Seawater Reverse Osmosis System Research Articles

Reverse osmosis desalination driven by low temperature supercritical organic rankine cycle

A supercritical organic rankine cycle (SORC) driven seawater reverse osmosis (RO) system (SORC-RO) is proposed. The proposed system is suitable for using both recirculating heat sources such as, solar thermal, and once-through thermal energy resources, such as, waste heat or geothermal. The SORC-RO system is analyzed using two types of low-grade heat sources with a maximum temperature of 150°C and compared with the conventional organic rankine cycle driven seawater reverse osmosis system (ORC-RO). The results show that the SORC-RO system is able to make use of different heat sources and provide relative stable performance. If the source is waste heat, the SORC-RO system could make full use of the heat source and reduce thermal pollution to the environment. A comprehensive list of working fluids candidates for the SORC-RO system using low-grade heat sources less than 150°C is proposed based on the critical pressure and temperature of the fluids.

Qatar water challenges

Qatar has experienced rapid economic growth due to the discovery and production of fuel oil and natural gas (NG). The natural renewable water resources (rainfall and groundwater [GW]) are depleted; and are estimated as 71-m3/per year per capita in 2005. This is far below the water poverty line of 1,000-m3/yca. The GW withdrawal is excessive (compared to replenishment) and is used mainly for irrigation. A very small amount of GW is treated to become potable water and is distributed to consumers. The municipal potable water mainly contains (99%) desalted seawater (DW) and 1% GW. The consumption of DW and electric power (EP) is continuously rising due to the increase in both population and the standard of living. The population have been more than doubled from 2000 to 2010. The DW is produced in power plants generating both EP and DW, and is called Cogeneration Power Desalting Plants (CPDP). These CPDPs are using either: simple gas turbines (GT) cycle or GT combined with steam turbine (ST) to form a GT combined cycle (GTCC). A thermally driven multi-stage flash (MSF) desalting system is mainly used to desalt seawater. Large MSF units are operated in the CPDP to get their thermal energy (as steam) needs either from: (i) heat recovery steam generators coupled with GT or (ii) steam extracted or discharged from the ST of the GTCC. The CPDPs consume large amounts of fossil fuel (FF), mainly NG. The burning FF pollutes the environment by emitting the carbon dioxide (CO2), carbon monoxides, and nitrogen oxides (NOx). The CO2 and NOx are greenhouse gases causing global warming. Raising the efficiencies of EP and DW production can reduce their negative impact on the environment. The sustainability of water in Qatar is questionable: the extracted GW is several times its replenishment rate. The municipal water supply depends almost on desalting seawater by MSF, which is energy intensive and costly process. Deploying a more energy-efficient desalting system such as Seawater Reverse Osmosis system can save a lot of NG, the nation’s main source of income. The use of treated wastewater (TWW) is limited to some agriculture and landscaping. The ratio of TWW to municipal water supply is low, about 25%. It is also essential to promote conservation measures for both water and power. This paper reviews the water profile in Qatar and recommends solutions to solve the growing water scarcity in Qatar.

An analysis of input choice, input prices, and environmental factors on the costs of seawater reverse osmosis systems

This paper examines optimal input allocations in the context of a seawater desalination reverse osmosis (SWRO) system used to produce municipal water. The objective of this research is to better understand the effects on the total costs and the input portfolio of a SWRO system from changes in water quality, daily operations schedule, and input prices. A cost-minimization model is developed, a production function is estimated, and sensitivity analyses are conducted. The results indicate that lower total system costs are associated with warm-weather water quality parameters and lower input prices. Conditional findings indicate a range of system characteristics that yield, in optimality, moderate levels of both capital and hourly operations. This finding is due to the substitution between capital and daily-hours of operation. Additionally, an interruptible (or off-peak) electrical power supply regime is evaluated and determined to contribute to lower system costs under realistic conditions.

