Activation of persulfate and peroxymonosulfate for the removal of herbicides from synthetic and real waters and wastewaters

Abstract

Over the last decades, the quantity and quality of crops have been maintained by means of large and increasing amounts of synthetic herbicides, thus ensuring a world food production. The high recalcitrance and stability of these compounds at ambient conditions avoid their effective removal in municipal wastewater treatment facilities. Among the potential powerful oxidation treatments that are being developed for removing herbicide pollutants, sulfate radical (SO4•−) based-advanced oxidation processes (AOPs) have experienced growing interest because they can compete with conventional AOPs only generating reactive oxygen species (ROS) like hydroxyl radical (•OH). This review presents a detailed, comprehensive, and critical analysis on the application of hybrid processes for the remediation of synthetic and real waters and wastewaters contaminated with herbicides at bench scale by using persulfate (PS) or peroxymonosulfate (PMS) as oxidant. Their activation originated SO4•−, which is partially transformed into •OH. Other ROS like O2•− and were formed depending on the experimental conditions. The fundamentals and main reactions involved in the activation with thermal, catalytic (with iron ions, Fe, and other materials), UV (with and without Fe2+), photocatalytic, and electrochemical processes are described. Papers with the application of each activation procedure to remove herbicide pollutants from each oxidant are summarized, being detailed for selected works their degradation and mineralization efficiency, the influence of scavengers, added inorganic anions, natural organic matter like humic acid, and water matrix. The by-products detected are reported as well. Comparative treatments with both oxidants and analogous processes with H2O2 were finally discussed.