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Reverse osmosis desalination: Water sources, technology, and today's challenges
Water Research
Reverse osmosis membrane technology has developed over the past 40 years to a 44% share in world desalting production capacity, and an 80% share in the total number of desalination plants installed worldwide. The use of membrane desalination has increased as materials have improved and costs have decreased. Today, reverse osmosis membranes are the leading technology for new desalination installations, and they are applied to a variety of salt water resources using tailored pretreatment and membrane system design. Two distinct branches of reverse osmosis desalination have emerged: seawater reverse osmosis and brackish water reverse osmosis. Differences between the two water sources, including foulants, salinity, waste brine (concentrate) disposal options, and plant location, have created significant differences in process development, implementation, and key technical problems. Pretreatment options are similar for both types of reverse osmosis and depend on the specific components of the water source. Both brackish water and seawater reverse osmosis (RO) will continue to be used worldwide; new technology in energy recovery and renewable energy, as well as innovative plant design, will allow greater use of desalination for inland and rural communities, while providing more affordable water for large coastal cities. A wide variety of research and general information on RO desalination is available; however, a direct comparison of seawater and brackish water RO systems is necessary to highlight similarities and differences in process development. This article brings to light key parameters of an RO process and process modifications due to feed water characteristics.
Advances in seawater desalination technologies
Desalination
A number of seawater desalination technologies have been developed during the last several decades to augment the supply of water in arid regions of the world. Due to the constraints of high desalination costs, many countries are unable to afford these technologies as a fresh water resource. However, the steady increasing usage of seawater desalination has demonstrated that seawater desalination is a feasible water resource free from the variations in rainfall. A seawater desalination process separates saline seawater into two streams: a fresh water stream containing a low concentration of dissolved salts and a concentrated brine stream. The process requires some form of energy to desalinate, and utilizes several different technologies for separation. Two of the most commercially important technologies are based on the multi-stage flash (MSF) distillation and reverse osmosis (RO) processes. Although the desalination technologies are mature enough to be a reliable source for fresh water from the sea, a significant amount of research and development (R&D) has been carried out in order to constantly improve the technologies and reduce the cost of desalination. This paper reviews the current status, practices, and advances that have been made in the realm of seawater desalination technologies. Additionally, this paper provides an overview of R&D activities and outlines future prospects for the state-of-the-art seawater desalination technologies. Overall, the present review is made with special emphasis on the MSF and RO desalination technologies because they are the most successful processes for the commercial production of large quantities of fresh water from seawater.
Potential of heat pipe technology in nuclear seawater desalination
Heat pipe technology may play a decisive role in improving the overall economics, and public perception on nuclear desalination, specifically on seawater desalination. When coupled to the Low-Temperature Multi-Effect Distillation process, heat pipes could effectively harness most of the waste heat generated in various types of nuclear power reactors. Indeed, the potential application of heat pipes could be seen as a viable option to nuclear seawater desalination where the efficiency to harness waste heat might not only be enhanced to produce larger quantities of potable water, but also to reduce the environmental impact of nuclear desalination process. Furthermore, the use of heat pipe-based heat recovery systems in desalination plant may improve the overall thermodynamics of the desalination process, as well as help to ensure that the product water is free from any contamination which occur under normal process, thus preventing operational failure occurrences as this would add an extra loop preventing direct contact between radiation and the produced water. In this paper, a new concept for nuclear desalination system based on heat pipe technology is introduced and the anticipated reduction in the tritium level resulting from the use of heat pipe systems is discussed.
Water desalination: An imperative measure for water security in Egypt
Water Desalination is an indispensable industry for the most of the Arab countries. In the last four decades, the number and capacities of desalination units have increased dramatically (45% Multi-Stage Flash (MSF) and 42% Reverse Osmosis (RO) of world capacity); especially in the Gulf States. Almost all available conventional water resources in Egypt - represented by the Nile water, renewable groundwater, and some scant annual precipitation- have been exhausted. Further development measures require review of current water allocations in order to raise efficiencies and protect against pollution, in addition to exploring new options of non-conventional water resources to narrow the gap between water supply and demand. These measures are the pillars of Egypt's integrated water policy and have been clearly postulated in its National Water Resources Plan 2023. The objective of this paper is to study and investigate water desalination as a solution for water scarcity in Egypt. Moreover, the present work demonstrates the significance of seawater desalination for national development in Egypt. At present, Egypt is encouraging, not only the public sector but also the private sector, to apply modern technologies for desalination, which historically started with Distillation then Electrodyalisis and followed by RO. The great achievements in desalination technology have now moved the costs for desalting in many applications from the realm of "expensive" to "competitive". Current technology is feasible for tourist villages in the north coast and the Red Sea, due to its far distances from conventional sources that makes the cost of water conveyance very high and subject to pollution problems. The results indicated that, in spite of research and developments, still the energy requirement and membrane know-how are limiting factors. Thus, Egypt's future vision is non-traditional in the field of desalination. It is based on a real breakthrough towards the use of renewable energy, namely, solar energy to be harnessed for operating high compression pumps needed for reverse osmosis modular systems. The reasons are obvious, since Egypt has great potential of brackish water wells, immense amounts of solar radiation in remote areas and future integrated development projects are located at a distance from the Nile water. This trend is what Egypt is focusing on as a prospective future for wide applications of desalination. Finally, this research concluded that, the water desalination as a conventional water resource should be considered as an imperative measure for water security in Egypt. The future use of such resource for different purposes will largely depend on the rate of improvement in the technologies used for desalination and the cost of needed power.
