Response surface methodology optimization of hydraulic conductivity change by microbially induced CaCO3 precipitation

The aim of this work was to formulate an empirical model using the data of the electrochemical treatment of cattle slaughterhouse wastewater. The empirical model was developed using response surface methodology with optimal design considering an irregular process space. As operational factors, current density, influent pH, flow rate, supporting electrolyte (NaCl or Na2SO4) concentrations, and H2O2 concentrations were examined. Under these circumstances, the aim was to represent the optimal region shown generally as a surface by obtaining the lowest possible value of chemical oxygen demand (COD). Therefore, as an outcome of experimentation, for current density, flow rate, initial pH of wastewater, and concentrations of H2O2 and Na2SO4, a linear effect was obtained on the removal of COD. The factors that have a quadratic effect on the removal efficiency of COD are pH and H2O2. There are interactive effects between current density and flow rate, between current density and H2O2 concentration, and between pH and flow rate on removal efficiency of COD. The best-fitting model was defined with a coefficient of multiple determination value (R2) of 93.90%. In optimal conditions, according to the model, the removal efficiency of COD is maximized as 91.34% when the following conditions are utilized: current density of 32.36 mA/cm2, pH of 4.07, the flow rate of 1,185.12 mL/min, the concentration of H2O2 of 0.005 M, and concentration of Na2SO4 of 0.008 M. The results showed that the model is appropriate for determining the factors for the electrochemical treatment of cattle slaughterhouse wastewater.