Degradação eletroquímica dos herbicidas tebutiuron e picloram usando anodo de diamante dopado com boro ou de dióxido de chumbo em um reator filtro-prensa

Abstract

The electrochemical degradation of the herbicides tebuthiuron (TBT) and picloram (PCL) was carried out in a filter-press reactor using boron-doped diamond (BDD) or lead dioxide as anode, investigating the effect of current density (j), pH, and the addition of Cl– ions to the solution. For both anodes, solution pH had no significant effect on the removal process of the tested molecules or the solution organic load (COD and TOC); however, the process was quite dependent on j, except for COD, when mass transport limitation was observed. In terms of current efficiency and energy consumption, the most favorable condition was the one for the lowest tested value of j (10 mA cm–2). On the other hand, the addition of Cl– ions to the solution had a positive effect only on the degradation of the PCL molecule, with a significant influence of pH; the best performance was attained at pH 6, at which HOCl is the predominant active chlorine species. Regarding mineralization, the presence of Cl– ions had little influence on the process. Once again increased j values led to higher rates of organic load removal, but simultaneously diminishing the process efficiency and increasing its energy consumption. LC-MS/MS studies of the intermediates from the degradation of the TBT molecule showed that the initial degradation steps consist in the introduction of OH groups, followed by subsequent oxidation processes up to the removal of carbon atoms. In the presence of Cl– ions, chlorinated intermediates were observed. Comparing the tested anodes, despite their similar results on the removal of the herbicides’ molecules, the DDB one yielded significantly superior results with respect to COD and TOC removal.