Showing papers on "Reverse osmosis published in 2019"

A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification.

Abstract: Sustainable and affordable supply of clean, safe, and adequate water is one of the most challenging issues facing the world. Membrane separation technology is one of the most cost-effective and widely applied technologies for water purification. Polymeric membranes such as cellulose-based (CA) membranes and thin-film composite (TFC) membranes have dominated the industry since 1980. Although further development of polymeric membranes for better performance is laborious, the research findings and sustained progress in inorganic membrane development have grown fast and solve some remaining problems. In addition to conventional ceramic metal oxide membranes, membranes prepared by graphene oxide (GO), carbon nanotubes (CNTs), and mixed matrix materials (MMMs) have attracted enormous attention due to their desirable properties such as tunable pore structure, excellent chemical, mechanical, and thermal tolerance, good salt rejection and/or high water permeability. This review provides insight into synthesis approaches and structural properties of recent reverse osmosis (RO) and nanofiltration (NF) membranes which are used to retain dissolved species such as heavy metals, electrolytes, and inorganic salts in various aqueous solutions. A specific focus has been placed on introducing and comparing water purification performance of different classes of polymeric and ceramic membranes in related water treatment industries. Furthermore, the development challenges and research opportunities of organic and inorganic membranes are discussed and the further perspectives are analyzed.

Osmosis, from molecular insights to large-scale applications.

Abstract: Osmosis is a universal phenomenon occurring in a broad variety of processes and fields. It is the archetype of entropic forces, both trivial in its fundamental expression - the van 't Hoff perfect gas law - and highly subtle in its physical roots. While osmosis is intimately linked with transport across membranes, it also manifests itself as an interfacial transport phenomenon: the so-called diffusio-osmosis and -phoresis, whose consequences are presently actively explored for example for the manipulation of colloidal suspensions or the development of active colloidal swimmers. Here we give a global and unifying view of the phenomenon of osmosis and its consequences with a multi-disciplinary perspective. Pushing the fundamental understanding of osmosis allows one to propose new perspectives for different fields and we highlight a number of examples along these lines, for example introducing the concepts of osmotic diodes, active separation and far from equilibrium osmosis, raising in turn fundamental questions in the thermodynamics of separation. The applications of osmosis are also obviously considerable and span very diverse fields. Here we discuss a selection of phenomena and applications where osmosis shows great promises: osmotic phenomena in membrane science (with recent developments in separation, desalination, reverse osmosis for water purification thanks in particular to the emergence of new nanomaterials); applications in biology and health (in particular discussing the kidney filtration process); osmosis and energy harvesting (in particular, osmotic power and blue energy as well as capacitive mixing); applications in detergency and cleaning, as well as for oil recovery in porous media.

Chlorination disadvantages and alternative routes for biofouling control in reverse osmosis desalination

Abstract: With an ever-increasing human population, access to clean water for human use is a growing concern across the world. Seawater desalination to produce usable water is essential to meet future clean water demand. Desalination processes, such as reverse osmosis and multi-stage flash have been implemented worldwide. Reverse osmosis is the most effective technology, which uses a semipermeable membrane to produce clean water under an applied pressure. However, membrane biofouling is the main issue faced by such plants, which requires continuous cleaning or regular replacement of the membranes. Chlorination is the most commonly used disinfection process to pretreat the water to reduce biofouling. Although chlorination is widely used, it has several disadvantages, such as formation of disinfection by-products and being ineffective against some types of microbes. This review aims to discuss the adverse effect of chlorination on reverse osmosis membranes and to identify other possible alternatives of chlorination to reduce biofouling of the membranes. Reverse osmosis membrane degradation and mitigation of chlorines effects, along with newly emerging disinfection technologies, are discussed, providing insight to both academic institutions and industries for the design of improved reverse osmosis systems.

