Intensification of supercritical water oxidation (ScWO) by ion exchange with zeolite for the reuse of landfill leachates

Abstract

The disposal of solid residues in sanitary landfills results in the formation of a complex, variable, and recalcitrant wastewater, known as leachates. Supercritical water oxidation (ScWO) can be applied to treat leachates although most studies are based on removing the most relevant contaminants, such as organic matter and ammonia. Therefore, comprehensive analysis of this process is essential for large-scale applications. In this study, we investigated a system composed of ScWO and ion exchange using zeolite (ScWO/zeolite) for the reuse possibilities of treated leachates based on different regulations for municipal wastewater reuse. This system was applied to both raw leachate (RL) and leachate treated via conventional processes at the studied landfill (PL). The continuous ScWO reactor operated under a pressure of 23 MPa at 600 °C without the addition of oxidants. A commercial zeolite (clinoptilolite) in a fixed-bed glass column was used for ion exchange. The intensified system significantly improved the characteristics of RL by removing 89% of COD and 99% of NH3-N. Moreover, the contaminant concentrations of PL were within the limits for discharge and reuse, except arsenic and molybdenum contents. The unexpected high concentrations of arsenic in RL and PL necessitated the requirement of further investigation of the complex and toxic characteristics of leachates. Nevertheless, the intensified process was conducted without the addition of oxidants or auxiliary substances and resulted in a less expensive and more environmentally -friendly process that can be applied for the treatment of leachates with similar characteristics.