Water, Water, Everywhere: A Profile of Water Purification Systems

Date: June 8, 1998 Author: Michael BrushPoint of Use Water Filtration Systems He was described as a "grey-beard loon," but the superstitious old sailor of Samuel Taylor Coleridge's The Rime of the Ancient Mariner clearly understood the value of a reliable and consistent source of pure water. Trapped on a ship becalmed in the doldrums and faced with an exhausted fresh water supply, the old sailor lamented, "Water, water, everywhere, nor any drop to drink." The pure water requirements of the modern life science lab are just as important as the fresh water needs of the old sailor. The convenience of obtaining as much water as needed at a moment's notice, free from worries about possible contaminants, can't be beat. In this profile, Labconsumer looks at point-of-use water purification systems that produce reagent grade, Type I water directly in the laboratory The production of Type I water involves the successful removal of a variety of impurities and contaminants. These are generally lumped into the following groups. Particulate matter: This includes suspended particles, such as silt, sand, and clay particles, ranging between 1 micron and 20 microns in size, and colloidal particles, which fall between 0.01 micron and 1.0 micron in size. Altogether, these particles cause water to appear unclear or cloudy. Microorganisms: Bacteria, protozoa, viruses, and algae are among the organisms that contaminate water. Microorganisms give rise to pyrogens, which are thermostable, lipopolysaccharide fragments of cell walls. Pyrogens cause immune responses such as fevers when injected into mammals, and hinder cell and tissue cultures. DNA, DNase, RNase, and the normal biological materials and waste products produced by living and dying organisms are also impurities that must be dealt with. Dissolved nonionized solids and gases: This group includes man-made organic chemicals and the natural organic remains from decaying plants and animals. Together, these may include proteins, tannins and chloramines, in addition to pesticide, herbicide and detergent residues. Oxygen also falls within this group. Dissolved organic compounds interfere with HPLC and may hinder electrophoresis and cell and tissue cultures. Dissolved ionized solids and gases: These come from the exposure of water to rocks and minerals, and include sodium chloride, calcium carbonate, silicates, nitrates, sulfates, phosphates, and other compounds. Carbon dioxide is the main ionized gas. Ions impact the results of inorganic analyses and may retard the growth of cells and tissues. Five major technologies exist to remove these impurities from water. Distillation: Distillation is the oldest and most widespread technology for the production of reagent grade water. This technology heats water to boiling, and then condenses the vapor back to liquid. The phase change from liquid to vapor separates water from its impurities. Distillation removes the widest range of impurities from water. Adsorption by activated carbon: Chlorine and organic compounds are removed from water by adsorption to high surface area activated carbon filters. Adsorption is generally employed as a first or second step in water purification systems. Ultraviolet irradiation: The irradiation of water by UV light at 254 nanometers and 185 nanometers kills microorganisms and reduces trace organics by photochemical oxidation, respectively. UV irradiation plays an important role in maintaining the sterility of purified water once the biocides, such as chlorine, have been removed by other purification methods. Deionization: Also known as ion exchange or demineralization, deionization uses both cationic and anionic exchange resins to remove ionized salts from water. The resins may be used separately or combined into mixed-bed systems. The mixture of the two resins promotes efficient removal inorganic ions. Filtration: Filtration can be broken down into subcategories based on the pore size of the filter devices. Particle filtration employs filters with pore sizes at least 1 micron in diameter. Microfiltration uses filter devices with pore sizes between 1 and 0.5 microns. These filters remove bacteria and submicron particles from water and are often used as a final step in water purification systems to ensure the removal of microorganisms from the final purified water. Ultrafiltration membranes have pore sizes that block the passage of contaminants over 10,000 daltons in size and are used to remove pyrogens, viruses, DNase, and RNase from water. Finally, reverse osmosis membranes have pore sizes on the order of 0.001 microns, and effectively block molecules exceeding 300 daltons. Capable of removing around 95 percent of the contaminants present in water, reverse osmosis is finding increased application for the pretreatment of water before distillation or deionization processes. The manufacturers of water purification systems combine these technologies together, with the exception of distillation, into various configurations to produce Type I water. In a typical system, the first step is the pretreatment of the feed water. Usually, carbon adsorption and particulate filtration are used for chlorine and sediment removal. Reverse