Response surface methodology was utilized to optimize the treatment of wastewater from a production of cephem pharmaceuticals using ultrasound/Fenton processes. Box–Behnken design with four variables (initial pH (3, 4 ,5), Fe²⁺ concentration (0.006, 0.008, 0.010 mol/L), mole ratio of H₂O₂ to Fe²⁺ (1:1, 2:1, 3:1), and ultrasound power (400, 450, 500 W)) was employed in this study to determine the most efficient combination of these variables for COD removal. The optimum conditions of initial pH, Fe²⁺ concentration, mole ratio of H₂O₂ to Fe²⁺, and ultrasound power were found to be 4.04, 0.008 mol/L, 2:1, and 487 W, respectively, for maximum COD removal efficiency (87.9%). A quadratic model was obtained for COD removal efficiency through this design. The experimental values are in good agreement with predicted values and the model was highly significant with the correlation coefficient of 0.999.

The stationary points, including the entrance complex, transition states, and the exit complex, for the reaction OH + (H₂O)₂ → (H₂O)OH + H₂O have been carefully examined using the “gold standard” CCSD(T) method with the correlation-consistent basis sets up to cc-pVQZ.