Author(s)

V O Okereke

Abstract

Simulation of landfill leachate and gas: application to leachate recirculation and land fill gas-to-energy projects. V.O. Okereke King County Solid Waste Division, Seattle, US.A. Abstract A one-dimensional coupled landfill leachate and gas model (LLGM) is developed for the continuous and simultaneous simulation of post-closure leachate accretion, gas generation, and to study the effects of leachate recirculation. A fully implicit finite difference scheme of the Fokker Plunck equation is used to simulate moisture transport and distribution in the temporal and spatial domains, and then is coupled to a two - stage landfill gas first order rate equation to simulate landfill gas. This latter equation is uniquely correlated to moisture transport and distribution with a substrate utilization equation. The effects of the variation of key hydrologic parameters on leachate simulation are examined. A leachate treatment cost sub-model is also developed by non-linear Simplex regression analysis for the prediction of average long-term secondary leachate treatment costs. The economic viability of leachate recirculation in horizontal and vertical wells is evaluated for a hypothetical landfill gas-to- electrical energy project. Disproportionate volumes of leachate are simulated for concurrent increases in moisture content and gas. The use of vertical wells for leachate recirculation yielded a higher net economic benefit than horizontal wells for the tested hypothetical energy project. Moisture transport and retention are demonstrated to be dependent on the antecedent moisture content, refuse saturated moisture content and saturated hydraulic conductivity.

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