Small reverse osmosis desalination plants without pH control normally use a feed water bypass to modify the permeate conductivity by mixing a little amount of feed water with the permeate. Plants with this characteristic have a different system configuration and the conductivity is usually not controlled. In this contribution, small plants with feed water bypass are studied from the dynamic point of view and a multivariable receding horizon controller is applied for the simultaneous control of permeate flow rate and conductivity. Results show the advantages of including the conductivity of permeate as well as the excellent performance of the designed controller.

A theoretical analysis on upgrading desalination plants with low-salt-rejection reverse osmosis

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.

Control performance evaluation of reverse osmosis desalination system based on model predictive control and PID controllers

Capital cost estimation of RO plants: GCC countries versus southern Europe

Saline groundwater is the primary water source for agricultural development in the United Arab Emirates (UAE). Many small-scale reverse osmosis (RO) desalination plants have been installed to desalinize saline groundwater for use in irrigating vegetables (mainly in green houses), forages, date palm and fruit trees. Twelve plants in inland areas and three plants in coastal areas were studied to evaluate the existing brine disposal practices. The capacity of ROs varied from 28 to 325 m3 d-1. Pre-treated brackish groundwater, salinity varying from 4 to 37 dS m-1, was used as feed water. Higher groundwater salinity was observed in coastal areas due to sea-water intrusion. Chemical analysis of brine and soils at the disposal sites showed trace existence of heavy metals. The methods of brine disposal include (i) surface disposal (to excavated/non-excavated pits or mountain terrain or steep edge of sand dunes), (ii) well injection or dug well, (iii) pipeline discharge to sea beach, (iv) irrigation of salt-tolerant plants or blending brine with feed water for irrigating date palm, (v) use in cooling pads of green houses, and (vi) discharge to wadi beds. Among the disposal methods, surface disposal and dug well near the RO plants are critical as feed water can be further polluted by brine and chemicals used in the desalination process. These disposal practices could be replaced by environmental friendly methods such as non-leaking evaporation ponds and biosaline agriculture.

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

Technical and economic analysis for the integration of small reverse osmosis desalination plants into MAST gas turbine cycles for power generation

Sea and ocean Reverse Osmosis (RO) desalination plants are often designed to remove more than 90% of dissolved ingredients (organic and inorganic) from feed water, thus creating a permeate water that is potable. Typically 40–60% of the feed water is recovered as permeate water. The water not recovered as permeate becomes concentrated into a stream of RO concentrate (brine) because the salts rejected by RO remain in the unrecovered water. The RO concentrate is usually about 1.67 to 2.5 times the salt concentration of the source water, but can be as high as four times. RO concentrate discharged into a source water body is a major environmental consideration during the planning and design of bay or ocean desalination plants. Co-location of desalination plants with wastewater treatment plants or power plants allows using a shared outfall to dilute the high salt concentration of RO concentrate. Diluting the RO concentrate in a shared effluent outfall mitigates the issue of high salinity around the outfall. This paper compares side by side two main classes of water bodies that receive concentrated brine discharge from Reverse Osmosis (RO) Desalination Plants: oceans (or open seas) and estuarine bays (under the influence of fresh water). These two classes of water bodies have inherent properties which drive not only the operation of RO plants, but also the physical and chemical reactions of outfall discharge. Major differences between oceans and estuarine bays are evident when comparing salinity levels, variability of salinity, and variability of the overall water quality. Furthermore, there are differences in terms of flora and fauna. Using a nuanced approach of comparing and contrasting oceans and estuarine bays as receiving waters for desalination plant concentrate, this paper brings to light the natural processes occurring offshore of potential desalination plant sites, and distinguishes what natural processes may be affected by brine entering the ecosystem.


 Seawater intake and its treatments are one of the main upstream processes of every seawater desalination plant (RO, ED, MSF, MED). However, the process has turned out to be of utmost importance for reverse osmosis (RO) desalination plant. It is to be sure that sufficient and steady flow and quality of water is available to the RO desalination plant. Prior to RO feed water, the seawater intake pre-treatment process has to be tailored and the quality of seawater intake to be treated either subsurface intake or open surface intakes, particularly when treating open surface intakes seawater (OSIS) with exceedingly unpredictable quality. According to the well-established membrane manufacturer and supplier, the RO membrane warranty and guarantee are depended on seawater intake quality and its pre-treatment. Thus, the current state-of-the-art RO membranes life and performance success for desalination processing depend upon OSIS pre-treatment processing techniques. This article is emphasizing an overview on recent OSIS and its pre-treatment techniques for RO desalination plant.

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.

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

Today, reverse osmosis membranes are the leading technology for new desalination installations, however, a challenge facing widespread application of RO technology is membrane fouling. In the present study, we used an environmentally friendly green inhibitor as anti-scaling and anti-biofouling in reverse osmosis (RO) desalination plants. The influence of Sargassum sp., Corallina mediterranea, and Avicennia marina on RO membrane mineral scaling was evaluated using gypsum as a model scalant. Antibacterial properties for three marine extracts from Sargassum sp., C. mediterranea, and Avicennia marina were investigated with Gram-positive bacteria (ArthrobactersulfureusYACS14, Staphylococcus aureus) and Gram-negative bacteria (VibrioanguillarumMVM425, Escherichia coli). The antimicrobial results were detected for the two selected extracts as the most potent extracts (ethyl acetate, methanol crude extracts of the Avicennia marina leaves). Data showed that ratios of 3 and 5% recorded the highest suppression percentages (100%) for all tested bacteria including bacterial community collected from Eastern Harbor. On the other side, data confirmed that the anti-scalant properties by 100 ppm of Avicennia marina leave extract giving 85% of scale inhibition. The effect of Avicennia marina leaves extract for calcium sulfate dihydrate (gypsum) scaling on selected reverse osmosis (RO) membrane surfaces was investigated. The effect of different concentrations of Avicennia marina leaves extract was observed in the extent of surface scale coverage and surface crystal size among the membrane studied.

Feed water temperature has a role in controlling the specific energy consumption (SEC) of reverse osmosis (RO) desalination plants. Higher feed water temperatures result in lower SEC values, making management of temperature a key consideration for optimum energy efficiency in RO desalination. This paper introduces an Axial Flux Eddy Current Heating (AFECH) device to increase the temperature of feed water with the help of eddy currents. A 3D model of AFECH is designed and developed in ANSYS to analyze the magnetic characteristics, heat flux, and temperature on the aluminum plate. A hardware setup is designed to prove the concept of AFECH. Different observations are tabled for different rotor speeds. The design of AFECH is extended into a more practical approach, and this paper proposes a novel design of a multilevel disk-type AFMECH device. Based on the observations, multilevel disk-type AFMECH has raised the temperature of feed water from 29 to 60 °C. Based on the comparison between normal RO desalination and RO with a multilevel disk-type AFMECH system, the specific energy consumption has observed to be decrease from 1.16 to 0.6213 kWh/m3.

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