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.     

Die Elektrodialyse — ein Membranverfahren mit vielen Anwendungsmöglichkeiten

Electrodialysis – a membrane process with considerable scope. Electrodialysis is a process by which electrically charged membranes are used to separate ions from an aqueous solution by the driving force of an electrical potential difference. Electrodialysis is used today mainly for desalination of seawater and brackish water. Other applications, such as the recovery of water and valuable metal ions from industrial effluents, the removal of salts and acids from pharmaceutical solutions and in food processing have only recently generated a broader interest. In this paper the principle of electrodialysis is described and the various parameters determining the technical feasibility and the economies of the process are discussed in more detail. Examples are given for the use of electrodialysis in the food and drug industry and in advanced waste water treatment. Finally, recent developments and future prospects of electrodialysis and related processes are discussed.     

Desalination by ED and EDR—state-of-the-art in 1981

The paper describes new developments in the electrodialysis (ED) and electrodialysis reversal (EDR) process and explains how EDR has achieved a major increase in the stability of membrane process performance. It reviews the growth in EDR usage and its installations for brackish water desalting, the wide spectrum of natural and man-made water salinities, and identifies areas where ED and EDR are now used and could be applicable as a result of the new developments.     

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.     

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.     

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 desalination designed for off-grid wind energy

An electrodialysis desalination plant has been set up and tested to treat brackish water while driven from an off grid wind energy system. The tests were carried out in the framework of a wider scope project, located on Gran Canaria Island (Spain). The main goal of this project was to test and identify the most suitable desalination systems for connection to the above-mentioned medium-scale off grid wind farm. After having previously analysed the behaviour of the system on-grid, the following stage was to develop an operational envelope for the electrodialysis reversal (EDR) unit while operating off grid, i.e., only coupled to the wind farm. The unit included power converters for the membrane stacks (DC-drivers) and variable frequency drivers (VFD) for the feed pumps. The tests were carried out to establish the power intervals for the EDR unit depending on the product flow rate specified as well as water quality. Product flow rate between 3 and 8.5 m³/h, power requirements between 4 and 19 kW, while product water conductivity ranged between 200 and 500 μS/cm were recorded. The desalination unit showed good flexibility, adapting smoothly to variations in wind power, even when sudden drops or rises occurred. The control system, slightly modified from a standard design, can cope with such sudden variations. Good agreement between performance predicted with software and the actual operating performance was observed. The presence of harmonics in the electric system due to DC drivers and VFD became harmful for the control and electric system, and care must be taken through appropriate mitigating measures.     

Nitric acid and sodium hydroxide generation by electrodialysis using bipolar membranes

An electrodialysis process with bipolar membranes was used to generate HNO3 and NaOH from NaNO3 which can be found in industrial waste waters. The current efficiency of this process is limited by proton leakage through the anion exchange membrane (AEM), co-ion leakage through bipolar membranes (BPM) and water transport through the ion exchange membranes. Three cell configurations using three or two compartment cells with different anion or cation exchange membranes (CEM) in stack series were used and compared. Electrodialysis with three compartments gives the best current efficiencies for nitric acid and sodium hydroxide production from sodium nitrate.     

Determination of the limiting current density in electrodialysis desalination as an empirical function of linear velocity

Electrodialysis is known to be a useful membrane process for water desalination. The limiting current density (LCD) in the electrodialysis process is an important parameter which determines the electrical resistance and the current utilization. Usually, LCD depends on membrane and solution properties as well as on the electrodialysis stack construction and various operational parameters such as the flow velocity of the diluate solution. Therefore, a reliable determination of LCD is required for designing an efficient electrodialysis plant. In this study, LCD was measured in an electrodialysis flow cell system of given geometry and spacer configuration as a function of the linear velocity. The coefficients a and b of an equation describing LCD as a function of the linear flow velocity of the diluate solution, i_lim=aCu^b, were determined from a plot of the measured LCD over the electrolyte concentration versus the linear velocity on a double logarithmic scale. It was found that the coefficient b was related to the hydrodynamic conditions, while the coefficient a was affected by the cell geometry, electrolyte concentration and the membrane properties.     

Comparison of electrodialysis and reverse electrodialysis processes in the removal of Cu(II) from dilute solutions

Electrodialysis (ED) and electrodialysis reversal (EDR) processes have been often used for separation of ions in dilute solutions. In this study, the performance of ED and EDR processes has been examined in the removal of copper from the dilute solutions. First, applied voltage, initial concentration, flow rate, type of electrolyte and the effect of concentration were determined for both processes. Then, separation efficiency, current efficiency, energy requirement and material flux of the processes were calculated, and the performances of the processes were compared. The separation efficiency and energy consumption of EDR process were higher compared to ED process under equal operating conditions. Also, the current efficiency (39.58%) of EDR process was lower than the current efficiency (67.46%) of ED process. It can be said that the ED process is more suitable in terms of energy consumption for separation in the low flow rate and concentration.     

