Sequential coagulation and heat activated persulfate-peroxide binary oxidation process for landfill leachate treatment

Abstract

This study investigated a sequential treatment of landfill leachate including coagulation and binary oxidation. In the first step, the chemical coagulation process in which alum was used as a coagulant was applied to the leachate and the Box-Behnken design was used for process optimization. Operating parameters of the chemical coagulation process were coagulant dose, initial pH, and reaction time while the model response was color number (CN) removal. As a second step, a heat-activated persulfate-peroxide (PS/PO) binary oxidation process was applied to the leachate, which was subjected to chemical coagulation under optimized conditions. The effects of initial pH, reaction time, PS/PO ratio, and temperature on the removal of chemical oxygen demand (COD), UV254, and CN were determined. Control experiments were carried out depending on reaction time, kinetic studies were performed and rate constants were obtained. Based on removal efficiencies, binary processes were more effective than single processes. Reaction rates were directly proportional to temperature and inversely proportional to the initial pH. The optimum operating conditions of the PS/PS/Heat process were as follows; total oxidant dose 100 mM, initial pH 5, reaction time 120 min, and temperature 80 °C. Consequently, 82.2% COD, 94.4% UV254, and 97.9% CN removal efficiencies were achieved by combined coagulation-advanced oxidation processes. Moreover, scavenging experiments were carried out to determine the types of radicals involved in the process. Under optimum conditions, it was determined that both sulfate and hydroxyl radicals were involved in the PS/PO/Heat process; however, the dominant radical type was hydroxyl radicals.