Ener y Considerations in

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Ener y Considerations in Labora 9 ory Water Purifiation here are seven methods ommonly T used to purify water: distillation, deionization, reverse osmosis, arbon adsorption, miroporous filtration,

1 Ener y Considerations in Labora 9 ory Water Purifiation here are seven methods ommonly T used to purify water: distillation, deionization, reverse osmosis, arbon adsorption, miroporous filtration, ultrafiltration, and ultraviolet oxidation. These methods are often used in ombination to ahieve the desired quality of water. The amount of energy and water required for water purifiation depends on the method(s) used. Distillation, although widely used, requires the most energy and wastes the most water. When energy osts and water onservation are a onern, distillation is not the method of hoie. Energy and water use an be minimized by using other innovative waterpurifiation methods that are disussed in this Tehnology Update. Bonneville PO WE R ADM I N I STRATI ON Tollfree Hotline Introdution Here in the United States lean water is abundant. Drinking water is available from most any fauet. If the water looks lear and tastes okay, we think of it as being quite pure. The water may ontain small amounts of impurities and still be safe to drink. In fat, water treated by muniipalities for drinking is permitted to ontain a ertain quantity of impurities, measured in parts per billion. For example, relatively low levels of bateria are permitted in potable water. In laboratory environments, however, even minute quantities of impurities in water an ause problems. Biotehnology experiments are espeially sensitive to heavy metals and dissolved organis. Therefore, water for laborator): use must be purified. Purified water has appliations in many areas: hospitals, ollege and university labs, pharmaeutial labs, and in failities that manufature miro hips, to name a few. Contaminants Beause water is an exellent solvent, it is easily ontaminated. Contaminants in water an be broken into five ategories: W Partiulates Dissolved inorganis (solids and gases) W Dissolved organis W Miroorganisms W Pyrogens Partiulates inlude silt, plumbing debris, and olloids. These suspended partiles an plug valves, laboratory tubing, and other equipment. They also an interfere with laboratory experiments and proesses. Dissolved inorganis inlude alium and magnesium ions dissolved from rok formations, gases suh as arbon dioxide that ionize in water, siliates leahed from sandy river beds or glass ontainers, ferri and ferrous ions from rusty iron pipes, hloride and fluoride ions from watertreatment plants, phosphates from detergents, nitrates from fertilizers, and many other substanes. Dissolved organis inlude pestiides, herbiides, gasoline, deayed plant and animal tissues, plastiizers leahed out of plumbing lines, styrene monomers from fiberglassreinfored storage tanks, and other resin materials. FAX Eletroni Bulletin Board

Miroorganisms that an be found in surfae water inlude amoebae, diatoms, algae, bateria, viruses, and others. Pyrogens onsist of ellular fragments of ertain baterial ell walls.

