Mathematical simulation to improve municipal solid waste leachate management: a closed landfill case

This article presents an example of the application of simulation tools to estimate the post-closure evolution of leachate in a non-hazardous waste landfill. The objective of this work is to predict the behavior of leachate after the closure of the landfill for use as basic information with which to design the leachate management strategy in the following years. The MODUELO 4.0 mathematical landfill simulation software package was used for this purpose. The results of the simulation show that the concentrations in the leachate increase during the post-closure period, from values close to 2200 mg/L of COD and 1500 mg/L of NH₄⁺ at the time of landfill closure to 3200 mg/L of COD and 5300 mg/L of NH₄⁺ 20 years later. This increase is mainly due to the reduction in the flows, from 105 to 17 m³/day on average, since the surface lining was installed. Consequently, pollutant fluxes decrease to values below 100 kg/day in both COD and NH₄⁺ 3 months after closure. This evolution indicates that the management of this leachate will be simpler in the future, especially if it is co-treated with urban wastewater, as its contribution decreases. On the other hand, external water connections to the leachate collectors may cause a relevant increase in the volume of the global landfill effluent. Controlling runoff management and underground infiltrations could lead to important savings in leachate treatment during the aftercare phase.