A large proportion of the bacteria present in water cannot be cultured and thus cannot be detected using cultural detection methods. Flow cytometry technology allows quantification of real bacteria present in water within 15 min.
In contrast to online measurements of important physical or chemical water quality parameters, microbiological water quality is traditionally measured in the laboratory. In recent years, there have also been pioneering developments in microbiological measurement technology that enable online measurements with high data resolution Flow cytometry in particular occupies a prominent position here. It allows the determination of total and intact bacterial cell counts within 15 min, making it possible for the first time to map changes in bacterial concentrations over time in near real time.
In the online version, a commercially available instrument placed in the MULTI-ReUse pilot plant quickly provided data on changes in the treatment process. By sampling at two different points along the treatment process, it was possible to distinguish between operational failures of ultrafiltration and reverse osmosis. The two treatment stages were considered critical control points for water quality. Microbiological germination of autochthonous microorganisms present in the water was typically detectable after 90 min following the failure of a filter stage. In addition, the effect of chloramine dosing was directly measurable.
On the other hand, the offline format of flow cytometry allowed the analysis of water samples from different sampling points in the laboratory. This made it possible to investigate the efficiency of microbiological elimination, especially in filter stages, but also the extent of biological stabilization after sand filter passage or activated carbon filtration. However, the offline measurements were not limited to measuring the bacterial concentration at the time of sampling, but also served to investigate the maximum microbiological germination potential of the water. This correlates with the nutrients present in the water and enabled the measurement of a continuous reduction of the nutrient content over the treatment process up to reverse osmosis. Overall, the measurement technology provided valuable information for the assessment of treatment performance and optimization of process stages.