Portable Service Deionization Tanks (SDI) Potential for Resurgence?

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Many applications in manufacturing, pharmaceuticals, and healthcare just to name a few need a reliable high purity water source, sometimes up to theoretically pure water of 18.23 megohms of resistivity. The key is to know what level of purity is truly needed for an application. It is all too often that too high of resistivity expectation can a have an adverse effect on a systems design and capabilities. When ultra-pure water is needed it is important to understand systems limitations and design needs. Service Deionization (SDI) also referred to as Deionization (DI) is a simple set up that is flexible and reliable. Based on a series of portable tanks filled with various chemically charged resin beads, the systems can run off of straight city/tap water and still produce anywhere from 5-20 microsiemens of conductivity for separate bed systems up to theoretically pure water of 18.23 megohms of resistivity with the use of a mixed bed resin system. Varying flow rates can be accommodated with this type of system as well. It’s important to realize that when speaking of resistivity versus conductivity it is an entirely higher realm of purity. Highly resistive water is not conductive but is resistive to electrical conductance and when placed in inappropriate pipes such as copper can actually pull minerals from the pipes due to its high level of resistive charge wanting to leach off ions from certain metals. A separate bed system of deionization tanks is usually set up as a carbon tank to remove some organics and chlorine (chlorine is harmful to the resin), a cation tank, followed by an anion tank incorporating a pre and post filter will give the end-user a quality of water typically produced by a reverse osmosis system. The upside is that on site there is little to no need for electricity and no waste of water going to the drain. Reverse Osmosis (RO) systems are very efficient at removing a number of materials that at times cannot be removed just by an SDI system. However, RO systems can use quite a bit of electricity and often dump 20-30 percent of their water if not more to drain therefore becoming an environmental concern. Double pass systems and a follow-up up recovery system is possible but it depends on the budget available if this is feasible. The potential benefit in this case where a DI system is coupled with post filters for other contaminants such as bacteria might make sense in regard to waste reduction to satisfy an operations environmental plan. A mixed bed SDI/DI system can produce up to 18.2 megohm of resistivity with 17 meghohm being easily achievable which meets many application requirements. This water is available on demand which is a good selling point in that highly pure water degrades if stored too long. A mixed bed system can be coupled with a recirculating system to keep the water in the tanks resistive when demand is needed and also incorporate an ultraviolet light and post filter to combat bacteria. There are other alternatives such as Electronic Deionization (EDI) systems that do not require tank exchanges as well as hybrid set ups such as Reverse Osmosis Systems (RO) followed by polishing DI tanks. EDI can work for certain flow rates but there is still water rejection to drain and the expense may outweigh other alternatives. So what is the downfall of DI / SDI? Sometimes the expense at certain usage levels makes the DI tanks seem more expensive than alternatives, and at times this is very true. There is also the need to have a delivery service come in and exchange tanks periodically. DI tanks can remove most contaminants but not all as is the case with many single components of a water filtration system. The quick summary of an SDI system is that they are very flexible in design, good for pilot testing, low start-up costs, typically a reasonable footprint, little to no on-site rejection to impact an environmental plan and water dumping fees, produce variable levels of water quality and have little chance of failure since they are not highly mechanical in design. The bottom line is that you must know what final water quality is really needed. You then must look at flow rates, consumption levels, and what you may be trying to achieve through an environmental plan to help you determine what is most cost-effective and efficient for your operation. SDI is often overlooked when it may be the best plan, especially with advances in most SDI regeneration facilities, and the increasing need to reduce on site waste water. At Absolute Water Technologies, we will help you investigate the best options to use in your system and help you engineer something specific to your needs. That’s Absolute value.

For more information on Service Deionization systems or Reverse Osmosis Systems (RO), please feel free to browse online or request a quote.


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