osmosis or deionization often is used next. Frequently, these systems are incorporated into a facility as a central water system and/or filling storage reservoirs that supply purified water for several users and applications. After pretreatment, the purified water enters a polishing system, where the real work of producing Type I water occurs. Polishing systems elevate the quality of the pretreated water to ultrapure or Type I status by removing the residual traces of impurities. Typically, a polishing system consists of activated carbon, mixed-bed deionization, organic scavenging mixtures and microfiltration combined together. For specific applications, ultraviolet irradiation and ultrafiltration mechanisms further enhance the quality of the water. Working together, proper pretreatment and polishing combinations produce water that is virtually free of organic, ionic, and microbial contamination. What is Type I water? Purified, reagent grade water is broken down into one of four types: Type I, Type II, Type III, or Type IV. Type I, or ultrapure water, is the most pure. To confuse the issue, five major standards organizations, CAP (College of American Pathologists), NCCLS (National Committee for Clinical Laboratory Standards), ASTM (American Society of Testing and Materials), USP (United States Pharmocopeia), and ISO (International Organization for Standardization) define the characteristics of these water types. With the exception of CAP accepting the NCCLS water standards, the organizations do not agree on the characteristics of the four types. The net result is that Type I water has varying qualities depending on which guidelines are used. The water types are defined in terms of specific resistance (megohm-cm), specific conductance (microhms per centimeter), total silica, total organic carbon (TOC), and bacterial count, among other attributes. For practical purposes, Type I water has a specific resistance of at least 18 megohms-cm and meets other criteria specified by the five standards organizations. Depending on the application, other traits, such as bacteria count, total organic carbon, and pyrogen levels are often specified by the ultimate user. The most common method used to measure the purity of Type I water is to determine its specific resistance. Inexpensive and easily done, specific resistance is measured by determining the current conducted by pure water flowing between a pair of electrodes. The lower the amount of ionic impurities, the greater the specific resistance and the purity of the water. In practice, the highest specific resistance value for pure water is 18.18 megohm-cm at 25°C. Unfortunately, specific resistance does little to measure the nonionic organic contaminates, or the total organic carbon, in water, so for systems without UV irradiation and ultrafiltration, it is possible to have an organic soup with 18 megohm-cm resistance. To illustrate the problem of undetected organic compounds, Millipore Corp.'s Jon DiVincenzo explains that simply dissolving sugar in 18 megohm-cm water can raise the TOC values to 1000 parts per billion (ppb) without reducing the specific resistance of the water. Normally, good TOC values fall between 1 ppb and 10 ppb. The measurement of TOC is expensive. Accurate TOC measuring devices can cost as much as $15,000, or three to six times the average cost of a water purification system. Consequently, TOC measuring devices have not found their way onto water purification systems with the exception of a small handful of instruments (see Millipore Corporation and Elga, Inc.) with specially designed, less expensive TOC meters. So, unless researchers have their purified water analyzed periodically or rigorously follow the recommended intervals between cartridge changes, they may not be aware of rising TOC levels in their Type I water sources. This is particularly insidious if a cartridge-based system component fails or has been exhausted. At the expense of generating waves in the water purification industry, Erich Gibbs of High-Q Inc. believes that the scientific community is not as aware as it should be of the "hidden" organic contaminant problem with Type I water. He states that the reliance upon specific resistance as the sole indicator of Type I water purity amounts to "the emperor's clothes" in that what one does not know can be very embarrassing for science. (For more information, see High-Q's website at www.high-q.com). High-Q relies on a unique glass laboratory water still as the final stage of purification for its systems. According to Gibbs, this approach produces water with extraordinarily low levels of organic contaminants -- reliably, conveniently, and without having to maintain expendables. To balance things out, Bob Applequist of Labconco Corp. points out that researchers frequently use water that is more pure than required simply because they have easy access to pure water through their Type I water purification systems. Often, organic impurities in this water are inconsequential to a number of applications, so it behooves researchers to thoroughly understand their water requirements based on those applications before worrying too much about TOC levels. The majority of the Type I water polishing systems available employ cartridge