Degradation of atrazine by electrochemical advanced oxidation processes using a boron-doped diamond anode.

ABSTRACT

Solutions of 30 mg L(-1) of the herbicide atrazine have been degraded by environmentally friendly electrochemical advanced oxidation processes (EAOPs) such as anodic oxidation (AO), electro-Fenton (EF), and photoelectro-Fenton (PEF) using a small open and cylindrical cell with a boron-doped diamond (BDD) anode. AO has been carried out either with a stainless steel cathode or an O(2) diffusion cathode able to generate H(2)O(2). Hydroxyl radicals ((*)OH) formed at the BDD surface in all EAOPs and in the bulk from Fenton's reaction between added Fe(2+) and electrogenerated H(2)O(2) in EF and PEF are the main oxidants. All treatments yielded almost overall mineralization, although the rate for total organic carbon (TOC) removal is limited by the oxidation of persistent byproducts with (*)OH at the BDD surface. In AO, TOC abatement is enhanced by parallel electrochemical reduction of organics at the stainless steel cathode, while in PEF, it also increases from additional photolysis of intermediates by UVA light under the synergistic action of (*)OH in the bulk. The effect of current and pH on the degradative behavior of EAOPs has been examined to determine their optimum values. Atrazine decay always follows a pseudo-first-order reaction, being more rapidly destroyed from (*)OH in the bulk than at the BDD surface. Aromatic intermediates such as desethylatrazine, desethyldesisopropylatrazine, and cyanuric acid and short linear carboxylic acids such as formic, oxalic, and oxamic have been identified and quantified by reversed-phase and ion-exclusion HPLC, respectively. Released inorganic ions such as Cl(-), NO(3)(-), and NH(4)(+) have been followed by ionic chromatography.