An optimization framework for the design of reverse osmosis desalination plants under food-energy-water nexus considerations

With a reverse osmosis (RO) desalination plant designed to satisfy only the contracted-for water supply, the water company would be missing out on potential benefits that could have been obtained selling water in periods of high demand. On the other hand, sizing the RO desalination plant to produce water to satisfy peak demand means incurring additional costs as well as having the plant partially idle during periods of average or low demand. A model was developed using Excel macros to perform dynamic programming to optimize the capacity expansion of an RO desalination plant. The objective function is to maximize the present value of the total net benefits over the lifetime of the RO desalination plant. The model can be used to test different scenarios to capture time-variant tourism demand and price uncertainties on investment decisions. This study focuses on tourism dominated arid coastal regions, using Sharm El Sheikh (Sharm) in South Sinai, Egypt, as an example.19 RO plants in Sharm were surveyed and data were collected including unit production costs, O&M costs, energy consumption rates, contracted-for water supply, and utilization. Unit production cost of an RO desalination plant varies according to the degree of operation of the plant. This fact has to be taken into consideration when calculating the costs of RO desalination and when deciding on the plant capacity in order to maximize the total net benefit. Using the collected data, cost functions were developed for O&M costs as a function of utilization and plant capacity. The cost model calculated similar values to the actual total net benefit for one of the surveyed RO plant taken as an example. Using the optimization model, the maximum total net benefit is obtained with a smaller installed capacity than the actual case. A modified pricing structure is suggested in the paper that ties the water selling price to consumption in an effort to reduce demand in excess of contracted-for water supply aiding the water company to fulfill its contractual commitments to all users. However, price elasticity has to be taken into consideration to determine the impact of price change on water demand.

The transition from fossil fuels to renewable energy sources is imperative to mitigate climate change and achieve sustainable development goals (SGDs). Hydrogen, as a clean energy carrier, holds great potential for decarbonizing various sectors, yet its production remains predominantly reliant on fossil fuels. This study explores a novel approach to sustainable hydrogen production by integrating offshore wind energy with reverse osmosis (RO) desalination technology. The proposed configuration harnesses offshore wind power to energize both a RO desalination system and water electrolysis unit. Initially, the wind energy powers the RO desalination process, purifying seawater, and then desalinated water is directed to water electrolysis system for generating green hydrogen directly from seawater. The resulting renewable hydrogen holds potential for diverse applications, including marine industries, and can be transported onshore as needed. The RO system is configured to treat 20 kg s−1 of seawater with a salinity of 35 000 ppm, aiming for a high recovery ratio and reduced freshwater salinity. A pressure exchanger (PX) is integrated to recover energy from high‐pressure brine stream and transfer it to the low‐pressure feed water, thus reducing the overall energy consumption of the RO process. The concentrated brine extracted from RO desalination is proposed to be utilized for the production of sodium hydroxide that can further pretreat incoming seawater and enhance the effectiveness of the filtration process by mitigating membrane fouling. This pressure exchanger increases the energy efficiency of the RO system from 63.1% to 64.0% and exergetic efficiency from 13.9% to 18.2% increasing the overall first and second law efficiencies to 37.9% and 33.5%. By leveraging offshore wind power to drive RO desalination systems, this research not only addresses freshwater scarcity but also facilitates green hydrogen generation, contributing to the advancement of renewable energy solutions and fostering environmental sustainability.

Multi-criteria decision-making for selecting a solar farm location to supply energy to reverse osmosis devices and produce freshwater using GIS in Iran

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.

Removal and Recovery of Phosphonate Antiscalants

Optimal design of a hybrid solar-wind power to drive a small-size reverse osmosis desalination plant

Exergy analysis of a reverse osmosis desalination plant in California

Design of a small mobile PV-driven RO water desalination plant to be deployed at the northwest coast of Egypt

Desalination is the production of fresh potable water from a saline water source (seawater or brackish water) via membrane separation or evaporation. Desalination plants operate in more than 120 countries worldwide, and some desert states, such as Saudi Arabia and the United Arab Emirates, rely on desalinated water for more than 70% of their water supply. Sea or brackish waters are typically desalinated using two general types of water treatment technologies—thermal evaporation (distillation) and membrane separation. All thermal desalination technologies use distillation (heating of source water) to produce water vapor that is then condensed into low‐salinity potable water. The thermal desalination technologies most widely used today are multistage flash distillation (MSF), multiple effect distillation (MED), and vapor compression (VC). Membrane desalination is a process of separating minerals from source water using semipermeable membranes. Two general types of technologies are currently used in membrane desalination—reverse osmosis (RO) and electrodialysis (ED). Reverse osmosis desalination is the most widely used membrane separation process today. Currently, there are more than 2000 RO membrane seawater desalination plants worldwide whose total production capacity is in excess of 3 million cubic meters per day (800 MGD).

