Seawater Reverse Osmosis Desalination Process Research Articles

A rapid-convergent particle swarm optimization approach for multiscale design of high-permeance seawater reverse osmosis systems

Directly solving sophisticated partial differential equation constrained optimization problems is not only extremely time-consuming, but also very hard to find unique optimal solutions. Here, we propose stable and efficient surrogate models for seawater reverse osmosis desalination processes that enable thorough quantitative description of hydrodynamics and local transport characteristics in narrow flow channels. Without iteratively solving complex multi-physics simulation problem taking several hours, the proposed multi-scale design optimization framework significantly reduces the problem complexity by computing the surrogate models in seconds. Moreover, a fast-converging active subspace particle swarm optimization framework is proposed to address the optimal design problem. Compared to the standard particle swarm optimization algorithm, the proposed method enhances the average optimum by 14% and the standard deviation of optimum results for multiple runs is reduced by no less than ten times. The optimized desalination system achieves 9% reduction on energy consumption and 30% improvement on water production efficiency.

Feasibility assessment of alternative environmentally friendly disinfection technique for reverse osmosis-based desalination process

In the seawater reverse osmosis (SWRO) process, the chlorine-based disinfection method poses significant incidental problems, such as producing disinfection by-products and damaging the SWRO membrane surface directly. Chlorine dioxide can control the biofouling layer and relatively stable disinfection approach during the operation. Major two perspective views, such as process stability (water flux and salt rejection) and membrane surface functionality, we evaluated chlorine dioxide feasibility as an alternative disinfection. Standard SWRO performance was evaluated at various operation conditions (inlet pressure and flow rate) using a customized SWRO system. For the stability of the chlorine dioxide disinfection approach, the chemical exposure test was conducted within the concentration and time-variant. While full total 30 days of long-term operation with continuous chlorine dioxide (0.5 mg/L) stripping during the SWRO desalination process, water flux and salt rejection rate maintain 26.7 L.min−1 and 99.7 % respectively.

Event-driven enabled regression aided multi-loop control for SEC minimisation in SWRO desalination considering salinity variation

This paper addresses the energy minimised operation of seawater reverse osmosis (SWRO) desalination process by simultaneous manipulation of feed pressure and reject valve opening. The specific energy consumption (SEC) analysis of SWRO desalination process for maintaining constant permeate flow during feed salinity variation is performed. The analysis is carried out to identify the suitable manipulating variables that can reduce the energy requirement for regulating permeate flow during feed salinity variation. Based on the analysis, a multi-loop control strategy using event-driven programming paradigm aided by regression based predictive model is proposed. The proposed methodology is more desirable than traditional event-driven multi-loop PID control due to smoother control transition and energy reduction. The investigation of SEC and analysis of proposed control strategy were performed using a previously validated dynamic model for SWRO desalination process. The simulation results show that the proposed methodology is superior to conventional PID control by enabling energy-minimised operation of RO process with significant reduction of feed pressure. The analysis shows that the proposed control approach reduces the feed pressure requirement by approximately 300 kPa during feed salinity variation.

Preliminary design of a hydraulic wind turbine drive train for integrated electricity production and seawater desalination

The integration of wind energy to desalinate seawater can address the freshwater scarcity issue and alleviate the environmental impact of desalination. This paper presents the use of the Delft Offshore Turbine, an unconventional wind turbine with hydraulic transmission which can be used to directly drive a seawater reverse osmosis desalination process and to produce electricity with a Pelton turbine. A steady-state model is used to identify the potential regions at which it is possible to operate the system and to propose a system settings for maximising water production. The results show that the proposed system provides up to 300 kW of electricity and can desalinate up to 25 m3/h, at rated operating conditions.

Thermodynamic analysis of a solar thermal facilitated membrane seawater desalination process

Seawater reverse osmosis (RO) desalination is an attractive but energy-intensive process used to produce freshwater. A reduction in high-grade energy (electricity) consumption during the seawater RO desalination process can be achieved by utilizing renewable energy sources and harvesting osmotic energy during the desalination process. This study proposes a novel method to reduce the energy consumption of RO desalination by incorporating solar thermal energy into the reverse osmosis-pressure retarded osmosis (RO-PRO) hybrid system (medium capacity of 5000 m3/day). Osmotic energy is harvested by mixing seawater and tertiary wastewater in PRO at an elevated temperature before the RO desalination step. Solar thermal energy is used to heat the solutions to enhance the energy production of the PRO. The hybrid system can achieve wastewater reclamation and RO brine management simultaneously. Energy analysis shows that the net specific energy (electricity) consumption of the hybrid system is as low as 0.39 kWh/m3, which is much lower than that of conventional RO desalination systems (∼1.1 kWh/m3). Exergy analysis is conducted on the system to determine the second law efficiency of the system. In addition, the analytic hierarchy process shows that the overall system operation benefits from a high PRO operating temperature.

