Calcium carbonate scaling in seawater desalination by ammonia–carbon dioxide forward osmosis: Mechanism and implications

Abstract

Forward Osmosis (FO) is an osmotically driven membrane process, where the membrane separates a draw solution (DS) with high salinity from a feed solution (FS) with low salinity. There can be a counter direction flow of salt (i.e., salt leakage) that may interact with the water flux through the FO membrane. For the first time reported, this study describes a new calcium carbonate scaling phenomenon in the seawater FO desalination process using ammonium bicarbonate as the DS. The scaling on the membrane surface at the feed side is caused by the interaction between an anion reversely diffused from the DS and a cation present in the FS, causing a significant decline of the water flux. The composition of the scaling layer is dominated by the solubility (represented as solubility product constant, Ksp) of salt formed by the paired anion and 2 cation. Membrane surface morphology plays a crucial role in the reversibility of the scaling. If the scaling occurs on the active layer of the FO membrane, hydraulic cleaning (increasing crossflow velocity) efficiency to restore the water flux is up to 82%. When scaling occurs on the support layer of the FO membrane, the hydraulic cleaning efficiency is strongly reduced, with only 36% of the water flux recovered. The present study reveals the risk of scaling induced by the interaction of feed solute and draw solute, which is different from the scaling caused by the supersaturation in reverse osmosis and other FO studies reported. The scaling investigated in this study can occur with a very low solute concentration at an early stage of the FO process. This finding provides an important implication for selection of draw solution and development of new membranes in the FO process.

Assessment of pilot scale forward osmosis system for Arabian Gulf seawater desalination using polyelectrolyte draw solution

“…This means that the quality of the product water does not meet the World Health Organization (WHO) standards. Furthermore, there is a strong propensity of membrane scaling with carbonate ions at the FS side [18]. In addition, regenerating NH 3 and CO 2 gases is usually accompanied with undesirable water evaporation, which eventually leads to an increase in the energy consumption as well as difficulties in maintaining a stable DS concentration for FO stage [19].…”

Scale formation mechanisms and its control by antiscalants in FO membrane under low temperature conditions

“…However, FO is not completely free from problems of membrane fouling, especially if the fouling occurs due to scale formation of sparingly soluble salts such as CaSO 4 , CaCO 3 , and silica [19,20]. Unlike particles and organics, the foulant layers formed from scaling are compact and strongly stick to the membrane surface even if there is no or negligible applied hydraulic pressure in FO.…”

“…Unlike particles and organics, the foulant layers formed from scaling are compact and strongly stick to the membrane surface even if there is no or negligible applied hydraulic pressure in FO. Thus, scale formation is a critical problem not only in RO processes but also FO processes as long as the feed water contains such salts [20]. Once scale formation occurs, it leads to a significant flux reduction and thus hinders efficient operation of the process [21].…”

“…Once scale formation occurs, it leads to a significant flux reduction and thus hinders efficient operation of the process [21]. Accordingly, there have been a lot of researches on the scaling of FO process [19][20][21][22][23].…”

Improving Anti-fouling Properties of Polyamide Forward Osmosis Membrane by grafting Poly ethylenimine and silver nanoparticles

“…Forward osmosis technology was widely used in seawater desalination [1][2][3], surfactant wastewater treatment [4] and other fields because of its low energy consumption, simple operation and high water recovery ratio. Polyamide composite forward osmosis membranes have a wide range of applications in the treatment of high salt-containing wastewater due to their high salt rejection and wide pH range.…”