Electrodialysis pretreatment

Efficient separation or pretreatment in the influent streams can include activated carbon absorption to reduce or prevent such problems. Principal applications of electrodialysis include ... 

Electrodialysis is a particularly economic process for low-salinity waters when compared to RO because, although the initial capital cost may be 10 to 15% higher, it generally requires no pretreatment, it produces a higher recovery rate (around 80-85%), it has a lower operating and maintenance cost, and the membranes last twice as long (up to 10 years). 

Process water applications include boiler water feed pretreatment before ion exchange or electrodialysis. RO is also used for ultrahigh-purity water production for use in laboratories, medical devices (kidney dialysis), microelectronic manufacturing (rinse fluids per ASTM D-19 D5127-90, 1990), and pharmaceutical manufacturing (purified water or water for injection as specified by USP). 

In the practical application of electrodialysis there are two main process operation modes. The first one is referred to as the unidirectional electrodialysis and the second as electrodialysis reversal [22]. In a unidirectional operated electrodialysis system the electric field is permanently applied in one direction and the diluate and concentrate cells are also permanently fixed over the period of operation. Unidirectional operated electrodialysis plants are rather sensitive to membrane fouling and scaling and often require a substantial feed-solution pretreatment and stack-cleaning procedures in the form of periodical rinsing of the stack with acid or detergent solutions. The unidirectional operating concept is mainly used today for applications in the... 

The second typical technology applied for d. of water is -> electrodialysis. After appropriate pretreatment (as above), the feed solution is pumped through the unit of one or more stacks in series or parallel. The concentrated and depleted process streams leaving the last stack are recycled, or finally collected in storage tanks. The plants operate unidirectionally, as explained, or in reverse polarity mode, i.e., the current polarity is changed at specific time intervals (minutes to hours), and the hydraulic flow streams are reversed simultaneously, thus preventing the precipitation in the brine cells. 

The ionic concentration to be treated is an overriding consideration governing the cost of plant of a given design and therefore for very high ion concentrations it is foreseeable that membrane pretreatments such as reverse osmosis and electrodialysis will continue to fulfil an important role as might a more widespread revival of continuous countercurrent ion exchange. 

A recent innovation by a U.S. manufacturer of ED systems has significantly minimized the need for pretreatment. This innovation, known as electrodialysis reversal (EDR), operates on the same basic principle as the standard electrodialysis unit, except that both the product and the brine cells are identical in construction. At a frequency of 3-4 times/hr, the polarity of the electrodes is reversed and the flows are simultaneously switched by automatic... 

With the infbimstion described above, predesign estimates of capital and operating costs can be prepared. Capital costs include costs for pretreatment equipment (if needed), electrodialysis slacks, storage tanks, and pumps. These costs may be estimated by standard predesign estimating methods. 

The first term on the right-hand side of the equation is independent of current density, such as the cost of sub-raw materials, pretreatment cost, storage tanks, etc., the second term is proportional to current density, such electric power consumption for electrodialysis or electrolysis, and the third term is inversely... 

Novic, M., Dovzan, A., Pihlar, B., and Hudnik, V., Determination of chlorine, sulphur and phosphorus in organic materials by ion chromatography using electrodialysis sample pretreatment, J. Chromatogr. A, 704, 530-534, 1995. 

In addition to the actual stack and the power supply unit, an electrodialysis plant consists of several components essential for proper operation, such as pumps, process monitoring and control devices, feed solution pretreatment systems, etc.. There are two operating modes for the electrodialytic process described in the literature [44]. The first is referred to as the unidirectionally operated electrodialysis plant and the second is a reversed polarity operated electrodialysis plant [7]. A flow diagram of a typical unidirectional operated electrodialysis plant is shown in Figure 10. 

Electrodialysis, reverse polarity for 4000 mg/L TDS alkalinity to 500 mg/L with minimum pretreatment including brine recirculation pumps, ED stack, electrical equipment, brine discharge facilities, product water treatment and storage, building, intake pipes and transfer pumps. TM cost = 25 000 000 at feed rate = 100 L/s with n = 0.82 for the range 40-1500 L/s. Feed factors 4000 ppm, X 1.00 2000 ppm, X 0.7 850 ppm, X 0.1. 

A variety of on line sample pretreatment procedures have been described for the coupling to on-line capillary zone electrophoresis (CZE)-MS, including capillary isotachophoresis, electrodialysis, liquid-liquid electroextraction and SPE on Empore disks. The latter system was applied to the analysis of the neuroleptic drug haloperidol in patients urine by on-line Empore-disk SPE-CZE-MS. 

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