The selection, operation, and maintenance of a reverse osmosis (RO) water purification system should be straightforward. However, systems are often 1) inaccurately specified, i.e., not matched to the application; or 2) used incorrectly, e.g., technicians sometimes store the purified water in unsterilized plastic containers. Poor specification and incorrect maintenance procedures can significantly reduce the quality of output from RO water purification systems, but a well-specified, well-managed RO water purification system will provide an efficient, economical, and reliable supply to an exceptionally high level of purity.
A water purification system supplier is the best source for anyone concerned with a water supply. Expert advice from a supplier can help all parties make the right decisions when specifying a water purification system, particularly when the application demands high standards of hygiene. The goal of this article is to help clarify some of the key points that need to be considered.
The first hurdle to overcome is to get the specification right. One should be aware of the standardized grades of water purity, the available methods of delivering them, and the typical volume requirements of the facility itself. This will ensure that any immediate and forthcoming needs are met and prevent unnecessary expense in the future.
There are several grades of water purity, expressed in terms of conductivity, defined in the current standards as BS EN ISO 3696 or ASTM D1193-06, “Water for analytical laboratory use.” ASTM Type 1 represents the highest level of purity at the maximum of 18.2 μsec/cm; Type 3 is <0.2 μsec/cm, Type 2 <1 μsec/cm, Type 4 <5 μsec/cm, ISO Grade 1 <0.1 μsec/cm, Grade 2 <1 μsec/cm, and Grade 3 <5 μsec/cm.
The specification may include deionization, which is an excellent method of producing a Grade 1 supply. Disposable deionization or ion exchange cartridges can be connected directly to a mains water supply. Each cartridge uses a mixture of resins to remove anionic and cationic contaminants from the feed water, exchanging them with active hydrogen and hydroxyl ions, which combine to form water molecules.
In some cases, the most efficient way to raise the level of purity is to apply a combination of reverse osmosis and deionization. This uses the RO membrane to manage the main purification process, and produces a prepurified feed to the deionizer cartridge, allowing it to “polish” the water, further improving the quality and extending the life of the resin.
Despite the fact that potable feed water processed by a standalone reverse osmosis water purification unit can achieve Grade 1 output, there are situations in which it is more efficient and economical to install a centralized system. There are many benefits to specifying a centralized system to feed a ring-main and supply a series of locations, for example, valuable space can be saved. Gains in efficiency can also be achieved by utilizing the standby facility on the pumps, thus preventing unnecessary energy consumption.
Water purification system maintenance and cleaning
Even the best water purification systems will only perform at their peak when supported by routine cleaning and maintenance. Therefore, to maximize efficiency, one should consider specifying equipment that is quick and easy to maintain with easy-to-change consumable parts. Similarly, the cost of consumables should be taken into account, since systems that use high volumes of resins, chemicals, and cleaning solutions can quickly become uneconomical.
Regular quarterly cleaning of RO membranes is relatively straightforward and is typically carried out using specialized cleaning solutions such as ROclean chemicals (Purite, Oxon, U.K.). Acid-based cleaners are used to remove scale, and alkaline-based solutions to remove organic matter; if required, special chemicals can also be used for disinfecting, but should only be added once all scale and organic matter have been removed. Solutions are simply circulated through the RO system and tank and then flushed to drain.
Figure 1 – Select Fusion system.The leading designers and manufacturers of advanced water purification equipment now have the ability to provide a range of solutions across applications with many specialized models available for laboratories. There are cost-effective solutions for applications such as humidification and hydroponics; units designed for routine pure water laboratory tasks, including glassware rinsing; water purifiers that provide a consistent, high-quality flow for chromatography, atomic absorption, and clinical analyzer feeds; and highly specialized machines that meet the need for high purity with an enhanced microbiological specification in tissue culture, in vitro fertilization (IVF), life science, and molecular biology applications.
The Select range of systems from Purite includes specialized models such as the Fusion (see Figure 1), which is purpose-built to provide analytical and life science applications with dual-quality water, ultrapure water to 18.2 MΩ.cm, and Type 2 water for everyday use. The Neptune offers that same quality with a higher flow. The Select Purewater 300 is designed specifically for use with laboratory glassware washing machines, providing rinse water to a purity of over 1 MΩ.cm at a flow rate of up to 48 L/hr.
The Integra HP from Purite is a modular, standalone water purification unit capable of producing up to 190 L/hr of laboratory-grade water to a purity that exceeds 1.0 MΩ.cm, making it well suited as a centralized system for larger laboratory and clinical analysis departments. Designed as a completely self-contained system requiring just power and water supplies before it can be used, and with a sophisticated color LCD touchscreen for control, the Integra HP has been designed for simple and cost-effective long-term use, delivering an optimal return on investment.
Steve Mines is Sales Manager, Purite Ltd., Bandet Way, Thame, Oxon OX9 3SJ, U.K.; tel.: +44 (1) 844 217141; fax: +44 (1) 844 218098; e-mail: [email protected].