Water Purification Buying Guide

Water Purification image

Water is a vital resource in the operation of all laboratories, from general cleaning procedures to the use in sensitive analytical techniques. Water can have a significant impact on your experimental results; therefore it is important to identify the quality of water required for your specific applications. This Buying Guide provides the information you should consider when selecting a new water purification system for your laboratory.

Impurities in Water

It is important to evaluate the water quality requirements for the different applications in your laboratory. Water contaminants are classified into five main groups, as shown in Table 1. These contaminants affect experiments in different ways.

Table 1. Water contaminants and how they affect laboratory experiments.

Inorganic Ions

    Interfere with protein-protein interactions

    Lead to inaccurate results in elemental analysis and ion measurements (e.g. AA, ICP, IC)

    Inhibit DNA polymerase activity, leading to poor PCR results

Organic Compounds

 

    Increase in baseline noise in HPLC

    Reduce sensitivity during HPLC experiments

    Decrease HPLC column life

    Bind non-specifically in place of DNA and RNA during hybridization, affecting cell cultures and blotting experiments

Particulates

 

    Degrade the performance of reverse osmosis membranes

    Clog small orifices in analytical instruments

    Hinder the operation of valves, fittings and meters

    Increase turbidity of the water and obstructs equipment operation

Microorganisms

 

    Release endotoxins and nucleases

    Endotoxins inhibit sensitive processes such as in vivo fertilization and affect cell cultures

    Nucleases disrupt many molecular biology applications, e.g. PCR

    Form Biofilms which excrete endotoxins, nucleases and bacteria randomly into the water supply

Dissolved gases

 

    Lead to bubble formation that affects spectrophotometer experiments

    High oxygen concentration can affect electrochemical and biochemical processes


Water Standards for Laboratories

As water is used in a vast range of laboratory applications, water is categorized into a particular grade, specified by standards. It is classified as Type I, II and II – Table 2 shows the parameters used to classify water type. Several professional organizations have detailed published or proposed standards for water quality, such as ASTM, CLSI, CAP, ACS, ISO, USP, and EU. If any of the applications in your lab must adhere to the standards required by these organizations, it is important that the water purification system you are purchasing meets the specifications of the standard.

Table 2. General parameters used to classify water

Parameter

Type III: Primary

Type II: Purified

Type I: Ultra Pure

Resistivity / M-cm

> 0.05

>10

>18

TOC / ppb

< 200

<100

<10

Bacteria / CFU mL-1

<1000

<100

<1

Endotoxins / EU mL-1

NA

NA

<0.03

Colloids / ppb

<1000

<10

<10

Selecting the Correct Water Quality for Your Application

Consider the intended use of your purified water, as some applications are very sensitive to certain contaminants. Table 3 highlights several applications and the type of water required.

Table 3. Water types and associated application.

Water Purification

Types of Water Systems

There are a number of configurations to provide purified water throughout a facility. The choice depends on the unique needs that have to be met. Figure 1 presents some water system configurations.

Figure 1. Types of water system configurations

Types of water systems

Water Purification Technologies

Several technologies can be used to purify water. See Table 4 for the benefits and limitations of each technology.

Reverse Osmosis (RO)

RO offers a cost-effective method to remove the majority of water contamination. Reverse osmosis membranes are stable over a wide pH range, and are capable of removing particulates of <1 nm diameter, approximately 90% inorganic ions, most organics. The PURELAB Chorus 3 from ELGA Labwater uses RO-membranes to produce Type III water for daily laboratory applications.

Distillation

Distillation is the oldest method of water purification, and removes a broad range of contaminants, providing the contaminants do not have vapor pressures close to water. Stills are used in the distillation process to produce Type III water. The Bibby Scientific Stuart Aquatron Water Still uses distillation to produce Type III water.

Ion Exchange

Figure 2.Deionization of water using ion exchange.

Deionization

Ion exchange resins remove ions from water and replace them with H+ and OH- ions. Water is formed in the process when the exchanged H+ and OH- ions combine (Figure 2). The resins are beads made of insoluble polymers with surface ionic exchange sites. The beads are packed into beds and are available as cartridges or cylinders, which are replaced or regenerated over time. When the H+ and OH- sites on the resins are occupied, the resins are exhausted and the cartridge/cylinder is replaced or recharged at a regeneration centre.

