Electrochimica Acta | 2021
Paired electrochemical removal of nitrate and terbuthylazine pesticide from groundwater using mesh electrodes
Abstract
Abstract Groundwater is one of the main freshwater resources on Earth, but its contamination with NO3− and pesticides jeopardizes its viability as a source of drinking water. In this work, a detailed study of single electro-oxidation (EO) and electrodenitrification and paired EO/electrodenitrification processes has been undertaken with simulated and actual groundwater matrices containing 100 mg dm−3 NO3− and/or 5 mg dm−3 terbuthylazine pesticide. Galvanostatic electrolyses were made with 500 cm3 of solutions at pH 4.0-10.5 and 250-100 mA in tank reactors with a RuO2 or boron-doped diamond (BDD) anode and one or two Fe cathodes, all of them in the form of meshes. Most of NO3− removals agreed with a pseudo-first-order kinetics. In Cl−-free media, NH4+ predominated as electroreduction product. In chloride media, a greater amount of N-volatiles was determined alongside a slower electrodenitrification, especially with RuO2 due to the partial re-oxidation of electroreduction products like NH4+ by active chlorine. The pesticide decays were also fitted to a pseudo-first order kinetics, and its presence led to a smaller release of N-volatiles. Overall, BDD always favored the pesticide degradation thanks to the action of BDD ( ⋅ OH ) , whereas RuO2 was preferred for electrodenitrification under some conditions. The EO/electrodenitrification of groundwater was successful once the matrix was softened to minimize its hardness. The NO3− concentration was reduced below the limit established by the WHO. Overall, the BDD/Fe cell was more suitable than the RuO2/Fe cell because it accelerated the pesticide removal with a simultaneous high degree NO3− electroreduction. However, it produced toxic chlorate and perchlorate. A final post-treatment with an anion exchange resin ensures a significant removal of both ions, thus increasing the viability of the electrochemical approach to treat this type of water. Chromatographic analyses revealed the formation of ten heteroaromatic products like desethyl-terbuthylazine and cyanuric acid, alongside oxalic and oxamic as final short-chain carboxylic acids.