What is Chemistry’s Role in Maximizing RO Recovery Rates?
By Lee Durham and Raul Gonzalez
MEMBRANE CLEANING HIGH-RECOVERY RO MEMBRANES REVERSE OSMOSIS SCALING
Introduction: More water treatment organizations globally are exploring and progressing on the path to improve sustainability. For reverse osmosis applications, the sustainability roadmap includes methods for water recycling, water savings, energy savings, and the increasingly prevalent desire to increase system recovery. In the early years of commercially available RO units, typical recovery rates ranged from 50% to 75%. Currently, recoveries are pushing the limits upwards of 96%.
While high recovery may sound like the way to go, special considerations must be given to the various components involved in the process such as the chemistry, system hydraulics, and the water’s detention time. Data shows that there is an exponential relationship between recovery and salt concentration, where a drastic increase in the concentration of salts occurs with recoveries greater than 85%. As water passes through the system, the impact of increased recovery on the concentration of salts, or concentration factor can result in greater potential for mineral scaling. This is one of the components that must be considered for high-recovery applications.
In many cases, an antiscalant or threshold inhibitor is required to prevent the precipitation of sparingly soluble salts on the membrane surface.
The chemical composition of any feedwater is a key consideration for maximizing recovery. As feedwater sources become more challenging, chemical dosing software should accurately predict scale saturations to determine the absolute maximum recovery. Having software that can accurately predict the scaling potential is key for any application but it becomes significantly more important for high-recovery applications.
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