Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
6974130 | Process Safety and Environmental Protection | 2018 | 26 Pages |
Abstract
The electrochemical oxidation of the neonicotinoid pesticide thiamethoxam (TMX) on a boron-doped diamond (BDD) anode was investigated. The effect of several operating parameters such as supporting electrolyte (0.025-0.1 M Na2SO4, 0.1 M NaCl), current density (4-40 mA cmâ2), TMX concentration (1-10 mg Lâ1 of active ingredient in a commercial formulation) and initial solution pH (3-11) on degradation was evaluated. The apparent rate constant of a pseudo-first order kinetic model was found to increase with increasing (i) current density (from 0.036 to 1 minâ1 at 4 and 40 mA cmâ2, 2 mg Lâ1 TMX and 0.1 M Na2SO4) and (ii) Na2SO4 concentration (from 0.037 to 0.25 minâ1 at 0.025 and 0.1 M Na2SO4, 2 mg Lâ1 TMX and 16 mA cmâ2 current density) and decreasing (iii) TMX concentration (from 0.05 to 0.73 minâ1 at 10 and 1 mg Lâ1 TMX, 0.1 M Na2SO4 and 16 mA cmâ2 current density) and (iv) initial solution pH (from 0.017 to 2.13 at pH 11 and 3, 0.1 M Na2SO4, 2 mg Lâ1 TMX and 16 mA cmâ2 current density). Experiments in actual matrices, such as secondary treated wastewater and bottled water, resulted in lower kinetics (0.02 and 0.04 minâ1, respectively) than in pure water (0.22 minâ1), signifying competitive interactions between TMX and the matrix constituents. Of the latter, organic matter (1-15 mg Lâ1 in the form of humic acid), bicarbonates (>100 mg Lâ1) and chlorides (>100 mg Lâ1) all had a detrimental effect on degradation. The rate constant of TMX degradation in pure water was reduced by 82%, 71% and 36% in the presence of 15 mg Lâ1 humic acid or 500 mg Lâ1 bicarbonates or 500 mg Lâ1 chlorides, respectively. Fast TMX degradation (i.e. complete removal of 2 mg Lâ1 TMX in 20 min at 16 mA cmâ2, 0.1 M Na2SO4, in pure water) is accompanied by slower mineralization (i.e. 91% total organic carbon removal at 120 min), indicating the formation of more resistant transformation by-products.
Keywords
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Chemical Health and Safety
Authors
Hafida Lebik-Elhadi, Zacharias Frontistis, Hamid Ait-Amar, Said Amrani, Dionissios Mantzavinos,