A Critical Appraisal of Leachate Recirculation Systems in Bioreactor Landfills

Leachate supplementation through liquid injection is applied widely in bioreactor landfills to increase moisture content within municipal solid waste (MSW) to facilitate waste decomposition and achieve early waste stabilization. This study provided a comprehensive picture of leachate supplementation systems with a critical evaluation of their advantages, applications, design aspects, and influence on the performance of bioreactor landfills. In this study, a critical review of the design characteristics of different leachate supplementation systems and their combinations was carried out, and the comparative performance of leachate supplementation systems by focusing on individual and combined systems to distribute a certain amount of injected liquid was made. In addition, this study considered the effects of MSW characteristics, the mode of leachate injection, the rate of leachate injection, the configuration of the leachate recirculation system (LRS), and the saturated and unsaturated hydraulic parameters to assess the performance of bioreactor landfills. The study identified the significant influence of LRS on moisture distribution, wetted area, pore pressures, landfill settlement, and slope stability. The majority of the literature reported that the unsaturated hydraulic properties and heterogeneous anisotropic waste (HTAW) conditions significantly resulted in an increase in lateral leachate migration and a decrease in pore pressures compared with homogeneous isotropic (HI) conditions. The field applications of these systems and their specifications in full-scale landfills were assessed. This study could help in the better planning of suitable leachate supplementation systems.