This research was conducted to investigate in situ treatment of leachate by pilot-scale permeable reactive barrier (PRB) with vegetation. Two different types of PRB media, with and without the presence of ferric chloride sludge, for the removal of pollutants were examined. The composite media of PRB comprised a clay and sand mixture of 40:60%w/w (system 1) and a clay, ferric chloride sludge and sand mixture of 30:10:60%w/w (system 2). The system was operated at a hydraulic loading rate of 0.028 m3/m2.d and hydraulic retention time of 10 days. The results showed that the performance of system 2 was better in terms of pollutant removal efficiencies, with average biochemical oxygen demand, chemical oxygen demand and total Kjeldahl nitrogen removals of 76.1%, 68.5% and 73.5%, respectively. Fluorescence excitation-emission matrix analyses of water samples and sequential extraction of PRB media suggested the removal of humic substances through the formation of iron–organic complex. Greenhouse gas (GHG) emissions during the treatment of PRB were 8.2–52.1 mgCH4/m2.d, 69.1–601.8 mgCO2/m2.d and 0.04–0.99 mgN2O/m2.d. The use of system 2 with vegetation resulted in lower GHG emissions. The results show that PRB with vegetation could be used as a primary treatment for leachate from closed landfill sites.

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