Operating experiences of a 15,000 cubic meter per day municipal desalting plant at Corfu, Greece

The initial eighteen month period of operation of the 15,000 m³/day municipal plant on the Island of Corfu, Greece, is described.

The 15,000 m³/day desalting plant employing the electrodialysis reversal process (EDR) produces potable water (500 ppm) from a blend of brackish sources with salinities up to 2000 ppm TDS. The paper describes the plant and integration of the plant into the municipal system. The unique system employed to segregate the treatment of the different brackish waters employing only the highest salinity water for blowdown water is also described.

The plant was started up in the fall of 1977 and provided water to the municipal system during the 1978 season.

The paper presents operating cost data for this period and compares these costs with projected costs which form part of the contractual agreement, with the Municipality.     

Desalting 36,000 ppm well water with electrodialysis — a 5-year report

The author reported on the design and initial operation of this unidirectional electrodialysis plant in July 1977. The 36,000 ppm TDS well water is saturated with calcium sulfate and contains high levels of hydrogen sulfide (reported as high as 190 ppm). The 42,000 USGPD plant has now been in service for nearly 5 years and has never failed to provide the potable water needs of the desert camp that it serves.The operation of the pretreatment section of the plant has been modified to reduce the amount of lime fed to the solids contact clarifier thereby reducing the quantity of acid required for pH reduction of the feed water.The only major modification to the electrodialysis portion of the plant has been the installation of new type anion membranes. The membrane stacks are now primarily equipped with two types of anion membranes, both of which operate at a lower electrical resistance and higher ion transfer efficiency. The result of these more efficient anion membranes is a lower power consumption and higher production rate. Improvements to the electrode system have resulted in continuous membrane stack operating periods of over 6000 hours between disassemblies.Equipment to increase the capacity of the plant by 50% is scheduled for installation and start-up in 1981.     

Optimal design of an electrodialysis brackish water desalination plant

This paper considers the optimal design and operation of electrodialysis (ED) desalination plants. In general an ED plant aims to produce potable water from a high salinity source, like brackish water or high salinity water. The system is modelled mathematically as mixed-integer non-linear programming (MINLP) optimization problem, determining the number of desalination stages, the membrane area, the total required energy so as to minimise the total annualised cost of the investment accounting for both infrastructure and operating costs. Two examples from the literature illustrate the applicability of the proposed approach and evaluate the quality of the results obtained.     

Pilot studies on high recovery BWRO-EDR for near zero liquid discharge approach

A hybrid process combining reverse osmosis and electrodialysis has been shown to be effective in recovering 97-98% of brackish water as product water with chloride levels of 200 mg/L or less. Potential for scaling on the brine side of the electrodialysis unit was prevented by acidification, operating the electrodialysis in a reversal mode (EDR), and a side loop crystallizer which prevented buildup of scaling components. Settlers, inline microfiltration, and side-loop ultrafiltration kept suspended solids from returning to the EDR unit. This process was demonstrated in a series of more than eighty batch experiments of 1.5 to 1.8 m³ of RO concentrate of raw brackish groundwater from the Negev Highland, Israel. Each batch could be processed within a single day. The feed-water was concentrated from 0.3% to over 10% TDS super-concentrate while producing the water that could be recycled to the RO permeate. This super-concentrate from the EDR unit was further concentrated in a wind powered WAIV unit that brought final brine TDS to > 30%, and showed promise as a method to recover mineral byproducts such as magnesium salt. Initial economic estimates show that this hybrid process is competitive with conventional RO and other enhanced recovery processes for inland desalination requiring use of evaporation ponds.     

Electrodialysis plant at Hatsushima

A commercial multistage batch system electrodialysis plant for desalination of brackish groundwater was installed at Hatsushima, Atami City in April 1973. The plant has three stages each of which is operated at a constant voltage. Each stage has a dialyzer which is provided with 150 pairs of ion exchange membranes having an effective area of 1 m² each. This plant is used for drinking water supply and has a capacity of 200 m³/day when the raw water has a saline concentration of 6,000 ppm TDS. The operation was very stable and easy, and it was possible to produce water of constant quality at all times regardless of fluctuations in the raw water concentration. The dialyzer was chemically cleaned for removal of deposits on membranes thereby reducing the maintenance cost by 62% without adversely influencing ion exchange membranes.     

