Advancements in reverse osmosis technology and economic prospects of desalination

The scope of this paper will be to discuss the technical and economical aspects of utilizing reverse osmosis technology for desalination of seawater for offshore operations. This paper will introduce the basic concepts of reverse osmosis technology and some of the history concerning the technology. Factors influencing the design, shipment, operation, and maintenance of reverse osmosis systems for offshore installations will be presented. In addition, field data concerning the technical and economical aspects of the operation of reverse osmosis systems on offshore installations will be given. This paper will illustrate the significance and practicality of seawater desalination via reverse osmosis technology on offshore installations. INTRODUCTION A reliable and consistent supply of potable water is one of man's most basic needs. This need is especially critical for the operators and occupants of offshore platforms. Presently, the sources of potable water for these installations are either desalination by distillation or transportation from land via barge or helicopter. The water obtained from these sources can vary in quality and quantity and can also be costly. It will be the purpose of this paper to present a third alternative, desalination of raw seawater by reverse osmosis. THEORY AND DEFINITIONS When a salt water or saline solution is separated from pure water by a semipermeable membrane, the pure water molecules will pass through the membrane into the more concentrated saline solution. This process is defined as osmosis. Osmotic pressure can be defined as the pressure that must be applied to the saline solution to establish equilibrium. If the pressure applied to the saline solution is in excess of the osmotic pressure, the osmotic process is reversed. Water molecules will pass from the saline solution through the membrane into the purer water. This latter process is known as reverse osmosis. The processes of direct and reverse osmosis are shown by Figure 1. The desalination of seawater by the reverse osmosis process is illustrated in Figure 2. By supplying seawater to the membrane at a pressure greater than the osmotic pressure of the solution, water with a lower level of dissolved solids is produced. Materials such as colloids, organic compounds, dissolved solids, and bacteria that do not pass through the membrane are continuously discharged from the system. This continuous discharge prevents accumulation of these materials on the surface of the membrane. In the practical application of reverse osmosis, a small percentage of the dissolved solids do pass through the semipermeable membrane along with the water molecules. The ratio of the concentration of these dissolved solids in the product water to that of the feed water is defined as salt passage and is expressed as a percentage. Due to chemical and physical limitations of the process, only a portion of the seawater fed to the system is desalted. The ratio of the amount of water produced to the amount of feed water is defined as recovery and is also expressed as a percentage.

Purpose: review of existing technologies and methods of seawater desalination for drinking water supply. Discussion. Based on modern research methods using statistical data and a review of domestic and foreign literature, a review of methods and technologies for desalination and desaltation of highly mineralized natural waters was carried out. The use of sea water for domestic purposes is impossible due to the high content of minerals, however, after desalination, such water can be used for drinking. The choice of technologies and methods of desalination is primarily determined by the quality of source water, as well as the requirements for the quality of treated water, plant productivity and technical and economic calculations. For the drinking water supply purposes, the most efficient and cost-effective method is desalination using reverse osmosis technology, used for both sea and groundwater with high salinity. Reverse osmosis technology has significant advantages over thermal desalination, especially when applied to small-scale plants of small domestic water supply systems. The use of reverse osmosis plants will significantly increase productivity of drinking water output per watt of electricity consumed. Conclusions. The introduction of modern technologies and careful attention to water consumption play a significant role in maintaining water balance in different countries. The most cost-effective and efficient method is seawater desalination using reverse osmosis plants. Despite the fact that water desalination and desaltion plants are very expensive, the conservation of natural waters is a priority nowadays.

Seawater desalination is one of the most widely used technologies for freshwater production; however, its high energy consumption remains a pressing global challenge. Both the development and utilization of sustainable energy sources are anticipated to mitigate the energy shortages associated with seawater desalination while also effectively addressing the environmental issues linked to fossil fuel usage. This study provides a comprehensive overview of the classification and evolution of traditional desalination technologies, emphasizing the advancements, progress, and challenges associated with integrating various sustainable energy sources into the desalination process. Then, the cost, efficiency, and energy consumption of desalination systems driven by sustainable energy are discussed, and it is found that even the most widely used reverse osmosis (RO) technology driven by fossil fuels has CO2 emissions of 0.3–1.7 kgCO2/m3 and the lowest cost of desalinated water as high as 0.01 USD/m3, suggesting the necessity and urgency of applying sustainable energy. A comparison of different seawater desalination systems driven by different sustainable energy sources is also carried out. The results reveal that although the seawater desalination system driven by sustainable energy has a lower efficiency and a higher cost than the traditional system, it has more potential from the perspective of environmental protection and sustainable development. Furthermore, the efficiency and cost of desalination technology driven by a single sustainable energy source is lower than that driven by multi-sustainable energy sources, while the efficiency of desalination systems driven by multi-sustainable energy is lower than that driven by hybrid energy, and its cost is higher than that of desalination systems driven by hybrid energy. Considering factors such as cost, efficiency, consumption, economic scale, and environmental impact, the integration of various seawater desalination technologies and various energy sources is still the most effective strategy to solve water shortage, the energy crisis, and environmental pollution at present and in the future.

