SWRO Desalination Research Articles

Comparison of DMF and UF pre-treatments for particulate material and dissolved organic matter removal in SWRO desalination

Dissolved air flotation (DAF) followed by dual-media filter (DMF) and ultrafiltration (UF) membrane pre-treatments were run in parallel in a seawater desalination pilot plant in order to compare performances in terms of particles and dissolved organic matter removal. Results indicate that both processes exhibit a high elimination of particulate and microbial contaminants. Both treatments successfully maintain the water turbidity to values <0.1 NTU and SDI15 <2. UF, however, fulfills its purpose by securing almost 100% elimination of algal content while DMF demonstrates an average algae removal of only 60%. Raw seawater shows very low dissolved organic matter content (DOC≈0.9mg C L−1), and LC-OCD technique revealed that the DOC is mainly composed of humic compounds with size range of 0.3-10kDa and low molecular weight (LMW) substances smaller than 0.3kDa (47% each). LC-OCD analyses of the DAF+UF and DAF+DMF filtrates give a proportion among the constituents almost constant. Biopolymers in raw seawater were partially removed by both pre-treatments tested (41% removal in UF permeate and 18% removal in DMF filtrate). Lower impact in LMW (6% removal by UF, 1% removal by DMF) and humics (removals of 8% by UF and 2% by DMF) was observed.

Optimal SWRO desalination network synthesis using multiple water quality parameters

This work introduces a systematic process synthesis and optimization approach that takes into consideration multiple water quality parameters in SWRO desalination network synthesis. Accounting for the multiple component feed water nature is particularly essential to gain insights into the distribution of components across the permeate and concentrate streams of the network, which is an important aspect of process performance. Building upon our previously developed synthesis representation and optimization scheme, we incorporate process models that are capable of addressing the multi-component nature of the problem. Analytical relations in terms of salt rejection capacities of individual ions, are developed to describe the performance of commercially available membrane elements. The designs are developed to maximize a detailed economic objective function so as to more closely resemble the costing for a commercial plant. We illustrate the approach using a case study numerical example involving four different feed water qualities with salinities ranging from 35,000 to 50,000ppm.

전산유체해석기법을 이용한 용존공기부상공정의 유동해석

Algae boom (Red tide) in south coastal area of Korea has been appeared several times during a decade. If algae boom appears in the desalination plant, media filter and UF filter are clogged quickly, and the plant should be shutdown. In general, Algae can be removed from water by flotation better than by sedimentation, because of the low density of algal cell. The purpose of this study conducts the CFD simulation of DAF flotation basin to apply the design of the dissolved air flotation with ball filter in the Test Bed for SWRO desalination plant. In this study, Eulerian-Eulerian multiphase model was applied to simulate the behavior of air bubbles and seawater. Density difference model and gravity were used. But de-sludge process and mass transfer between air bubbles and seawater were ignored. Main parameter is hydraulic loading rate which is varied from 20 m/hr to 27.5 m/hr. Geometry of flotation basin were changed to improve the DAF performance. According to the result of this study, the increase of hydraulic loading rate causes that the flow in the separation basin is widely affected and the concentration of air is increased. The flow pattern in the contact zone of flotation basin is greatly affected by the location of nozzle header. When the nozzle header was installed not the bottom of the contact zone but the above, the opportunity of contact between influent and recycle flow was increased.

Flow transport modelling of feed species (water and salt) through a seawater RO membrane

