Degradation of direct yellow 9 by electro-Fenton: Process study and optimization and, monitoring of treated water toxicity using catalase

•Successful application of EF for the removal of DY9 by iron and stainless steel electrode.•Novel and appropriate design (DOEHLERT) using for the optimization of conditions.•Feasibility of monitoring of quality water treated using biomarkers of oxidative stress.•Catalase can be qualified to assess the effect of dye and its by-product generated during EF.

The present study was undertaken to investigate the degradation and removal of direct yellow 9 (DY9) by the electro-Fenton (EF) process in batch reactor using iron and stainless steel electrodes. DY9 removal decreased with the increase in pH (3 to 8) and increased with the increase in current intensity (0.05 to 0.2 A) and [H2O2] (0 to 0.5 g L−1, but not with high doses which led to low rates of DY9 removal and OH∙ uptake). The regression quadratic models describing DY9 degradation yield “R (percent)” and electrical energy consumption “EEC (kW h kg−1)” were validated by the analysis of variance (ANOVA) and were both noted to fit well with the experimental data. The R2 correlation coefficients (0.995, 0.978), those adjusted coefficients (0.986, 0.939), and F values (110.7, 24.9) obtained for the responses validated the efficiency of model. The results revealed that among several other parameters, EEC depended essentially on the degradation yield. The eco-toxicity tests showed a positive correlation between catalase activity and DY9 concentration, and catalase could be qualitatively identified to assess the effect of dye and its by-products generated during the EF process.

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