Electrodeionization (EDI)

Electrodeionization (EDI) combines ion exchange resins and ion-selective membranes in the presence of an electric field to purify water. Electrodeionization modules consist of two electrodes (anode and cathode) that are separated by columns of ion exchange resins and ion-selective membranes. The impure water passes through columns containing ion exchange resins and attach to the resins. An electric field applied across the EDI module pulls the ions from the resins through the ion-selective membranes towards the electrode. Cations travel through the cationic-membrane towards the cathode, and anions move through the anionic-membrane to the anode. Some ions are trapped within a concentration chamber and are flushed to waste. The ion-exchange resins are continuously regenerated throughout the process as the electric current splits water into H+ and OH- ions, overcoming the limitations of water purification using ion-exchange resins. The Thermo Scientific Barnstead Lab Tower EDI and the Elix Advantage Laboratory Water Purification system from EMD Millipore are examples of systems using EDI technology.

Ultrafiltration

Ultrafiltration uses a porous membrane filter (pore size 1-10 nm) to purify water. Water passes through the membrane and filters out colloids, microorganisms, particulates, enzymes and endotoxins, depending on the contaminants’ size. EMD Millipore has introduced BioPak® Point-of-Use Ultrafilter final filters that can be attached directly on to a dispensing unit for specific applications; watch this video to learn more.

Ultraviolet (UV) Radiation

Ultraviolet radiation is an effective bactericide; it can also be used to ionize some organic contaminants to produce ionic species that can then be removed using ion-exchange resins. The UV lamps used in water purification systems are capable of producing radiation at wavelengths of 254 nm and 185 nm. Radiation with a wavelength of 254 nm damages DNA and RNA polymerase in microorganisms to prevent replication, whereas at wavelengths of 185 nm, most organic contaminants are photo-oxidized to produce ionic species. In this video, learn how bacterial contaminants are kept under control using the AFS 10E and 15E Systems from EMD Millipore.

Activated Carbon

Activated carbon can be used with purified water to remove organic contaminants. It has a large surface area and organic compounds adsorb onto the surface by Van der Waals forces and surface active attraction.

Table 4. Benefits and limitations of water purification technologies.

 

Benefits

Limitations

Reverse Osmosis

·  Removes a broad range of contaminants to various levels

·  Minimum maintenance

·  Economical

·  Easy-to-use and monitor

 

·  RO membrane prone to fouling

·  Limited flow rate therefore requires water storage solution

·  Requires pre-treatment to avoid membrane damage

·  Produces only Type III water

Ion Exchange

·  Provides water resistivity of 18.2 MΩ-cm

·  Cost effective option for producing small volumes of purified water on demand

·  Easy-to-use

·  Resins regenerated by deionization

·  Microorganisms, particulates and organics are not removed

·  Resin beds prone to fouling if feed water contains high levels of organic contamination

·  Resin beds require regeneration; beds that are chemically regenerated can form organics and particulates

EDI

·  Provides water resistivity of 5-17 MΩ-cm and TOC below 20 ppb

·  Resins are continuously regenerated and do not require disposal

·  Not capable of producing 18.2 MΩ-cm water

·  Feed water must be good quality for economical operation

 

UV Radiation

·  Provides water with <5 ppb TOC

·  Effective at removing microorganisms

·  Ions, particulates and colloids are not removed

·  To achieve <5 ppb TOC, photo-oxidation is required

·  CO2 produced during photo-oxidation decreases the water’s resistivity

Distillation

·  Removes broad range of contaminants

·  Low capital cost

·  No filters or cartridges required

·  Slow process

·  High energy and water consumption

·  Requires periodic heater changes

·  Requires cleaning with strong acids

·  May necessitate the use of pretreatment

Ultrafiltration

·  Removes most particulates, colloids, microorganisms, enzymes and endotoxins

·  Efficient and easy-to-use

·  Long lifetime if regularly flushed with high speed water

·  Dissolved inorganic and organic substances are not removed

·  Membrane pores can block if the water contains a high level of high molecular weight contaminants

Activated Carbon

·  Chlorine removed effectively

·  Significantly reduces TOC

·  Long life span

·  Not all dissolved organic contaminants are removed

·  Carbon fines can be released


Buying Guide Tip: If your lab needs more than one type of water, some manufacturers have systems that produce two water types from a single system, e.g. Type III and Type I, or Type II and Type I water from a single unit (at different dispensing points).