technology to contain the various resins and carbon adsorbents needed to prepare Type I water. Usually, the manufacturers build four versions of a water polishing system. The first version is the basic model without the ultrafiltration and ultraviolet light technology used for pyrogen and trace organic removal. These technologies are incorporated separately into the basic model to create the next two versions, and are added together on the fourth version. The fourth version delivers the highest quality water but also carries the highest price. Fiberglass and virgin polypropylene canisters provide yet another means of containing the resins and filters, and the "Hot Finger" appears in a specialized distillation system. Here are brief profiles of eight companies and their laboratory Type I water purification systems. Barnstead Thermolyne Barnstead/Thermolyne E-pure Water Purification System NANOpure Infinity Systems EASYpure Systems Barnstead's family of Type I water purification systems begins with the E-pure Water Purification System. The wall-mounted E-pure system features a bowl and cartridge setup with the choice of three or four cartridge holder configurations. Four different cartridge kits are available to meet various applications. The E-pure also includes a continuous circulation pump and a 0.2 micron filter. The NANOpure Infinity family of products consists of four individual units, as well as modules capable of converting one unit to another in the laboratory. The individual units represent the Base unit which produces water for most analytical procedures involving Type 1 water with resisitivities up to 18.3 megohm-cm and TOC levels below 4 ppb. The UV model is designed to be used for the most demanding organic determinant analyses providing Type 1 water with TOC values below 1 ppb. The Infinity UF unit utilizes an ultrafilter for the removal of pyrogens, providing water with less than 0.001 EU/ml. The fourth model is the UV/UF that utilizes a combination of most water purification technologies including ultraviolet oxidation and ultrafiltration, producing water that is virtually free of all contamination, including DNA, DNase, and RNase. According to the company, this model and the EASYpure UV/UF model have demonstrated through independent studies total removal of nucleases even when challenged with various concentrations of these impurities. The units feature a remote dispenser allowing water to be dispensed up to eight feet away from the system. Designed for labs with Type I water requirements of less than 15 liters per day, the compact EASYpure system is composed of 5 models. The unique, portable Batch Feed model includes a 7 liter, filtered storage reservoir. The Line Feed model is fed by a pressurized feed line or gravity feed storage tank. Both produce water with less than 10 ppb TOC content. The UV Line Feed and UF Line Feed models deliver water with less than 3 ppb organic content and effectively remove pyrogens, respectively. The newly introduced UV/UF model combines these together to create pyrogen free, 18.3 megohm-cm water with less than 3 ppb TOC and demonstrated RNase A removal. All EASYpure models feature easy-to-change disposable cartridges. Elga UHQ II Elga, Inc. UHQ II Maxima Scientific, Analytical, HPLC UHQ PS and Life Science models The two machines comprising Elga's UHQ water purification systems are designed to operate on different feed water supplies. Incorporating a reverse osmosis membrane, the UHQ II operates automatically on raw potable water. The UHQ PS excludes the RO membrane and instead operates from a source of pretreated water. Both instruments include adsorption, deionization, microfiltration, and photo-oxidation technologies as standard components. Water of identical quality is produced by the UHQ instruments, and is suitable for HPLC, AA spectrometry, ICP mass spectrometry, and several other applications. The Maxima water purification system is available in a choice of four models. The Scientific model economically generates water with low inorganic levels suitable for ion chromatography and AA spectrometry. The Analytical model turns out water with TOC values less than 5 ppb, which is suitable for critical analysis applications. Incorporating an enhanced photo-oxidation system, the HPLC model delivers water with exceptionally low TOC levels designed specifically for HPLC and other trace organic analyses. The HPLC model is one of the few water purification systems to include a TOC monitor as a standardcomponent. Finally, the Life Science model features a 10,000 molecular weight cut-off ultrafilter for pyrogen removal. This water meets the demands of sensitive biotechnology applications, including cell culture, in vitro fertilization, and monoclonal antibody production. 