Treatment of dye wastewaters by nanoparticles is an attractive research in environmental engineering. In this research, for the treatment of wastewater containing methylene blue, a novel process was introduced in which a hybrid of ultrasound and photocatalysis was used. ZnO nanoparticle was employed as the catalyst. A synthesis technique for ZnO nanoparticles was used, and the resulted nanoparticle was capable of conducting photocatalytic activity in the visible light spectrum. Since the efficiency of a photocatalytic process in strongly dependent on the characteristics of the nanoparticle, in this study, the synthesis temperature parameter along with other parameters (that affect the ultrasonic/photocatalytic hybrid process such as pH, nanoparticle concentration, ultrasonic power, light source power, dye concentration, and time) were investigated as independent variables. Since treatment cost plays an important role in the selection for a proper treatment process, the cost of energy consumed in the hybrid process was chosen as the dependent variable. Examining the simultaneous effect of independent variables on the cost was one of the innovations of this research. Another novel aspect of this research is the determination of the synergetic or antagonistic effects of independent variables on each other. Furthermore, the optimal conditions to reach the optimum energy consumption level were also determined. Based on the SEM test results, the morphology of optimal nanoparticle (synthesized at 300 °C) was achieved, and the nanoparticle produced at this temperature was then analyzed via FTIR, XRD, EDS and BET techniques. The most appropriate conditions of the independent variables to reach the minimum energy consumption in treatment were observed at the pH of 8.76, nanoparticle concentration of 1.401 g/l, ultrasonic power of 119 W, light source power of 21.909 W, dye concentration of 45.905 ppm, and the process time of 13.695 min. According to the results, the optimum cost of the energy was about 0.001 ¢ for removing each milligram of dye and it obtained for optimum reaction conditions.