Optimal System Designs

The water purification technologies outlined in this Buying Guide highlight the benefits and limitations of each method, demonstrating that a single technology is not capable of removing all water impurities. It is therefore important to combine technologies to design a system that meets your specific water purification needs.

Producing Type I water from tap water requires two steps – primary treatment and polishing. The pretreatment stage produces Type II or III water and reduces the water impurities by >95 %. Figure 3 shows the different combinations of water purification technologies that can be used as primary treatments and polishing treatments.

Figure 3. Technologies used as primary and polishing treatments to generate Type I, II and III water.

primary treatment

Buying Guide Tip: When buying a Type I water system, determine the source of the feedwater. There are Type I systems that feed directly on tap water. If you have an existing source of Type II or III water, you may decide to purchase just a polishing system. However, it is important to consider how reliable this existing source of Type II or III water is. Has the system broken down before? Does it have a history of contamination? Remember, the quality of Type I water depends a lot on the feedwater.

The new ELGA PURELAB Chorus 1 with Halo Dispense is a scalable, modular water purification system designed to deliver Type I water to suit the application, budget and configuration of any laboratory. Watch this informative video (Figure 4) to learn more about the features of the PURELAB Chorus range.

Figure 4.Martin White discusses the new ELGA PURELAB® Chorus range for Type I ultrapure water.

Martin White

Buying Guide Tip: Some manufacturers have dedicated water purification systems for 'sensitive' applications, or they may have application-specific, point-of-use polishers that can be connected to their polishing system to produce such application-specific Type I water.

Choosing the Correct Water Purification System

When purchasing a new water system for your laboratory or facility, the following considerations and questions are useful to ask yourself before discussing your options with a manufacturer.

Application

Will you use the water solely for specific experiments? What are these experiments? This is important because some experiments have particular water requirements.

What analytical instruments will it be used for? Will it also be used for more general purposes in the lab, such as feeding a dishwasher, autoclave or water bath? It is common to have multiple intended uses for water in a laboratory. Refer to Table 3 to identify the water type for your application.

Cost/Budget

In order to get the best water purification system for your lab for the best price, be sure to ask these questions:

  • What is the initial investment for the system?
  • Are you buying the system as a bundle or as many individual parts?
  • What are the annual costs?
  • What are the costs for consumables?
  • What will be the power consumption?
  • What are the costs for a manufacturer’s service contract?
  • How much water goes to waste?

Buying Guide Tip: Make sure your water system is not oversized. In the same way that you need a water system that is large enough to deliver the volume you need, it also should not be any larger than necessary. Oversized systems will take up more space, and will allow the purified water to be stored for longer periods, which increases the chance of bacterial contamination.

Volume of Water Required

It is important to consider the amount of water used in your lab, and to buy a system that matches your needs. The quantity of water required should be based on when your water demand might peak, instead of total consumption levels over a period of time (daily, weekly, etc). For example, a system may be able to deliver the total volume of purified water required for a day, but it may not be able to generate the volumes of water required during peak times, such as the filling cycle of a lab glassware washer.

Consider your future water needs. It may be wise to future-proof your lab by buying a system that slightly exceeds your current requirements, allowing you to cope should there be an increase in demand for pure water in the near future.

Buying Guide Tip: Make sure the water is circulated regularly, as moving water stays purer for longer, especially when considering biological impurities.

Operation and Maintenance

How user-friendly is the system? Many systems have remote dispensing options that allow delivery of purified water some distance from where it is generated, with monitors on the remote dispenser allowing you to check the quality of water that is being dispensed right at the point of use. Some systems have volumetric dispensing options, which may be convenient.

