The most common method of preventing microbiological contamination in a water system is thermal sanitisation. There are systems in which the pharmaceutical water is stored hot and systems that are heated cyclically to an elevated, germicidal temperature. However, excessive temperatures not only increase costs, they also can damage the materials.
In many pharmaceutical companies, the sanitising temperature of 80 °C is prescribed. This was written earlier in the US Pharmacopoeia USP “Temperatures of at least 80° are most commonly used“.
Yet, this high temperature can have a negative effect on the longevity of materials such as seals or membranes (as in reverse osmosis). In addition, there is a connection between the formation of rouging in the system and rising temperature. The hotter a system made of stainless steel or with stainless steel components is operated, the greater the level of rouging. Overlaying the tank with nitrogen further increases this phenomenon. Now, the question is whether a sanitising temperature of 80 °C is actually mandatory?
The US Pharmacopoeia (USP) addresses this question in the current Chapter 1231. It is important to know that the elimination rate of microorganisms is a temperature function. For example, the D-value for most microorganisms at 80 °C is five milliseconds. This means that in 5 milliseconds, the initial germ load is reduced to one tenth.
According to the USP, a temperature of 80 °C during sanitisation serves to achieve the necessary germicidal temperature even at colder points in the (ring pipe) system. However, the USP already considers temperatures of 65 to 80 °C to be sufficient for sanitization. The reaching of these temperatures at the so-called “cold spots” in the system must – of course – be ensured. Compliance with the 3D-rule in the design of the system also contributes to safe sanitization at temperatures of < 80°C. The rule is: the colder, the shorter – the shorter, the better. The USP now says “Temperatures of 65°-80° are most commonly used for thermal sanitization“. In the FAQs regarding pharmaceutical water, the USP even mentions only 60 °C, which must be reached on the surfaces: “…to assure that all surfaces reach sanitizing temperatures greater than 60 °C. ”
A suitable reduction of the sanitising temperature can therefore reduce operating costs, decrease rouging and extend the longevity of plant components. Especially when one considers that some facilities store their WFI at 85 °C, in order to have a safety margin from the 80 °C due to the measurement inaccuracy.