Modeling and optimizing Fenton and electro-Fenton processes for dairy wastewater treatment using response surface methodology

Abstract

In this paper, dairy wastewater treatment was investigated by Fenton and electro-Fenton (EF) processes in respect of removal efficiencies of chemical oxygen demand (COD), orthophosphate, suspended solid (SS), and color. The response surface methodology (RSM) approach using Box–Behnken design was carried out to develop mathematical model and to optimize process parameters. Experimental data were analyzed by the analysis of variance (ANOVA) to identify the interaction mechanism between the process variables and the dependent variables. According to ANOVA results of Fenton process, COD removal increased with an increase in H2O2/COD ratio and reaction time but decreased with increased H2O2/Fe2+ ratio and initial pH. Opposing to that, in the EF process, COD removal increased with an increase in H2O2/Fe2+ ratio and reaction time but decreased with an increase in H2O2/COD ratio and initial pH. The COD removal efficiencies were 65.5 and 72% under the optimum conditions for Fenton (H2O2/COD ratio 1.9, H2O2/Fe2+ ratio 5, pH 4 and reaction time 10 min) and electro-Fenton (H2O2/COD ratio 2, current density 32 mA/cm2, pH 2.4 and reaction time 45 min) processes, respectively. No significant removal differences for orthophosphate, SS and color were determined between the two processes because the removal efficiencies were over the 88% for each process configuration where P value was greater than 5.6 * 10−5 with 99% confidence level and greater than 1.7 * 10−3 with 95% confidence level for all responses for Fenton and EF processes, respectively).