established in the bottom sand layer. Rapid degradation process took place as the leachate move through the sand layer at an infiltration of 1.6 cm/day. This resulted in high gas production rate with an average of 77 mL/kg/day of which 57% was methane. The rate was about double the amount of reported gas collection from landfills. In conclusion gas collection from landfill can be enhanced by allowing in-situ degradation of leachate in the sand layer at the bottom of the landfill.