Hybrid constructed wetlands amended with zeolite/biochar for enhanced landfill leachate treatment

Landfill leachate contains high concentrations of ammonia and recalcitrant organic compounds, which can interfere with wastewater treatment processes. Hybrid constructed wetlands (CWs), consisting of Vertical Flow (VF) CWs followed by Horizontal Flow (HF) CWs, are low cost technologies for onsite leachate treatment. This study investigated the potential of low-cost adsorbent materials, a natural zeolite mineral (clinoptilolite) and biochar, to enhance leachate treatment in hybrid CWs. Two mesocosm hybrid CWs were set up at a Florida (US) landfill. In the Adsorbent-CW 10% (v/v) of zeolite was added to the VF-CW to enhance nitrification and 13% (v/ v) biochar was added to the HF-CW to increase microbial activity and plant growth. A Control-CW contained only gravel. Both systems were planted with cattails (Typha latifolia) and cordgrass (Spartina alterniflora) and operated at varying hydraulic loading rates for similar to 2 years. A HF-CW containing wood chips (Woodchip-CW) was added downstream of the Adsorbent-CW during the final 6-months of operation to enhance denitrification. Results showed that zeolite addition to the VF-CW significantly increased nitrification rates by 16-93% due to cycles of ammonium adsorption and bioregeneration under intermittent loading conditions. Biochar addition increased removal of organic matter (21-26% to 29-44%) and color (1-18% to 7-49%), and improved wetland plant growth and nitrogen removal due to enhanced plant growth and rhizosphere microbial activity. Addition of the Woodchip-CW reduced nitrate accumulation, resulting in total nitrogen removals of up to 79%.