Elimination of Eriochrome Black T by gliding arc plasma
The elimination of an aqueous solution of Eriochrome Black T, an organic compound widely used in the textile industry, was carried out using a gliding arc plasma. This advanced oxidation process (AOP) involves the active gaseous species created in the discharge, mainly OH° radicals, its dimer H2O2, and peroxynitrite ONOO- (a nitric oxide derivative). These species induce highly oxidizing properties which are widely used for the destruction of organic wastes. In addition to the oxidizing species, some derivatives of the NO radical (HONO and ONOOH) present in solution also confer on the plasma some acidifying properties, which accelerate the oxidation reactions. The spectrophotometric study of an Eriochrome Black T solution exposed to an electric discharge showed that an intermediate compound which absorbs at 750 nm forms at the beginning of the treatment (t < 3 min) with a relevant pseudo first order kinetic rate constant k = 2.11 min‐1. After 45 min of treatment, a decolouration rate of 85.1% was obtained and the compound initially present in solution at a concentration of 15 μM was mineralized (57.3%) with a rate constant k1 = 0.0188 min‐1. The observation of a concurrent 67% decrease in chemical oxygen demand with a rate constant k2 = 0.0253 min‐1 confirms the degradation of the compound as a result of the discharge. Although the kinetics of disappearance of a more concentrated solution (150 μM) are slow (k3 = 0,0178 min‐1), the compound faded at 82.0% and a degradation of 86.6% was obtained for an exposure time of 50 min. Qualitative analysis performed immediately after the discharge also revealed the presence in solution of mineral ions derived from the degradation of the parent molecule.