Inorganic Scaling in Membrane Desalination: Models, Mechanisms, and Characterization Methods

Abstract

Inorganic scaling caused by precipitation of sparingly soluble salts at supersaturation is a common but critical issue, limiting the efficiency of membrane-based desalination and brine management technologies as well as other engineered systems. A wide range of minerals including calcium carbonate, calcium sulfate, and silica precipitate during membrane-based desalination, limiting water recovery and reducing process efficiency. The economic impact of scaling on desalination processes requires understanding of its sources, causes, effects, and control methods. In this Critical Review, we first describe nucleation mechanisms and crystal growth theories, which are fundamental to understanding inorganic scale formation during membrane desalination. We, then, discuss the key mechanisms and factors that govern membrane scaling, including membrane properties, such as surface roughness, charge, and functionality, as well as feedwater characteristics, such as pH, temperature, and ionic strength. We follow with a critical review of current characterization techniques for both homogeneous and heterogeneous nucleation, focusing on the strengths and limitations of each technique to elucidate scale-inducing mechanisms, observe actual crystal growth, and analyze the outcome of scaling behaviors of desalination membranes. We conclude with an outlook on research needs and future research directions to provide guidelines for scale mitigation in water treatment and desalination.

Nanofiltration Membranes with Crumpled Polyamide Films: A Critical Review on Mechanisms, Performances, and Environmental Applications

“…In short, although a smooth polyamide film generally has a low fouling propensity, a crumpled polyamide film with well-designed morphologies could potentially out-perform its smooth counterpart as a result of the associated antifouling mechanisms such as the enhancement of local shear and the reduction of local flux. In addition to membrane fouling, inorganic scaling could also be influenced by surface morphologies. , A rough surface often has a higher scaling potential, possibly because of the favorable formation/deposition of scaling nuclei at the valleys , and the enhanced concentration polarization at the hydraulic stagnant spots. , However, similar to membrane fouling, membrane scaling may also be mitigated by a well-designed crumpled morphology. For example, with a crumpled polyamide, the enhancement of local shear and the reduction of local flux may promote the detachment of scaling nuclei and crystals, , thereby inhibiting the development of scaling.…”

“…In addition to membrane fouling, inorganic scaling could also be influenced by surface morphologies. , A rough surface often has a higher scaling potential, possibly because of the favorable formation/deposition of scaling nuclei at the valleys , and the enhanced concentration polarization at the hydraulic stagnant spots. , However, similar to membrane fouling, membrane scaling may also be mitigated by a well-designed crumpled morphology. For example, with a crumpled polyamide, the enhancement of local shear and the reduction of local flux may promote the detachment of scaling nuclei and crystals, , thereby inhibiting the development of scaling.…”

“…In addition to membrane fouling, inorganic scaling could also be influenced by surface morphologies. 207,208 A rough surface often has a higher scaling potential, possibly because of the favorable formation/ deposition of scaling nuclei at the valleys 209,210 and the enhanced concentration polarization at the hydraulic stagnant spots. 172,179 However, similar to membrane fouling, membrane scaling may also be mitigated by a well-designed crumpled morphology.…”

“…172,179 However, similar to membrane fouling, membrane scaling may also be mitigated by a well-designed crumpled morphology. For example, with a crumpled polyamide, the enhancement of local shear and the reduction of local flux may promote the detachment of scaling nuclei and crystals, 207,211 thereby inhibiting the development of scaling.…”

Engineering Surface Wettability to Alleviate Membrane Scaling in Photothermal Membrane Distillation

“…The first step of membrane inorganic scaling is to initiate heterogeneous nucleation on the membrane surface . A more hydrophobic surface provided a higher energy barrier, thereby weakening the tendency to nucleate. , Therefore, the #PCNT-2 should possess a better antiscaling property. However, during the PMD process, the membrane scaling is highly dependent on membrane surface temperature.…”