This study optimises the degradation of a cocktail of the dyes methyl orange and bromothymol blue by atmospheric air plasma. Response surface methodology (RSM) was employed to investigate the efficacy of the plasma process parameters on degradation efficiency. A Box–Behnken design (BBD) was employed to optimise the degradation of dyes by air plasma discharge. A second order polynomial equation was proposed to predict process efficiency. It was observed that the predicted values are significant (p<0.001) with coefficients of determination 0.98, 0.96, 0.98 for dye degradation, pH value and ozone concentration, respectively. The analysis of variance results showed that the coefficients of the polynomials for the percentage degradation and ozone concentration responses indicated positive linear effects (p<0.001), whereas a negative linear effect was found for pH. The positive linear effect of variable emphasises that voltage and treatment time were the most dominant factors (p<0.001), meaning that higher degradation efficiencies are achieved with an increase in treatment duration. This study showed that a BBD model and RSM could be employed to optimize the colour degradation parameters of non-thermal plasma treated model dyes while minimising the number of experiments required.

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