Desalting in Australia : The development of a new process for brackish water

The present status of desalination in Australia, the world's driest continent, is reviewed. The well-established techniques of distillation, electrodialysis and reverse osmosis have been utilized to obtain potable water from underground sources or the sea. In remote areas where mining and tourism are major industries, about 30 plants with capacities of up to 900 m³/day have been installed.The future application of large scale desalting is likely to be for municipal purposes in more highly populated regions. The emphasis has been on the treatment of water of moderate salinity which may be of surface, underground, sewage or industrial origin.A new ion exchange desalination process is described which has been developed in Australia to upgrade mildly brackish water to potable or industrial standards. Developed jointly by CSIRO and ICI Australia, the process uses “Sirotherm” resins which are regenerated by hot water, in contrast to the conventional regeneration by chemicals. This uses low grade or waste heat, reduces operating costs compared with existing processes and saves adding extra regenerant chemicals to the environment.Operation of a 600 m³/day plant to remove 80% of the salinity in a 600 ppm municipal supply has recently commenced at a factory site in Adelaide, Australia. A 20 m³/day pilot plant has successfully demonstrated the removal of salt from reclaimed sewage in Tokyo, Japan, where water reuse is fast becoming mandatory. The resin is now available commercially throughout the world.     

Electrodialysis, a mature technology with a multitude of new applications

Electrodialysis is a mature process which is applied since more than 50 years on a large industrial scale for the production of potable water from brackish water sources. But more recently electrodialysis in combination with bipolar membranes or with ion-exchange resins has found a large number of new interesting applications in the chemical process industry, in the food and drug industry as well as in waste water treatment and the production of high quality industrial water.In this paper the principle of electrodialysis is described and its advantages and limitations in various applications are pointed out. More recent developments in electrodialysis as well as in related processes such as electrodialytic water dissociation or continuous electrodeionization are discussed and their present and potential future applications are indicated. Research needs for a sustainable growth of electrodialysis and related processes are pointed out.     

Simulation of a forward feed multiple effect desalination plant with vertical tube evaporators

In recent years, vertical tube falling film evaporators have been widely used in desalination industries. In this paper mathematical modeling of a multiple effect evaporators (MEE) system has been carried out for brackish water desalination. The system includes a set of forward feed vertical tube evaporators with thermal vapor compression (TVC) and a condenser. Modeling has led to calculation of several parameters such as overall heat transfer coefficients, entrainment ratio and recovery of the process which is restricted by scale formation. A scaling prediction chemical model has been employed to calculate the allowable rate of recovery for prevention of scale formation. Physical properties of streams have been assumed as functions of temperature and salinity. A code has been developed for simulation of the process based on mass and energy balance equations. Results showed maximum allowable recovery of 74% for the treated brackish water sample with total dissolved solid (TDS) of 14,761 ppm is achievable. Dealing with mentioned sample under specified set of conditions, it was concluded that changing the number of effects from 3 to 8, enhances gained output ratio (GOR) value from 3.8 to 7.5. However, specific heat transfer surface is increased from 215 to 1052.     

Long term experiments on sea water desalination at the Chigasaki Laboratory

The technology of producing fresh water from sea water by the reverse osmosis (RO) process has been developed since 1974 under the supervision of the Ministry of International Trade and Industry. Highly satisfactory and stable performances have been recorded for the two-stage desalination process using RO modules developed in Japan. Durability of the membranes under testing is expected to last more than three years. The quality of the product water can be kept below TDS 200 ppm that is suitable for potable consumption. Construction of a demonstration plant of 500 m³ /day using domestic modules is now being planned.     

Nitrate removal of brackish underground water by chemical adsorption and by electrodialysis

Nitrate content has increased in Morocco, especially in underground water of agrarian areas. Several processes including degradation processes and separation processes can remove nitrate from water. Two separating processes were studied to remove nitrate from brackish underground water: adsorption on industrial animal waste and electrodialysis equipped by anion monovalent membrane. The results show that a desired product water quality can easily be obtained by electrodialysis contrary to chemical adsorption which requires a great reactional surface.     