Throughout recent years, there has been various research studies on seawater RO membrane modelling concerned with analysing RO membrane transport theories and touching on significant issues of the unique molecular separation mechanism of reverse osmosis that affect areas of our everyday life. However, much of this research could be largely characterised as being empirical in nature. The scope of this flow transport modelling analysis was to develop a mathematical model that would determine variations in the transport of water (solvent) and salt (solute) species within a seawater RO membrane module during reverse osmosis. Hence, the modelling analysis was performed in terms of flow, pressure and concentration of the seawater feed, whilst traversing through the module from point of entry at the axial–centre along the length of module (travelling as feed) to the point of exit at outer periphery (exiting as retentate). The modelling analysis in this paper has been devised based on a generalised capillary diffusion model for the transport of “water” and “salt” through a seawater RO membrane combined with relevant performance evaluation expressions for a SWRO membrane using actual operating data of a SWRO membrane module. For this purpose, the essential first year operating data for a new seawater RO membrane module (DuPont HFF membrane B-10 6835TR, operated at the Addur SWRO Desalination Plant) were compiled; (Note: the essential operating data for one seasonal year from this new SWRO membrane module were used so as to obtain more accurate results). This modelling analysis work was performed by the Author of this technical paper at the University of Newcastle Upon Tyne in the UK as part of the Author’s PhD research work during 2000 (modified in 2007). It is undeniable that concentration polarisation has detrimental effects on the performance of any RO membrane process, with its magnitude being of a vital importance (though not been determined before as no literature cited). Likewise, the resulting concentrated boundary film thickness and salt concentration of boundary solution on the high pressure side of the membrane were also determined in the overall application of this modelling analysis. Thus, the correlations developed for this model, the concept of the generated model and the entirety of merging the expressions (as well as the results achieved) are to provide significance in determining the performance of a seawater RO membrane and to add novelty with a sense of innovation to this modelling work.

Optimization of energy costs for SWRO desalination plants

The global expansion of seawater desalination and the associated excessive energy consumption have serious economic and environmental consequences. Various technological and operational approaches have been applied in an attempt to mitigate these impacts by improving the desalination process and by increasing plant efficiency, with the emphasis on reduction of the energy consumption and costs. In this study, a Linear Programming (LP) model was developed to optimize operation of a large Seawater Reverse Osmosis desalination plant (140 MLD). The objective was to minimize energy costs, using the extra hourly installed capacity of the plant and the advantages offered by the power pricing system, based on time and peak load demand (Time Load Tariff [TLT]). For annual production of 45 million m3 of desalinated water (88% of the maximum possible production capacity), a reduction of 15% of the electricity bill, equal to a saving of about US$ 2 million, can be achieved reflecting a weighted average cost of 7.66 ¢/kWh vs. a normative weighted average tariff of 8.95 ¢/kWh. The results indicate that the LP model could serve as an effective decision-making tool of desalination plants that are dependent on the supply of power from the national grid, where the price of energy is based on TLT. The model can assist in the daily operation and maintenance of the plant. It can also serve as a planning tool during the design stage. The model can be used to optimize the trade-off between plant capacity and its related investment cost to the energy expenses. It can be used to compare a smaller capacity plant having a lower investment cost but higher annual energy costs, to a plant with extended capacity having a higher investment cost but lower annual energy costs.

Reuse and management of brine in sustainable SWRO desalination plants

Reverse osmosis is a widely used and rapidly growing desalination technology. Despite the many benefits the technology has to offer, still challenging to all desalination plants is the environmentally sensitive effects attributed to the discharge into the sea of the rejected brine, which can very often severely damage the receiving environment, and air pollutant emissions attributed to the energy demand of the process. The list of potential impacts can be extended; however, the available information on the marine discharges alone indicates the need for environmental mitigation measures. In order to safeguard a sustainable use of the desalination technology, there is a need to develop, in the short term, new management proposals to achieve a minimization of the impact and valorization of brine. These alternatives should be both economically viable and effective, not only for new setting up plants, but also for those already installed. An adequate treatment sequence has been proposed and developed for reusing and valorizing this saline waste from seawater reverse osmosis desalination plants (SWRO), in the well-known chlor-alkali industry by NaCl electrolysis in membrane cells. This alternative has been described from a technological, economical, and environmental point of view towards sustainability of SWRO desalination plants of Gran Canaria (Canary Islands, Spain). The conclusions drawn out of this work refer to knowledge and control improvements concerning to the sustainability of desalination processes, to reduce the impact generated by brine disposal, and to reassess this saline residue as raw material in the chlor-alkali manufacturing industry.

