Short-term microbial dynamics in a drinking water plant treating groundwater with occasional high microbial loads. (15th December 2016)

• Record Type: Journal Article
• Authors: Besmer, Michael D.; Hammes, Frederik
• Is Part Of: Water research. Volume 107(2016)
• Page Start: 11
• Page End: 18
• Publication Date: 2016-12-15
• Subjects: Online flow cytometry -- Microbial monitoring -- Drinking water treatment -- Bacterial dynamics -- Process monitoring; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2016.10.041
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Short-term fluctuations in bacterial concentrations in drinking water systems, occurring on time scales of hours-to-weeks, are essentially unexplored due to a lack of microbial monitoring tools that allow high frequency measurements. Here, we applied fully automated online flow cytometry to measure the total cell concentrations (TCC) in both raw water (karstic groundwater) and treated water (flocculation – ultrafiltration (UF) – ozonation – granular active carbon (GAC) filtration) during a period of 70 days at high temporal resolution (n > 4000 for both water types). We detected and characterized in considerable detail aperiodic fluctuations in the raw water following regional precipitation, with TCC increasing up to 50-fold from a dry weather baseline of approximately 120 cells μl −1 to an event peak of > 5000 cells μl −1 . Moreover, we observed the buffering of the treatment plant against these fluctuations, but in addition we recorded a completely unexpected periodic fluctuation of TCC in the treated water after GAC filtration. We concluded that the latter was the result of fluctuating water abstraction from the treatment plant reservoir by two connected water utilities, which resulted in variations in water throughput in the plant. This in turn influenced bacterial detachment and dilution in the GAC filter. This study provides strong evidence of multiple different microbial dynamics occurring in a drinking water treatment system. Given numerous possible sources of natural and operational fluctuations in raw water and drinking water treatment plants, such microbial fluctuations should be expected in many systems. The high-frequency monitoring approach presented herein can improve the understanding and eventual mitigation of such fluctuations. Graphical abstract: Highlights: More than 8000 flow cytometric measurements of raw and treated groundwater in 70 days. Raw water total cell concentrations increased up to 50-fold after regional precipitation. A multi-step treatment train hedged against aperiodic microbial peak loads in raw water. Periodic variations treated water throughput caused variations in total cell concentrations.