Applications of Nanoparticles in Wastewater Treatment

Abstract: High-quality water is the most sought-after resource for human survival. Various natural and anthropogenic activities have contributed to groundwater pollution and have affected the quality of drinking water in the past few decades. Release of toxic effluents from the industrial sector is a major source of groundwater pollution. Different conventional methods used for purification of water involve use of adsorbents, reverse osmosis, ion exchange, and electrostatic precipitation, with the disadvantages of high cost, poor recyclability, and low efficiency. Despite progress made in the development of sustainable technologies, their use has been limited, largely because of the limitations of the materials’ properties, including their costs. Use of nanoparticles would help to solve this problem and would address the consequences of the presence of pesticides and heavy metals in water. Nanoparticles possess useful characteristics such as a direct bandgap, a high optical absorption coefficient, a layered structure, tunable band edges for optimized catalysis, low cost, and low toxicity. This review addresses different properties of nanoparticles contributing to water treatment and nanoadsorbents used for removal of numerous pollutants in groundwater purification.

A tale of two treatments: the multiple barrier approach to removing chemical contaminants during potable water reuse

Abstract: ConspectusIn response to water scarcity and an increased recognition of the risks associated with the presence of chemical contaminants, environmental engineers have developed advanced water treatment systems that are capable of converting municipal wastewater effluent into drinking water. This practice, which is referred to as potable water reuse, typically relies upon reverse osmosis (RO) treatment followed by exposure to ultraviolet (UV) light and addition of hydrogen peroxide (H2O2). These two treatment processes individually are capable of controlling many of the chemical and microbial contaminants in wastewater; however, a few chemicals may still be present after treatment at concentrations that affect water quality.Low-molecular weight (<200 Da), uncharged compounds represent the greatest challenge for RO treatment. For potable water reuse systems, compounds of greatest concern include oxidation products formed during treatment (e.g., N-nitrosodimethylamine, halogenated disinfection byproducts) and...

Photothermal Membrane Water Treatment for Two Worlds.

Abstract: In meeting the increasing need for clean water in both developing and developed countries and in rural and urban communities, photothermal membrane water treatment technologies provide outstanding advantages: For developing countries and rural communities, by utilizing sunlight, photothermal membrane water treatment provides inexpensive, convenient, modular, decentralized, and accessible ways to clean water, which can reduce the consumption of conventional energy (e.g., electricity, natural gas) and the cost of clean water production. In developed countries and urban communities, photothermal membrane water treatment can improve the energy efficiency during water purification. In these water purification processes, the light absorption and light-to-heat conversion of photothermal materials are important factors in determining the membrane efficacy. Nanomaterials with well-controlled structure and optical properties can increase the light absorption and photothermal conversion of newly developed membranes. This Account introduces our recent work on developing scalable, cost-effective, and highly efficient photothermal membranes for four water purification applications: reverse osmosis (RO), ultrafiltration (UF), solar steam generation (SSG), and photothermal membrane distillation (PMD). By utilizing photothermal materials, first, we have demonstrated how sunlight can be used to improve the membrane's resistance to biofouling in RO and UF processes by photothermally induced inactivation of microorganisms. Second, we have developed novel SSG membranes (i.e., interfacial evaporators) that can harvest solar energy, convert it to localized heat, and generate clean water by evaporation. This desalination approach is particularly useful and promising for treatment of highly saline water. These new interfacial evaporators utilized graphene oxide (GO), reduced graphene oxide (RGO), molybdenum disulfide (MoS2), and polydopamine (PDA). The solar conversion efficiency and environmental sustainability of the interfacial evaporators were optimized via (i) novel and versatile bottom-up biofabrication (e.g., incorporation of photothermal materials during bacterial nanocellulose (BNC) growth) and (ii) easy and cost-effective top-down preparation (e.g., modification of natural wood with photothermal materials). Third, we have developed membranes for PMD that incorporate photothermal materials to generate heat under solar irradiation, thus providing a higher transmembrane temperature difference and higher driving force for effective vapor transport, making the membrane distillation process more energy-efficient. Lastly, this Account compares the photothermal membrane applications, summarizes current challenges for photothermal membrane applications, and offers future directions to facilitate the translation of photothermal membranes from the laboratory to large engineered systems by improving their scalability, stability, and sustainability.

Catalytic Converters for Water Treatment.