103S Glass Water Still High-Q Inc. 103S Glass Water Still The 103S Glass Water Still is included in this profile because it provides a new and intriguing alternative technology for reagent grade water purification. The resistivity of the water produced in a 103S still exceeds 10 megohm-cm, which is not as high as the resistivity of deionized water; however, the difference is due to traces of ionized gases, like CO2, and the sparingly soluble ionized components of chemically resistant glass. Overall, High-Q touts the water produced by the 103S as pure, or more pure, than the water produced by cartridge systems. The components of the 103S still do not bleed organics, do not support the growth of microorganisms, and do not exhaust with use. Distillation is the single most effective technology for removing impurities from water. With that in mind, High-Q has developed the components of its 103S still to take full advantage of the power of distillation. Billed as fully automatic, self-sanitizing, self-cleaning, and reliable, the 1.5 meter-tall 103S produces about 75 liters of high-purity water per day. A high-efficiency boiler stage is equipped with a combination hydrophobic/hydrophilic interface that traps mist particles, equilibrates the steam temperature, and blocks surface entrainment. The most striking component of the still is the compound, hot-finger, counter-current condenser. Water vapor condenses at the very top of the still on a large surface area "hot finger" heat exchanger, so named because its temperature stays at essentially the boiling point of water. As a consequence of this high-temperature condensation, the volatile impurities concentrate in the steam phase, so they can be efficiently vented from the condenser. The condensed water runs down the inside of the segmented counter-current stage of the compound condenser as a film, remaining in equilibrium with the steam rising from the boiler. The net effect is to further concentrate volatile contaminants toward the still's vents, while physically separating the purified water from contact with these contaminants. Hydro Picosystem HYDRO Service and Supplies Hydro Picosystem® Plus, Picosystem® UV Plus, Picotech® 2, Picotech® 2 UV Plus, Picopure® 2, Picopure® 2 Plus, and Picopure® 2 UV Plus A departure from the usual cartridge-type water purification system, the Hydro Picosystem is comprised of three 6-inch by 18-inch fiberglass canisters. Arranged in a linear series, the three canisters produce Type I water from either tap or pretreated feed water. The first canister contains an organic adsorption media and feeds water into the primary mixed bed deionizer tank. This tank generates water with a specific resistance of at least 5 megohm-cm. A 5 megohm-cm resistivity cell light is attached to the tank's outlet line and indicates when the water falls below 5 megohm-cm. From here, the water enters the polishing deionizer canister designed to consistently maintain 18 megohm-cm water until the system is serviced. The Hydro canisters are recycled (regenerated) by Hydro. For point-of-use sterilization, a high intensity UV lamp and ultrafiltration filter are housed within the Picotech. When attached to the output of the polishing deionizer canister, this compact cabinet provides sterile water right at the sink. Finally, the addition of the UV Plus component produces the Picopure's highest purity water by removing RNase and trace organic compounds. A recirculation pump is incorporated into the system to make certain that the high quality water is maintained at all times. Various instruments for monitoring the water quality are available, as are many system configurations to provide exactly the quality required. Labconco Water Pro Labconco Corp. WaterPro® PS Polishing Stations: General Chemistry, HPLC, Life Sciences, and HPLC/UF Hybrid versions Labconco's WaterPro PS Polishing Stations are four of the newest water purification systems on the market. With several new features, such as an automatic timed dispense mode that allows unattended filling of carboys without the risk of overfilling and flooding the lab, and an optional built-in dispensing pistol, the WaterPro PS stations are designed to meet specific applications. The General Chemistry version delivers Type I water suitable for AA, flame emission spectroscopy and trace metal analysis. This version may also be upgraded to the Analytical or Life Sciences versions. The Analytical version features a UV reactor and TOC flush valve that allows a small amount of water to drain during recirculation to maintain low TOC levels. HPLC, electrophoresis, and fluoroscopy are suitable applications for this water system. The Life Sciences version produces pyrogen free water with the incorporation of a UV flush valve, UV reactor and ultrafilter into its components. The water created with this system is suitable for clinical and life science applications. For HPLC, electrophoresis, fluoroscopy and clinical applications, the HPLC/UF Hybrid version relies on both TOC and UV flush valves, an ultrafilter, and a UV reactor to deliver pyrogen-free water with less than 5 ppb TOC levels. Millipore Milli-Q Millipore Corp. Milli-Q RG Reagent Grade Water Purification System Milli-Q Ultrapure Water Systems: Academic and Academic/A10; Gradient and Gradient/A10; Biocel and Biocel/A10; Synthesis and Synthesis/A10 Millipore Corporation has addressed the undetected organic contaminant problem in Type I water head on with the incorporation of a TOC measuring device into its Milli-Q Ultrapure Water Systems. Compact and designed to greatly simplify cartridge replacement, the four Milli-Q systems are sold with and without the A10 TOC Meter. This meter displays TOC values from 1 ppb to 199 ppb, and offers