Fresh water deficit has been an increasingly critical global environmental issue, and seawater desalination is considered as the most effective and promising solution, which promotes the development of different desalination technologies. In order to provide a comprehensive knowledge about the development of desalination technologies, state-of-the-art of research and development on the application of desalination technologies is reviewed in this paper. At first, the overview of desalination technologies is briefly introduced, including the definition of desalination, the evaluation index of water quality and the resulting classification of water resources, the overview of desalination industry, the usages of freshwater produced by desalination, and the sources of raw water. Besides, conventional desalination methods are categorized into physical method and chemical method according to whether there is new substance generated in the desalination process. In the following section conventional desalination methods are reviewed from the perspectives of basic processes and principles, the performances and technical characteristics. However, the shortcomings of conventional desalination technologies mainly lie in high energy consumption and complex treatment process, such as the decrease of heat transfer coefficient caused by the scaling and fouling generated on the solid heat transfer walls for multi-stage flash (MSF) and multiple effect distillation (MED), and rigorous pre-treatment and low recovery factor for reverse osmosis (RO). With the aims of overcoming these disadvantages and thus decreasing the energy consumption, different improvements have been put forward and new desalination methods have been developed. Therefore, the development of desalination technology is then exhaustively analyzed and forecasted in the following four aspects: improvement for the existing technology, combination of different technologies, desalination technology in combination with new energy, and development of new desalination technologies utilizing unemployed physical phenomena. The improvements mainly focus on the shortcomings of MSF, MED and RO, which are the current major large-scale industrial desalination technologies. The combination of different technologies can integrate their respective advantages to improve the desalination performance and decrease the energy consumption and the cost. The limitations of the decrease of traditional fossil energy and its increasing cost can be broken through the combination with solar, wind, geothermal, ocean and nuclear energies, which is also regarded as a potential solution for climate change. The newly developed desalination technologies have the advantages of lower energy consumption and cost, but most of which are still in lab-scale and need further improvement. Due to the important role in the assessment of the desalination efficient, special attention is paid to the analysis of energy consumption of each desalination technology.

The Most Advanced Membrane Analysis and the Save-Energy Type Membrane-Low-Pressure Seawater Reverse Osmosis Membrane Developed by “Mega-ton Water System” Project

Desalination allows the use of non-conventional water sources such as seawater for the production of potable water. Reverse osmosis (RO), one of the technologies for desalination, is becoming popular in the water industry. In this chapter, theory of RO process, plant configurations, and practical considerations related to the plant operation are addressed. Factors such as high permeate flux, high solute rejection, and mechanical and chemical stability govern the production of membranes for RO. Cellulose acetate membrane is popular due to the chlorine and fouling resistance. When it comes to rejection, thin film membranes are advantageous. Membranes are usually arranged in modules. Concentration polarization and compaction are two major limiting factors in the RO technology. Feed water must be pretreated using conventional and/or membrane filtration technologies in order to minimize membrane fouling. Reduction in permeate, pressure drop over the system, and decrease in rejection are the indications for the requirement of cleaning and regeneration of membranes. Chemical and/or physical methods can be used for the cleaning and regeneration of membranes. A case study and the recent developments are discussed in order to enhance the understanding of the process.