A seawater RO desalination process driven by dynamic pressure of high-speed seawater droplets

Seawater reverse osmosis (RO) desalination requires driving pressure of 5~8 MPa which is usually offered by the high-pressure pump, the standard device employed in the commercial application, accompanied by a series of problems. To replace the high-pressure pump, a seawater RO desalination technique driven by the dynamic pressure of high-speed seawater droplets is proposed. By theoretical calculation and computational fluid dynamic (CFD) simulation, the required operating conditions for the acquisition of effective impacting seawater droplets were investigated. The results showed that the velocity of the seawater droplets should exceed 70 m/s to achieve the driving pressure of 5 MPa, and simultaneously the air flow velocity should exceed 70 m/s to act as the accelerating medium. The proper size of the accelerated droplets at different air flow velocity within the range of 70~100 m/s was determined not only considering the final velocity of the droplets but also their gravitational settling limitation. In addition, five structures of the RO membrane module were designed and tested, in which the ring-shaped and semicircle-shaped structure exhibited good performance with droplet trap rate greater than 90%. Furthermore, the energy balance of the whole system was analysed, and some constructive suggestions are provided to reduce the energy consumption.

A modeling framework to evaluate blending of seawater and treated wastewater streams for synergistic desalination and potable reuse

A modeling framework was developed to evaluate synergistic blending of the waste streams from seawater reverse osmosis (RO) desalination and wastewater treatment facilities that are co-located or in close proximity. Four scenarios were considered, two of which involved blending treated wastewater with the brine resulting from the seawater RO desalination process, effectively diluting RO brine prior to discharge. One of these scenarios considers the capture of salinity-gradient energy. The other two scenarios involved blending treated wastewater with the intake seawater to dilute the influent to the RO process. One of these scenarios incorporates a low-energy osmotic dilution process to provide high-quality pre-treatment for the wastewater. The model framework evaluates required seawater and treated wastewater flowrates, discharge flowrates and components, boron removal, and system energy requirements. Using data from an existing desalination facility in close proximity to a wastewater treatment facility, results showed that the influent blending scenarios (Scenarios 3 and 4) had several advantages over the brine blending scenarios (Scenarios 1 and 2), including: (1) reduced seawater intake and brine discharge flowrates, (2) no need for second-pass RO for boron control, and (3) reduced energy consumption. It should be noted that the framework was developed for use with co-located seawater desalination and coastal wastewater reclamation facilities but could be extended for use with desalination and wastewater reclamation facilities in in-land locations where disposal of RO concentrate is a serious concern.

Comparative performance of FO-RO hybrid and two-pass SWRO desalination processes: Boron removal

The boron removal and behavior in seawater forward osmosis (SWFO) and seawater reverse osmosis (SWRO) were evaluated under various operating conditions. Similar trends in boron removal for both SWFO and SWRO were observed: boron removal increased as the feed solution/water pH increased. In addition, the optimal operating conditions for the SWFO as a pretreatment step for SWRO were investigated considering the boron concentration in the diluted draw solution and the dilution rate. When the boron and NaCl concentrations were 2 mg/L and 24,000 mg/L in the SWFO diluted draw solution, the boron concentration in the permeate was 0.4 mg/L for the SWFO-SWRO hybrid process. Therefore, the SWFO-SWRO hybrid process did not require any pH adjustment, whereas the two-pass SWRO required a pH adjustment to 11 in the second SWRO in order to remove boron, which affects the economic feasibility, such as the operating expenditure. Thus, the SWFO-SWRO hybrid process can save the 19,200,000 $/yr than the two-pass SWRO because it is an economical and efficient process in pH adjustment or dilution aspects compared to the two-pass SWRO process.

Environmental sustainability assessment of seawater reverse osmosis brine valorization by means of electrodialysis with bipolar membranes.