Spiral-wound new thin film composite membrane for a single-stage seawater desalination by reverse osmosis

New thin film composite membrane system, designated PEC-1000, formed by the acid catalyzed polymerization on the surface of a reinforced-porous supporting membrane, make it possible to produce potable water from seawater by reverse osmosis in a single-stage with a high recovery operation. TDS rejection over 99.9% and stable water fluxes of 0.20–0.30 m³/m²-day (5.0–7.4 gal/ft²-day) have been attained with 3.5% synthetic seawater at an applied pressure of 56Kg/cm²(800psi). For brackish water, sodium chloride rejections of 99.6–99.9% and fluxes of 0.61–0.81m³/m²-day(15.0-20.0 gal/ft²-day) have been attained with 5000 ppm sodium chloride feed at an applied pressure of 40Kg/cm² (571psi). TDS rejection of 99.8% and water flux of 0.30 m³/m²-day (7.4 gal/ft²-day) have been attained with two- or four-inch diameter PEC-1000 composite membrane elements at an applied pressure of 56Kg/cm²(800psi) in a single-stage synthetic seawater desalination test. This performance is kept for more than 1500 hours in PEC-1000 thin film composite membrane and two-inch diameter element. 280 ppm in TDS and water flux of 0.11 m³/m² day (2.7 gal/ft²-day) are observed at an applied pressure of 56Kg/cm²-40% water recovery with one four-inch diameter spiral-wound PEC-1000 composite membrane element in a single-stage seawater desalination. This membrane shows high selectivity for low molecular weight valuable organic materials such as ?-caprolactam, dimethylsulfoxide, dimethylformamide. The thickness of ultrathin salt barrier of the composite membrane is found to be 300Å by the Electron Microscopy with special ultrathin section techniques.     

电渗析苦咸水淡化技术研究进展

电渗析苦咸水淡化技术具有脱盐效果好、成本较低、绿色环保等优点,但存在制膜工艺繁琐、传质模型不够精确、能效有待提升等问题。本文首先分析了苦咸水电渗析用离子交换膜的制备及改性方法,对膜材料存在的问题进行了探讨。综述对比了苦咸水电渗析在简化模型、理论模型、半经验模型方面的原理及最新进展,系统总结了常规苦咸水电渗析过程的运行方式和工艺优化策略,并进一步介绍了以新型电去离子、冲击电渗析、可再生能源驱动电渗析为代表的新型电渗析过程在苦咸水淡化方面的原理及应用。在此基础上,提出了今后的研究方向集中于降低制膜成本、优化传质模型、探究集成膜法淡化工艺以及新型电渗析过程等方面。     

Electrodialysis on the American continent

The Electrodialysis process has been used commercially in the United States to desalt brackish waters for over twenty years. The first municipal installation in Coalinga, California, was commissioned in 1959. The first plant continuously used to produce the total water supply for a community was installed in Buckeye, Arizona, in 1962.

Development of the Electrodialysis Reversal (EDR) process in the early 1970's resulted in a system featuring reduced operation and maintenance due to the elimination of the need to continuously feed acids and chemicals. This process is in use in typical municipal applications in Dell City, Texas, and Coupeville, Washington, along with industrial applications in electronics manufacture. Safe drinking waters are produced by EDR units at a number of highway rest and service areas.

Research and development in electrodialysis is sponsored by Corporate and Government funding. New membrane systems, membrane stack design and applications are under study. High temperature membranes and spacers have been developed for use in a 100,000 gpd seawater desalting system now being assembled for test. The combination of solar electric power and electrodialysis is also under study for use in purifying water in remote locations.

The application of electrodialysis to the treatment of brackish water has grown significantly over the past seven years. Improvements in system reliability, combined with a lowering of operating and maintenance costs resulting from new developments in equipment and technology, should enable electrodialysis applications to continue to grow in the future     

Designing of an electrodialysis desalination plant

The design and operation of an electrodialysis desalination process are based on a set of fixed and variable parameters such as stack construction, feed and product concentration, membrane properties, flow velocities, current density, recovery rates, etc. These parameters are interrelated and may be rather different for different applications. For an efficient operation of an electrodialysis desalination plant, the process has to be optimized in terms of overall costs considering component properties and operating parameters. In this study the design and optimization of an electrodialysis plant to be used for brackish water desalination has been treated. The required equations were derived or, as in the case of the limiting current density, were experimentally determined. As an example, an electrodialysis plant with a sheet-flow stack construction and given feed solution composition was designed and optimized in terms of overall costs and the sensitivities of the different parameters are analyzed.     