Flux dependency of particulate/colloidal fouling in seawater reverse osmosis systems

Abstract Fouling is the main operational problem in seawater reverse osmosis systems (SWRO). Particulate fouling is traditionally measured through the silt density index (SDI) and through the modified fouling index (MFI). In recent years, ultrafiltration membranes were used successfully at constant flux – MFI-UF – to measure particulate/colloidal fouling potential and tested in sea water applications. Furthermore, constant flux operation allows predicting the rate of fouling in RO systems. The objectives of this study are: (1) to measure the flux effect in MFI-UF with different membranes (100, 30 and 10 kDa) for raw seawater and pre-treated water before reverse osmosis in three different locations; (2) to study the particulate and colloidal fouling potential of seawater in reverse osmosis systems; (3) to project the increase in pressure due to cake resistance in reverse osmosis systems. In this research, flat ultrafiltration membranes (100, 50, 30 and 10 kDa) are used in a constant flux filtration mode to test and compare real seawaters from various locations (North and Mediterranean Sea) and from various full scale facilities including different pre-treatments (i.e., ultrafiltration and coagulation + dual media filtration). The operated fluxes range from 350 down to values close to real RO operation, 15l (m2 h)−1. After each filtration test, the MFI-UF is calculated to assess the particulate fouling potential. The obtained results showed that: (1) the articulate and colloidal fouling potential is directly proportional to the applied flux during filtration. This proportionality is related to the compression of the cake deposit occurring at high flux values; (2) the higher the flux, the higher the required pressure, the less porous the cake and therefore the higher the specific cake resistance; (3) particulate and colloidal fouling potential of seawater is site specific and is influenced by pre-treatment.

Flux dependency of particulate/colloidal fouling in seawater reverse osmosis systems

Flux dependency of particulate/colloidal fouling in seawater reverse osmosis systems

Theory of isobaric pressure exchanger for desalination

Abstract A theory is developed to predict the time of sustained operation of a rotary pressure exchanger used for energy recovery in seawater reverse osmosis system. Based on past experiments for oscillating pipe flows, it is found that the existing plug flow velocity in the ducts is not high enough to induce turbulence in the wall boundary layer. Modeling the time series of the flow velocity in the inviscid core as a periodic series of rectangular pulses, the structure of the laminar momentum boundary layer is first derived. The mass boundary layer induced by the oscillating velocity is then solved in order to obtain the slow diffusion of the averaged brine concentration along the duct. With the result the effective longitudinal diffusivity (dispersivity) is found explicitly for arbitrary Schmidt number. The dispersivity is found to be small due to the small viscosity and mass diffusivity in the very thin boundary layers, however it is still augmented to hundreds times of the molecular diffusivity. For a range of duct and rotor dimensions and rotor frequencies, the time needed for the mixing zone to spread to the ends of the duct is predicted for large Schmidt number appropriate for salt in water. After transient mixing is over, a certain amount of salt leaks steadily into the fresh seawater reentering the membrane. However the leakage is shown to be small due to the small dispersivity.

A comparative life cycle assessment of hybrid osmotic dilution desalination and established seawater desalination and wastewater reclamation processes

The purpose of this study was to determine the comparative environmental impacts of coupled seawater desalination and water reclamation using a novel hybrid system that consist of an osmotically driven membrane process and established membrane desalination technologies. A comparative life cycle assessment methodology was used to differentiate between a novel hybrid process consisting of forward osmosis (FO) operated in osmotic dilution (ODN) mode and seawater reverse osmosis (SWRO), and two other processes: a stand alone conventional SWRO desalination system, and a combined SWRO and dual barrier impaired water purification system consisting of nanofiltration followed by reverse osmosis. Each process was evaluated using ten baseline impact categories. It was demonstrated that from a life cycle perspective two hurdles exist to further development of the ODN-SWRO process: module design of FO membranes and cleaning intensity of the FO membranes. System optimization analysis revealed that doubling FO membrane packing density, tripling FO membrane permeability, and optimizing system operation, all of which are technically feasible at the time of this publication, could reduce the environmental impact of the hybrid ODN-SWRO process compared to SWRO by more than 25%; yet, novel hybrid nanofiltration-RO treatment of seawater and wastewater can achieve almost similar levels of environmental impact.

The effects of feed water temperature and dissolved gases on permeate flow rate and permeate conductivity in a pilot scale reverse osmosis desalination unit

Feed water temperature is an important parameter in determining the optimum conditions for an efficient seawater reverse osmosis (SWRO) process. Increased feed water temperatures are known to increase the permeate flux rate in commercial SWRO systems. There are several factors which link feed water temperature to the operational efficiency of the fundamental membrane desalination process. In this study we have obtained precise data on these effects using two different types of RO membranes in a small scale pilot unit with feeds of seawater, brackish water and pure water. The mechanisms involved have been examined in this work. Pre-heating the feed water to enhance RO efficiency may lead to greater cavitation within the RO membrane. Vapour cavities formed by cavitation have the potential to hinder permeate flow by blocking sections of the polymer matrix in the skin layer of the membrane. In earlier work, it was identified that the presence of dissolved atmospheric gases in seawater leads to a potential for cavitation within the porous membranes used in high pressure RO processes. It was also established that the almost complete removal of these dissolved gases prevented this cavitation. The effects of de-gassing on the permeate rate in a small scale pilot SWRO system was reported recently. This work has been extended here to include more hydrophobic membranes, which are more likely to produce cavitation. In addition, there is new evidence to support the view that de-gassing the feed water can remove/reduce vapour cavities in the membrane for improved flow, which is maintained even when the feed water is re-gassed.