The integration of electrodialysis with bipolar membranes (EDBM) with seawater reverse osmosis (SWRO) process influences the two main environmental burdens of SWRO desalination process: climate change, accounted here as carbon footprint (CF) andassociated to the high-energy consumption, and the environmental alteration of the vicinities of the facility, due to brine disposal. EDBM powered by photovoltaic (PV) solar energy is able to meet the above-mentioned challenges that arise in SWRO desalination. In addition, HCl and NaOH, both employed in thedesalination industry, can be produced from the brines. Hence, environmental benefits regarding the potential self-supply can be achieved. The environmental sustainability assessment by means of life cycle assessment (LCA) of a SWRO and EDBM has been carried out considering four different scenarios. The percentage of treated brines and the influence of the grid mix used for electric power supply has been taken into account. The three different electric power supplies were 100.0% renewable energy (PV solar energy), 36.0% renewable energy (average Spanish grid mix), and 1.9% (average Israeli grid mix). The results showed that the CF per unit of volume produced freshwater for SWRO and the self-supply reagent production scenario for the three Spanish grid mix, the Israeli grid mix, and the PV solar energy were 6.96kg CO2-eq·m-3, 12.57kg CO2-eq·m-3, and 2.17kg CO2-eq·m-3, respectively.

Impact of well intake systems on bacterial, algae, and organic carbon reduction in SWRO desalination systems, SAWACO, Jeddah, Saudi Arabia

The intake system can play a significant role in improving the feed water quality and ultimately influence the performance of downstream components of the seawater reverse osmosis desalination processes. In most cases, open-ocean intakes produce poor feed water quality in terms of the abundance of naturally occurring organic matter, which increases the risk of membrane fouling. An alternative intake is the subsurface system, which is based on the riverbank filtration concept that provides natural filtration and biological treatment of the feed water prior to the entry of the water into the desalination plant. The use of subsurface intakes normally improves the raw water quality by reducing suspended solids, algae, bacterial, and dissolved organic carbon concentrations. Therefore, the risk of biofouling caused by these substances can be reduced by implementing the appropriate type of intake system. The use of well intake systems was investigated along the Red Sea shoreline of Saudi Arabia in the Jeddah region. Data were collected from a seawater reverse osmosis (SWRO) plant with a capacity of 10,000 m3/d. The well system produces feed water from an artificial-fill peninsula that was constructed atop of the seabed. Ten wells have been constructed on the peninsula for extracting raw seawater. Water samples were collected from nearby surface seawater as a reference and from selected individual wells. The percentage of algae and bacterial removal by induced filtration process was evaluated by comparison of the seawater concentrations with the well discharges. Transparent exopolymer particles and organic carbon fractions reduction was also measured. The quality of raw water extracted from the well systems was highly improved compared with the raw seawater source. It was observed that algae were virtually 100% removed and the bacterial concentration was significantly removed by the aquifer matrix. The detailed analysis of organic carbon fraction using liquid chromatography-organic carbon detection instrument showed a high-percentage removal of the organic fractions consummate with the molecular weight. The results of this study can be used to improve the intake system design of existing SWRO facilities that might require expansion in future or new facilities that will be located along the Red Sea coastline.

Evaluation of scaling potential in a pilot-scale NF–SWRO integrated seawater desalination system

Pilot-scale experiments were carried out on a nanofiltration (NF)–seawater reverse osmosis (SWRO) integrated membrane system (IMS) to evaluate scaling potential on NF and SWRO membrane surface using a kind of loosen NF membrane and costal seawater. The effect of NF permeate recovery (RNF) increasing on the occurrence of scaling in the NF and SWRO module was investigated in term of concentration polarization modulus (CP) of scalant ions, Stiff and Davis Stability Index (S&DSI), as well as Supersaturation Index (SI) of CaCO3 and CaSO4. The results show that the salt rejection by the loosen NF module is only about 10%, while the rejection of SO42− is higher than 95%; S&DSI is always less than zero, indicating that CaCO3 scaling could not form on the NF membrane surface when RNF was less than 35%. CPSO42− is much higher than CPCO32−; and at RNF of higher than 30%, SI of CaSO4 on NF membrane surface increased gradually higher than 1.0, which indicated that CaSO4 scale is more apt to form on the NF membrane surface than CaCO3 at that NF permeate recovery. This scaling sequence in the loose NF module was different from that in traditional SWRO desalination processes.

