Optimisation of Electro-Fenton denitrification of a model wastewater using a response surface methodology

Electro-Fenton denitrification of a model wastewater was studied using platinised titanium electrodes in a batch electrochemical reactor. The model wastewater was prepared from components based on the real aquaculture effluent with nitrate concentrations varying from 200 to 800 mg L−1. The technical as well as scientific feasibility of the method was assessed by the relationship between the most significant process variables such as various Fenton's reagent to hydrogen peroxide ratios (1:5; 1:20 and 1:50) and current densities (0.17 mA cm−2, 0.34 mA cm−2 and 0.69 mA cm−2) and their response on denitrification efficiency in terms of nitrate degradation using central composite Box-Behnken experimental design was determined. The goodness of the model was checked by the coefficient of determination R2 (0.9775), the corresponding analysis of variance P > F and a parity plot. The ANOVA results indicated that the proposed model was significant and therefore can be used to optimize denitrification of a model wastewater. The optimum reaction conditions were found to be 1:20 Fenton's reagent/hydrogen peroxide ratio, 400 mg L−1 initial nitrate concentration and 0.34 mA cm−2 current density. Treatment costs in terms of electricity expenditure at 0.17, 0.34 and 0.69 mA cm−2 was 7.6, 16 and 41.8 €, respectively, per kilogram of nitrates and 1, 2 and 4 €, respectively, per cubic meter of wastewater.