12-14 September 2023
In pharmaceutical water systems, the TOC value (Total Organic Carbon) is usually determined online. Since bacteria also consist to a large extent of hydrocarbons, the question arises as to whether information about the microbial status of the water system can also be obtained by means of TOC monitoring.
Unfortunately, this is not possible. There are fast microbiological test procedures (without agar plates), also for pharmaceutical water systems. However, these usually work with other technologies, often by particle measurement and fluorescence. However, it is not possible to convert TOC values into bacterial counts. Nor is it possible to draw any conclusions about a possible biofilm in the system.
Bacteria in water systems are typically only present to a minimal extent in the free-flowing medium water (aquatic). They rather collect in a biofilm that grows on surfaces in places in the system with less flow (stationary). In order to trigger a measured value in the TOC system, the germs would have to flow through the TOC. It is always possible that a part of a biofilm tears off and moves through the system for a short time. But even then it is statistically rather unlikely that it will flow straight and reproducibly through the measuring system at the time of measurement. Short-term peaks in TOC monitoring could therefore be caused by a biofilm, but they do not have to be. And to get close to the limit value of 500 ppb TOC, the water would have to be contaminated so heavily that this would probably already be recognisable by turbidity and odour.
On the other hand, a very low TOC value in the water system is a very good starting point to prevent the formation of a biofilm, as the organic material is the food for the biofilm-forming bacteria.