2 Miroorganisms that an be found in surfae water inlude amoebae, diatoms, algae, bateria, viruses, and others. Pyrogens onsist of ellular fragments of ertain baterial ell walls. When water ontaining a pyrogen is injeted into a mammal, a rise in body temperature ours. Pyrogens an also have a negative impat on tissue ulture appliations. Thus, pharmaeutialgrade water must be pyrogenfree. WaterQuality Standards Developments in sientifi tehniques and preise proesses have reated a need for waterquality standards. Standards have been developed by several sientifi groups: the College of Amerian Pathologists (CAP), Amerian Soiety for Testing and Materials (ASTM), the National Committee for Clinial Laboratory Standards (NCCLS), and others. Eah group has its own standards, onsisting of three to four levels of water quality. Type I is the highest level of quality in the standards of eah group. There are some differenes, however, among the groups standards with respet to the quantities of ertain ontaminants allowed in the various levels. The CAP Standard is desribed below: Type I. Impurities undetetable. Resistivity minimum of 10 megohms x entimeters (Ma m). Soluble siliate ontent of 0.05 mg/l. Mirobiologial ontent of 0, 10, or 100 olony forming units/milliliter (fu/ml) for subtypes A, B, and C, respetively. Type 11. Resistivity minimum of 2 MQ m. Soluble siliate ontent of 0.1 mg/l. Mirobiologial ontent of 10,000 fu/ml. Type 111. Resistivity minimum of 0.1 Ma m. Soluble siliate ontent of 1.0 mg/l. WaterPurifiation Methods There are seven ommonlyused methods for purifying water: W Distillation W Deionization W Reverse osmosis W Carbon adsorption W Miroporous filtration W Ultrafiltration W Ultraviolet oxidation The different waterpurifiation methods vary as to how effetively they remove partiular ontaminants. For example, distillation is highly effetive in removing partiulates, but is not effetive in removing dissolved gases. Deionization (DI), on the other hand, is effetive in removing dissolved gases, but does not remove partiulates effetively. Depending on the level of purity desired, methods are usually ombined in a system to provide the user with the quantity and quality of water needed. Many vendors have units that ombine these methods so that ustom units are not neessary. The effetiveness of the seven waterpurifiation proesses has been ompared by the NCCLS (Figure 1). This table is provided as a general guideline. The effetiveness of these proesses is variable, as is the feedwater supply. Therefore, it is reommended that potential users obtain assistane from a reputable manufaturer of purifiation equipment before seleting a partiular purifiation system. The features of these seven proesses are desribed below. Distillation. In distillation, a still or distillation unit uses heat to evaporate water, produing a vapor low in ontaminants. The vapor is then ondensed bak to a liquid by means of a ondenser. Water is used in the ondensing proess through the use of a heat exhanger to ondense the water vapor. Muniipal water is ommonly used; however, some large units may inorporate a ooling tower. The positive features of distillation are that the equipment is relatively inexpensive and the water produed is of Type I1 or I11 quality. There are some drawbaks, however. Distilla tion is not an ondemand proess. Beause the proess is too slow to provide produt water as needed, the purified water must be stored for later use. With storage, there is a risk that the water will be reontaminated. If the storage vessel is not made of inert material, ions or plastiizers will leah out from the ontainer and reontaminate the water. Furthermore, bateria are known to grow in standing water. Storing the purified water also requires additional spae. Another drawbak to distillation is the maintenane requirements. Stills require regular leaning beause of the buildup of mineral deposits from the feedwater. Beause of the potential for mineral buildup, distillation systems often require pretreatment systems, whih redue the frequeny of leaning. Deionization. This proess exhanges hydrogen ions for ationi ontaminants in the feedwater and hydroxyl ions for anioni ontaminants. The feedwater passes through tiny spherialshaped gel beads where the ions are exhanged. Deionization (DI) is an ondemand proess, whih means the purified water does not need to be stored before use. In some systems the bead artridges or tanks need to be regenerated or replaed. If they are regenerated, the osts an be kept low. If they are replaed, this proess an be expensive. One drawbak to this method is that it does not effetively remove dissolved organis, whih an foul the ion exhange beads. Another is that stagnant water in the aboratory Water Purifiation 2

artridges/tanks may allow the growth of bateria. Reverse Osmosis. This proess reverses the natural proess of osmosis by means of a high pressure pump.

