Membrane-based separation has gained increased popularity over the past few decades, particularly reverse osmosis (RO). A major impediment to the improved performance of membrane separation processes, in general, is membrane fouling. Fouling has detrimental effects on the membrane’s performance and integrity, as the deposition and accumulation of foulants on its surface and/or within its pores leads to a decline in the permeate flux, deterioration of selectivity, and permeability, as well as a significantly reduced lifespan. Several factors influence the fouling-propensity of a membrane, such as surface morphology, roughness, hydrophobicity, and material of fabrication. Generally, fouling can be categorized into particulate, organic, inorganic, and biofouling. Efficient prediction techniques and diagnostics are integral for strategizing control, management, and mitigation interventions to minimize the damage of fouling occurrences in the membranes. To improve the antifouling characteristics of RO membranes, surface enhancements by different chemical and physical means have been extensively sought after. Moreover, research efforts have been directed towards synthesizing membranes using novel materials that would improve their antifouling performance. This paper presents a review of the different membrane fouling types, fouling-inducing factors, predictive methods, diagnostic techniques, and mitigation strategies, with a special focus on RO membrane fouling.

A Comprehensive Review on Membrane Fouling: Mathematical Modelling, Prediction, Diagnosis, and Mitigation

Fouling control in reverse osmosis for water desalination & reuse: Current practices & emerging environment-friendly technologies.

Reverse osmosis is the leading technology for desalination of brackish water and seawater, important for solving the growing problems of fresh water supply. Thermal technologies such as multi-effect distillation and multi-stage flash distillation still comprise an important portion of the world’s desalination capacity. They consume substantial amounts of energy, generally obtained from fossil fuels, due to their low efficiency. Hybridization is a strategy that seeks to reduce the weaknesses and enhance the advantages of each element that makes it up. This paper introduces a review of the most recent publications on hybridizations between reverse osmosis and thermal desalination technologies, as well as their integration with renewable energies as a requirement to decarbonize desalination processes. Different configurations provide improvements in key elements of the system to reduce energy consumption, brine production, and contamination, while improving product quality and production rate. A combination of renewable sources and use of energy and water storage systems allow for improving the reliability of hybrid systems.

Recent Desalination Technologies by Hybridization and Integration with Reverse Osmosis: A Review

Metal-organic framework (MOF) materials have received extensive attention for the design of advanced thin-film nanocomposite (TFN) membranes with excellent permselectivity. However, the relationship between the unique physicochemical properties and performance of engineered MOF-based membranes has yet to be extensively investigated. In this work, we investigate the incorporation of porous zinc-based MOFs (Zn-MOFs) into a polyamide active layer for the fabrication of TFN membranes on porous poly(phenylsulfone) (PPSU) support layers through an interfacial polymerization approach. The actual effects of varying the amount of Zn-MOF added as a nanofiller on the physicochemical properties and desalination performance of TFN membranes are studied. The presence and layout of Zn-MOFs on the top layer of the membranes were confirmed by X-ray photoelectron spectroscopy, scanning electron microscopy, and ζ potential analysis. The characterization results revealed that Zn-MOFs strongly bind with polyamide and significantly change the membrane chemistry and morphology. The results indicate that all four studied TFN membranes with incorporated Zn-MOFs enhanced the water permeability while retaining high salt rejection compared to a thin-film composite membrane. Moreover, the highest-performing membrane (50 mg/L Zn-MOF added nanofiller) not only exhibited a water permeability of 2.46 ± 0.12 LMH/bar but also maintained selectivity to reject NaCl (>90%) and Na2SO4 (>95%), similar to benchmark values. Furthermore, the membranes showed outstanding water stability throughout 72 h filtration and chlorine resistance after a 264 h chlorine-soaking test because of the better compatibility between the polyamide and Zn-MOF nanofiller. Therefore, the developed TFN membrane has potential to solve trade-off difficulties between permeability and selectivity. Our findings indicate that porous Zn-MOFs play a significant role in the development of a TFN membrane with high desalination performance and chlorine resistance.

Thin-Film Nanocomposite Membrane Incorporated with Porous Zn-Based Metal-Organic Frameworks: Toward Enhancement of Desalination Performance and Chlorine Resistance.

The demand for new water resources has been increasing worldwide due to the growing global population and industrialization. Membranes play a central role in water purification processes with continuous technology improvements, new uses and cost reductions. Phase inversion is the most commonly used technique for preparing polymeric membranes. However, most commercial membranes are prepared from hydrophobic materials, which make them more susceptible to suffer the adsorption or deposition of molecules over their surface or inside their pores. This phenomenon, commonly termed as fouling, is one of the major operational problems in membrane processes. This review covers different membranes modification techniques to enhance permeability and to reduce fouling and the accumulation of microorganisms on membrane surface. The physicochemical properties of membrane surface can be tuned by grafting or coating to introduce functionalities like hydrophilic moieties or charged groups. Blending hydrophilic additives into the casting solution is another approach to increase membrane hydrophilicity and to improve water filtration performance. This review summarises the variety of porous materials that have been used to introduce inorganic nanoparticles into the casting solution. Porous carriers are used to introduce antimicrobial metals by preserving nanoparticle stability. Additionally, organic compounds, especially dendritic structures, have attracted considerable interest due to their highly branched structure, and their large number of terminal functional groups, which can also be used to enhance membrane properties. This work reviews the modification and functionalization techniques recently proposed to improve permeability and durability of the membranes used in pressure-driven separations.

A critical review of membrane modification techniques for fouling and biofouling control in pressure-driven membrane processes

An efficient pretreatment system forms the backbone of a sea water desalination unit using reverse osmosis process. The pretreatment of sea water is done to bring down the turbidity, microorganisms, colloidal contaminants, total dissolved solids and silt density index of the raw sea water to acceptable levels and make it suitable for the Reverse Osmosis membrane process. The two kinds of pretreatment processes used are the conventional system and the membrane systems. The present review paper makes an effort to understand the conventional process, microfiltration, ultrafiltration, nanofiltration and integrated membrane systems for the seawater pretreatment, their advantages and limitations and the effect of the pretreated water on the performance of reverse osmosis membranes through the studies conducted by researchers as well as by considering certain case studies.

A.R. Phani

Papers

Pretreatment processes for seawater reverse osmosis desalination systems—A review