As the need for drinkable water increases, thermal and membrane desalination of seawater have emerged as the two most effective solutions. Both thermal and membrane desalination systems, however, release large quantities of concentrated brine back into the sea. The continuous discharge of enormous amount of brine into the sea will disrupt the aquatic ecosystem and increase the seawater salinity level. In this study, spray dry technology is utilized for isolation of minerals from reverse osmosis brine and there by achieving zero liquid discharge concept. The procedure involves spraying feed into a chamber, followed by the introduction of heated air. The flow rates of the spray dryer and hot air can be adjusted. Consequently, the amount and concentration of feed residue in the chamber can be altered. The residue from the first vaporization chamber was cooled to a specified temperature and centrifuged to separate the minerals in crystal form. The centrifuge reject was fed to a second vaporization chamber for further concentration and separation of pure mineral salts. This cycle was repeated between two and six times to isolate all significant minerals from the brine. The vaporized water from all chambers was condensed to generate pure water as a by-product.
The separation of toxic boron from seawater using nanofiltration (NF) membrane technology is challenging due to the neutral charge associated with boric acid at seawater pH. In this study, the ethylenediamine functionalized Graphene oxide (EDA-GO) derivative is utilized as a nanofiller to coat the active top layer of the NF membrane over the polyethersulfone ultrafiltration support. The coating involved a self-assembly reaction of hydrolyzed trimesic acid (TMA) molecules facilitated by a triethylamine base. The unique hypothesis for coating enabled the –NH2 of EDA-GO to interact with the –COOH of TMA via hydrogen bonding interactions. The rejection shown by the M-0.05 membrane with 0.05wt% loading of EDA-GO towards MgSO4, Na2SO4, and NaCl was >98%, >97%, and 63%, respectively. The same membrane produced water flux in the range of 35-37 L/m2h with the modest significance of the salts on the membrane flux. The M-0.05 membrane showed significantly higher rejection towards boron (>47%) with a flux of 16.7 L/m2h for the beachwell seawater feed owing to the repulsive interaction between the borate ions and -NH2 and -OH groups. The rejection and flux offered by the M-0.05 membrane towards seawater's monovalent and divalent constituents were much higher than the commercial NF-90 and NF-270.
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