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system specification is correct. Currently the most common solution, and the one that is recommended in the HTM guidance, is a reverse osmosis (RO) system. This technology is one of the most cost-effective water purification technologies currently on the market due to its efficiency in generating final rinse quality water cost effectively. RO systems use a semi-permeable membrane to separate and remove 99% or more of the dissolved solids, particles, colloids, organics, bacteria and pyrogens from a water supply. However, it is important to look carefully at the RO systems available before making a selection as they will vary in effectiveness. In a reverse osmosis system, the feed water enters the membrane under pressure and the water molecules pass through, while the contaminants are captured and discharged.
Among the key advantages of a RO solution is that the system is simple and final rinse quality water can be achieved without the need to combine multiple technologies. Also, RO does not require the addition of hazardous or expensive chemicals for maintenance or regeneration that could add particulates to a water supply. In addition, as the only operational expense is electricity, the cost of running a RO system to produce the required water is low. In addition, understanding the quality of the incoming mains water supply is an important consideration when working with a water treatment solutions supplier to create a specification for the system. The characteristics of the incoming water will influence the design of the treatment system itself. The supply should be monitored and tracked for between 6 and 12 months prior to specification and commissioning. Therefore, planning ahead with regard to the purchase of new or replacement systems is essential. The ideal scenario is for there to be 12 months data on the supply characteristics
to capture any and all seasonal variances. Having an understanding of this will ensure that the correct system can be selected and installed. In particular, it is important that the system’s capabilities allow flexibility to deal with the anticipated variation as well as adapt to any unexpected changes in the mains water quality. As well as impacting the choice of treatment system, the assessed quality of the incoming mains water may also highlight the need for pre- treatment measures. For example, carbon filtration should be considered where there are high levels of free chlorine in incoming mains water. This will ensure the longevity of the chosen system, especially if using a RO membrane.
The geographic location of the healthcare facility has an important impact on the design of the water treatment system due to the variability of the UK’s mains water make-up, especially with regard to the hardness of the water. The hardness depends on the level of mineral content that has dissolved in the water as it has filtered through the ground. Mains water with over 200mg of calcium carbonate per litre is defined as hard water. Large areas of the UK have hard water, particularly in the south-east and east. In these areas, a water softener should be installed ahead of the RO to improve the performance of the selected system and remove a potential food source for any bacteria.
Understanding the characteristics of water supplied to the building can also help to improve the efficiency of other systems that use the mains water, including thermal disinfection units. The HTM notes that where scaling from hard water occurs on heating elements or heat exchange components it can quickly lead to inefficiency. It states that energy costs to run the unit can be increased by 50% to 100%. It also advises that water used in the cleaning of stainless- steel instruments should have a chloride
concentration less than 120 mg/L and warns that where the levels are greater than 240 mg/L it can cause pitting to occur on the surface of the instruments.5 Once the type of water purification system and any pre-treatment measures have been selected, the next step is to establish the requirements for the system to make sure that a supply of purified water is always available to suit demand. A system should be selected that delivers on those requirements at all times but also has the flexibility to allow the water specification to be tightened in response to future updates to legislation. Firstly, it is important to consider the volume of water that will be needed to meet demand. This will be influenced by the number of AER and WD units that the system will be supplying, the total volume of water each will draw during a cycle, the peak volume per disinfection cycle and the number of cycles possible per hour. These figures will vary significantly depending on the make and specification of each AER and WD unit, as well as the layout of the facility. For example, some WDs or AERs will have
a short cycle time and require a large volume of water over a relatively short period of time. Another unit may require a similar total but take longer per cycle and draw water off from the system at a slower rate. This means it is also important to check this when replacing AER or WD units to make sure the existing purified water system was designed to meet the new level of demand. There are RO systems that have been engineered to produce large volumes of water but for very high draw units or systems a storage tank can be specified that will safely store the purified water to ensure demand can be met at all times. The required performance and level of operation of the water treatment system should also be considered, including the number of hours per day it will be operating and the level of up-time it must meet. For example, if redundancy is required, a duplex RO plant or twin ring pumps can be used to achieve close to a 99% up-time. Furthermore, potential future plans also need to be considered when specifying the treatment solution – for example, whether the system needs to include additional capacity or the option for simple expansion to meet increased future needs, or the purchase of additional disinfection units. In addition, having a sufficient number of units that can run when required, including simultaneously, is an important issue to ensure that medical equipment is always available when needed. This capacity is also important to minimise the risks to patients and staff. This is because the reprocessing of the instruments and devices is most effective when carried out directly after use, especially for surgical equipment.
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