The system’s performance depends on proper maintenance. Parts and cartridges have to be replaced; most systems require regular sanitization. Maintenance of the system should be as easy as possible, allowing for minimal downtime. New systems may have built-in alarms and calibrators that warn if certain components are coming to the end of their lives. Make sure parts and accessories are easily obtainable. Ask the following questions to ensure your system will be well maintained:

  • Does your laboratory have someone who oversees the maintenance of the water system?
  • Are the parts and cartridges easy to replace?
  • What is the parts warranty for the system?
  • Does the manufacturer provide technical support?
  • What are the manufacturer’s service options?
Feedwater

Feedwater is critical to a water purification system’s performance. Make sure the feedwater requirements of the water system are met. If the system feeds on tap water, and the tap water does not meet the specifications set by the purification system manufacturer, pre-treatment might be necessary. For example, very high organic load in the tap water will require activated carbon to bring it down to acceptable levels.

Laboratory Space

Laboratory space is at a premium, so it is important to choose a system that is flexible enough to be accommodated in your laboratory.

  • Where will you locate your lab water system?
  • Is the water system modular to fit your lab?
  • Can the water system be mounted on the wall or under the bench?
  • Does the water system have a remote dispenser that will free bench space?

ELGA has developed a configuration tool to help you build a system to fit your laboratory.

Buying Guide Tip: Type II or III water is used as feed water for Type I water systems. The performance of a Type I water system, and the quality of the water it produces, relies heavily on feedwater. It is therefore critical that you made a good decision about your Type II or III system if it is to be used to produce Type I water.

Online Monitoring

Is it important to your application that the water quality is monitored? If your application is sensitive to ionic contamination, it would be useful to monitor the resistivity of the water. Whereas if organic contamination is critical for your applications, it is best to purchase a system with online TOC monitoring, and not just rely on the resistivity of the water. There is no correlation between ionic contamination and organic contamination. Water that has resistivity of 18.2 MΩ-cm does not necessarily mean it has low TOC.

Regulatory Guidelines

Some manufacturers offer programs to facilitate validation procedures, deliver certificates of calibration, or offer features ensuring full regulatory compliance. If you are concerned about traceability, you can select a system that stores a history of key information, or that allows remote access to the system status and water quality parameters through an internet browser. An example is the Millitrak® Compliance e-Solution from EMD Millipore.

Environmental Impact

Carefully consider the technologies used; compare the electricity and water consumption. What is the frequency of cartridge replacement? Some manufacturers have cartridge return programs and recycle the exhausted DI modules. Consider a system that uses electrodeionization (EDI); it uses small quantities of ion exchange resin that are rapidly and continuously regenerated, avoiding the environmental impact of chemical regeneration associated with service deionization.

Current and Future Trends in Water Purification

Current water purification technologies consistently produce high purity water, but the ever increasing improvements in analytical instrumentation have demanded water purification systems to become even more flexible, high performing and user-friendly. To ensure water purification systems will produce the required water purity for future analytical instruments, water purification systems are being designed in conjunction with analytical instrument manufacturers. Systems are also being developed to meet the needs of individual applications and requirements.

With the emergence of new contaminants in tap water, such as pharmaceuticals and personal care products, researchers are seeking to develop water purification systems that can remove these. Manufacturers of water purification systems are currently investigating whether their products are able to eliminate these contaminants, or if their existing water purification processes need to be modified.

Environmental considerations are driving the development of water purification systems as more manufacturers are making sustainability an integral part of their business. Further development of technologies such as electrodeionization (EDI), which regenerates ion exchange resins and eliminates the need for chemical regeneration, is a focus to reduce the environmental impact of water purification systems. Additionally, developing systems that limit the amount of waste water via recycling is also an important consideration, along with the need to advance water monitoring and reporting technologies.

Water purification manufacturers are also working to make their software more flexible and apps may soon be available to remotely control water systems.

Summary

It is important to select the best water purification system to ensure the water produced is suitable for your applications and research.

Visit the SelectScience water purification product directory for an overview of the latest water purification technologies from leading manufacturers and read product reviews.

Keep up-to-date with the latest advances in water purification technologies by visiting the SelectScience General Lab pages for application notes, news and videos.

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Kathryn Rix Kathryn Rix
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