3 artridges/tanks may allow the growth of bateria. Reverse Osmosis. This proess reverses the natural proess of osmosis by means of a high pressure pump. The solution of water and ontaminants (feedwater) is separated from the pure solvent (ontaminantfree Figure 1. WaterPurifiation Proess Comparison water) by a semipermeable membrane. Ordinarily, when a solution and its pure solvent are separated by a semipermeable membrane, the pure solvent will move aross the membrane to dilute the solution of higher solute onentration. The movement of the solvent will ontinue until the onentration of solvent on either side of the membrane is equal or until the osmoti head pressure in the solution beomes high enough to stop the flow of solvent aross the membrane. In reverse osmosis (RO), pressure greater than the osmoti head iressure is applied to the solution by I Distillation Deionization Reverse Osmosis Carbon Adsorption Filtration U It raf i ltrati on U.V. Oxidation EIG P G E ~ ~ E E E E P P P P GC P G E E E P Pd EIG e P P P P P P E E P P P Gf E E E P P EIG P Gh P E = Exellent (apable of omplete or near total removal) G = Good (apable of removing large perentages) P = Poor (little or no removal) Footnotes: a Treatment with ozone, although urrently not ommonly used in linial laboratory water purifiation systems, has been shown preliminarily to be very effetive in oxidizing bateriahiruses and their organi metabolites. bthe resistivity of water purified by distillation is an order of magnitude less than that produed by deionization, due mainly to the presene of C02 and sometimes H2S, NH3, and other ionized gases if present in the feedwater. The residual onentration of dissolved ionized solids is partly dependent on the original onentration in the feedwater. Ativated arbon will remove hlorine by adsorption. e When used in ombination with other purifiation proesses, speial grades of ativated arbon and other syntheti adsorbents exhibit exellent apabilities for removing organi ontaminants. Their use, however, is targeted toward speifi ompounds and appliations. We reommend onsultation with the manufaturer before use. Ultrafilters, being moleular sieves, have demonstrated usefulness in reduing speifi feedwater organi ontaminants based on the rated moleular weight utoff of the membrane. 185 nm UV oxidation (bath proess systems) has been shown to be effetive in removing trae organi ontaminants when used as posttreatment. Feedwater makeup plays a ritial role in the performane of these bath proessors. They should not be onfused with inline UV sterilizers whih use 254 nm UV light to inativate bateria. 254 nm UV sterilizers, while not physially removing bateria, may have bateriidal or bateriostati apabilities limited by intensity, ontat, time, and flow rate. Permission to reprint portions of C3A2, Preparation and Testing of Reagent Water in the Clinial Laboratory Seond Edition; Approved Guideline, 1991, has been granted by the National Committee for Clinial Laboratory Standards. NCCLS is not responsible for errors or inauraies. 3

~ means of a highpressure pump, ausing the solvent to move aross the membrane in the opposite diretion. Contaminantfree water (feedwater minus ontaminants) rosses the membrane to the pure solvent.