Ultrafiltration used as pre-treatment for SWRO desalination: dynamic coagulant control under extreme conditions

The increasing global needs of individuals, communities, industries and countries cause a worldwide stressed water infrastructure. The new AquaFlex ultrafiltration (UF) technology addresses these emerging circumstances by delivering a water purification technology for municipalities and industries worldwide to secure their future potable and process water requirements. The concept is specifically designed for the treatment of seawater, surface water and polishing of effluents. The newly upgraded AquaFlex UF system combines the vertical design of Pentair X-Flow’s AquaFlex inside-out technology with the advantages of a minor bleed flow across the membrane surface as well as a module with a larger surface area. This allows your system to be designed with higher flux rates and a reduced footprint, thus providing the flexibility to treat a broader range of feed water qualities. In order to achieve a stable operation of the UF process in-line coagulation is often used. The application of in-line coagulation, however, increases the operating costs due to chemicals consumption and the increased disposal costs of the concentrate stream. Hence, it is desirable to develop a good dosing strategy, which applies the minimum addition at which the UF process still shows the desired performance. In this study, a dynamic control algorithm is proposed which enables to control the coagulant dosing, thus minimizing the coagulant consumption without destabilizing the filtration process. The dosing strategy for in-line coagulation was tested successfully at full pilot scale (with 8-inch Pentair X-Flow UF membrane modules). Experiments were carried out for both surface water from a canal in The Netherlands and seawater with strongly changing characteristics during the season. Compared to the current coagulant dosing strategy, a large reduction in coagulant consumption was achieved; in average up to 75%!

A novel approach for SWRO desalination plants operation, comprising single pass boron removal and reuse of CO2 in the post treatment step

A different approach is presented for the operation of seawater RO desalination plants in which the boron concentration in the product water should not exceed 0.3mgB/l. The approach is based on strong acid (either H2SO4 or HCl) dosage to the feed water to attain pH∼4.3, followed by CO2 stripping and subsequently strong base addition to pH 9.00–9.25. At this high pH range, a high B removal efficiency is attained, and since the water is practically devoid of carbonate species, no CaCO3(s) scaling takes place, and pH elevation is limited by Mg(OH)2(s) precipitation, expected only at pH>9.45. The approach enables operation in the absence of antiscalants. Furthermore, CO2 stripping is effected in stripping towers in two steps: the high CO2(aq) concentration is first stripped by vacuum-operated stripping towers and the CO2-rich air is used for dissolution of calcite in the post treatment stage. The remaining CO2 mass is stripped to the atmosphere using blower-assisted stripping towers. This paper aims at introducing the new concept and providing “proof of concept”. The paper addresses experimental and theoretical aspects of the proposed process, as well as engineering and economic evaluation. The proposed approach is shown to be both technically feasible and cost effective, as compared with conventional boron removal alternatives.

Retrofitting and enlargement of the Palmahim SWRO desalination plant (150,000 m3d−1)

Abstract The Palmahim Sea Water Desalination plant supplies to the Israeli water net potable water in accordance with all contractual requirements of water quality and quantity. The plant was commissioned on 2007 and produced 110,000 m3 d−1 (30 million m3 per year). Recently, the plant production capacity was enlarged to 150,000 m3 d−1 (45 million m3 per year). Plant enlargement was performed without interrupting the potable water supply while minimizing capital cost investments. The plant original relatively small footprint (3.2 Hectare) and the high degree of operation flexibility remained the same. The enlargement involved the addition of energy recovery devices, membranes and pressure vessels and the modification of the filtration media. As a result of the enlargement, the specific energy consumption of the plant was reduced by 0.2 kWh m−3.

Retrofitting and enlargement of the Palmahim SWRO desalination plant (150,000 m3 d-1)

Retrofitting and enlargement of the Palmahim SWRO desalination plant (150,000 m3 d-1)

Design optimization of large SWRO plants utilizing time-of-use (TOU) energy prices

The Israeli electricity pricing system is characterized by a sophisticated TOU (time-of-use) tariff. Different prices apply to different hours of the day and different seasons of the year following the electricity system management considerations. Current pricing system defines three yearly seasons, each having peak, shoulder and off-peak prices. This obviously can significantly affect design optimization of large SWRO desalination plants by shifting the Capex/Opex tradeoff. The effect of utilizing TOU differential prices to reduce energy and consequently unit water cost is demonstrated and parametrically analyzed. Two design options satisfying the same water demand are compared: (a) a plant having constant hourly production capacity; (b) a larger plant designed to avoid operation at electricity peak loads. Unit water cost savings demonstrated are in the range of (–1.8)–9.1 UScent/m3 depending strongly on prevailing average electricity price and economy of scale factor. A TOU utilization optimization model is proposed, composed of two steps: (i) optimizing plant design to achieve the lowest possible specific energy consumption, especially while operating at high energy prices; (ii) maximizing water production while operating at off-peak energy prices. Energy cost savings of approximately 18% are achieved given a peak to off-peak price ratio of 2.8:1.