A Novel Approach for Targeting and Optimal Design of Efficient Seawater Reverse Osmosis Desalination Networks

Seawater reverse osmosis (SWRO) desalination processes are widely used. The optimal design of such systems resembles a network synthesis problem and has been addressed using superstructure optimization approaches. However, to date these approaches suffer from a limited ability to identify structurally distinct design alternatives, despite requiring significant computational times to determine globally optimal solutions, even for simple cases involving superstructures of only two membrane units. Moreover, existing approaches do not adequately take into consideration water quality information to keep the optimization problems solvable within reasonable times. However, SWRO design strongly depends upon the quality of the feed water and the product water specifications. This casts doubt about the relevance of the results obtained from current superstructure optimization approaches. This paper introduces a novel approach to optimal SWRO design that addresses the major shortcomings of previous approaches. We introduce a novel SWRO synthesis approach, based on the coordinated use of process superstructure representations and global optimization. The approach determines globally optimal solutions to the SWRO network synthesis problems from optimization of full superstructures. It further supports design engineers with a better understanding of the design space and trade-offs between complexity and efficiency. This is achieved through reduced superstructures of distinct design classes. The approach takes into consideration all relevant process conditions and constraints typically associated with SWRO systems. Thermodynamic insights have led to lean superstructure representations throughout which can be solved within short computational times. In contrast to previous approaches that consider sea water to consist of two components only, i.e. “water” and “salt (TDS)”, our superstructure models account for detailed water quality information to ensure practicality. The models capture the performance of the most commonly used membrane elements, as predicted by commercially used simulators including ROSA (Dow) and IMSDesign (Hydranautics) and allow tracing of individual components throughout the system. A detailed economic assessment captures all the significant capital and operating costs associated in SWRO processes, including intake, pre and post treatment. The approach is illustrated using a case study involving four different seawater qualities for which design targets and optimal designs are obtained within short CPU times.

The role of inorganic ions in the calcium carbonate scaling of seawater reverse osmosis systems

In supersaturated solutions the period preceding the start of ‘measurable’ crystallization is normally referred to as the ‘induction time’. This research project aimed to investigate the induction times of CaCO 3 in the presence of Mg 2+ and SO 4 2−. The prepared synthetic solutions have the same ionic strength values found in the Gulf of Oman SWRO concentrates at 30% and 50% recovery. The results showed a significant increase in the induction time by 1140%, 2820%, and 3880% for a recovery of 50%, when adding SO 4 2− only, Mg 2+ only, or both Mg 2+ and SO 4 2−, respectively, to synthetic SWRO concentrate compared to that obtained in the absence of Mg 2+ and SO 4 2− at an initial pH of 8.3. The increase in the induction time in the presence of SO 4 2− was more than likely to be due to nucleation and growth inhibition while the presence of Mg 2+ affected the nucleation and growth through both complexation and inhibition. After a 5-month solution stabilization period, ESEM and XRD analyses showed aragonite in solutions containing Mg 2+. On the contrary, calcite was the final crystal phase formed in solutions with no Mg 2+. This suggests that magnesium may play an important role in inhibiting the formation of calcite.

Field experience with a 20,000 m3/d integrated membrane seawater desalination plant in Cyprus

The desalination plant in Moni (Cyprus) is designed, built and operated by Nirosoft Industries Ltd. together with SubSea Infrastructure Ltd. The plant is a fully integrated membrane system using ultrafiltration (UF) membranes as pretreatment for sea water reverse osmosis (SWRO) membranes. The UF system consists of twelve racks with a total number of 792 DOWTM ultrafiltration modules; the SWRO system is a single pass design in three trains with 1,953 DOW FILMTECTM1 elements. It was started up in December 2008, only nine months after signing the contract. Since then it supplies 20,000 m3/d of potable water with less than 360 mg/l TDS and less than 1 mg/l boron to Limassol city and surroundings. This is a mobile plant, and the equipment can be removed to an alternate location or placed onto a barge at the end of the contractual period, which is the end of 2011. In order to optimize operational costs the operating conditions of the UF plant have been adjusted during the first months. The average transmembrane pressure (TMP) ranges at around 0.8 bar, and the consumption of acid, caustic and chlorine for chemical enhanced backwash (CEB) has been minimized. A cleaning-in-place (CIP) has not been required since the start-up in December 2008. The RO plant reliably achieves the required permeate flow at a recovery of 43–44% and feed pressure of 65–69 bar. Salt and boron rejection values have been better than predicted. The pressure drop has always been below 1 bar. The characteristics and the performance of the integrated membrane system, and the experiences during start-up and the first 1½ years of operation will be discussed in detail in this paper.