Proposed new fouling monitoring indices for seawater reverse osmosis to determine the membrane cleaning interval

This study focuses on how to systematically determine the membrane cleaning interval of the seawater reverse osmosis (SWRO) desalination process by proposing two new fouling indices as well as comparing the fouling model with the fouling-free model. A fouling-free mathematical model of the SWRO desalination process based on the effects of temperature on flux as well as operation data obtained from a full-scale SWRO desalination plant in Korea was developed in order to normalize the permeate flow rate and feed pressure values. The normalized permeate flow rate was monitored in order to determine the proper cleaning interval of the RO membrane based on the membrane manufacturing company's cleaning protocol. The normalized feed pressure was modeled based on the linear cake filtration theory and dynamic fouling indices including an updated slope β and intercept γ that were proposed using the recursive least square (RLS) method. In addition, statistical control charts for the dynamic fouling indices were proposed in order to determine the proper membrane cleaning interval based on standard rules. The proposed fouling model was calibrated by the Monte-Carlo and principal component analysis (PCA). The experimental results from a full-scale SWRO plant in Geojae Island, Korea, indicate that the proposed fouling model and fouling monitoring indices were able to analyze the fouling mechanism of the RO membrane and were also able to determine the optimal membrane cleaning intervals.

Full-scale simulation of seawater reverse osmosis desalination processes for boron removal: Effect of membrane fouling

The objective of this study is to further develop previously reported mechanistic predictive model that simulates boron removal in full-scale seawater reverse osmosis (RO) desalination processes to take into account the effect of membrane fouling. Decrease of boron removal and reduction in water production rate by membrane fouling due to enhanced concentration polarization were simulated as a decrease in solute mass transfer coefficient in boundary layer on membrane surface. Various design and operating options under fouling condition were examined including single- versus double-pass configurations, different number of RO elements per vessel, use of RO membranes with enhanced boron rejection, and pH adjustment. These options were quantitatively compared by normalizing the performance of the system in terms of Emin, the minimum energy costs per product water. Simulation results suggested that most viable options to enhance boron rejection among those tested in this study include: i) minimizing fouling, ii) exchanging the existing SWRO elements to boron-specific ones, and iii) increasing pH in the second pass. The model developed in this study is expected to help design and optimization of the RO processes to achieve the target boron removal at target water recovery under realistic conditions where membrane fouling occurs during operation.

A fouling model for simulating long-term performance of SWRO desalination process

A fouling model for the seawater reverse osmosis (SWRO) process is required to propose an appropriate strategy for membrane maintenance (i.e., membrane cleaning and replacement). In this study, a fouling model that considered the concentration polarization was properly developed to simulate the long-term performance of the SWRO process based on models from the literature. The model was practically applied to one-year operation data obtained from the Fujairah SWRO desalination plant with parameter estimation, and good agreement between the measured data and simulated results was obtained for both the rejection and recovery rates. Compared to an integrated model consisting of two models from the literature, the fouling model proposed in this study showed reliable performance for membrane fouling such as the increase in the permeate TDS concentration according to operating time. In addition, simulations for membrane maintenance were conducted based on the variation in membrane resistance, which reflects the fouling state of the membrane. These revealed that the rearrangement of membranes is not significantly effective without cleaning the fouled membrane. Instead, a partial replacement of membranes can be an effective maintenance scheme to increase the recovery rate. Accordingly, the results of the study presented here can be used to save operation and maintenance (O&M) costs in SWRO plants through the optimized management of fouled membranes.

Application of World Ocean Atlas data for estimating the relative performance of a new construction of SWRO desalination plant

Desalination offers one of the reasonable alternatives as a solution to water scarcity. Among the desalination technologies, seawater reverse osmosis (SWRO) process becomes increasingly attractive for freshwater supply with comparatively low energy consumption and cost-effective operation. In this study, a benchmark of operating Fujairah SWRO desalination plant in the United Arab Emirates is applied to assess the relative performance of a new and large plant construction in other sites. A process model was developed to simulate the performance of SWRO desalination process and to estimate its operating cost. The developed model was validated using one-year SWRO operation data obtained from Fujairah SWRO desalination plant. Temperature and salinity data were collected from World Ocean Atlas 2005, and then applied to the model to estimate the operating cost under the site-specific conditions of 9 different countries. The results of this study present that the performance of the SWRO desalination process was significantly influenced by feed water concentration (i.e., mainly salinity) and temperature, and that the total operating cost is significantly dependent of the local electricity costs. As a conclusion, World Ocean Atlas data and the benchmark provide a method of comparing the performance of various SWRO desalination systems among different countries. Furthermore the methodology is applicable to simulate the process model with site-specific water quality data and to estimate the operating cost before a new construction of SWRO desalination plant at a target area elsewhere.