Advanced energetics of a Multiple-Effects-Evaporation (MEE) desalination plant. Part II: Potential of the cost formation process and prospects for energy saving by process integration
This paper represents the 2nd part of a paper in two parts. In part I a 2nd Principle analysis of a Multiple-Effects-Evaporation (MEE) process has been proposed. In this Part II perspectives for process improvement will be investigated, along two distinct research lines: the thermoeconomics-aided optimization of a new system and the increase of thermal efficiency for existing systems by a pinch-based plant retrofit. As concerns the first research line, a detailed productive structure for the plant stage (i.e. effect) examined in Part I is presented; the cost formation structure is then used to improve a simplified optimization process, revealing capable to properly reflect the interactions among exergy flows. It is shown that the flash at brine inlet and the exergy destruction at the pre-heaters, both apparently playing a secondary role with respect to heat transfer at the evaporators, become main sources of irreversibility when the ΔT between two consecutive effects increases. Then, as a corollary to the low exergetic efficiency calculated in Part I of this paper, the potential for exergy saving through process integration is discussed. Although detailed calculations are not included, a conceptual application of pinch-based techniques is proposed, which reveals scarce margins for integration at process level and a much higher potential for process/hot-utility integration. The use of heat cascades can be optimized looking at the Thermal Desalination Process as a black box; economics of cogeneration systems integrated with the desalination plant and targeted on heat supply, in fact, essentially depends on the cost of feed steam, fuel and electricity.
Feasibilty study of renewable energy powered seawater desalination technology using natural vacuum technique
Renewable Energy
With an ever-increasing population and rapid growth of industrialization, there is great demand for fresh water. Desalination has been a key proponent to meet the future challenges due to decreasing availability of fresh water. However, desalination uses significant amount of energy, today mostly from fossil fuels. It is, therefore, reasonable to rely on renewable energy sources such as solar energy, wind energy, ocean thermal energy, waste heat from the industry and other renewable sources. The present study deals with the energy-efficient seawater desalination system utilizing renewable energy sources and natural vacuum technique. A new desalination technology named Natural Vacuum Desalination is proposed. The novel desalination technique achieve remarkable energy efficiency through the evaporation of seawater under vacuum and will be described in sufficient detail to demonstrate that it requires much less electric energy compared to any conventional desalination plant of fresh water production of similar capacity. The discussion will highlight the main operative and maintenance features of the proposed natural vacuum seawater desalination technology which seems to have promising techno-economic potential providing also advantageous coupling with renewable energy sources.
Evaluation of technologies for a desalination operation and disposal in the Tularosa Basin, New Mexico
According to the United Nations Environment Programme, one-third of the world's population lives in a situation of water stress. In the case of New Mexico, about 90% of the 1.8 million inhabitants depend on ground brackish water as their only source of potable water in many areas of the state. This report presents a technically-supported, economically-feasible and environmentally friendly proposal to desalinate brackish water to supply potable water to inland, isolated communities in southwest New Mexico. Several existing technologies were reviewed to identify opportunities for optimization by combining them to provide potable water and reduce the waste stream. Alternatives were studied and experimentation was conducted for some of them. The alternatives proposed were the use of natural coagulants for pretreatment, various solar collectors' arrangements for energy supply, reverse osmosis (RO), low temperature multi-effect distillation (LT-MED), multi-stage flash distillation (MSF), solar distillation (SD), and electrodialysis for desalination process; Spirulina cultivation and SD for waste treatment, and deep well injection (DWI) for waste disposal. Some alternatives were eliminated because they are either technologically or economically not feasible for this case and present high environmental impact. Three plant configurations were analyzed. Option A involves using the linear Fresnel systems (LFS) to produce steam for the first effect of a nine-effect evaporation plant. The number of effects was determined to achieve the optimal relation between equipment investment costs and steam production cost. This plant operates 8 h per day with solar energy and the rest of the 24 hour operating time is provided with fossil fuels. The waste produced will be further evaporated with SD to minimize its flow and the concentrated brine will be injected into a deep well. Option B has the same elements as option A, except that it does not consider the SD, but direct brine injection into a deep well. Option C considers the use of SD as the only process for distillation with DWI as the waste disposal method. The selection criteria for the best configuration were optimal use of solar energy resources, minimization of fossil fuel consumption and waste stream generation and disposal. Operation requirements and economic analysis were considered to select a proposal easy to implement and operate in rural isolated communities. For the following reasons option A is the best configuration to cover the necessity of potable water in New Mexico: (A) the plant is easy to construct and operate. In addition, it can handle different ranges of brackish water flow. (B) The 76% water recovery of the system almost matches the recovery achieved in a RO plant (80%), with the advantage that maintenance costs are reduced and treatment flowrates cannot be matched by the RO plant. (C) Use of the LFS reduces the emission of combustion gases to the atmosphere by 33%. This manifests as a positive point in a LCA evaluation. (D) The minimum environmental impact of the process facilitates the public involvement plan (PIP) because it gives the plant an environmentally responsible image in terms of avoiding greenhouse gases emissions. (E) The return on investment (ROI) is 10.2% at a price of $5.00/m3 of desalinated water, which is superior to the estimated minimum attractive rate of return (MARR) used for LT-MED plants as 9.5% annually.
Technical and economic assessment of photovoltaic-driven desalination systems
Solar desalination systems are approaching technical and cost viability for producing fresh-water, a commodity of equal importance to energy in many arid and coastal regions worldwide. Solar photovoltaics (PV) represent an ideal, clean alternative to fossil fuels, especial
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