Showing papers on "Reverse osmosis published in 2017"

Graphene membranes for water desalination

Abstract: Extensive environmental pollution caused by worldwide industrialization and population growth has led to a water shortage. This problem lowers the quality of human life and wastes a large amount of money worldwide each year due to the related consequences. One main solution for this challenge is water purification. State-of-the-art water purification necessitates the implementation of novel materials and technologies that are cost and energy efficient. In this regard, graphene nanomaterials, with their unique physicochemical properties, are an optimum choice. These materials offer extraordinarily high surface area, mechanical durability, atomic thickness, nanosized pores and reactivity toward polar and non-polar water pollutants. These characteristics impart high selectivity and water permeability, and thus provide excellent water purification efficiency. This review introduces the potential of graphene membranes for water desalination. Although literature reviews have mostly concerned graphene’s capability for the adsorption and photocatalysis of water pollutants, updated knowledge related to its sieving properties is quite limited. Water desalination plants stand to markedly reduce their energy consumption once nanoporous graphene-based membranes are optimized. Purifying brackish water with reverse osmosis works most efficiently when membranes are as thin, selective and strong as possible. Mady Elbahri from Aalto University in Finland reviews efforts to achieve these goals using graphene monolayers perforated with nanoscale pores. Recent roll-to-roll fabrications of graphene onto polymer supports show that inexpensive, large-scale production of these ultrathin membranes is feasible. It remains challenging, however, to tailor the nanochannels and selectivity of single-atom-thick material. An alternative may be to switch to multilayered graphene oxide membranes. These substances can be engineered with different molecular cross-linking agents between each carbon layer, opening room to insert negatively charged functional groups that target and electrostatically repel sodium ions. Graphene nanomaterials hold great promise for the development of advanced water purification membranes, especially for water desalination. Their atomic thickness, extraordinary mechanical stability and potential for size-selective transport are ideal features, encouraging the membrane scientist across the world to investigate their applicability for water desalination. Graphene can potentially desalinate water either as monolayer or as multilayer membranes. In this review, we discuss these different classes of graphene membranes and highlight their merits and shortcomings. In addition, the theory behind their performance is presented in detail.

Fruit juice processing using membrane technology: A review

Abstract: Membrane technology has emerged as a substitute to traditional juice clarification and concentration processes as they require less manpower, reduce operating cost and low temperature. It is a low temperature process in which the organoleptic quality of the juice is almost retained. The advantages of these membrane processes over traditional methods are lower thermal damage to product, increase in aroma retention, less energy consumption, and lower equipment costs. Membrane concentration of fruit juice not only provides microbiological stability but also permits economy in packaging and distribution of the finished product due to a reduction in bulk by weight and volume. The biggest problem in the use of membrane based processes for the clarification/concentration of fruit juices is membrane fouling. Membrane fouling manifests itself as a decline in flux with the time of operation, reducing the membrane permeability. The degree of membrane fouling determines the frequency of cleaning, the lifetime of the membrane, the membrane area needed and consequently costs, design and operation of membrane plants. In this review, different membrane separation methods including microfiltration, ultrafiltration, nanofiltration and reverse osmosis for fruit juice clarification/concentration reported in the literature in the last fifteen years are discussed. Membrane Distillation methods for juice concentration is also covered in this review.

Relating Silica Scaling in Reverse Osmosis to Membrane Surface Properties.

Abstract: We investigated the relationship between membrane surface properties and silica scaling in reverse osmosis (RO). The effects of membrane hydrophilicity, free energy for heterogeneous nucleation, and surface charge on silica scaling were examined by comparing thin-film composite polyamide membranes grafted with a variety of polymers. Results show that the rate of silica scaling was independent of both membrane hydrophilicity and free energy for heterogeneous nucleation. In contrast, membrane surface charge demonstrated a strong correlation with the extent of silica scaling (R2 > 0.95, p < 0.001). Positively charged membranes significantly facilitated silica scaling, whereas a more negative membrane surface charge led to reduced scaling. This observation suggests that deposition of negatively charged silica species on the membrane surface plays a critical role in silica scale formation. Our findings provide fundamental insights into the mechanisms governing silica scaling in reverse osmosis and highlight th...

Reverse osmosis desalination powered by photovoltaic and solar Rankine cycle power systems: A review

Abstract: In this work, reverse osmosis water desalination plants powered by PV and solar RC cycle systems are reviewed in detail. This review focused on the display of different designs and software used to improve productivity of the desalination plants as well as the types of solar collectors used, membrane, heat transfer fluid and working fluid of the Rankine cycle. The specific energy consumption and cost of fresh water production are also of great interest in this work. According to the results presented in this review it is not recommended to use batteries with PV to drive RO desalination plants because of the high capital and replacement cost of batteries. It is also found that when the energy recovery devices are used, the pre-heating of feed water is not required, especially in the case of PV-RO systems. Currently most of working RO plants are driven by PV, whereas solar thermal power systems (usually using PTC with ORC) are still at the stage of theoretical research. Although, the PTC-ORC-RO desalination system is recommended, it has not yet been implemented on a large scale.

Biofouling in reverse osmosis: phenomena, monitoring, controlling and remediation

Abstract: This paper is a comprehensive review of biofouling in reverse osmosis modules where we have discussed the mechanism of biofouling Water crisis is an issue of pandemic concern because of the steady rise in demand of drinking water Overcoming biofouling is vital since we need to optimize expenses and quality of potable water production Various kinds of microorganisms responsible for biofouling have been identified to develop better understanding of their attacking behavior enabling us to encounter the problem Both primitive and advanced detection techniques have been studied for the monitoring of biofilm development on reverse osmosis membranes Biofouling has a negative impact on membrane life as well as permeate flux and quality Thus, a mathematical model has been presented for the calculation of normalized permeate flux for evaluating the extent of biofouling It is concluded that biofouling can be controlled by the application of several physical and chemical remediation techniques

Rational Design and Strain Engineering of Nanoporous Boron Nitride Nanosheet Membranes for Water Desalination

Abstract: Through systematic molecular dynamics simulations we theoretically investigate the potential applications of hexagonal boron nitride (h-BN) for seawater desalination. Our results indicate that the rationally designed h-BN membranes have great permeability, selectivity, and controllability for water desalination. The size and chemistry of the pores are shown to play an important role in regulating the water flux and salt rejection. Pores with only nitrogen atoms on the edges have higher fluxes than the boron-lined pores. In particular, two-dimensional h-BN with medium-sized N4 pores show 100% salt rejection with outstanding water permeability, which is several orders of magnitude higher than that of conventional reverse osmosis membranes. Furthermore, we study the mechanical strain effect on the desalination performance of monolayer h-BN with relatively small N3 pores, suggesting that water flux and salt rejection can be precisely tuned by tensile strain. The findings in the present work unambiguously prop...

Advances in Polymeric Nanofiltration Membrane: A Review

Abstract: The nanofiltration membrane was first introduced during late 1980s possessing properties between reverse osmosis and ultrafiltration membrane. Nanofiltration membranes have been used for applications including food industry, pharmaceutical, wastewater treatment, and desalination. This review presents an inclusive outlook of recent research and advances in polymeric nanofiltration membrane technology. Various methods were reported for nanofiltration membrane preparation particularly through electron beam irradiation, UV/photografting, layer by layer, plasma treatment, interfacial polymerization, and nanoparticle incorporation. Nanofiltration membranes were reported to remove microorganisms, turbidity, dissolved salts, and hardness. Major problem in application is nanofiltration membrane fouling, thus efforts regarding fouling mitigation are discussed.