5 ~ means of a highpressure pump, ausing the solvent to move aross the membrane in the opposite diretion. Contaminantfree water (feedwater minus ontaminants) rosses the membrane to the pure solvent. RO typially removes 90 to 99 perent of all ontaminants. The RO proess is very effetive at removing bateria, viruses, pyrogens, and other organis, as well as suspended solids. For this reason, an RO system often preedes a deionization unit, prolonging the life of the ionexhange artridges/ tanks. RO an be an ondemand proess, requiring no storage of produt water. However, it is typially used in ombination with other purifiation proesses that inorporate water storage. The maintenane osts for RO are minimal beause the membrane is ontinuously washed as a part of the proess. Carbon Adsorption. An ativatedarbon filter removes hlorine and dissolved organis by adsorption. This is an ondemand proess, typially used in ombination with other purifiation proesses. Beause membranes used in RO an be damaged by hlorine and, to a lesser degree, dissolved organis, an ativatedarbon filter is often plaed before the RO membrane. Miroporous Filtration. This proess uses a membrane or hollow fiber with a pore size of less than 1.O miron, whih prevents the passage of ontaminants larger than the partiular filter rating. Also prevented from passing are many smaller partiles that are trapped by eletrostati attration, inluding arbon partiles from the arbon filters, any resin fragments from the deionization artridges, and bateria that may have entered the system. When attempting to ahieve Type I water, miroporous membranes are generally onsidered to be indispensable elements of a waterpurifiation system, unless an ultrafilter is used. Miroporous filtration is an ondemand proess. Ultrafiltration. This proess uses a membrane similar to that used in RO systems. However, the pores in ultrafiltration membranes are slightly larger. It is an ondemand proess, typially used in ombination with other purifiation proesses. A high perentage of the water that is brought to the ultrafilter passes though it; therefore, it will eventually log if not maintained. If the filter is washed free of ontaminant buildup on a regular shedule, ultrafiltration is an exellent proess for insuring onsistent prodution of Type I water. Ultraviolet Oxidation. This proess uses ultraviolet radiation to eliminate bateria and to leave and ionize ertain organis for subsequent removal by the deionization, ativatedarbon filtration, and miroporous filtration systems. Ultraviolet oxidation is an ondemand proess, typially used in ombination with other purifiation proesses. Energy and Water Use Distillation is an energyintensive proess, using 750 watthours per liter. Heat is used to vaporize the water, whih is subsequently ondensed, typially with readilyavailable muniipal water. For small lab units, the heat typially is generated from eletriity. Larger units use natural gas or entrallygenerated steam to vaporize the water. In ontrast to distillation, alternative methods of purifiation use small amounts of energy. The energy used in deionization (DI), arbon adsorption, miroporous filtration, and ultrafiltration is the energy required to pump the feedwater, a negligible amount. Reverse osmosis (RO) uses more energy than the other filtration methods as a result of the high pressure pump, but 1.4 watthours per liter is small in omparison to that required for distillation. maviolet oxidation uses a mere watthours per liter. In addition to being the most energy ~~~ intensive method, distillation uses the most water of any purifiation method. In distillation, the ratio of water used to produt water (purified water) is 1O:l. Only 10 perent of the water used in the distillation proess is produt water. In RO, the ratio of water used to produt water is 3:l for units rated 1800 gallons per day or smaller. Larger units an ahieve 2:l or better. In DI, arbon adsorption, miroporous filtration, ultrafiltration, and ultraviolet oxidation, the ratio is loser to 1:l. A system ombining RO and DI an oneivably replae a distillation unit, yielding produt water of omparable or better quality and providing it on demand, so that storage may not be neessary. For the sake of omparing energy and water use by different purifiation systems, the RO/DI system and distillation are ompared in Figure 2. Distillation vs Alternative Methods Distillation, used for water purifiation for many years, is still one of the most widelyused methods of purifiation. However, with the high ost of energy and the importane of water onservation, distillation is no longer a desirable tehnology. The availability of more reliable, lower maintenane, less energyintensive tehnologies makes a good ase for adopting alternative methods of purifiation. ~~ 4 Laboratory Water Purifiation

6 V Eletri Ideas Clearinghouse is a omprehensive informa tion soure for ommerial and industrial energy users. It is operated by the Washington State Energy Offie and is part of the Eletri Ideas tehnology transfer program sponsored by partiipating utilities and the Bonneville Power Administration. V Neither the United States nor the Bon nevi1 1 e Power Administration, the state of Washington, the Washington State Energy Offie, nor any of their ontrators, subontrators, or their employees make any warranty, expressed or implied, or assume any legal responsibility for the auray, ompleteness, or usefulness of any information, apparatus, produt, or proess dislosed within this publia tion. V Tehnology Update CH 3 V Tollfree Hotline: Fax: Eletroni Bulletin Board: Figure 2. Energy and Water Use of RO/DI vs Distillations 2A. Energy Used to Produe 1 Liter of Purified Water 1000 & a e a & T g RO/DI Bib I i ogra p h y 750 DISTILLATION 28. Ratio of Water Used to Purified Water Produed 1O:l & 8:l s 0 3 6:1 U a e & 5 2:l 0 3:1* ROlDl DISTILLATION *For units 1800 gallons per day or less. Larger units an ahieve 2:l or better. Labono Corporation. A Guide to Laboratory Water Purifiation. Kansas City, Missouri Lorh, W. Handbook of Water Purifiation. Chihester, England: Ellis Horwood Limited Publishers National Committee for Clinial Laboratory Standards. Preparation and Testing of Reagent Water in the Clinial Laboratory Seond Edition; Approved Guideline. Publiation Number C3A To obtain the urrent C3 edition of the Guideline, ontat NCCLS, 771 E. Lanaster Avenue, Villanova, Pennsylvania DOEIBP Deember M

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