On the feasibility of community-scale photovoltaic-powered reverse osmosis desalination systems for remote locations

This paper presents a generalized methodology to evaluate the feasibility of photovoltaic-powered reverse osmosis (PVRO) systems for small, remote communities in challenging environments. The economic feasibility is determined by comparing the cost of water from a photovoltaic reverse osmosis system with the cost of water obtained using conventional diesel-powered reverse osmosis. For PVRO systems, the feasibility is a function of location due to variation in solar resource, water type, system demand and local governmental policies. A series of sample cases were analyzed to demonstrate the method. Analysis for community-scale seawater reverse osmosis systems was carried out for various locations using Geographic Information System (GIS) data. A site-specific analysis has been completed for seawater and brackish water reverse osmosis systems. It was found that photovoltaic-powered reverse osmosis is feasible for the majority of remote locations with a large solar resource.

An ambitious step to the future desalination technology: SEAHERO R&D program (2007–2012)

In Republic of Korea, seawater engineering and architecture of high efficiency reverse osmosis (SEA- HERO) research and development (R&D) program started from 2007 to lead the top seawater reverse osmosis (SWRO) plant technologies for desalination with the fund of US $165 million for 6 years including test-bed plant construction. There are three technical strategies for SEAHERO R&D program called 3L, which represents large scale, low fouling, and low energy, respectively. Large scale means design, construction, and operation of the largest unit SWRO train (daily water production rate = 8 MIGD (36,000 m 3 /day)) in the world. Low-foul- ing strategy targets the decrease of RO membrane fouling by 50%. The specific target for low energy is total energy consumption of whole SWRO plant (including intake, pretreatment, SWRO systems, and so on) less than 4 kWh/ m 3 . The core parts for SWRO plant, such as 16 in. diameter RO membrane and energy recovery device, were devel- oped and will soon be introduced to a test-bed including the largest unit SWRO train. The next step of SEAHERO is real field scale test-bed application of the unit technologies developed for the past 4 years (2007-2010) such as stra- tegic pretreatment, energy-saving technology, and reliable system monitoring.

Integrated solution for boron removal from seawater using RO process and sorption-membrane filtration hybrid method

The main objective of this work was to investigate the possibility of implementing a new hybrid system which combines reverse osmosis (RO) process with sorption-membrane filtration method. The RO tests were performed using a small-scale seawater reverse osmosis (SWRO) system which was established in Urla Bay, Izmir, Turkey. Dowex (XUS 43594.00) ion exchange resin with a particle size of 0–20 μm was employed for removal of boron from RO permeates. A submerged-style hollow-fiber module containing two polypropylene membranes (diameter: 1.3 mm, thickness: 200 μm, pore diameter: 0.4 μm) and a ZW-1 model submerged ultrafiltration module was used throughout the sorption-membrane filtration hybrid system. Sorption of boron was performed on a fine powdered boron selective ion exchange resin and boron loaded resin was separated by submerged membranes later on. The main advantage of sorption-membrane filtration hybrid process is the opportunity of using very fine particles of the resin, which increases specific surface and results in faster kinetics. Process variables such as resin concentration in the suspension, flow rates of fresh and saturated resins, and permeate have been evaluated in order to determine the efficiency of the hybrid process for boron removal from RO permeate.

Decreasing water resources and a comprehensive approach to seawater reverse osmosis (SWRO): Case study—Cost analysis of a sample SWRO system

Water is used for a number of different purposes that are predicted to be affected by global warming. Good management of future water resources will become increasingly important as global warming takes its toll. The purpose of this study was to make a cost analysis of seawater desalination in Turkey for reverse osmosis systems, which would be filling a gap in the current literature. Investment costs, operating costs and total production costs of these systems were analyzed. Furthermore, the effects of varyingly priced consumption materials on operating and total production costs were determined. Due to the fact that energy costs constituted the greatest part of the operating costs (70%), the most discussed part of Seawater Reverse Osmosis systems, has been the energy recovery booster pumps. Thus leading to the utilization of energy recovery booster pumps as the decision criterion, as it was examined in detail in this study. It was concluded that implementation of the energy recovery system was beneficial...