an important, useful feature to researchers concerned about nonionic organic contaminants in their Type I water supplies. Both versions of each model produce the same quality water, but differ in price by about $1,200. The Academic model is the standard Milli-Q Ultrapure Water System. The addition of UV photo-oxidation technology, creating the Gradient model, delivers water with low TOC levels; the Biocel model incorporates an ultrafilter for pyrogen removal. Millipore's best water is generated by the Synthesis System with both pyrogen removal and low TOC levels. Millipore's Milli-Q RG Reagent Grade Water Purification System is a simplified, economical version of Millipore's Milli-Q Plus System. The Milli-Q RG prepares Type I water suitable for atomic adsorption spectrometry, HPLC, and ion chromatography. Solution 2000™ Type I System Solution Consultants, Inc. Solution 2000™ Type I Reagent Grade Systems: Analytical model, Ultra-low TOC model, Biological model, Ultra-low TOC Biological model Solution 2000™ Type I Compact RO+DI Systems Dedicated exclusively to manufacturing and selling laboratory water purification systems, Solution Consultants Inc. offers the widest range of Type I water purification systems in the profile. Its 24 Solution 2000 Reagent Grade systems are designed to use tap or pretreated water and are available in either Standard output (2 to 3 liters per minute) or High Flow/Capacity output (4-10 liters per minute) versions. The 24 systems are built around 4 model themes. The Analytical model provides basic Type I water, and the Ultra-low TOC delivers water containing little, if any, TOC. For life science applications, the Biological model's water is free from pyrogens and/or nucleases, and the Ultra-low TOC Biological model puts out water that is pyrogen free, optionally free of nucleases, and contains little, if any, TOC. These instruments feature quiet, continuous recirculation and operation, modular cartridge design for easy cartridge exchange, and high capacity for lower operating costs. The Solution 2000 Compact Type I RO+DI Systems combine a 5 liter per hour reverse osmosis system with a Type I Analytical or Biological grade purification system into a single cabinet design. The Compact RO+DI systems have been designed for settings with an unreliable, overtaxed, or nonexistent central water pretreatment facility, for facilities with high water usage and for areas with very poor tap water quality. They feature a 42 liter pressurized storage tank for the RO water and a remote dispenser with a 0.22 micron filter. Both the Analytical and Biological versions are available with and without a built-in Ultraviolet Sterilizer. United States Filter Corporation PURELAB Plus PURELAB Plus UV PURELAB Plus UF PURELAB Plus UV/UF The compact PURELAB Plus and its three sister versions feature quiet operation and an easily accessed front-loading cartridge design built to simplify cartridge change-out for both the bench-top and floor-mounted configurations of this system. The cartridges have been built with a down-flow design to maximize the capacity of the ion exchange resins. An electronic flow control that precisely delivers the desired amount of water is a standard feature on The PURELAB Plus systems, and all four incorporate suitable connections for the installation of an on-line TOC meter. System sanitation features with tablets or hydrogen peroxide kill microorganisms detrimental to critical life science applications. Additionally, the PURELAB Plus UF membrane can be autoclaved to ensure removal of contaminating microbes. The PURELAB Plus systems have been configured to meet specific high purity water needs. The PURELAB Plus UV delivers water with greatly reduced organic contaminants, and the PURELAB Plus UF provides pyrogen free water. Used together in concert on the PURELAB Plus UV/UF, the combined technologies enable the production of RNase-free water. Before purchasing a water purification system, it is important to understand the water purity requirements needed for the specific applications in mind. A lab performing tissue culture work or HPLC, for example, may be much more concerned about microbial and organic contaminants than a lab doing trace metal analysis. Feed water testing also bears consideration because it provides information useful to the design of water purification systems. Consider the water quality of Santa Barbara, Calif., for instance. When measured in terms of total dissolved solids (TDS), Santa Barbara's water has a value of 1,400 ppm. The water from Oakland, Calif., on the other hand, has a TDS value of 38 ppm. Obviously, different approaches to water purification are required. To that end, several water purification system manufacturers provide water testing as a free service to help guide the selection of an appropriate system. The author thanks Jon DiVincenzo and Bob Ventura of Millipore Corporation for their help with the preparation of this profile article. Point of Use Water Filtration Systems Michael Brush is an Associate Scientist at Hitachi Chemical Company in Irvine, California. He can be reached at mdbrush@compuserve.com

Water, Water, Everywhere: A Profile of Water Purification Systems

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