A system designed to last the longest and most cost-effectively remove bacteria is the best endoscope reprocessing filter system. But what does that mean? Well, that depends on a few factors, which we will discuss below and, hopefully, give you the information you need to get the best performance out of your filters.
We all know that the quality of the water used to rinse endoscopes is critical to patient safety. Even though the water may be supplied by a municipality and treated using widely accepted methods, it could still contain organisms1-7. Those organisms may form biofilms (as discussed in the previous blog posting) or remain on a scope and harm a patient if introduced during an endoscopic examination.
Water can also affect the aesthetics of the endoscope after reprocessing. The water could leave visible particles or hard water deposits on scopes after drying. Even the chlorine level n the water can affect the efficacy of the chemicals used in cleaning and disinfecting.
Filters can treat water with high particulate counts, bacteria, high chlorine levels and water with some organic chemicals. Other treatment methods such as softening, de-ionization or even reverse osmosis are needed for water chemistry issues like hardness or dissolved materials.
We won’t review the water quality requirements for endoscope reprocessing, that has been done in a previous post. We will look at how to design cost-effective filter systems based on the water conditions and facility demands. For more detail, you can e-mail me at email@example.com and ask for the “How-To Guide – Water Filter Systems for Endoscope Reprocessing”.
The “normal” flow rate through the system is the most important design consideration. A widely-adopted rule of thumb is to use a 10-inch filter element for every 3 gallons per minute of “average” flow. If practical, the maximum flow rate per 10-inch element should be below 5 gallons per minute. This is true no matter the filter media or pore size rating. So, to calculate the number of filter elements required, divide the normal gallon per minute flow by 3 and round up to the next whole number.
What Has to Be Removed? In endoscope reprocessing, the final goal is to remove bacteria. That dictates the use of a 0.22μm or 0.10μm rated, membrane-based filter as the last in the system. If the water were clean except for bacteria, that could be the only filter in the system. However, virtually all water systems deliver water with a wide range of particles and organisms of various sizes. Those particles may foul (plug, in laymen’s terms) the final filter very quickly. So, to protect the final filter, prefilters are used. What prefilters depends on the number, size distribution and organic or inorganic nature of the particles.
A more detailed discussion of the nature of the particles in various water systems was discussed in our blog post on filter life. Since most endoscope reprocessing filter systems are made up of a single prefilter and the bacteria filter, the choice of prefilter is critical to the life of the bacteria filter and will have a big impact on the cost of operating the system.
A fact of life in most healthcare facilities is the shortage of space. Reprocessing rooms are sometimes no larger than a walk-in closet. Finding space for a filter system on the wall can be challenging.
Most facilities install a separate filter system for each reprocessing machine, even though that creates overcrowding on the wall of the room. Most systems are a series of 2 or 3 10-inch filters in plastic housings. Combining the filters for 2 machines into a single system may be as simple as replacing the 10-inch filters in one system with 20-inch versions, and replacing the 10-inch filters with 20-inch filters. This simple design change will allow the removal of one filter system and can save almost half the wall space taken up by the two systems. However, you should check with your reprocessor manufacturer to make sure that their machine warranty or instructions do not require dedicated filters for each machine.
Getting Longer Filter Life
Some of you may be wondering how to increase the time between filter changes. Some of you might also wonder how filter life might be affected by combining systems.
It is not intuitively obvious, but a single system with 20-inch elements can process more than double the water of a system with 10-inch filter elements if it is operated at the same flow rate. If the 20-inch system is replacing two 10-inch systems for two machines, this assumes that the machines fed by the combined system are demanding water at different times. In other words, a 20-inch filter will process more than twice what a 10-inch filter can process (at the same system flow rate).
How can that be? Well, without using too much filter industry jargon, the end point of a filter’s life is when the pressure drop reaches a set limit, usually 20 or 30 pounds differential between the upstream pressure and downstream pressure. The pressure drop increases as the amount of particles clogging the filter pores increases, restricting the flow and requiring more pressure to force water through the filter media. If the flow rate AND filter area were both doubled, then the filter life would be the same because the flow rate per 10-inch filter element would be the same. However, in most cases the flow rate per 10-inch element will be cut in half, so the pressure drop starting point is lower by about half. That means that the amount of water that can be filtered before reaching the maximum is higher per 10-inch element, meaning that more than twice the amount of water can be filtered in a 20-inch system than a 10-inch system.8
I know. That sounds confusing, but the phenomenon has been proven in real life applications thousands of times.
The best filter system installations are positioned so the filter housings are at about chest height (4 or 5 feet off the floor) and are above drains to allow the draining of the housings without needing buckets and mops. There should be no other equipment or materials, even storage, in front of the filter housings.
Finding a place to install a filter system that allows that kind of access can be difficult. The space shortages mentioned above sometimes force systems into tight spaces. In my opinion, the most important consideration is making sure that the water that is released during a filter change doesn’t fall onto any equipment or supplies.
Reaching the housings should also be easy and not require long reaches or excessive bending.
Filter systems for endoscope reprocessing can be optimized based on flow rate, the particle content of the water, and space available. The systems can be designed and operated in a cost-effective manner, even if the facility water supply contains high levels of particulates. Users can contact Filter Supply or their filter supplier for assistance in system optimization.
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- Repetti, RV and Ponchick, AR. Selecting the Most Economic Cartridge Filter. Chemical Processing Online, http://www.chemicalprocessing.com/articles/2004/149/?show=all. Accessed 8/27/2013