Optimization, modeling and uncertainty investigation of phenolic wastewater treatment by photocatalytic process in cascade reactor

Wastewater containing phenol is one of the problems that environmental engineering tries to solving it. Cascade reactors are used in water treatment to increase the dissolved oxygen. In this study, this reactor is used for increasing the removal efficiency of phenol treatment in the photocatalytic process. The parameters studied in this research are the initial phenol concentration, UV source power, retention time and flow rate. For the first time, the individual, simultaneous and interactive effects of these four parameters were examined in cascade photocatalytic reactor using the response surface methodology. In this research, a predictive model was presented based on response surface methodology, and the phenol treatment conditions were optimized by this method. According to the results, the optimum removal efficiency occurred at 4.93619 h, with the flow rate of 5.19626 L/min, the initial phenol concentration of 34.7437 mg/L and the UV source power of 40 W. Analysis of variance was done on the experimental data, and its result showed that the UV source power had the most significant effect and that the flow rate had the least significant effect on the removal efficiency. So that by increasing the UV source power from 35 to 55 W, the removal efficiency increased from 54% to approximately 78%. But by increasing the flow rate from 5 to 8 L/min, the removal efficiency increased from about 63% to approximately less than 70%. Prediction of removal efficiency has an uncertainty because of simultaneous and interactive effects of the independent variables on the process; therefore, in this research, Monte Carlo calculations were used to determine the uncertainty of the efficiency prediction. Based on Mont Carlo result, the efficiency will be at the range of 37.542–91.898% at the confidence level of 5–95%. According to the results, this reactor can be used for the treatment of phenolic wastewater.