Treatment of Wastewaters Containing Sulfonylurea Herbicides by Electroflotation: Chemical and Ecotoxicological Efficacy

Abstract

Electroflotation (EF) is an electroanalytical technique applied for separating substances suspended in phase and is reported to be efficient for effluents and wastewater treatments. To date, there are no studies employing EF for the treatment of wastewater containing toxic organic compounds. In the present study, EF was tested as an electro-oxidative process to decontaminate wastewater containing the sulfonylurea herbicide chlorimuron-ethyl. To evaluate the value of EF, both the chemical and ecotoxicological efficacies were assessed in non-treated and treated wastewaters; the former monitored the herbicide and degradation products in the reaction medium through analytical chromatographic methods, whereas the latter comprised testing the 72 h growth of the green microalga Raphidocelis subcapitata and the 48 h lethality of the cladoceran Daphnia magna. Analysis by HPLC-UV allowed the monitoring of the electrochemical reaction, and a degradation mechanism based on gas chromatography–mass spectrometry was proposed. Despite the compromised herbicide structure, non-treated and treated wastewaters were similarly toxic for the microalgae Raphidocelis subcapitata and the invertebrate Daphnia magna. Even though EF did not remove the wastewater toxicity, the results indicate that toxic organic compounds are potentially oxidized by EF while signaling the need to combine chemical and ecotoxicological approaches to gauge the environmental sustainability of EF.