Recent development of electrochemical advanced oxidation of herbicides. A review on its application to wastewater treatment and soil remediation

Abstract

Herbicides have been largely utilized during the last decades to maintain the quality and quantity of agricultural crop, ensuring the need of an increasing world food production. However, these synthetic organics are highly biorecalcitrant and stable at mild conditions and cannot be effectively destroyed in conventional wastewater treatment facilities. Among the advanced oxidation processes used to remove herbicides, electrochemical technologies have been recently developed at bench scale as potential powerful treatments. This review presents a critical, exhaustive and detailed analysis on the application of single and combined electrochemical advanced oxidation processes to remediate wastewaters and soils contaminated with common herbicides, covering the period 2010-2019. Nine kinds of treatments, including single methods like anodic oxidation, anodic oxidation with electrogenerated H2O2, homogeneous and heterogeneous electro-Fenton, photoelectro-Fenton, solar photoelectro-Fenton and photoelectrocatalysis, as well as combined ones involving hybrid and sequential processes, have been examined. The fundamentals of each technology are briefly described, and the main results obtained for the removal of the most used herbicide families from synthetic solutions and soil-washing effluents are carefully exposed and discussed. The role of generated oxidizing agents and/or photolytic reactions in photo-assisted processes is explained to justify the mechanisms proposed for herbicide mineralization. The comparative oxidation ability of the different methods is discussed. Finally, future challenges remarking the need of treating real agricultural wastewaters and contaminated soils, the construction of electrochemical systems with stable electrodes at industrial scale and the realization of techno-economic studies are envisaged.