Abstract: ConspectusFresh water demand is driven by human consumption, agricultural irrigation, and industrial usage and continues to increase along with the global population. Improved methods to inexpensively and sustainably clean water unfit for human consumption are desired, particularly at remote or rural locations. Heterogeneous catalysts offer the opportunity to directly convert toxic molecules in water to nontoxic products. Heterogeneous catalytic reaction processes may bring to mind large-scale industrial production of chemicals, but they can also be used at the small scale, like catalytic converters used in cars to break down gaseous pollutants from fuel combustion. Catalytic processes may be a competitive alternative to conventional water treatment technologies. They have much faster kinetics and are less operationally sensitive than current bioremediation-based methods. Unlike other conventional water treatment technologies (i.e., ion exchange, reverse osmosis, activated carbon filtration), they do not ...

Electroactive Membranes for Water Treatment: Enhanced Treatment Functionalities, Energy Considerations, and Future Challenges.

Abstract: To meet the increasing demand for water, potable water providers are turning toward unconventional waters, such as seawater and wastewater. These highly saline and/or heavily contaminated water sources are difficult to treat, demanding the use of advanced technology not typically used to treat conventional water sources such as river water or fresh groundwater. Of these advanced technologies, membrane separation processes are fast becoming the most widely used methods to convert these marginal waters into useful resources. The main factors contributing to the widespread adoption of membrane separation processes for water treatment include their modular nature, small physical footprint, and relative energy efficiency compared to traditional distillation processes. In addition, membranes present a physical barrier to pathogens, which is an attractive feature in terms of disinfection credits. However, traditional membrane materials suffer from several distinct drawbacks, which include membrane fouling (the accumulation of material on the membrane surface that blocks the flow of water), the need for high-pressure membranes (such as reverse osmosis (RO) or nanofiltration (NF)) or membrane/thermal processes (e.g., membrane distillation (MD)) to remove small contaminant compounds (e.g., trace metals, salt, endocrine disrupting compounds), and a pressure-driven membrane's inability to effectively remove small, uncharged molecules (e.g., N-nitrosodimethylamine (NDMA), phenol, acetone, and boron). Electrically driven physical and chemical phenomena, such as electrophoresis, electrostatic repulsion, dielectrophoresis, and electricity-driven redox reactions, have long been coupled to membrane-based separation processes, in a process known as electrofiltration. However, it is only in recent years that appropriate membrane materials (i.e., electrically conducting membranes (EMs)) have been developed that enable the efficient use of these electro-driven processes. Specifically, the development of EM materials (both polymeric and inorganic) have reduced the energy consumption of electrofiltration by using the membrane as an electrode in an electrochemical circuit. In essence, a membrane-electrode allows for the concentrated delivery of electrical energy directly to the membrane/water interface where the actual separation process takes place. In the past, metal electrodes were placed on either side of the membrane, which resulted in large potentials needed to drive electrochemical/electrokinetic phenomena. The use of a membrane-electrode dramatically reduces the required potentials, which reduces energy consumption and can also eliminate electrocorrosion and the formation of undesirable byproducts. In this Account, we review recent developments in the field of electrofiltration, with a focus on two water treatment applications: desalination and water reuse (wastewater or contaminated groundwater recycling). Specifically, we discuss how EMs can be used to minimize multiple forms of fouling (biofouling, mineral scaling, organic fouling); how electrochemical reactions at the membrane/water interface are used to destroy toxic contaminants, clean a membrane surface, and transform the local pH environment, which enhances the rejection of certain contaminants; how electric fields and electrostatic forces can be used to reorient molecules at the membrane/water interface; and how electrical energy can be transformed into thermal energy to drive separation processes. A special emphasis is placed on explicitly defining the additional energy consumption associated with the electrochemical phenomena, as well as the additional cost associated with fabricating EM materials. In addition, we will discuss current limitations of the electrofiltration process, with particular attention given to the current limitations of membrane materials and the future research needs in the area of membrane materials and module development.

