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From lab to practice: how flow cytometry is revolutionising the water industry

Updated: Dec 5, 2023

The well-established flow cytometry technology is now used to enumerate and characterise microbial cells. To delve into how this technology transforms the water industry and evaluate its advantages and practical applications for drinking water, we interviewed Prof. Dr Thomas Egli, microbiology scientific consultant to bNovate. This article reveals his expertise.

Prof Dr Thomas Egli

The history of flow cytometry in the water industry


While flow cytometry has been used on human cells in various medical fields since the seventies, it took another 20 to 30 years to expand the application field towards detecting microbial cells and viruses. Flow cytometry can be used as a rapid measurement method (RMM) for fast and economical water analysis.


Around 2000, Thomas Egli got involved in an OECD/WHO expert group that reviewed the state of methods and future needs in microbiological water analysis, which introduced him to drinking water problems. Flow cytometry (FCM) was listed as a potential fast method, but it was believed to be too tricky and expensive. Despite this, Thomas Egli and his research group at Eawag started adapting methods for counting microbial cells and determining metabolic activities for application in surface and drinking water. In parallel, the suitability of these methods in the real world was tested in collaboration with the Zürich Water Works, and the knowledge and measurement principles were transferred from academia to industry with tangible benefits.


In 2010, Thomas Egli and his collaborators jointly won the “Mühlheim Water Award” for this transition from the lab to practice. When Peter Ryser and Simon Kuenzi, founders and today’s Board Chairman and CEO of bNovate, respectively, started to develop an automated, robust and portable flow cytometer, they approached Thomas Egli, and this was the beginning of a strong collaboration and partnership with bNovate Technologies.


Prof Dr Thomas Egli

Advantages of flow cytometry


Counting microbial cells in ecosystems has been a long-standing challenge. The conventional cultivation-dependent method, heterotrophic plate counting (HPC), has been criticized by microbial ecologists for more than 50 years as it fails to display the true microbial abundance in environmental samples. Flow cytometric total cell counting (FCM-TCC) is based on staining cells with a fluorescent DNA-binding dye; it is not only faster than HPC, with detection times of minutes instead of days, but it detects >99% of the cells present in a water sample. Moreover, it delivers a typical microbial fingerprint of water of a specific origin. FCM-TCC allows the quantification and monitoring of microbial events from catchment to various treatment processes to the distribution network.


The abundance and composition of microbial communities vary over time through seasonal changes, heavy rainfalls, growth from nutrient pollution, or disinfection measures. This requires immediate, real-time and online monitoring. Traditionally used parameters are physico-chemical, like turbidity, pH or conductivity, but they do not reflect microbiological events reliably.


Total cell count (TCC) determination with a flow cytometer reacts sensitively to environmental conditions. It can monitor biological disturbances or stability of raw water from the catchment to the consumer’s tap. This requires an instrument that is compact, transportable, robust and works independently with hardly any maintenance.


“With BactoSense, bNovate has developed a ‘plug-and-play’ instrument with unique properties that enable practitioners to use FCM without dealing with toxic stains or daily maintenance. (…) BactoSense allows them to concentrate on the results they obtain.”, Thomas Egli says.


Application fields


Monitoring water microbiology is one of the main application fields since distinguishing groundwater from surface water enables setting limits to cell counts and fingerprints, thus being a central parameter in early warning systems. BactoSense allows water professionals to continuously monitor their production processes and distribution or use online data for microbial contamination control in catchments. Big and small waterworks with restricted personnel can benefit from using Bactosense.


It also brings substantial advantages and time savings for cleaning and rinsing processes: this includes monitoring process waters from sand and active carbon filters after back-flushing or flushing pipes in the distribution networks after repair. FCM-TCC and fingerprints can indicate whether cleaned units are ready for use.


Regrowth after stagnation periods or due to long residence times are amongst the most common problems in distribution networks and can be easily detected through elevated TCC values. For these applications, a mobile and transportable flow cytometer like the BactoSense is a timesaving solution because analytical results become available quickly, and decisions can be made on the spot.


The future of flow cytometry in the water industry


Within the next two decades, molecular methods like polymerase-chain-reaction will become cheaper and allow for a quicker assessment of the composition of microbial consortia. However, Thomas Egli doubts they will become automated, online routine methods.


No other method can deliver basic microbiological information rapidly and online at such a low cost as FCM-TCC and intact cell counts (FCM-ICC). Thomas Egli is confident that FCM-TCC will become a new microbiological drinking water analysis standard. Switzerland has already gone through the process of big waterworks using this technology successfully. With these influential users, the standardization of the method and recommendations by the Federal Health Authorities and the Swiss Gas and Water Board (SVGW) were achieved. This year, FCM methods will be included in the SVGW Educational Course for Swiss Water Professionals (Brunnenmeister).


“In several European countries, FCM methods are included in official recommendations and worksheets today, for example in Germany and Austria, and are now already accepted for specific applications like assessing the filtration efficiency and backwash processes”, concludes Thomas Egli. This bottom-up pressure should lead to the establishment of FCM methods in other countries and, finally, an ISO-standard method.

Do you want to read the full interview with Prof. Dr Thomas Egli, including his outlook on the developments in the market during the next 20 years? Click here to request the full interview.

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