High advanced open channel membrane desalination (disc tube module)

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.

Fouling of high pressure-driven NF and RO membranes in desalination processes: Mechanisms and implications on salt rejection

A feasibility study of a small-scale photovoltaic-powered reverse osmosis desalination plant for potable water and salt production in Madura Island: A techno-economic evaluation

Design and economics of RO seawater desalination

The pursuit of sustainable and clean energy solutions has led to increased interest in hydrogen as an efficient energy carrier. This paper presents a comprehensive analysis of state-of-the-art technologies for hydrogen production through seawater electrolysis and desalination, addressing the critical need for clean energy generation and sustainable water supply. It emphasizes the importance of hydrogen as a versatile and environmentally friendly energy source, as well as the significance of seawater desalination in addressing water scarcity challenges. “The analysis encompasses a comparison of the three existing commercial electrolysis technologies”: solid oxide electrolysis (SOE), alkaline electrolyzers (AE), and proton exchange membrane (PEM) electrolysis. Factors such as energy requirements, capital and maintenance costs, and offshore suitability are considered, facilitating an informed evaluation of the most suitable electrolysis method for seawater hydrogen production. Additionally, three desalination technologies with commercial applications are under evaluation: reverse osmosis (RO), thermal desalination, and membrane desalination. The assessment takes into account investment and operation costs, energy demand, and environmental impact, providing insights into the feasibility and sustainability of integrating hydrogen production with seawater desalination. The findings reveal the energy, economic, and environmental aspects of hydrogen production via seawater electrolysis and desalination, shedding light on the synergies and challenges involved. The study concludes by summarizing the main results, identifying research gaps, and outlining future directions for further advancements in the field. This condensed review serves as a valuable resource for policymakers, researchers, and practitioners in understanding the complex interplay between hydrogen production, seawater electrolysis, and desalination. It provides a perspective on energy demands, environmental impact, and investment of various technologies, enabling informed decision-making toward a more sustainable and resilient energy–water nexus. Overall, this study contributes to the growing body of knowledge on hydrogen production and seawater desalination, offering insights that can inform strategic planning, policy development, and technological advancements in achieving a greener and more sustainable future.

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.

Future of the osmotic processes

Production of drinking water through seawater desalination using reverse osmosis (RO) membranes is becoming increasingly attractive especially in coastal areas with limited freshwater sources. However, one challenge in such conventional desalination RO plants is the difficulty of meeting boron standards in product waters. Therefore, most of the current desalination plants employ additional treatment steps including pH adjustment of feedwater, dilution of RO permeate with other sources, ion exchange post-treatment of RO permeate, and/or double-pass staging for permeate. All these further treatment options increase the cost of desalination. Although membrane manufacturers have been developing modified RO membranes with enhanced boron removal capacities such membranes still should be improved from operational flux and pressure perspectives. The main objective of this work was to determine the impacts of operational conditions (membrane pressure, cross-flow velocity and flux) and water chemistry on boron rejections using two commercial RO membranes specified for enhanced boron removal (TorayTM UTC-80-AB and FilmtecTM SW30HR). A lab-scale cross-flow flat-sheet configuration test unit (SEPA CF II, Osmonics) was used for all RO experiments. Seawater samples were collected from the Mediterranean Sea, Alanya-Kizilot shores, south Turkey. For all experiments, mass balance closures were between 91 and 107%, suggesting relatively low loss of boron on membrane surfaces during 14 h of operation. Boron rejections were relatively constant (a maximum change of ±3%) during the 14 h of operation period for all experiments, suggesting that steady state dynamic membrane conditions were immediately achieved within couple hours. Boron rejections obtained with Toray and FilmTec membranes at pH of original seawater (8.2) and at other various operating conditions ranged between 85 and 92%, resulting in permeate boron concentrations of about 0.2–0.9 mg/L. On the other hand, for both membranes, much higher boron removals were achieved at a pH of 10.5 (>98%), resulting in permeate boron concentrations less than 0.1 mg/L. The charged boron species are expected to be dominant at pH values >9.24 (pKa of boric acid) compared to the neutral boric acid. Therefore, as expected, both membranes exhibited higher boron rejections at a pH of 10.5. Salt rejections (as measured by conductivity) were generally 97–99% at both pH values. Boron rejections were independent of feed water boron concentrations up to 6.6 mg/L. For each membrane type, permeate fluxes at constant pressure were generally lower at pH of 10.5. The ranges of permeate fluxes measured in all experimental conditions were 11–15, 13–17 and 19–21 L/m2-h for 600, 700 and 800 psi (41, 48 and 55 bar) pressures, respectively, after an operation period of 14 h. For all experimental conditions, permeate fluxes gradually decreased during the 14 h operation although a leveling off was observed after 12 h. At constant membrane pressure of 800 psi and pH of 8.2, feed flowrate thus the cross-flow velocity (0.9 and 0.5 m/s) did not exert any significant impact on boron rejection.

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.

Life cycle assessment of reverse osmosis for high-salinity seawater desalination process: Potable and industrial water production

Chapter 4 - Osmotic Pressure

Desalination energy minimization using thin film nanocomposite membranes

To solve the problems of high specific energy consumption and excessive harmful ions in the water production of a small reverse osmosis (RO) plant, a desalination system coupling RO and membrane capacitive deionization (MCDI) is proposed in this study. Aiming at producing two cubic meters per day of fresh water with a salt concentration of less than 280 mg L−1, parameter matching optimization was carried out on two desalination system schemes of one-stage two-section RO and one-stage three-section RO coupled with MCDI. The results were compared with the parameter matching optimization results of the one-stage one-section RO and the one-stage two-section pure RO desalination system. The results show that compared with the pure RO desalination mode, the seawater desalination mode coupled with RO and MCDI reduces the specific energy consumption under the same effluent salt concentration. Moreover, it decreases the feed water pressure in front of the RO membrane, which can reduce the standard of high-pressure pump in a small seawater desalination plant. The energy consumption of the one-stage three-section RO and MCDI coupling system is lower than that of the one- stage two-section RO and MCDI coupling system, and the feed water pressure is also lower.

Optimised desalination of seawater by a PV powered reverse osmosis plant for a decentralised coastal water supply

Seawater desalination in China: Retrospect and prospect