Acid and base recovery from softened reverse osmosis (RO) brines. Experimental assessment using model concentrates

Managing high salinity concentrates generated during membrane water desalination processes is a primary need due to the potential threat to the receiving ecosystems that brine discharge represents. Brines from desalting techniques contain inorganic salts that may be further purified to increase their commercial value. This study presents a beneficial reuse strategy for reverse osmosis (RO) brines generated in a seawater desalination plant. Bipolar membrane electrodialysis (BMED) has been the selected technology for the conversion of RO concentrates into acid and base products. The viability results presented prove that BMED can be considered a technically feasible option for the production of 1.0 M or higher concentrated acid and base with current efficiencies in the 60–90% range. Main factors affecting the current efficiency are proton and sulphate migration through anionic exchange membranes towards the acid stack and to a minor extent the migration of co-ions, Cl −, through cation exchange membrane towards the base stack. These results indicate that the application of the BMED process to real seawater RO brines needs the implementation of pre-treatment steps in order to eliminate interference compounds. From this work it can be further conclude that application of BMED process will contribute to ensure the recovery of valuable compounds. © 2012 Elsevier B.V. All rights reserved.

This study suggests that the application of a BMED-based process allows the recovery of beneficial products such as acids and bases solutions and provide environmental benign by reducing the environmental impact of the discharged seawater RO desalination brines. Working with model seawater concentrates in a laboratory benchscale set-up, this technology has proved to be technically feasible option for the production of 1.0 M or higher acid and base solutions that can potentially be used within the treatment plant. Current efficiencies in the range 60–90% are obtained. The main factors affecting the current efficiency are the proton and sulphate migration though the anionic exchange membranes towards the acid stack and to a minor extent the migration of co-ions, Cl−, through the cation-exchange membrane towards the base stack. The application of the BMED process to real seawater RO concentrates needs the implementation of pre-treatment steps in order to remove multivalent cations and anions responsible for the potential scaling and fouling problems in the membranes. Additionally the identification of optimized pretreatment options needs to be conducted to determine application of these processes in the rapidly growing membrane desalination industry. Table 3 Quality Standards of Commercial Chemicals. Impurities in commercial grade NaOH Fig. 8. Evolution of chloride in base stack from BMED at different current densities.