Development of graphene oxide-cellulose acetate nanocomposite reverse osmosis membrane for seawater desalination

Abstract: Cellulose acetate (CA)/Graphene oxide (GO) nanocomposite membrane was prepared by phase inversion method. GO nanosheets were added to CA matrix with the aim of improving seawater desalination performance of asymmetric CA reverse osmosis (RO) membrane and enhancing mechanical and thermal stability. GO with grain size of 2.7 nm was synthesized through modified Hummer method and dispersed in CA matrix to prepare GO/CA nanocomposite membranes. The membranes were fabricated by casting of GO/CA onto a polyester fabric. The results showed that the GO concentrations would affect the morphology, hydrophilicity, porosity, roughness, mechanical strength and thermal stability of membranes. Incorporation of GO into the CA matrix changed the porosity structure from finger-like to sponge-like. Hydrophilicity nature, storage modulus and thermal stability of CA membranes were greatly improved with incorporation of 1 wt% GO. In addition, synthetic seawater salt rejection of CA membrane modified with 1 wt% GO at 25 bar was 1.8 times higher than that of pristine CA membrane, while flux of CA membrane exhibited small reduction with the presence of 1 wt% GO.

Treatment of landfill leachates with biological pretreatments and reverse osmosis

Abstract: Landfill leachates from municipal landfills are usually heavily contaminated and thus require treatments before direct discharge into natural waters. Selecting the appropriate technology for leachate treatment is still a major challenge for operations in municipal landfills. Biodegradation is effective for treating young leachates, whereas old leachates require processes such as chemical oxidation, coagulation–flocculation, chemical precipitation, ozonation, activated carbon adsorption, and reverse osmosis. Recently, the combination of biological pretreatments followed by physico-chemical processes has been shown to be very efficient. Here we review the efficiency of biological treatment in combination with reverse osmosis to clean landfill leachates. We studied in particular processes including a membrane bioreactor, activated sludge, a rotating biological contactor, and up-flow anaerobic sludge blanket treatments, followed by reverse osmosis. We found a 99–99.5% removal of the chemical oxygen demand (COD), and a 99–99.8% removal of N–NH4+ using reverse osmosis and activated sludge. Using reverse osmosis with a rotating biological contactor, we observed 99% removal of COD, biochemical oxygen demand and N–NH4+. The combination of reverse osmosis, activated sludge and rotating biological contactor removed 98–99.2% of Cl− and 99–99.7% of Pb. Total suspended solids are best removed, up to 99%, by either a combination of reverse osmosis with membrane bioreactor, or reverse osmosis with activated sludge.

Biofuel types and membrane separation

Abstract: Global warming induced by greenhouse gases is major issue worldwide. There is therefore a need to develop renewable sources of energy, such as biofuels. Here, we review the various types of biofuels such as biodiesel, bioethanol, biomethane, hydrotreated vegetable oils and fats, and lignocellulosic-based fuels. First, second, and third generations of biofuels are compared in terms of economics, environmental aspects and energy yield. Economically, raw materials account for 60–75% of the final price of produced biofuels. The high cost of biodiesel compared to the lower price of diesel fuel is a major challenge toward commercializing biodiesel production from vegetable oils. Environmentally, biofuels can reduce carbon emissions and are more biodegradable compared to fossil fuels. For instance, biodiesel and diesel fuels are degraded by 95% and 40%, respectively, during one month in water. Among liquid biofuels, biodiesel has the best energy yield, such that the amount of net biodiesel energy production is more than three times than that of diesel fuel. We also review membrane technologies for the purification and separation of biofuels such as bioethanol, biobutanol, biodiesel, and biogas. Commonly used membrane processes are ultrafiltration, microfiltration, nanofiltration, pervaporation, membrane distillation and reverse osmosis. Reverse osmosis is used for water treatment due to the very small pore size of membranes, which allow the water molecules to get through. Membrane bioreactors can be used for wastewater treatment with a combination of ultrafiltration and reverse osmosis. Ultrafiltration and nanofiltration membranes have applications in the production of biomass from olive mill wastewaters. Pervaporation and membrane distillation are efficient in the third generation of bioethanol production plants.