Electrodialysis costs

Treatment of brackish waters in the production of potable supplies has been the largest application of electrodialysis. Costs associated with electrodialysis processes depend on such factors as the total dissolved solids (TDS) in the feed, the level of removal of TDS (percent rejection), and the size of the plant. In brackish water treatment, operating costs for very large ED installations (on the order of millions of gallons a day) have been between 40 cents to 50 cents per 1,000 gallons for brackish feed waters, which compares favorably with RO costs. 

Electrodialysis. Electro dialytic membrane process technology is used extensively in Japan to produce granulated—evaporated salt. Filtered seawater is concentrated by membrane electro dialysis and evaporated in multiple-effect evaporators. Seawater can be concentrated to a product brine concentration of 200 g/L at a power consumption of 150 kWh/1 of NaCl (8). Improvements in membrane technology have reduced the power consumption and energy costs so that a high value-added product such as table salt can be produced economically by electro dialysis. However, industrial-grade salt produced in this manner caimot compete economically with the large quantities of low cost solar salt imported into Japan from Austraha and Mexico. 

Advantages to Membrane Separation This subsertion covers the commercially important membrane applications. AU except electrodialysis are pressure driven. All except pervaporation involve no phase change. All tend to be inherently low-energy consumers in the-oiy if not in practice. They operate by a different mechanism than do other separation methods, so they have a unique profile of strengths and weaknesses. In some cases they provide unusual sharpness of separation, but in most cases they perform a separation at lower cost, provide more valuable products, and do so with fewer undesirable side effects than older separations methods. The membrane interposes a new phase between feed and product. It controls the transfer of mass between feed and product. It is a kinetic, not an equihbrium process. In a separation, a membrane will be selective because it passes some components much more rapidly than others. Many membranes are veiy selective. Membrane separations are often simpler than the alternatives. 

Equipment and Economics A veiy large electrodialysis plant would produce 500 /s of desalted water. A rather typical plant was built in 1993 to process 4700 mVday (54.4 /s). Capital costs for this plant, running on low-salinity brackish feed were 1,210,000 for all the process equipment, including pumps, membranes, instrumentation, and so on. Building and site preparation cost an additional 600,000. The building footprint is 300 itt. For plants above a threshold level of about 40 m Vday, process-equipment costs usually scale at around the 0.7 power, not too different from other process eqiiip-ment. On this basis, process equipment (excluding the ouilding) for a 2000 mVday plant would have a 1993 predicted cost of 665,000. 

TDS affects taste also, and waters over 500 - 600 ppm can taste poor. When the levels top 1500 ppm, most people will report the water tastes very similar to weak alka-seltzer. TDS is removed by distillation, reverse-osmosis or electrodialysis. In our area, most desalination projects, both large and small are accomplished with reverse-osmosis. Depending on the water chemistry, reverse osmosis systems are the most popular, given their low cost and ease of use. Distillers work very well also, and produce very high quality water, but require electricity and higher... 

Electrodialysis is a well-established technology but suffers from poor recovery rates and is very susceptible to scaling problems. (A derivative, EDI, however, is able to overcome these problems, albeit at a higher capital cost.)... 

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). 

As with ED, RO, and other membrane techniques, the primary operational cost of EDR is that of pumping water through the system, and pumping costs are proportional to the TDS of the incoming water. Cost for the actual electrodialysis is low. 

There are several companies and groups that are developing bio-based succinic acid production for commercial use. The Showa group possesses a unique technology for purification of succinic acid from fermentation broth. This is the fractional crystallization method starting from sodium succinate. The yield by this method is around 70%, but we can recycle the residual solution so that we can minimize the loss of the product. We also compared the cost-effectiveness of this method with the bipolar electrodialysis method. The cost of our purification process seemed to be about half (our internal data). 

Table 1 shows treatment costs for the technology (based on a processing rate of 20 gpm) in comparison to other groundwater treatment technologies (i.e., chemical reduction and precipitation, chemical precipitation with sedimentation or filtration, activated carbon adsorption, ion exchange, reverse osmosis, and electrodialysis) (D168869, Table 13). 

Therefore, an effective water system is required. Nowadays, several techniques can be used to obtain water of high pharmaceutical quality. These include ionexchange treatment, reverse osmosis, distillation, electrodialysis, and ultrafiltration. However, there is no single optimum system for producing high-purity water, and selection of the final system is dependent on factors such as the quality of raw water, intent of its use, flow rate, and costs. In the pharmaceutical industry, the different water classes normally encountered are well water, potable water, purified water, and specially purified grades of water, such as water for injection (e.g., MilliQ water). 

The AQUATECH technology, used in conjunction with conventional separation techniques such as filtration and electrodialysis is able to overcome the disposal problem in a cost effective manner while recycling valuable resources back to the processing plant. The net result is a cleaner environment and the avoidance of long term liabilities to the processor. 

W., Design, Construction and Field Testing Cost Analyses on the Experimental Electrodialysis Demineralizer for Brackish Waters, Ionics, Inc., Office of Saline Water, Research and Development Progress Report, No. 11, Washington, D. C., 1956. 

To produce low-cost water, a plant must meet two main conditions a moderate cost per square foot of active area and a relative freedom from expensive supervision and frequent overhaul. These conditions can be met by large cells. In fact, large scale, community-sized electrodialysis plants can allow the freedom of design needed to make desalinization economically feasible. 

Power Supply and Process Control Unit. Electrodialysis systems use large amounts of direct current power the rectifier required to convert AC to DC and to control the operation of the system represents a significant portion of a plant s capital cost. A typical voltage drop across a single cell pair is in the range 1 -2 V and the normal current flow is 40 mA/cm2. For a 200-cell-pair stack containing 1 m2 of membrane, the total voltage is about 200-400 V and the current about... 

The efficiency of electrodialysis is determined to a large extent by the properties of the membranes. But it is also affected by the process and system design that determine the limiting current density, the current utilization, the concentration polarization and the overall efficiency and costs [20, 21]. 

The total costs in electrodialysis are the sum of fixed charges associated with the amortization of the plant capital costs and the plant operating costs. Both the capital costs as well as the plant operating costs per unit product are proportional to the number of ions removed from a feed solution, that is, the concentration difference... 

Figure 5.9 Schematic diagram illustrating the various cost items in electrodialysis as a function of the applied current density.

Electrodialysis with Bipolar Membrane Process Costs... 

The determination of the costs for the production of acids and bases from the corresponding salts follows the same general procedure as applied for the costs in electrodialysis desalination. The contributions to the overall costs are the investment-related cost and the operating costs. 

Investment costs in electrodialysis with bipolar membranes Investment costs include nondepreciable items such as land and depreciable items such as the electrodialysis stacks, pumps, electrical equipment, and monitoring and control devices. The investment costs are determined mainly by the required membrane area for a certain plant capacity. The required membrane area for a given capacity plant can be calculated from the current density in a stack that is in electrodialysis with a bipolar membrane not limited by concentration-polarization effects. The required membrane area for a given plant capacity is given by ... 

Strathmann, H. (2004) Assessment of electrodialysis water desalination process costs. Proceedings of the International... 

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