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Rapperswil, Switzerland

Hammes F.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Berger C.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Koster O.,Zurich Water Supply WVZ | Egli T.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Egli T.,ETH Zurich
Journal of Water Supply: Research and Technology - AQUA | Year: 2010

Biological stability refers to the inability of drinking water to support microbial growth. This phenomenon was studied in a full-scale drinking water treatment and distribution system of the city of Zürich (Switzerland). The system treats lake water with successive ozonation and biological filtration steps and distributes the water without any disinfectant residuals. Chemical and microbiological parameters, notably dissolved organic carbon (DOC), assimilable organic carbon (AOC), heterotrophic plate counts (HPC) and flow-cytometric total cell concentration (TCC), were measured over an 18-month period. We observed a direct correlation between changes in the TCC, DOC and AOC concentrations during treatment; an increase in cell concentration was always associated with a decrease in organic carbon. This pattern was, however, not discerned with the conventional HPC method. The treated water contained on average a TCC of 8.97 × 104 cells ml-1, a DOC concentration of 0.78mgl-1 and an AOC concentration of 32μgl -1, and these parameters hardly changed in the distribution network, suggesting that the treated water had a high level of biological stability. This study highlights the descriptive value of alternative parameters such as flow-cytometric TCC for drinking water analysis, and pinpoints some of the key aspects regarding biological stability in drinking water without disinfectant residuals. © IWA Publishing 2010. Source

Zeder M.,University of Zurich | Van Den Wyngaert S.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Koster O.,Zurich Water Supply WVZ | Felder K.M.,University of Zurich | And 2 more authors.
Applied and Environmental Microbiology | Year: 2010

Quantification and sizing of filamentous cyanobacteria in environmental samples or cultures are timeconsuming and are often performed by using manual or semiautomated microscopic analysis. Automation of conventional image analysis is difficult because filaments may exhibit great variations in length and patchy autofluorescence. Moreover, individual filaments frequently cross each other in microscopic preparations, as deduced by modeling. This paper describes a novel approach based on object-oriented image analysis to simultaneously determine (i) filament number, (ii) individual filament lengths, and (iii) the cumulative filament length of unbranched cyanobacterial morphotypes in fluorescent microscope images in a fully automated high-throughput manner. Special emphasis was placed on correct detection of overlapping objects by image analysis and on appropriate coverage of filament length distribution by using large composite images. The method was validated with a data set for Planktothrix rubescens from field samples and was compared with manual filament tracing, the line intercept method, and the Utermöhl counting approach. The computer program described allows batch processing of large images from any appropriate source and annotation of detected filaments. It requires no user interaction, is available free, and thus might be a useful tool for basic research and drinking water quality control. Copyright © 2010, American Society for Microbiology. All Rights Resevered. Source

Lautenschlager K.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Lautenschlager K.,ETH Zurich | Hwang C.,University of Illinois at Urbana - Champaign | Liu W.-T.,University of Illinois at Urbana - Champaign | And 7 more authors.
Water Research | Year: 2013

Biological stability of drinking water implies that the concentration of bacterial cells and composition of the microbial community should not change during distribution. In this study, we used a multi-parametric approach that encompasses different aspects of microbial water quality including microbial growth potential, microbial abundance, and microbial community composition, to monitor biological stability in drinking water of the non-chlorinated distribution system of Zürich. Drinking water was collected directly after treatment from the reservoir and in the network at several locations with varied average hydraulic retention times (6-52h) over a period of four months, with a single repetition two years later. Total cell concentrations (TCC) measured with flow cytometry remained remarkably stable at 9.5 (±0.6)×104cells/ml from water in the reservoir throughout most of the distribution network, and during the whole time period. Conventional microbial methods like heterotrophic plate counts, the concentration of adenosine tri-phosphate, total organic carbon and assimilable organic carbon remained also constant. Samples taken two years apart showed more than 80% similarity for the microbial communities analysed with denaturing gradient gel electrophoresis and 454 pyrosequencing. Only the two sampling locations with the longest water retention times were the exceptions and, sofar for unknown reasons, recorded a slight but significantly higher TCC (1.3(±0.1)×105cells/ml) compared to the other locations. This small change in microbial abundance detected by flow cytometry was also clearly observed in a shift in the microbial community profiles to a higher abundance of members from the Comamonadaceae (60% vs. 2% at other locations). Conventional microbial detection methods were not able to detect changes as observed with flow cytometric cell counts and microbial community analysis. Our findings demonstrate that the multi-parametric approach used provides a powerful and sensitive tool to assess and evaluate biological stability and microbial processes in drinking water distribution systems. © 2013 Elsevier Ltd. Source

