With almost 15 years experience working in the purified water industry, Lorcan Kennedy is a highly skilled Technical Services Engineer working with Veolia Water Technologies. Lorcan has extensive knowledge of the pharmaceutical, healthcare, industrial and electronic sectors and he specialises in the trouble-shooting of pure water systems, design of bespoke projects & conducts system audits for multinational customers. Read below Lorcan's own invaluable advice regarding The Causes of Out of Specification Bacteria and Endotoxin occurring in Purified Water Systems.
Causes of Out of Specification Bacteria and Endotoxin in Pure Water Distribution Systems
In broad terms, the levels of bacteria and endotoxin present in a purified water system will be affected by:
- System design. Is the system designed to prevent the passage of bacteria and endotoxin from feed water to the purified water system points of use? Is the system designed to prevent the development of bacteria and endotoxin in the system itself?
- System operation. Is the purified water system being operated correctly?
- Environmental conditions. Is the system located in an environment conducive to bacteria / endotoxin control?
- Testing methods. Are the bacterial / endotoxin testing methods providing an accurate representation of the bacteria and endotoxin levels in the purified water system. Bacterial growth in water will be affected by the following parameters.
- Temperature: In broad terms, the warmer the water the more rapid the bacteria growth. However, heat can also be used as a sanitisation method (typically >80 deg C).
- Static versus flowing / turbulent water: Bacterial growth will generally be more rapid in static water - compared to flowing / turbulent water.
- Pipework / storage materials of construction and design: Pipes and storage tanks constructed of materials with rough internal surfaces; have crevices present; have dead legs / dead areas (ie areas of static water) etc are more conducive to bacteria development than those that do not.
- Food source: Bacteria development will be more rapid if a suitable food source for growth is present.
- Presence of bacterial suppressant chemicals: Bacteria development will be less rapid if bacterial suppressant chemicals are present in the water. This is the typical method used to suppress bacterial development in mains water in the UK. These chemicals are, however, typically removed by purified water systems.
Drawing upon the above information, the following checks can be used to systematically assess a purified water system to identify possible causes of out of specification bacterial and / or endotoxin levels.
- System Design. Is the purified water system designed to be able to provide the bacterial / endotoxin levels required by the specification? The assessment of this may require the assistance of a specialist purified water equipment supplier. Veolia are pleased to provide this assessment service for all manufacturers of purified water system.
- Ring Main and Water Storage Design. Items to assess are the presence of dead-legs in the ring main, water storage temperature, tank design, materials of construction, internal surface roughness. As above, the assessment of this may require the assistance of a specialist purified water equipment supplier. Veolia are pleased to provide this assessment service for all manufacturers of purified water system.
- Connections to other equipment. Very often purified water systems are directly connected to other equipment (eg washers, autoclaves, reaction vessels etc). It is possible to experience back-contamination from these other items of equipment - depending upon their frequency of use, their sanitary design and the design of the connection to the purified water system.
- Water Usage Pattern. Is the purified water in the system regularly used or are there long periods where no water is being used from the system. The latter is more conducive to bacteria / endotoxin development.
- Environment: How hot is the location of the purified water system? Does the ring main run close to a source of heat? Factors such as these can have an effect on bacteria growth.
- Sanitisation frequency. How often is the system being sanitised (chemical and / or thermal)? Is this in line with manufacturers' instructions? If no manufacturers' instructions are available, has a testing and validation process been completed on the frequency of sanitisation (ie sanitise system and monitor bacterial / endotoxin levels through time to determine bacterial deterioration and thus determine a suitable sanitisation frequency).
- Sanitisation method. Is the sanitisation method being completed in accordance with manufacturers' instructions? Is the sanitisation method actually fit for purpose? Are required temperatures, chemical concentrations, sanitisation times etc actually being attained? How are these parameters verified? Bacteria can develop resistance to certain chemical sanitants. This can be addressed by periodically changing the sanitisation chemical.
- Water temperature. What temperature is the purified water? For ambient systems, the cooler the water the better. Although there are no particular specification requirements, ELGA aim to have purified water under 20 deg in our systems. For systems with temperature dump features, we typically set these to <20 deg C. In broad terms, if a system is producing out of specification water and is routinely running at temperatures in excess of 30 deg C, we would look to install some form of temperature control.
- Sampling method: This can often be the cause of out of specification test results. Is there a suitable sample point on the system that will not impart bacteria to the sample? Is the sampling method aseptic? Are the bacterial collection vessels free of bacteria and endotoxin?
- Time to analysis. Bacterial samples will deteriorate is the time to analysis is too long or the sample is not kept cool. The water analysis laboratory should be able to provide guidance on what is suitable.
- Analysis method. Bacterial and endotoxin results will be affected by the test methods used for analysis. For example, some test methods are more conducive to bacterial growth than others. Most water purification specifications with bacteria / endotoxin limits will also include a test method for analysis. This is the method that should be always be used.
- Laboratory variables. The reliability of the test results can be affected by methods, equipment and personnel in the test laboratory. Using a suitably accredited laboratory (eg ISO9001, ISO13485 etc) that uses clearly defined standard operating procedures (SOP's) will help to minimise this potential variable.
As mentioned previously, Veolia use the above list to help us assess the causes of purified water samples with out of specification bacteria / endotoxin. In our experience, the cause of out of specification purified water is rarely due to one specific cause. It is more often a number of factors that combine together to produce the problem. The identification of the causes of out of specification purified water can be a complex task. Veolia Water Technologies can provide support to identify these causes.
Well that's my lot for now, I really hope that you have found this information of interest and hopefully it will help you to safeguard your Pure Water Systems into the future. My colleagues and I will be giving more practical advice and guidance on this page in the future, so keep an eye out for the next hot topic!