Nowadays, the drinking water shortage is increasing, mainly due to rapid population growth, climate change, wasteful overuse of water, and pollution. Under the current circumstances, a quarter of the world's population will not have access to good quality drinking water. Thus, another solution must be adopted in areas with insufficient freshwater. One possible line is the desalination of seawater, one of the most practical solutions to solve the problem of drinking water shortage along the oil availability shore and continues to expand globally. Water produced may also be utilized for irrigation, reducing a region's reliance on imports, contributing to the local economy, and improving food supplies. However, this process is not a consequences-free procedure; it may cause several environmental and human health problems.The three most applied desalination technologies are reverse osmosis (RO), multi-stage flash distillation (MSF), and multi-effect distillation (MED). In this study, the emissions of greenhouse gases (GHGs) of drinking water produced from seawater using these three technologies with fossil and renewable energy sources were investigated based on two methods: life cycle assessment (LCA) using SimaPro life cycle analysis software and carbon footprints. As a result, RO technology has significantly lower CO2 emissions than thermal technologies. The RO combined renewable energy is the most environmentally friendly; provides outstanding benefits in terms of human health and ecosystem quality. This technology may still evolve in the future to produce longer-lasting, cheaper membranes, and the energy requirements of this process are lower with applying modern energy recovery systems.

Reverse osmosis (RO) technology has emerged as a leading desalination and wastewater treatment solution to partially solve this worldwide shortage of fresh water. The present review is a critical appraisal of performance limitations and prospects for improvement in RO plants. The primary factors affecting RO performance include membrane properties, biofouling treatment and prevention, energy recovery devices (ERDs), membrane modifications like surface texturing functionalization and renewable integration. Water permeable and salt rejection properties of membranes are critical to accessing quality water output. Breakthroughs in thin polyamide layers have significantly increased the efficiency of desalination, allowing for greater water flux rates and salt rejection. With the efficiency implications that can result from it, biofouling management is essential in both sustaining and optimizing RO performance. These efforts include the use of pressure exchangers, energy recovery devices and membrane modifications which improve system performance while reducing overall power consumption. Energy Consumption is an Important Indicator of RO Plant Performance, Based on Which Emission Patterns Need to be Reduced Integrating renewables, such as PV-powered systems will help to improve performance and reduce carbon footprints. In addition research to develop pre-treatment technologies and optimize operational conditions has been performed in order to succeed against changes in feed water salinity and prevent membrane fouling. On the other hand, correct comprehension and operation of key performance indicators (KPIs) including permeate flux, salt rejection rate or energy consumption as one superior inter-relating process individual to bypass others that alone are not supportive for each advancements in RO technology. Therefore, this review article provides a comprehensive and synthetic overview of these problems as well as strategies, progress in improving the performance efficiency of RO plants to produce clean water for various end-uses which is intended towards achieving sustainable supply.

Desalination is probably the only means for fresh water supply to countries in decertified climate. The majority of GCC counties rely on desalinated water for fresh water supply to major cities. Over 70% of the desalinated water in the GCC comes from thermal desalination plants including Multi Stage Flash (MSF) and Multi Effect Distillation (MED). The new trend in the desalination plant in the GCC is 30% Reverse Osmosis (RO) and 70% thermal. However, these percentages vary from one to another country depending on feed water quality and expertise. For example, Oman Sea has lower salinity than the Gulf water and hence Oman uses more RO for desalination than MED and MSF. This decision is also driven by economy as RO process less energy intensive and hence the produced water is less expensive as compared to thermal plants. On the contrary, Qatar and Kuwait use more MSF followed by MED due to the high salinity and low quality feed water. This is also because trials of RO in both Qatar and Kuwait were not successful because of the problems of membrane fouling and restrict pre-treatment requirements due to the quality of the water intake.The advantages of RO over thermal technologies are well known in terms of lower energy consumption and the cost of produced water; but are not yet taken advantage of in the GCC zone. One of the reasons is blamed on high feed water salinity and bad water quality; other reasons such as lack of experience, red tides and reliability are contributed to the dominance of thermal plants. However, field experience showed that good pretreatment and optimized RO design may overcome the problems of high feed salinity and bad water quality. Several RO plants, such as Fujairah in UAE, are good examples of a working RO technology in the harsh water environment. Good RO design includes design and optimization of both pretreatment and post-treatment. Field experience showed that most of RO plants failure was due to inefficient pretreatment which resulted in providing low quality water to the RO membrane that caused fouling. Fouling, including biological and scaling, can be handled once an efficient pretreatment process is available. Recent advances in pre-treatment techniques include the combination of Forward Osmosis (FO) with RO among other methods. Recent studies by the authors including commercial implantations have shown that the combination of FO with RO addresses the most technical challenge of RO process and that is fouling, which results in lower energy consumption and less chemical additives. Experience showed fouling in FO process in reversible, i.e. can be removed by backlashing while fouling in conventional RO process is irreversible.In this study, the feasibility of integrating FO with RO process for the desalting of the Gulf water in Qatar is presented. The results are expressed in terms of specific energy consumption, process recovery, produced water quality, chemical additives and overall process cost.The implementation of RO for desalination is not only reducing the cost of desalination but also the environmental impact. More R&D should be done to provide useful data about RO application and suitability for the Gulf water. The R&D should be focused on laboratory to market development of RO technology using rigorous lab scale and pilot plant testing program.

