Three strategies to treat reverse osmosis brine and cation exchange spent regenerant to increase system recovery

Concentrate streams from industrial processes entail an important risk for the environment, as they are often discharged into it. Therefore, efforts must be made to reduce the load of contaminants discharged to the environment. Eutectic freeze crystallization (EFC) is a novel technique which allows separation of salts and water from aqueous streams. In this research, three treatment options for reverse osmosis (RO) concentrate and cation exchange (CIEX) spent regenerant are investigated. First, application of EFC to RO concentrate was investigated. The stream was rich in HCO− and Na+. Application of 3 EFC to this solution, led to the formation of ice and NaHCO3 at −3.9 °C with 5.8 wt.% NaHCO3. Second, precipitation of CaCO3 by mixing the RO concentrate with the CIEX regenerant in a ratio of 2.8:1 and adjusting the pH to 11 was investigated. A 0.25 M NaCl solution remained after the treatment, which upon concentration could be used to regenerate the resin. Third, application of EFC to a synthetic CIEX regenerant was also investigated. The multicomponent solution contained NaCl, MgCl2 and CaCl2. Upon EFC treatment, ice formed first and then NaCl · 2H2O at −29 °C. The composition of eutectic point at −29.4 °C was 2.48 wt.% Na and 15.85 wt.% Cl. © 2014 Elsevier B.V. All rights reserved.

In this study three different strategies were studied to increase the total recovery of a system composed of cation exchange resin, nanofiltration and reverse osmosis. Both the RO concentrate and CIEX spent regenerant are usually disposed of, but they contain valuable water and salts. • The RO concentrate stream was partially separated into salt and water. EFC was applied to 6 times pre-concentrated and filtered RO concentrate. The application of EFC led to the production of pure ice and pure nahcolite. The eutectic conditions were reached at −3.9 °C and 5.8 wt.% NaHCO3 in the presence of 9 wt.% total dissolved ions. The eutectic line decreased by the production of ice and salt to −4.1 °C in the presence of 9.6 wt.% total dissolved ions content. The total water recovery could potentially be increased by application of EFC to the RO concentrate from 98.0 to 99.7%.