Abstract
Leachate recirculation (LR) was pioneered in the USA in the 1970s as a means to enhance the degradation of landfill wastes, degrade or immobilize harmful compounds within the waste mass, and store excess leachate. LR offers many economic and environmental benefits to municipal solid waste (MSW) landfills. The main objective of this study was to investigate the migration law of LR and develop design guidelines for leachate recirculation systems consisting of spray irrigation when considering the stratification of MSW permeability. A bioreactor landfill will experience more rapid and complete settlement than a traditional landfill, which is mostly attributed to the weight of MSW. The waste at each layer in the landfill experiences a different pressure depending on the depth, which leads to vertical gradients in the void ratio and permeability coefficients of the waste in the landfill. To study LR in bioreactor landfills when considering the stratification of the MSW permeability, a new model was developed based on the law of conservation of mass, the modified Darcy's law, and Stoltz's settlement model. Using this model, the transport law of injected leachate into bioreactor landfills was determined under unsaturated conditions. The effects of various parameters (e.g., permeability stratification, compaction degree, initial void ratio, and injection intensity) on the water content of MSW and unit surface area recirculation were analyzed.