A control methodology for the feed water temperature to optimize SWRO desalination process using genetic programming

This paper presents a novel methodology to determine an optimized control method for feed water temperature in a seawater reverse osmosis (SWRO) desalination process using genetic programming (GP) which is an evolutionary algorithm used to find functional forms through training data. Two functional models were determined by GP with operation data collected over four years from Fujairah SWRO plant. The models showed high accuracy (>99.0%) in terms of the average error rate between the observed and the predicted values. The first model involved the permeate water flow rate with a functional temperature correction factor (TCF), water transfer coefficient, and net driving pressure (NDP) and the second is the salt passage ratio with a functional TCF, salt transfer coefficient, and total dissolved solids (TDS) in the feed. To determine the optimized control of the feed water temperature, a new control methodology with the two functional models was proposed and applied to a simulation of the feed water temperature, which showed better performance in terms of the permeate flow rate. Applying the optimized control of feed water temperatures to a plant under identical operational conditions, it was found that the permeate flow rate could be increased by approximately 900 m 3/day under a steady condition of 600 ppm in permeate TDS.

Energy saving methodology for the SWRO desalination process: control of operating temperature and pressure

This study proposes a new operation methodology for energy saving in the Fujairah seawater reverse osmosis (SWRO) plant, as the optimum feed pressure is determined at the controlled operating temperature. To this end, two functional models were developed by genetic programming (GP) using two-year operational data. The data revealed that the required feed pressure for the plant operation was potentially overestimated. Based on the developed models, simulation of a three-step sequential control was carried out to reduce and optimize the required feed pressure. The simulation results first indicate that the temperature control significantly reduces the required feed pressure at a reasonably high temperature. Second, as the permeate water flow rate (PFR) is determined by the optimized feed pressure instead of the permeate pressure actually used to maintain a steady PFR in Fujairah, the required feed pressure could be substantially reduced. As a result, the proposed methodology can potentially reduce the required feed pressure, by approximately 10 bar, under the identical performance of both PFR and permeate water total dissolved solids (TDS). This study implies that the optimization of operation and management of MSF-hybridized SWRO processes can considerably improve the efficiency of the desalination process in terms of energy and, eventually, cost saving.

Development of a package model for process simulation and cost estimation of seawater reverse osmosis desalination plant

Seawater reverse osmosis (SWRO) desalination is rising as an alternative solution for the water shortage problem which is more severe than before. In this study, a package of process models was developed and tested by four-year SWRO plant operation data obtained from Fujairah in UAE, as a tool not only for simulating the performance of SWRO desalination process but for estimating the total profits of the plant operation. The simulation results based on the developed process models were reasonably satisfied to predict the SWRO desalination plant performance in terms of permeate water concentration and flow rate. And the results of cost estimation show a possibility that the models can successfully predict total annual profits (TAP) within the order of magnitude of USD/year, according to operating date, feed water concentration, and permeate water condition. Consequently, the developed package model is applicable to support design criteria and efficient operation of SWRO desalination plant as references.

Pretreatment of seawater: Results of pilot trials in Singapore

In this paper, performance ofdifferent pretreatment systems used in the seawaterreverse osmosis desalination process is presented. The different pretreatment techniques analyzed included conventional media-filtration technique and non-conventional membrane filtration techniques. For the membrane filtration techniques, two ultrafiltration and one microfiltration pilot plants were used in the experimental study. During the experiments, the silt density index (SDI) of the filtrate samples was regularly measured to quantify the performance of pretreatment systems in rejecting colloidal particles. Measurements of other important parameters included filtrate flux, transmembrane pressure, total suspended solids, colloidal silica, total organic carbon, etc. According to the experimental findings, the quality of the filtrate produced by the conventional media-filtration technique was inferior and highly inconsistent. SDI of filtrate varied from 2.8 to 3.8 and spikes as high as 6.3 were frequently observed. Membrane pretreatment produced filtrate of a better quality. SDI ofthe filtrate produced was consistently below 3.0, a prerequisite for proper operation of a RO desalination plant. The ease of operation of the membrane pretreatment processes was also noted. Together with improved maintenance procedures such as filtrate backwashing and air scouring, complete flux and pressure recoveries were achievable with minimal use of chemicals during the experiments.