Desalination energy minimization using thin film nanocomposite membranes

The strengthening of requirements for the protection of surface-water sources and increases in the cost of reagents lead to the necessity of using membrane (especially, reverse osmosis) technologies of water desalination as an alternative to ion-exchange technologies. The peculiarities of using reverse osmosis technologies in the desalination of waters with an increased salinity have been discussed. An analogy has been made between the dependence of the adsorptive capacity of ion-exchange resins on the reagent consumption during ion exchange and the dependence of the specific ion flux on the voltage in the electrodialysis and productivity of membrane elements on the excess of the pressure of source water over the osmotic pressure in reverse osmosis. It has been proposed to regulate the number of water desalination steps in reverse osmosis plants, which makes it possible to flexibly change the productivity of equipment and the level of desalinization, depending on the requirements for the technological process. It is shown that the selectivity of reverse osmotic membranes with respect to bivalent ions (calcium, magnesium, and sulfates) is approximately four times higher than the selectivity with respect to monovalent ions (sodium and chlorine). The process of desalination in reverse osmosis plants depends on operation factors, such as the salt content and ion composition of source water, the salt content of the concentrate, and the temperatures of solution and operating pressure, and the design features of devices, such as the length of the motion of the desalination water flux, the distance between membranes, and types of membranes and turbulators (spacers). To assess the influence of separate parameters on the process of reverse osmosis desalination of water solutions, we derived criteria equations by compiling problem solution matrices on the basis of the dimensional method, taking into account the Huntley complement. The operation of membrane elements was analyzed and the dependence of the output of desalinated water (permeate) through the membranes on the pressure of influent water for desalination and the dependence of the permeate output on the water viscosity and the dependence of the specific permeate output on the velocity and length of the motion of the desalination water flux were built. The values of the optimum pressure of source influent water for desalination in a reverse osmosis device were found. Provided the current prices for membrane elements (800 to 1200 USD) and cost of electricity (0.06–0.1 USD), the optimum pressure is 1.0 to 1.4 MPa.

Reverse osmosis (RO) technology requires high energy input in order to extract freshwater from seawater. Improvements in RO technology have led to seawater RO (SWRO) becoming the dominant form of large scale desalination around the world. However, the specific energy consumption (SEC) of SWRO remains substantially higher than that for surface water treatment and indirect potable recycling, making SWRO less cost effective than other alternatives for producing potable water. Furthermore, where non-renewable energy sources are used to supply SWRO energy demand, higher levels of greenhouse gas are emitted compared with lower energy alternatives. The purpose of this paper is to review the RO process configurations currently available and their impact on reducing SWRO energy consumption. This paper highlights the main factors contributing to SWRO energy consumption and presents some of the commonly adopted approaches to reducing SEC in SWRO plants. The use of energy recovery devices (ERDs) in SWRO is explored and the relative effectiveness of the various types of ERDs in reducing SEC presented.

Comparison of energy consumption in desalination by capacitive deionization and reverse osmosis

Seawater desalination by the reverse osmosis (RO) method is an energy‐saving system compared with the evaporating method, and can perform seawater desalination efficiently. Seawater RO desalination technology has been established and become a reliable system. Seawater desalination plants using RO technology have spread and the scale of the plants has increased significantly. More economical and efficient RO method seawater desalination systems have come to be required. A high recovery system, which offers reduction of plant construction cost and running cost was devised. Towards realization of this high recovery system, simulation and the field tests were done to confirm the practicality. Furthermore, a high recovery system was adopted for the biggest desalination plant in Japan, and it is performing favorably. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Detailed analysis of reverse osmosis systems in hot climate conditions