Long term membrane process and performance in Ashkelon Seawater Reverse Osmosis Desalination Plant

In this paper the operation of Ashkelon SWRO desalination plant since it was started five years ago is reviewed. This particular installation is key for the history of seawater desalination by reverse osmosis not only because of its permeate production capacity of 100 Million m3/a (later increased to 133 Million m3/a) but also due to the low cost of water attained (50 US $/m3) when it was started up. The performance assessment made to each one of the four stages in Ashkelon indicates that no major variation in terms of energy consumption, yearly production and permeate quality has occurred since the beginning of the operation. The evaluation has been made using normalization tools together with a direct comparison between the operating values collected at the start-up and the current performance. These findings are especially remarkable if we take into consideration that the big majority of the reverse osmosis elements installed in Ashkelon and still in operation are currently more than five years old.

Sustainability analysis of different SWRO pre-treatment alternatives

The two main alternatives for the pre-treatment of seawater for reverse osmosis desalination, membrane- (UF) and granular media filter based, have been compared and analyzed for their sustainability potential. An environmental life cycle assessment (LCA) has been conducted using commercial software and an economic life cycle costing assessment (LCC) followed according to SETAC guidelines in order to form an eco-effi ciency analysis. In addition, other sustainability relevant aspects such as societal factors and process performance have been discussed. The results show why a broad sustainability analysis should be an indispensable part of every process synthesis and how the design and operation of a SWRO desalination plant could be influenced by it.

Simultaneous power recovery of gauge and osmotic pressure from brine of SWRO desalination plants

The process of recovering gauge pressure from SWRO desalination plants is well known, and based on implementation work exchangers like DWEER or ERI. The possibility to recover osmotic pressure as mechanical work was developed by Prof. Sidney Loeb 30–35 years ago and patented by the Ben-Gurion University of the Negev. Till now the osmotic pressure present in SWRO brine stream was practically not recovered. The paper presents a way that allows simultaneous power recovery of gauge and osmotic pressure. Simultaneous power recovery of both power sources gives a higher power yield then the two processes applied separately. Recovery of osmotic pressure is made by high fluxes and requires an effective membrane cleaning method. The paper presents a direct osmosis high salinity (DO-HS) membrane cleaning technology. The DO-HS technology provides a new approach to keeping membranes continually clean by frequent and short membrane backwash. RO membranes can be backwashed on-line ones a day without stopping a high pressure pump or decreasing the RO separation pressure. A few second injection of NaCl solution redirects the process from RO to DO and within 1 min the membranes are cleaned, and the process comes back to RO production.

Performance prediction of hydraulic energy recovery (HER) device with novel mechanics for small-scale SWRO desalination system

The biggest proportion of the cost of desalted water is the energy consumption, especially for small-scale SWRO desalination system. In order to decrease the cost of desalted water, the energy recovery device is preferred to be considered in small-scale SWRO desalination system. However, the investigation of energy recovery device for small-scale SWRO system is scarce. Until now the design of energy recovery device has not been based on the results of the mathematical simulation but almost on experimental and empirical knowledge, and there are few detailed reports about the optimal design of energy recovery device for small-scale SWRO desalination system in previous articles. In the current paper, a hydraulic energy recovery (HER) device with novel mechanics is introduced, the detailed simulation results of the HER device and specific energy consumption of small-scale SWRO system equipped with the HER device are presented. The simulated results are very useful for optimal design of the HER device and its coupling SWRO desalination system.

