Round the clock purity

From glass washing to reagent preparation and instrumental analysis ­– high quality water is a vital lab staple. It is all too easy to take this for granted yet, behind the scenes, a great deal of thought goes into designing a facility that reliably provides water of the required quality on a round the clock basis

Water is the most important solvent in the laboratory, and it is crucial to think carefully about the laboratory’s requirements and how best to meet them when designing or refurbishing a facility.

Even though tap water has undergone extensive purification to ensure it is safe to drink, low level impurities remain – suspended particles, inorganic and organic compounds, microorganisms and dissolved gases – which can have a significant impact on laboratory analyses. For analytical chemists, the consequences of using the wrong grade of water include baseline interference and degradation of HPLC columns. In molecular biology, impurities can inhibit enzyme reactions and interfere with gel polymerisation, while false negative microbiology test results can arise due to the growth of microorganisms being constrained.

Design considerations

There are many things to consider when designing a water purification system. Firstly, it is important to characterise the feed water, as this helps to determine the pre-treatment required – softener and carbon or granulated filter – and associated running costs. It is also essential to establish which grades of water the laboratory needs (Table 1), as this will determine the treatment technologies to be implemented. The average use, peak use and duration, and the number of hours per day and days per week that water must be supplied, should be established, as well as the demand for direct feeds to equipment, such as glasswashers and autoclaves. The size of the storage tanks is another important consideration, and should be matched to the expected usage; ideally, water should be drawn and replaced several times a day to avoid becoming stagnant.

Table 1: Selection of water grades for laboratory applications.

There are also practical considerations regarding the building itself:

• Where is the plant room – top floor or basement?
• How much room is there in the plant room and the labs, and is there any restricted space?
• Are there any access limitations?
• Are there floor loading restrictions?
• What is the location and capacity of the building’s drainage system?

Finally, some thought should be given to whether or not the water quality needs to be monitored, who will be responsible for system maintenance and whether it should be integrated into the building management system, and what level of security is required.

Over 99 % of bacteria live in biofilm communities, which can accumulate in water manifolds, sinks, taps and other water lines

Centralised or modular?

Having considered their needs, laboratories can choose between centralised systems – a single loop that distributes water throughout the whole facility – or a modular system with a single loop, floor-by-floor configuration. The advantages of the centralised system are lower consumables costs, and central management and servicing. However, there is no redundancy built in – the entire facility is without water during maintenance, for example – and a long length of pipework is costly and increases the risk of contamination. Modular systems offer more flexibility, enabling the water quality to be optimised according to the needs of the department, with built-in redundancy and a lower risk of contamination due to the shorter pipework. Floor-by-floor designs can be more expensive to install than centralised systems, and each level must be serviced and maintained separately, although running costs are easier to assign.

Possibly the most flexible option is to configure the system to supply water floor-by-floor and at individual points of use. This enables water to be distributed throughout the facility on a single loop with benchtop or under-bench purification units installed as necessary, allowing the purity and delivery to be matched to the needs of each individual lab. This can be particularly beneficial for departments running critical applications that depend on Type I ultrapure water, which is inherently unstable; ideally, ultrapure water should be drawn as and when it is required, as it will start to absorb carbon dioxide once it is dispensed. Although the capital investment required may be greater for this type of system – and a higher degree of maintenance and services management will be necessary – this is, to some extent, offset by the convenience of having water available at the point of use, avoiding the need for scientists to collect water from elsewhere in the building. The redundancy options are also excellent and the system is adaptable in the future, should demands change.

Material considerations

Once the type of system has been chosen, there are crucial decisions to make concerning the individual components and materials used. Storage tanks should be a closed design with air vent filtration to avoid contamination of purified water, and safe and easy to clean and sanitise. Bunding is also necessary to ensure any overflow is contained. If point-of-use systems are to be incorporated, the unit installed must be application specific, and deliver the correct flow and pressure to meet equipment needs, with a footprint that is appropriate for the available laboratory space. The unit should be easy to use and maintain, with operation and maintenance status indicators, user prompts and system alarms, and enable straightforward monitoring of water resistivity and total organic carbon content.

Close attention should be paid to the choice of piping material – PVC, polypropylene, ABS, PVDF or stainless steel – and how it is joined together, not only to ensure that it meets the requirements for optimum pump performance and delivers the correct flow and pressure, but also to avoid introducing any contamination into the purified water. Biofilms are a particular problem. Over 99% of bacteria live in biofilm communities, which can accumulate in water manifolds, sinks, taps and other water lines. Once established, biofilms and the organisms they play host to are extremely difficult to eradicate completely. Prevention is better than cure, and a key part of this process is to use a recirculating loop, creating a turbulent flow that keeps the water moving to minimise any build-up of biofilm. The use of diaphragm rather than ball valves is preferable, as these do not trap water when closed – which can lead to bacterial contamination – and offer flow control. Inline UV and sterilising filters can also help to reduce the presence of microorganisms.

The complete package

The key to success is teamwork, with architects, engineers and consultants working together to devise, install and validate a laboratory water purification system that meets the client’s exact specifications, taking into consideration the various points mentioned above. When complemented by a support service offering training, technical advice and tailored preventative maintenance programmes, the laboratory will benefit from the provision of high quality water suited to its specific applications for many years to come.

The Author: Amanda Cove is Business Development Manager for Projects at Veolia Water Technologies