Transport properties of charge-mosaic membranes III. Piezodialysis

A nonequilibrium thermodynamic analysis of piezodialysis is presented. The expressions derived in Part I for the flows as linear functions of the global forces are used to predict the fractional recovery and rate of production of potable water in desalination by piezodialysis. An illustrative calculation is performed for a cylindrical tube (or hollow fiber) made from a hypothetical mosaic membrane whose properties have been calculated from those of Zeo-karb 315 cation exchange membrane. Perfect radial mixing and the absence of concentration polarization are assumed in order to focus attention on the role played by the membrane elements and circulating currents. For a 1 mm thick membrane under an applied pressure difference of 100 atmospheres, the calculation shows an 81% recovery of potable water of 350 ppm from a brackish water feed of 1500 ppm, the rate of production being 23 gpd/ft². A thinner mosaic with a correspondingly reduced pattern size would give a proportionately higher production rate with no loss in recovery, provided that significant polarization could be prevented. This calculation sets upper limits on the performance of a given membrane by assuming that its properties, rather than the hydrodynamic conditions, are rate controlling. The analysis suggests ways of changing membrane properties to improve performance.     

Desalination of brackish water by electrodialysis

The performance of an electrodialysis unit comprising interpolymer type cation and anion-exchange membranes developed in this institute in single-stage and two-stage operation for desalting of brackish waters having different total dissolved solids has been studied highlighting the energy requirement and pressure drop under different conditions. For higher salinity waters, a two-stage reduction is advantageous with lower power requirements and power index. The results will be useful for design and installation of ED plants in brackish water sectors.     

Maintenance problems of the electrodialysis plants in Libya

Many electrodialysis plants have been installed in the last seven years in Libya. In this paper we shall analyse the operation features, the difficulties occurring in pretreatment and degasification, the locally adopted solutions to the maintenance problems encountered and last but not least why the operational costs are far beyond the tolerable allowance margin.The two plants studied extensively are Benina and Dahra—Benina because it was intended to be the world's largest ED plant with an installed capacity of 19,200m³/day (5.1mgd), and Dahra because of its unusually brackish water supply. Other electrodialysis plants are also considered and in each case the effects of the deteriorating input of brackish water, the pretreatment, the design gaps and sometimes faults are indicated together with the solutions developed on-site.Finally, using Libyan field experience with electrodialysis, some recommendations are presented for developing countries with ambitious desalination programs.     

The water problem in egypt

Egypt faces the prospect of rapid growth of populatlon which is a vital problem since agricultural land is not available at the same rate. More land should be reclaimed through development of water resources.The Nile river constitutes an immense water supply but one third of its water is lost through pumping low salinity drainage water to the Mediterranean Sea utilizing costly electric power. Therefore, feasibility studies on recycling this water must be carried out.Along the banks of the Nile, drinking water could be obtained supplied through either small water purification plants or electrodialysis desalination plants, and the economics of the two methods should be compared before deciding on either method.Another source is underground water with a salinity varying between 2000 and 11,000 ppm. For such brackish water, either the electrodialysis or reverse osmosis process can be used.Then there is the Egyptian sea shore which extends over 3000 km. and where the salinity of the sea varies between 33,000 and 45,000 ppm. Here flash distillation processes are suitable.The present paper briefly describes available water resources in Egypt and discusses possible solutions to supplying the fresh water required in different areas.The present investigation concentrates on the feasibility and economics of utilizing the electric supply from the grid at periods other than the peak loads for operating electrodialysis plants. It is estimated that a series of electrodialysis plantsrunning for lOh/day would provide 2.6 million m³/day at an operating cost of 10¢/m³ in addition to capital costs.     

Desalination costs in Australia: A survey of operating plants

A survey of desalination costs in Australia was conducted using data obtained from plant operators, and is reported in second quarter 1986 A$. Unit water costs range from $0.76/kL (for a precursor to deionisation for boiler feed) to $14/kL (for emergency supplies for an island resort).

However, an average figure for desalination of brackish water is $3–$4/kL, and for seawater, $5–10/kL in medium-sized installations.

Capital costs for brackish water plants have been correlated with plant design capacity ranging from 10 to 3400 kL/d.

There is insufficient information to allow a proper comparison between reverse osmosis and electrodialysis for brackish water desalination.