An electrokinetic approach to fabricating aquaporin biomimetic membranes for water purification

The desalination technology of choice today is reverse osmosis (RO). In this process saline water is forced using mechanical pressure across a membrane that can selectively pass water and reject almost all ions and most neutral molecules. Reverse osmosis proved to be robust and most energy efficient technology that can be exploited for a wide range of water sources. Nevertheless water desalination is still an energy intensive process. Theoretical calculations show that the minimum required energy for seawater desalination is about 1 kW hr m-3, whereas the most energy optimized plants require 2-4 kWh m-3, suggesting that there is much room for improving the membranes performance and energy efficiency (Shannon et al. 2008). Despite the numerous improvements the RO membranes have gone through over the last 5 decades, they are still inferior to cell membranes both in terms of permeability and, especially, selectivity. The fast and selective water transport in biological membranes is achieved by means of aquaporins, specialized trance-membrane proteins. The osmotic water permeability of aquaporins was shown to be in the range of 6×10-14 11×10-14 cm3 sec-1 channel-1 for AQP1 (Saparov et al. 2001) and their ion rejection exceeds by far the ion rejection of the most advanced commercial membranes. Estimates show that a biomimetic lipid bilayer with incorporated aquaporins with a lipids to protein ratio (LPR) of 50, would yield a membrane with a hydraulic permeability of ~9 – 16.5 L m-2 hr-1 bar-1 whereas the permeability of seawater RO membrane does not exceed 2 L m-2 hr-1 bar-1 (Kaufman, Berman & Freger 2010). Biological membranes are also known to reject small molecules, such as urea or boric acid, which are poorly removed by commercial membranes (Borgnia et al. 1999). The combination of ultra-selectivity with extremely high water permeability makes biomimetic membranes highly attractive for water purification applications. It is important to emphasize that water transport through biological membranes, usually existing as microscopic free-standing self-supporting structures, is usually driven by electrochemical potential gradients, i.e. osmotic pressure or electric field (Tanaka, Sackmann 2005). However, for practical membrane applications, such as water purification, the use of hydraulic pressure as a driving force and planar membranes of macroscopic dimensions, the common configuration in membrane technology, will be far more preferable. However, the preparation of such biomimetic membranes poses a number of challenging questions, such as: how can one prepare a large and defect-free biomimetic planar membrane? can they be made to withstand hydraulic pressures? how can aquaporins be incorporated in such membranes? will aquaporins keep their activity under a hydraulic pressure gradient?

Hybrid membrane system for desalination and wastewater treatment : Integrating forward osmosis and low pressure reverse osmosis

Flat sheet thin film composite forward osmosis membranes for water treatment and purification: A review on modification techniques and concepts

In recent years, membrane technology has been widely used in wastewater treatment and water purification. Membrane technology is simple to operate and produces very high quality water for human consumption and industrial purposes. One of the promising technologies for water and wastewater treatment is the application of forward osmosis. Essentially, forward osmosis is a process in which water is driven through a semipermeable membrane from a feed solution to a draw solution due to the osmotic pressure gradient across the membrane. The immediate advantage over existing pressure driven membrane technologies is that the forward osmosis process per se eliminates the need for operation with high hydraulic pressure and forward osmosis has low fouling tendency. Hence, it provides an opportunity for saving energy and membrane replacement cost. However, there are many limitations that still need to be addressed. Here we briefly review some of the applications within water purification and new developments in forward osmosis membrane fabrication.

