Effect of Leachate Recirculation on Enhancement of Biological Degradation of Solid Waste: Case Study

Abstract

This paper presents a case study of leachate recirculation at the Trail Road landfill site, located in Nepean, Ontario, Canada. The leachate collected from the landfill leachate collection system is pumped into infiltration lagoons that were built on the working face of the landfilled waste. The locations of these infiltration lagoons are constantly changing to accommodate the landfilling of the municipal solid waste in Stage 3, which has a composite liner consisting of 600 mm of compacted clay and an 80 mil high-density polyethylene geomembrane. The initial estimation of the leachate generation rates in 1991, using the Hydrological Evaluation of Landfill Performance model indicated that leachate recirculation into the landfill could be feasible for a period of 5 to 6 years, after which time a substantial amount of leachate would have to be removed from the system. The average pH of the leachate in the early stage of recirculation was on the acidic side of the pH scale; however, the pH value was in the range of 7 to 8 after 2 years of leachate recirculation. The leachate recirculation accelerated the reduction of organic load, measured as BOD and COD. The concentration of chloride remained fairly constant at about 1,000 mg/L during the leachate recirculation period. The recovery of landfill air space was also noted as a during active periods of landfilling as an added benefit due to the enhanced subsidence of the solid waste.