Application of Zwitterions in Forward Osmosis: A Short Review

Abstract

Forward osmosis (FO) is an important desalination method to produce potable water. It was also used to treat different wastewater streams, including industrial as well as municipal wastewater. Though FO is environmentally benign, energy intensive, and highly efficient; it still suffers from four types of fouling namely: organic fouling, inorganic scaling, biofouling and colloidal fouling or a combination of these types of fouling. Membrane fouling may require simple shear force and physical cleaning for sufficient recovery of membrane performance. Severe fouling may need chemical cleaning, especially when a slimy biofilm or severe microbial colony is formed. Modification of FO membrane through introducing zwitterionic moieties on the membrane surface has been proven to enhance antifouling property. In addition, it could also significantly improve the separation efficiency and longevity of the membrane. Zwitterion moieties can also incorporate in draw solution as electrolytes in FO process. It could be in a form of a monomer or a polymer. Hence, this review comprehensively discussed several methods of inclusion of zwitterionic moieties in FO membrane. These methods include atom transfer radical polymerization (ATRP); second interfacial polymerization (SIP); coating and in situ formation. Furthermore, an attempt was made to understand the mechanism of improvement in FO performance by zwitterionic moieties. Finally, the future prospective of the application of zwitterions in FO has been discussed.

Surface Zwitterionization via Grafting of Epoxylated Sulfobetaine Copolymers onto PVDF Membranes for Improved Permeability and Biofouling Mitigation

“…where W w is the weight of the wetted membrane and W d is the weight of the dried membrane. The densities of PVDF (ρ p ) and butanol (ρ b ) are 1.78 and 0.81 g/cm 3 , respectively. 2.5.…”

“…Because of these advantages, it can easily be adapted on a commercial scale for a wide variety of applications comprising wastewater treatment, desalination, gas-oil, biomedical, pharmaceutical, and nuclear technology. , However, a major challenge faced by membranologists is membrane fouling. Different types of membrane fouling can occur during the membrane separation process, such as concentration polarization, bacterial adhesion and biofilm formation, and the formation of reversible/irreversible cake layers. , Mitigating biofouling of membranes is clearly needed to extend the life of membranes for application in biomedical fields …”

“…Introducing zwitterions on membrane surfaces or interfaces has been attempted through in situ formation of the active layer, surface coating, interfacial polymerization, and atom transfer radical polymerization for biomedical applications. ,− Nayak et al simultaneously modified the PVDF membrane using polydopamine and alkylamines. Afterward, the amino groups in the modified PVDF membrane were zwitterionized using 1,3-propanesultone.…”

Comparison of Fouling Behavior in Cellulose Triacetate Membranes Applied in Forward and Reverse Osmosis

“…Reverse osmosis (RO) has been the leading membrane separation process for production of clean water. It has been applied in desalination, wastewater treatment, and recovery of resources. , However, RO requires a large amount of energy to produce clean water because it operates at high hydraulic pressure to surpass the osmotic pressure of the saline feedwater. , Aside from RO, forward osmosis (FO) has been considered as an alternative for desalination, wastewater treatment, and solvent recovery in this decade. − Because its driving force depends on natural osmotic pressure, it only involves minimal usage of energy for pumping the fluids . The hybrid FO system has a generation of a draw solution process that may outperform the RO process when treating challenging feedwater. − The performance of the FO process relies on the type of membrane modules and the characteristics of the membrane …”

“…16 Membrane fouling reduces the water flux for long-term operating because of the adsorption and deposition of contaminants on the surface of the membrane. 11,17,18 This increases the mass transfer resistance for water to permeate. Hence, it becomes a severe problem for water treatment, design of membranes, and unit operation.…”