Dispersion of brine discharge from seawater reverse osmosis desalination plants

Desalination of seawater has been considered as a potential solution for the water shortage problem in coastal areas and the number of projected and constructed desalination plants has significantly increased in recent years. The challenge of the desalination industry is to produce new water resources without increasing the pressure on the marine environment. Environmental impact of SWRO desalination plants is mainly associated with the discharge into the sea of the brine produced. To estimate the area of influence of the brine several models have been proposed, but validation with real data is needed. The objective of this paper is to present the results of the monitoring of the brine effluent emanating from several SWRO desalination plants in the western Mediterranean Sea in order to estimate the area of influence of the hypersaline plume. We also illustrate how the behavior of these brine discharges can differ significantly according to discharge characteristics. This information may be useful to predict effluent distribution in order to minimize the harmful effects of brine discharges into the sea.

SWRO desalination plant uses ERI pressure exchanger

SWRO desalination plant uses ERI pressure exchanger

Long term experience with membrane performance at the Larnaca desalination plant

The Larnaca SWRO desalination plant has successfully operated for more than 6 years. It was one of the first major SWRO plants to have a tight boron specification. With some management of the membrane elements at the site, the plant has consistently met the water quality and quantity requirements of their customer. The unique plant design allows for changes in the second pass that optimize the power requirements, while ensuring boron quality is just made. This has made the plant very efficient and cost-effective. The performance of the SWRO and BWRO elements has met expectations and performed stably for a number of years. As a result, this process design has become a proto-type for other SWRO plants with tight (especially boron).

Implementation of ISO 14001:2004 (environmental management system standard) for reverse osmosis desalination plants for the first time in Iran

Implementation of ISO 14001:2004 (environmental management system) has been executed for reverse osmosis desalination plants for the first time in Iran at Noor Vijeh Company (N.V. Co), a water and wastewater firm based in Tehran. The scope of work was the activities and product of company's BWRO desalination plant in the city of Qom (3000 m3 per day) and SWRO desalination plant in Assaluyeh, Pars Special Economic and Energy Zone, Iran. The aims of this project were in line with company’s approach to sustainable development and its direction towards conducting environmental friendly activities and production characteristics.Initially the famous PDCA (Plan, Do, Check, Act) was used to identify the aspects and evaluate their effects. The significant aspects of each plant affecting the environment are then identified and preventive control measures and reducing their probabilities of loss are anticipated. These cover the normal activities within each plant and those aspects arising from emergency conditions such as earthquakes, fire, etc.Elements of this system are•Environmental policy and its targets and programmes•Practical methods for environmental management system processes•Executive manuals for implementing special activities•Tables and indexes for environmental aspects for each plant•Organizational charts, positions, qualifications, and necessary trainings for the involved personnel.Environmental aspects are evaluated through their interaction with and effects over, releases to water, emissions to air, land contamination, waste management, energy use, and use of natural resources and raw material.

Parametric analyses of energy consumption and losses in SWCC SWRO plants utilizing energy recovery devices

The reduction of energy consumption constitutes one of the major thrust areas of research in SWRO desalination process industries. The cost of energy in the SWRO process is usually about 30 to 50% of the total production cost of water and can be as much as 75% of the operating cost, depending on the cost of electricity. Thus, energy forms the major contributing factor in determining the water production cost. Hence reducing the energy consumption, which is mainly due to wastage of energy in high-pressure brine, is a major goal of desalination industries. Excepting Jeddah and Al-Birk, all the SWCC SWRO plants are equipped with several types of energy recovery devices, which are utilized to recover otherwise wasted energy in the reject. These energy recovery devices (ERD) are of varying efficiencies and their ability to recover the wasted energy is different in each case. ERD performance is very much dependant on the operating parameters such as flow as well as pressure, which of course is influenced by the feed water temperature. This paper describes in detail the performance of several ERD systems used in various SWCC SWRO plants and compares their efficiencies with regard to operating conditions for a period of one year and its effect on total energy saving and total power consumption by the high pressure pump in addition to the energy loss occurring in the process stream of SWRO plants. The average overall efficiency of the ERDs ranged from 3.2% to 65% which enabled savings of about 1.5% to 27% of total energy consumed by the high pressure pump. The average power consumed by the high pressure pump was in the range of 5.56–7.93 kWh/m 3. However, it was observed that a substantial amount of energy is lost by throttling that ranged from 6.4% to 21.8% of the total energy input to the high pressure pump. It was found that only at Al-Jubail plant, the performance of ERD was affected by the seasonal variation in operation parameters and for the rest of the plants the variation was not large enough to cause any significant change in the ERD performance.