Background: This study aimed to model optimization of strategic environmental management decisions in the operation of reverse osmosis desalination, emphasizing the costs required for the environmental protection during the production of freshwater using reverse osmosis technology. Methods: This analytical research was conducted in five cities of Hormozgan province in Iran for 18 months from February 2018 to September 2019. The research includes eight phases of defining the research problem, data collection, preliminary data analysis and decision criteria, mathematical modeling, model validation, information preparation, analysis and finally discussion, conclusions and suggestions. The main environmental issues were the carbon dioxide (CO2 ) release rate due to power demand and rejected brine water (RBW) were entered the mathematical model. Results: The desalination plants of Abu Musa, Bandar Abbas, Qeshm, Sirik, and Hormoz with water production flow rate of 2100, 89 000, 5300, 3300 and 1500 m3 /d can generate 2360.82, 100053.80, 5958.260, 3709.86 and 1686.30 tons/year of CO2 emissions respectively. This output requires 1.35, 57.47, 3.42, 2.13 and 0.97 million USD for controlling the process, respectively. For reduction of the negative effect of RBW 0.75, 22.79, 1.78, 1.15 and 0.55 million USD respectively, is needed. Conclusion: Recommendations for environmental impacts protection of RBW, for desalination capacity up to 50 000 m3 /d, are; (a) for desalination capacity up to 50 000 m3 /d; dilution the RBW using raw water before entering into the sea, (b) for capacity of 50 000-100 000 m3 /d; dispersing RBW in sea using diffuser, and (c) for capacity more than 100 000 m3 /d; hybrid water desalination plants and power plant. Application of power plant cooling water to dilute RBW may reduce cost.