Economic comparison of pressure driven membrane processes to electrically driven processes for use in hydraulic fracturing

Hydraulic fracturing has become a reliable source for oil and natural gas, yet widespread use has led to significant issues with water consumption and sustainable sourcing. Research into the reuse of produced water and flowback water have focused on mitigating water demand in this industry through membrane separation technology. In general, nanofiltration and reverse osmosis have been thought to be more economically viable for the treatment of produced and flowback water at high flowrates. However, electrodialysis and electrodeionization are generally more flexible for production of produced water and brackish water for reuse in fracturing operations when contaminant concentrations in produced water and flowback water are low. Electrodialysis and electrodeionization can also significantly reduce wastewater produced from water treatment, decreasing the amount of water that must be disposed by deep well injection. Thus, there are many cases where electrically driven processes compete well with pressure driven processes due to high water recovery and each case must be analyzed in terms of water quality variability and overall desired water treatment rate. This paper finds that at low ion concentration of inlet water, electrodialysis and electrodeionization are energy-efficient, cost-effective attractive technologies for water recovery.     

Pilot investigation on the treatment of fertilizer manufacturing process effluent using lime and electrodialysis reversal

The treatment of a fertilizer company's effluent was evaluated using lime and electrodialysis reversal (EDR) for phosphate removal, water and chemical recovery, and effluent volume reduction. Phosphate could be reduced from 3 800 to less than 50 mg/1 at pH 8.5 with lime; however, phosphate removal from the lime treated effluent using EDR was poor (75% removal). The EDR product water complied with the requirements for cooling tower make-up except for TDS and phosphates. However, the required specifications should be met using 10 stage EDR.

In addition, plant nutrients (NH₄⁺ NO₃⁻) may be recovered from the brine, which comprised 20% of the initial effluent volume. Membrane scaling was virtually absent. A full scale EDR plant should run well with electrical adjustments and/or frequent acid cleaning. Electrical energy consumption for EDR treatment was found to be 4.5 kWh/m³ feed (pumping costs excluded). The capital cost for a 30 m³/h EDR plant and clariflocculator (PO₄ removal) was estimated at US $750 000.     

Removal of hardness in fermentation broth by electrodialysis

Lysine fermentation broth was desalinated by electrodialysis to reduce hardness concentrations as a pretreatment procedure for the purification and recovery of amino acids. Electrodialysis performance was investigated in terms of the rate of reduction in conductivity in dilute solutions and electrodialysis cell resistance for different ion exchange membranes at a constant current density. Among the membranes investigated in this study, membranes with high water content showed the better performance for hardness removal. Fouling experiments revealed that organics gave rise to fouling effects on the anion exchange membrane during demineralization of the lysine fermentation broth. The pulsed electric field with the half‐wave power enhanced the electrodialysis performances by mitigating membrane fouling in desalination of the lysine fermentation broth. This study successfully demonstrated the potential use of pulse power as an effective cleaning‐in‐place (CIP) method during electrodialysis of fermentation broth. © 2002 Society of Chemical Industry     

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.     

Electrodialysis of effluents from treatment of metallic surfaces

Electrodialysis is applied for treatment of effluents from washing after galvanization, and specifically from washing after nickel galvanization. This method is useful for recovery of galvanization reagents used in various processes. Electrodialysis seems to be applicable for treatment of effluents from washing after cyanide galvanization or galvanization with other substances.For the purpose of establishing a closed system for the effluents discharged during the treatment processes for metallic surfaces, techniques for industrialization of electrodialysis have been developed not only for the recovery of useful components, but also for recycled use of water. Industrialization of electrodialysis is expected in the near future. In order to establish these techniques, technical development is needed not only in ion-exchange membranes and electrodialyzers, but also in systematized processes, including all related techniques such as pretreatments.     

Limestone selection criteria for EDR water remineralization

Water scarcity in Mediterranean regions has led to projects that increase water resources by desalination. In this context, it is planned to expand and improve the drinking water treatment plant of the Llobregat River near Barcelona (Catalonia, NE Spain), building the largest electrodialysis reversal (EDR) plant in the world. Llobregat River water shows high salinity due to the occurrence and exploitation of several geological formations upstream with minerals having high contents of Na, K, Cl, and Br. EDR desalinated water is highly reactive and shows a low degree of mineralization. In consequence, remineralization is necessary to equilibrate the water in order to avoid aggressiveness and corrosion in pipelines and to re-introduce some essential ions for human health. Running outlet water through limestone (CaCO₃) is a simple and cheap process for remineralization. Five commercially available limestones were characterized (mineralogical and chemical composition, BET surface area, SEM analysis) and compared experimentally at both laboratory and pilot-plant scales during the EDR remineralization process. The main criteria in selecting a limestone for EDR water remineralization are its compositional purity in terms of both mineralogy and chemistry, and its textural characteristics. Texture mainly influences the suspended particulate matter (PM) generation, i.e., consumption and system performance. To minimize the negative effects of these features, an assessment, using SEM analysis and batch tests contacting limestones and desalinated water, of the capacity of PM generation is recommended.     

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.     

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.     

关于电渗析除盐系统的节水问题

电渗析除盐设备在我国已被广泛地用来生产软化水、纯净水,但目前的电渗析系统水利用率很低,有的电渗析设备水利用率仅在４０％左右。广泛地使用这样的电渗析设备造成水资源的大量浪费。究其原因,主要是设计者和制造者的盲目性所致。文中介绍了自动频繁例极浓水循环电渗析除盐系统的节水方法和原理,从而制定了在不同的原水水质,不同的除盐率要求的情况下,水的利用率应该达到指标。避免了盲目排放所谓浓水,并为排放的浓水含盐量