Lautenschlager K.,Eawag - Swiss Federal Institute of Aquatic Science and Technology | Lautenschlager K.,ETH Zurich | Hwang C.,University of Illinois at Urbana - Champaign | Ling F.,University of Illinois at Urbana - Champaign | And 6 more authors.
Water Research | Year: 2014

Indigenous bacterial communities are essential for biofiltration processes in drinking water treatment systems. In this study, we examined the microbial community composition and abundance of three different biofilter types (rapid sand, granular activated carbon, and slow sand filters) and their respective effluents in a full-scale, multi-step treatment plant (Zürich, CH). Detailed analysis of organic carbon degradation underpinned biodegradation as the primary function of the biofilter biomass. The biomass was present in concentrations ranging between 2-5×1015cells/m3 in all filters but was phylogenetically, enzymatically and metabolically diverse. Based on 16S rRNA gene-based 454 pyrosequencing analysis for microbial community composition, similar microbial taxa (predominantly Proteobacteria, Planctomycetes, Acidobacteria, Bacteriodetes, Nitrospira and Chloroflexi) were present in all biofilters and in their respective effluents, but the ratio of microbial taxa was different in each filter type. This change was also reflected in the cluster analysis, which revealed a change of 50-60% in microbial community composition between the different filter types.© 2014 Elsevier Ltd. Source

Juttner F.,University of Zurich | Watson S.B.,Environment Canada | von Elert E.,University of Cologne | Koster O.,Zurich Water Supply WVZ
Journal of Chemical Ecology | Year: 2010

β-Cyclocitral is often present in eutrophic waters and is a well known source of airborne and drinking water malodor, but its production and functional ecology are unresolved. This volatile organic compound (VOC) is derived from the catalytic breakdown of β-carotene, and evidence indicates that it is produced by the activation of a specific carotene oxygenase by all species of the bloom-forming cyanobacterium Microcystis. Previous work has shown that β-cyclocitral affects grazer behavior, but the nature of this interaction and its influence on predator-prey dynamics was unresolved. The present study combined analytical and behavioral studies to evaluate this interaction by using Microcystis NRC-1 and Daphnia magna. Results showed that β-cyclocitral was undetectable in live Microcystis cells, or present only at extremely low concentrations (2.6 amol /cell). In contrast, cell rupture activated a rapid carotene oxygenase reaction, which produced high amounts (77 ± 5.5 amol β-cyclocitral/cell), corresponding to a calculated maximum intracellular concentration of 2.2mM. The behavioral response of Daphnia magna to β-cyclocitral was evaluated in a bbe© Daphnia toximeter, where β-cyclocitral treatments induced a marked increase in swimming velocity. Acclimation took place within a few minutes, when Daphnia returned to normal swimming velocity while still exposed to β-cyclocitral. The minimum VOC concentration (odor threshold) that elicited a significant grazer response was 750 nM β-cyclocitral, some 2,900 times lower than the per capita yield of a growing Microcystis cell after activation. Under natural conditions, initial grazer-related or other mode of cell rupture would lead to the development of a robust β-cyclocitral microzone around Microcystis colonies, thus acting as both a powerful repellent and signal of poor quality food to grazers. © 2010 Springer Science+Business Media, LLC. Source

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