In this study, a newly developed liquid-phase plasma discharge (LPPD) process was evaluated for removing methylene blue (MB) in water. Three independent variables, i.e., liquid flow rate (LF), air flow rate (AF), and MB concentration in water, were all tested at five levels (37, 68, 81, 94, and 103 mL/min for LF; 1, 2, 3, 4, and 5 L/min for AF; and 10, 30, 50, 70, and 90 mg/L for MB) using Central Composite Design (CCD) and Response Surface Methodology (RSM) to optimize the operation for the plasma reactor. The results showed that the regression model produced by the CCD/RSM analysis could adequately predict the MB removal rate of the LPPD process with a model p value of less than 0.0001. The uncertainty analysis further confirmed the error range for the regression model was from -3.93% to 0.63% in predicting the MB removal rate within the ranges of the three independent variables tested. The removal rates were all above *Address correspondence to Dr. Sarah Wu, Department of Biological Engineering, University of Idaho, 875 Perimeter Drive MS 0904, Moscow, ID 83844-0904. 99% for the MB concentrations experimented at LF 68 mL/min and AF 4 L/min. The results concluded that the novel LPPD process was effective in removing MB from dye wastewater.
Keywords: Liquid and air flow rates; central composite design; process optimization; quadratic model.