Polymeric PDI-based photocatalytic nanoarchitectures promoting the performance of thin film composite membrane for forward osmosis water purification

Membrane technologies for heavy metals removal from water and wastewater: A mini review

Characterization of novel forward osmosis hollow fiber membranes

Water desalination by forward (direct) osmosis phenomenon: A comprehensive review

A wide variety of methods are used for water treatment and purification. The use of membranes allows efficient treatment by reverse osmosis, nanofiltration, ultrafiltration, microfiltration, membrane distillation and forward osmosis. Membrane technology has been researched extensively for water treatment and desalination. Desalination is the technology predominantly used to solve water scarcity. The sustainability of desalination processes aims at reducing energy costs and increasing water recovery. In recent years numerous large-scale seawater desalination plants have been built in water-stressed countries. Construction of new desalination plants with the latest emerging technology is expected to increase in the future. Despite major advances in desalination technologies, seawater desalination is still more energy intensive compared to conventional processes uszd for the treatment of fresh water. However, forward osmosis and membrane distillation are emerging for sustainable desalination.

Forward osmosis (FO) is an emerging membrane separation technology. It is different from the well-studied pressure-driven membrane separation processes. The FO process is based on water transport under an osmotic pressure difference across a semi-permeable membrane. The distinct operating conditions lead to unique technical challenges during the exploitation of FO technology. According to a comprehensive literature investigation, one of the stringent barriers is lacking of effective FO membranes. The objectives of this research were to develop high performance FO membranes, and furthermore, to systematically study the mass transport and the governing mechanisms in FO process. Thin film composite (TFC) FO membranes with a tailored support structure were developed in this study. The membranes consisted of a highly porous substrate with finger-like pore structure, which was prepared via phase inversion, and a polyamide rejection layer synthesized by interfacial polymerization. The TFC FO membranes had small structural parameters due to the thin cross-section, low tortuosity, and high porosity of the substrates. The membrane rejection layers exhibited superior separation properties (higher water permeability and excellent selectivity) relative to commercial FO membranes. Under FO testing conditions, these membranes achieved high water flux while maintaining relatively low solute reverse diffusion. Comparison of the synthesized TFC FO membranes with commercial FO and reverse osmosis (RO) membranes revealed the critical importance of the substrate structure, with a straight finger-like pore structure preferred over a spongy pore structure to minimize internal concentration polarization (ICP), a unique and critical problem resulting in low water flux in the osmotically driven membrane processes. In addition, membranes with high water permeability and excellent selectivity are preferred to achieve both high FO water flux and low solute flux. The results proved that TFC membranes with a tailored porous substrate and rejection layer are promising for FO applications. In the study of polyamide rejection layer synthesis, the influence of monomer concentrations (i.e., m-phenylenediamine (MPD) and trimesoyl chloride (TMC) concentrations) on the membrane separation properties as well as the FO performance was systematically investigated. A strong trade-off between the water permeability and salt rejection of the membranes was observed, where reducing the MPD concentration or increasing the TMC concentration may result in a higher membrane permeability but a lower salt rejection. In FO tests, membranes with poor salt rejection had severe solute reverse diffusion, which enhanced the severity of ICP. It was found that the FO water flux was governed by both the membrane water permeability and solute rejection. For a membrane with higher water permeability but lower solute rejection, the reduced membrane frictional resistance was compensated simultaneously by the more severe solute-reverse-diffusion-induced ICP. The net effect on the FO water flux depends on the competition of these two opposing mechanisms. Under conditions where solute reverse diffusion may cause severe ICP (e.g., high draw solution concentration and high water flux level), membranes need to be optimized to achieve a high salt rejection even if this is at the expense of lower water permeability. In view of the importance of the water permeability and salt permeability on FO performance, a systematic comparison study of prevailing semi-permeable FO membranes with nanofiltration (NF)-like and RO-like separation properties in terms of flux performance and fouling behavior was conducted. Due to the crucial influence of solute reverse diffusion on FO water flux, the high-rejection RO-like FO membranes generally performed better than the NF-like counterparts in sodium chloride based FO tests. On the other hand, the high permeability of NF-like FO membranes could achieve higher water flux, when proper draw solutes were used to minimize draw solute leakage. Fouling tests suggested that the NF-like TFC FO membranes tended to be more fouling resistant due to their relatively smooth membrane surface. This work further elucidated the major mechanisms that govern the FO performance. These mechanisms were summarized as a frictional resistance loss mechanism (MR), solute-reverse-diffusion-induced ICP (MICP-Js), concentration of feed solutes (concentrative ICP or MICP-feed in the active-layer-facing-draw-solution orientation) and dilution of draw solutes (dilutive ICP or MICP-draw in the active-layer-facing-feed-solution orientation). These mechanisms are related to the properties of membrane, draw and feed solutions. This work led to a set of systematic criteria for the selection of FO membranes, draw solution and optimization of other operating conditions, of which the practicability was demonstrated in potential FO applications.

