Abstract
The electro-Fenton process combined with a boron-doped diamond-positive electrode in a one-compartment cell has shown efficient degradation of Cartap (95% in Padan 95SP) by hydroxyl radicals (•OH) generated in the electro-Fenton and the electrochemical oxidation processes. The influence of added NaOCl in a pretreatment step, effects of H2O2 concentration, Fe2+-ion addition, presence of further metals acting as co-catalysts, and solution pH on the efficiency of Cartap degradation were studied. The concentration of Cartap was determined by UV-vis spectroscopy according to the 5,5-dithiobis-(2-nitrobenzoic acid) procedure. The efficiency reaches approximately 80% when measured as total carbon concentration decrease, even with increased concentrations of H2O2, Fe2+, or metal ions added as co-catalyst. This limitation is presumably due to recalcitrant intermediates, which cannot be destroyed by •OH.
Highlights
The removal capability of sodium hypochlorite was tested with a solution containing 700 mg L−1 Padan 95SP
Pretreatment with 15 mM NaOCl can effectively remove Cartap in 700 mg L−1 Padan 95SP down to 22% of TOC at very short reaction time due to active chlorine, but it has a negative impact on the electro-Fenton process because of the remaining of Cl− ions in solution
Using Cu2+ can enhance the TOC removal at the early stages but does not increase the effectiveness of process after 120 min of treatment. This limited effectiveness is due to the refractory byproducts which cannot be decomposed by the attack of further OH radicals
Summary
Cartap hydrochloride (CH) is used in agriculture in Vietnam as a popular pesticide generally assumed to be of low toxicity [1], for further humanhealth-related information see [2]. Cartap in its hydrochloride form is highly water-soluble causing toxicity in agricultural waste and runoff water. Due to its high insecticidal activity, Cartap is widely used all over the world [3]. The presence of Cartap and its hydrochloride depends on the pH of the aqueous environment. A study of a conceivable distribution between both forms was not the subject of this study; we use the term Cartap in the following text
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