Reverse Osmosis Desalting of Inland Brackish Water of High Gypsum Scaling Propensity: Kinetics and Mitigation of Membrane Mineral Scaling

Abstract

The potential for mineral scaling that may limit the generation of new potable water resources by reverse osmosis (RO), from inland brackish water of high gypsum scaling propensity, was experimentally explored via flux decline measurements and real-time RO membrane surface imaging. Antagonistic gypsum and calcium carbonate scaling kinetics were demonstrated for high-sulfate brackish water desalting. RO scaling studies with brackish water from the California San Joaquin Valley (approximately 10 000 mg/L total dissolved solids) revealed that membrane gypsum scaling was increasingly retarded with rising bicarbonate concentrations. Crystal growth rate, fractional membrane scale coverage, and flux decline decreased by up to about 63, 78, and 73%, respectively, as the bicarbonate concentration increased, at the membrane surface, from < 0.01 to 7.81 mM, for a gypsum saturation index of 2. Inhibition of gypsum crystal growth was attributed to bicarbonate adsorption onto the crystal surfaces, and CaCO3 scaling was undetected even up to a calcite saturation index of approximately 16. Given the suppression of gypsum scaling by bicarbonate, it is essential to considerthis effect in the conventional practice of pH adjustment to suppress CaCO3 scaling. The present results suggest that antagonistic and synergistic mineral crystallization kinetics effects are important for optimizing scale-control strategies (e.g., acid and antiscalants addition to the RO feed).

Inland Desalination: Potentials and Challenges

“…However in presence of calcium, saturation and hence scaling due to calcium sulfate is very likely to happen (Rahardianato et al, 2008;Sheikholesami, 2003a;Sheikholesami, 2004). Precipitative softening processes were found to be very effective in removal of calcium, magnesium, carbonate, and silica.…”

“…In addition sulfate may result from biological oxidation of reduced sulfur species. As a result the different aspects of scaling by calcium sulfate and calcium carbonate has been intensively studied (Sheikholesami, 2003a;Sheikholesami, 2003b;Rahardianato et al, 2008).…”

Synthesis and evaluation of phosphate-free antiscalants to control CaSO 4 ·2H 2 O scale formation in reverse osmosis desalination plants

“…Effectiveness of several commercial antiscalants against gypsum scale formation was evaluated by Shih et al [10]. Based on precipitation studies, Rahardianto [11] found that increasing bicarbonate concentrations led to minimized membrane scaling with gypsum. Amjad [12] examined the inhibition of gypsum precipitation by a variety of polymeric materials and concluded that compared to polymers, surfactants perform poorly against gypsum precipitation.…”

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

“…reverse osmosis (RO) and nanofiltration (NF) [1][2][3]. Scaling is an impediment for the application of high pressure membrane process since it causes a significant decline of permeate flux and irreversible damage to the membrane.…”

“…Generally, scaling in RO and NF process is due to the supersaturation of salts at the interface of the membrane and feed solution, followed by crystallization and growth [3]. Various factors, such as temperature, hydrodynamic conditions, pH, and interaction of solutes, can affect the formation of scaling [4][5][6][7].…”