Investigation of carbon dioxide for scale control in reverse osmosis systems.

The operation of a reverse osmosis (RO) system is often severely hindered by the deposition of inorganic scales such as calcium carbonate on the membrane surface. Mitigation of this scaling phenomenon requires suitable pH control strategies, with the use of strong mineral acids (e.g., sulfuric acid) being widely adopted throughout the industry. However, there are several challenges associated with sulfuric acid use, such as chemical handling hazards and high concentrations of sulfates in the discharged water. Antiscalants for scale control are associated with challenges such as high chemical costs and their impact on the receiving water bodies. The present study investigates the suitability of a carbon dioxide-based approach as an alternative solution for scale control in RO systems. A commercial software was used to evaluate various scale control strategies - mineral acids, CO2, and antiscalants and identify the operational limitations of CO2-based scale control. Heatmap plots were developed to evaluate the suitability of using a CO2-based approach for RO feedwaters of varying alkalinity and hardness. Simulation results demonstrated the viability of using CO2 for scale control and underlined the associated challenges, such as the free CO2 concentration in the RO permeate stream and high CO2 dosing required under high alkalinity and hardness conditions. Pilot-scale trials at an industrial food processing plant were also performed to validate the simulation results and to identify the operational challenges in a CO2-based pretreatment approach.