Fresh water demand is growing drastically in many parts of the world. Desalination of seawater, brackish water, and waste water is one solution to meet the demands of fresh water. Currently, reverse osmosis (RO) desalination process is one of the best methods for the desalination process. In this study, a modified controller design is proposed for RO desalination system based on symbiotic organisms search (SOS) algorithm. A multivariable model of RO desalination plant is considered for experimentation. The RO system considered here is first decoupled using a simplified decoupling process to obtain two non-interacting loops. Then, a proportional-integral-derivative controller with second order derivative (PID-DD) scheme based on SOS algorithm is proposed for each loop to find optimal control parameters of the RO system. To design the PID-DD controller for each loop, integral of squared error (ISE) is considered as fitness function. Four other state-of-the-art optimization algorithms, namely, teacher-learner-based-optimization (TLBO), differential evolution (DE), particle swarm optimization (PSO), and artificial bee colony (ABC), algorithms are also tested for the considered system. To show competitiveness of the proposed SOS-based PID-DD controller, a comparative study based on time domain analysis is performed. Results show the SOS-based PID-DD controller is superior to other PID-DD controllers.

Impact of solar energy cost on water production cost of seawater desalination plants in Egypt

A complementary approach of response surface methodology and an artificial neural network for the optimization and prediction of low salinity reverse osmosis performance

This paper explores the application of genetic algorithms (GA) for optimal design of reverse osmosis (RO) water desalination systems. While RO desalination is among the most cost and energy efficient methods for water desalination, optimal design of such systems is rarely an easy task. In these systems, salty water is made to flow at high pressure through vessels that contain semi-permeable membrane modules. The membranes can allow water to flow through, but prohibit the passage of salt ions. When the pressure is sufficiently high, water molecules will flow through the membranes leaving the salt ions behind and are collected in a fresh water stream. Typical system design variables for RO systems include the number and layout of the vessels and membrane modules, as well as the operating pressure and flow rate. This paper explores models for single and two-stage RO pressure vessel configurations. The number and layout of the vessels and membrane modules are regarded as discrete variables, while the operating pressures and flow rate are regarded as continuous variables. GA is applied to optimize the models for minimum overall cost of unit produced fresh water. Case studies are considered for four different water salinity concentration levels. In each of the studies, three different types of crossover are explored in the GA. While all the studied crossover types yielded satisfactory results, the crossover types that attempt to exploit design variable continuity performed slightly better, even for the discrete variables of this problem.

Modeling, control, and dynamic performance analysis of a reverse osmosis desalination plant integrated within hybrid energy systems

A systematic measurement of ions and 2H/1H, 7Li/6Li, 11B/10B, 18O/ 16O, and 87Sr/86Sr isotopes in feed-waters, permeates, and brines from commercial reverse osmosis (RO) desalination plants in Israel (Ashkelon, Eilat, and Nitzana) and Cyprus (Larnaca) reveals distinctive geochemical and isotopic fingerprints of fresh water generated from desalination of seawater (SWRO) and brackish water (BWRO). The degree of isotope fractionation during the passage of water and solutes through the RO membranes depends on the medium (solvent-water vs. solutes), chemical speciation of the solutes, their charge, and their mass difference. O, H, and Sr isotopes are not fractionated during the RO process. 7Li is preferentially rejected in low pH RO, and B isotope fractionation depends on the pH conditions. Under low pH conditions, B isotopes are not significantly fractionated, whereas at high pH, RO permeates are enriched by 20 per thousand in 11B due to selective rejection of borate ion and preferential permeation of 11B-enriched boric acid through the membrane. The specific geochemical and isotopic fingerprints of SWRO provide a unique tool for tracing "man-made" fresh water as an emerging recharge component of natural water resources.