Separation of Peptides and Interaction with Forward Osmosis Biomimetic Membranes: A Solution Diffusion Model

Mechanically robust and highly permeable AquaporinZ biomimetic membranes

Rapid industrial growth and urbanization will be the major causes of environmental pollution, wastewater, and water quality deterioration. However, the technological advancement in water purification and the water treatment area will be the breakthrough. In recent ten years, membrane-based technology evolved for wastewater treatment, water desalination and power generation. Integration of technology like reverse osmosis(RO) and forward osmosis(FO) provides ambitious benefits like efficient recovery of osmotic energy from brine, improvement in the tendency of fouling and scaling and less quantity of chemical required for pre-treatment. This study reviews various technology that helps towards the wastewater treatment and water desalination with different integration and configuration. Majorly RO and FO integration gives promising outcome in both the situation and it could be price competitive with reverse osmosis systems when its recovery rate of the system is very high, the membrane flux and the membrane cost of the forward osmosis are like those of the reverse osmosis, and the electricity cost is expensive. The most important thing in commercializing the FO process is enhancing performance by improving flux and increasing recovery. An industrial-scale RO-FO hybrid system will be lucrative with membrane that provides greater flux, high selectivity, batter mechanical stability and robustness.

Efforts have been rendered by researchers to address water purification and desalination challenges through membrane separation processes. However, the trade-off phenomenon in permeability and selectivity constrained the membranes’ usage. Recent advances made in fabricating membranes, especially thin film nanocomposite (TFN) membranes using functionalized nanofillers, have high performance in water purification and desalination. In this review, state-of-the-art thin film composite (TFC) membranes in water purification and desalination along with their drawbacks are discussed. The urgent demands as an alternative of TFC membranes are highlighted for high-performance membranes. Then, the fabrication and development of high permeability and selectivity of TFN membranes are discussed. Thin film nanocomposite membranes manufactured using rational nanofillers are systematically summarized. Finally, the applications of TFN membranes in water purification and desalination are reported.

Biomimetic and bioinspired membranes are the efficient membrane technology when it comes to multiple usage scenarios, including next generations of biomaterials within the commercial separation applications, as well as, water and wastewater treatment technologies. In recent years, aquaporin biomimetic membranes for water separation have raised considerable interest. These membranes have displayed distinguished properties and outstanding performances, as diverse interactions, varying selective transport mechanisms, superior stability, maximum resistance to membrane fouling, and distinct adaptability. The biomimetic membranes have made significant contributions when it comes to water stress, environmental threats and energy. It has the potential to produce clean water more efficiently than reverse osmosis membranes (RO), while saving up to 80% of the energy used for desalination processes. More than half of the 15000 desalination plants around the world utilize RO technologies, and the implementation of biomimetic membranes on a large scale could save hundreds of millions of dollars in energy cost annually (potential savings of $1.45 million/year for 100 ML/day desalination plant). This paper discusses the interplay of the main components of aquaporin biomimetic membranes: aquaporin proteins, block copolymers for aquaporin proteins reconstitution, and polymer-based supporting structures. We focus specifically on the challenges and review recent developments on the interplay between aquaporin proteins and block copolymers. The recent efforts in embedding reconstituted aquaporin proteins in membrane designs that are based on conventional thin film interfacial polymerization techniques are evaluated. In addition, emerging challenges and opportunities for biomimetic membranes are studied from the perspective of current and future applications.