Comparative electrochemical degradation of the herbicide tebuthiuron using a flow cell with a boron-doped diamond anode and identifying degradation intermediates

Abstract

The electrochemical degradation of tebuthiuron (TBH; 100 mg L À1) was carried out under enhanced mass transport conditions (using a flow cell with a BDD anode), while investigating the effect of solution pH, absence and presence of Cl À ions in the supporting electrolyte solution (0.1 mol L À1 Na 2 SO 4), and current density (j = 10, 30, 50 mA cm À2) on the herbicide degradation and resulting oxidation intermediates. The enhanced mass transport conditions led to significantly improved performances, comparatively to previous results obtained with a common electrochemical cell. The solution pH or presence of Cl À ions did not affect the TBH removal rate. However, the COD removal rate, despite being independent of pH, was significantly faster in the presence of Cl À ions, most probably due to false results caused by organochlorinated intermediates. In the absence of Cl À ions in solution, the TBH removal rate increased with j, whereas the COD removal rate was not affected, but significantly increased removal rates were attained in the presence of Cl À ions, most probably because of increased formation of organochlorines. As expected, higher values of the general and mineralization current efficiencies as well as lower energy consumptions per unit TOC mass removed (EC TOC) were attained at 10 mA cm À2 ; in the absence of Cl À ions, complete removal of TBH and 80% removal of TOC were attained with EC TOC = 0.2 kW h g À1 (less than 1/10 of those for electrolyses using a conventional electrochemical cell). From the identified intermediates, an initial TBH oxidation pathway like those of coupled processes involving photochemistry is expected. Most carboxylic acid intermediates were removed or being removed by the end of the electrolyses (except tartronic acid, which accumulated). As expected, organochlorinated intermediates were identified in the presence of Cl À ions, but were completely removed by the end of the electrolyses. In summary, the electrochemical degradation of TBH in the presence of Cl À ions is not advantageous; no significant improvement in the TBH and TOC removal rates, or in the energy expense, is achieved and the formation of organochlorines is a real possibility.

Electrochemical degradation of norfloxacin using BDD and new Sb-doped SnO2 ceramic anodes in an electrochemical reactor in the presence and absence of a cation-exchange membrane

“…As mentioned previously, the greater efficiency of the BDD anode is due to the very weak electrode-•OH interaction, being more •OH available to react with NOR. The differences observed between both materials are similar to those found by other authors when comparing the BDD with other electrode materials [34,36,38,43,44]. show the effect of the applied current density on the mineralization current efficiency (MCE), calculated using Equation (2), for the BDD and the ceramic electrodes, respectively.…”

Exploring the applicability of a combined electrodialysis/electro-oxidation cell for the degradation of 2,4-dichlorophenoxyacetic acid

“…The treatment of wastewater containing pesticides and organochlorine compounds has recently attracted a growing commitment from the scientific community because of their high toxicity and persistent character [1][2][3][4][5][6]. Despite the fact that the use of many of these hazardous compounds has been forbidden or restricted, an intensive or inappropriate use in the past, an inappropriate storage or transportation and even some accidental spills are still causing serious problems.…”

On the performance of HOCl/Fe2+, HOCl/Fe2+/UVA, and HOCl/UVC processes using in situ electrogenerated active chlorine to mineralize the herbicide picloram

“…The use of BDD anodes to oxidize and mineralize different types of organic pollutants using the electrochemical method and its derived processes is already known to result in high organic removal rates and energy efficiencies if hydrodynamic settings are properly used [49][50][51].…”