Seawater RO treatment of RO concentrate to extreme silica concentrations

Severe restrictions exist in the disposal of the concentrate from the 15 mgd (2370 m3/h) reverse osmosis (RO) plant in El Paso, Texas (i.e., 15 mgd blended to 27.5 mgd). The current permit for the disposal by deep well injection limits the total dissolved solids in the brine to 10,000 mg/l. This limits water recovery in the plant and drives up the cost of sending a large volume of the concentrate a long distance for discharge. We have continued to work on developing a concentrate treatment process aimed at zero liquid discharge or a greatly reduced concentrate volume suitable for evaporation ponds. This is an interim report documenting an exciting demonstration of the feasibility of using a seawater RO system and synergistic antiscalant and low pH inhibition of reactive silica polymerization to concentrate the primary brackish water RO concentrate to total silica concentrations exceeding 1000 mg/l. This approach makes possible the use of tandem brackish RO followed immediately by a seawater RO (SWRO) to a...

Boron removal efficiency in small seawater Reverse Osmosis systems

Small single-pass desalination seawater Reverse Osmosis (SWRO) plants may be a solution to freshwater demand in North African countries. In the plant design, the selection of commercial SWRO membranes plays an important role in efficiency, according to the feed and product water qualities. Although the SWRO specific energy consumption has been the main parameter employed to describe the SWRO performance, other parameters such as the salt and boron rejection are of major importance. Therefore, this work analyses the salt and boron removal ability of commercial composite-polyamide membranes to comply with the European Union water normative and the World Health Organization guideline values. The salt rejection and the specific energy consumption are evaluated together to study the relation between these parameters. The analysis of 14 different commercial membranes shows that it is possible to obtain high boron rejection with the best membranes in small single-pass SWRO, at the expense of consuming about 12% more energy.

High performance boron removal from seawater by two-pass SWRO system with different membranes

Boron in the desalinated water produced by the seawater reverse osmosis (SWRO) system is one of the most challenging issues for drinking or irrigation water uses. In recent years, many post-treatment methods and designs for boron elimination have emerged and attracted lots of attention, but only a few cases have demonstrated high performance and economic efficiency. The main aim of this work was to evaluate the efficiency of boron removal from seawater using a two-pass SWRO system employing different RO membranes at Qingdao Jiaozhou Bay, the Yellow Sea of China. In this study, HYDRANAUTICS SWC3+ and ESPAB were chosen as the first and second pass membrane, respectively. The impact of feed properties including temperature, pH, salinity, boron concentration, and operational conditions such as feed pressure on boron rejection and permeate flux was determined. In addition, a relative long term run of the two-pass SWRO system was investigated and compared with performance of system that uses Filmtec membrane as reported in the literature. Although the pilot system in this study experienced more severe feed conditions with lower pH, higher feed boron concentrations and lower operational pressures: all potential negative factors for boron rejection, it still achieved good performance for boron reduction. The results of three-month long term operation indicated that, at optimum conditions, two-pass SWRO system at Qingdao Jiaozhou Bay achieved a high performance and stability without anti-scalants to produce permeate which has much a lower boron concentration than the World Health Organization (WHO) guideline.

Siemens provides treatment packages for oil production

Modec International Inc has selected Siemens Water Technologies to provide sea-water reverse osmosis (SWRO) systems for several floating, production, storage and offloading (FPSO) vessels that are to be operated in deep-water locations. Siemens is also supplying a wastewater reuse system to one of Brazil's largest refineries.

Comparative study on stand-alone and parallel operating schemes of energy recovery device for SWRO system

As known, positive displacement (PD) energy recovery device (ERD) transfers hydraulic energy from the ejected brine of the RO modules directly to the seawater feed and its energy recovery efficiency achieved can be as high as 95% or more. The PD type ERD has been concerned widely in the market place and globally adopted into seawater reverse osmosis (SWRO) desalination plant by designers and operators. Usually, to satisfy the needs of large to super-large SWRO plant capacity, parallel operations of ERD facilities are the most convenient and effective way that can be chosen. In this article, a PD type ERD, named FS-ERD was introduced and a parallel FS-ERD setup was designed and built. Operating schemes for stand-alone operation and parallel operation of the setup were developed and experimentally compared for different test capacity.