Bacteria Prevention in High Purity Water Systems, Part 3

USP recommends the installation of “corrective facilities” in piping systems as a way to handle bacteria levels in water systems. These would include “access to the system for sanitization or introduction of steam, ozonation, chlorinators, storage at elevated temperatures”, etc. This is mostly commonly needed for smaller less advanced manufacturing facilities or highly regulated processes such as seen in the pharmaceutical industry.

Sanitization cannot prevent bacterial contamination of a system. Water systems will contain bacteria, thus regular sanitization of the system is required to prevent the prolonged growth of bacteria.  If bacteria are allowed to grow, they will eventually form a biofilm layer “slime” on the water contact surfaces. Once this film forms, it can be exceedingly difficult to remove and it will continue to release microbes into the system which will result in a spike in bacteria levels. This is exceedingly detrimental to any process and can result in process downtime and the loss of product, which in turn becomes expensive.

Sanitization requires that the system be taken out of service and flushed when complete, prior to returning to service. The most preferred and most common methods of sanitization include steam or ozonation, with ozone use becoming a more frequently used option. This is especially true when dealing with high purity systems that utilize stainless steel piping.  Some processes use heated permeate water instead of steam for heat sanitization.

Specifically for heat sanitizable RO membranes, when using heat sanitization it is recommended to increase the temperature of the water gradually and hold the high temperature setpoint before cooling down gradually. Below is a typical heat sanitizing temperature path followed by a steam fed heat exchanger controlled by a temperature setpoint.

In some instances plants may choose to use sodium hypochlorite or bleach for sanitization. This method poses risks to the system. For example, over time bleach can be corrosive to stainless steel piping. Also, by using bleach, you are introducing a contaminant into the system. Lastly, many systems need to adhere to a chloride limit. These systems are required to monitor chlorine levels and may need to flush for a prolonged amount of time before being able to return into service.

Sanitization should occur regularly and as required based on testing and historical data. Each process is different but for example, sanitization may occur twice per month for laboratory grade water.

Throughout the design process a documented protocol should be generated in order to validate that the quality standards are being met. One way to do this is to follow a Performance Qualification, PQ, which seeks to answer two main questions:

  1. Does the process or device do what it's intended to do?
  2. And, if so, for how long does it do it?
Performance qualification is a protocol which generally shows that the system and its components perform consistently and according to design specification. Consistently should be defined as the “duration and extent that a component performs”. This protocol aims at checking the responsiveness of instrumentation.

Performance qualification is in the form of a document that includes sections on quality testing such as a sampling plan:  how often are samples to be taken, at which location is the sample to be taken, etc.  The document also includes the acceptance criteria of samples and the methodology of how the samples are to be taken and who the authorized personnel are.  The operating parameters of the system should be outlined and defined in this document as well.  Since the performance qualification is likely to be executed often and more than once as part of the testing time frame, it is recommended to include this section as a table on its own sheet, or in the form of an appendix, to provide for operators to document the results.

Typically the testing time frame or duration of the performance qualification is four to eight weeks, or roughly one month.  After this period, results are documented and reviewed by approving body and stored for historical reference or for required reports to governing bodies such as the FDA.

Because the presence of bacteria has an effect on the quality of water, bacteria levels must be monitored throughout the purification process. The further upstream of a process that you can apply the performance qualification, the more likely you are to catch issues that may cause a system to fall away from specifications. Also, the location of sample points is critical to the design of a system. Point of use sampling, or sampling after the treatment component is critical in order to identify the locations of bacteria growth and contamination.

The method of testing can vary depending on the measured constituent and to what specification the system must adhere to. ASTM standards are available that outline the acceptable testing methods for water constituents and water treatment equipment.

Water temperature may vary based on the time of year as seasons change and a water turnover occurs. Throughout the year the growth of flora may also cause fluctuations in microbial content of source water. The sampling and testing plan should include testing frequently and a process to handle these changes in water quality should be in place.

When monitoring, the use of proper instrumentation should be taken into account in order to give plants the ability to alert operations of significant changes from the normal operating conditions. The limits of an alert should be defined and acceptable in accordance with the system requirements.

Once a system is designed and installed, it is important to continuously monitor for bacteria levels. The best way to handle monitoring is to have well-defined validation criteria, to have the proper type and location of sampling points and finally to incorporate corrective facilities in the system.

When bacteria exist in high purity water systems, it can cause interference in water quality and potentially damage products. Also, additional sanitization and testing must take place, both of which will cause unwanted expenses and delays. Therefore it is critical to properly design a water system to identify bacteria and contamination sources. Operations should follow a validation process on new and existing system installations in order to verify adherence to their required performance.

During operation, plants are recommended to follow approved monitoring and sampling plans which should include regular sanitization processes of their equipment. By taking these steps, plants are able to prevent introduction of bacteria into their systems. They are also prepared to deal with growth of bacteria on an ongoing basis. This will allow for minimal down time and a more consistent product.

For more information on this topic or how bacteria prevention can be achieved in your plant, contact us or your U.S. Water representative.

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