[Bacterial regrowth in drinking water. IV. Bacterial flora in fresh and stagnant water in drinking water purification and in the drinking water distribution system]. / Bakterielle Wieder-Verkeimung im Trinkwasser. IV. Mitteilung: Bakterienflora in Frisch- und Stagnationswasser bei der Trinkwasseraufbereitung und im Trinkwasser-Verteilersystem.

Six dead end water pipes were installed inside a Zurich drinking water plant and five others over a distance of 12 km along the distribution system and the water was left stagnating in there for 2 weeks. A total of 1508 bacteria from fresh and stagnating water were isolated and identified. Of these, 241 bacterial isolates from the distribution system were examined using the nutrient-tolerance test, i.e. testing the ability to grow in tap water and in media with low and very high nutrient content. In the fresh water of the treatment plant specific bacterial populations were obtained, these occurring particularly after the filters. According to different chlorine dosage and chlorine demand, they were finally washed into the distribution system in varying amounts and compositions. It was shown that in the fresh water of the distribution system the genera of Pseudomonas, Azotobacter and Actinobacteria were each present at a level of approximately 30%. After two weeks stagnation non-fluorescing pseudomonads were dominating in the treatment plant as well as in the fresh water of the distribution system. All isolated Actinobacteria and Azotobacter and almost half of the Pseudomonads proved to be oligotrophic oligocarbotolerants or oligocarbophilic organisms in the nutrient-tolerance test. The other half of the Pseudomonads plus the Flexibacter species were mesotrophic oligocarbotolerants, since they could grow in tap water and in culture media with very high nutrient content. Attention is drawn to the unrecognized danger of recontamination of mesotrophic bacteria growing rapidly in stagnating drinking water, which is used as rinsing water for cleaning food processing equipment.

[Bacterial regrowth in drinking water. III. Reasons for regrowth with oligocarbotolerant bacteria]. / Bakterielle Wieder-Verkeimung im Trinkwasser III. Mitteilung: Ursachen der Verkeimung mit oligocarbotoleranten Bakterien.

Investigations have been undertaken into the bacterial regrowth in a Zurich drinking water plant and over a distance of 12 km along the drinking water distribution system. This required installation of eleven chromium steel dead-end water pipes. Counts of oligocarbotolerant bacteria were carried out in 7 or 8 repetitions in fresh water and water left to stagnate for 7 and 14 days respectively (7,8). Additionally ten different biological, chemical and physical parameters were determined in the fresh water samples. Multiple linear regression analysis was used to determine what influence the different parameters had on the bacterial regrowth during stagnation. Two regression models were evaluated, one for the data obtained during treatment, and the other for the data obtained along the distribution system. In both models the content of DOC (Dissolved Organic Carbon) and the content of phosphate was correlated with the growth of oligocarbotolerant bacteria. Further, a relationship between the contents of organic matter and bacterial regrowth was discovered during two measuring series conducted in different seasons. The model of data obtained during treatment generated two additional parameters correlated with aftergrowth: Firstly the initial colony content, which probably resulted because the stagnation period was only half that of the model. Secondly, the oxygen content which resulted because of ozonization. Under the given test conditions the following parameters did not appear in the regression model (Cp-statistics according to Daniel and Wood, 5): AOC (Assimilatible Organic Carbon) and UV-absorption used for measuring organic matter, nitrate content, content of chlorine/chlorine dioxide, electrical conductivity, pH-values and the room temperature during the 14 days stagnation in the distribution system model.

[Bacterial regrowth in drinking water. II. Drinking water distribution systems]. / Bakterielle Wieder-Verkeimung im Trinkwasser II. Mitteilung: Trinkwasser-Verteilersystem.

Five chromium steel dead-end water pipes were installed over a distance of 12 km along the Zurich city drinking water distribution system. Cell counts were determined in two series of four samplings in fresh water and stagnating water using three different methods. The colony counts of oligocarbon tolerant bacteria (1:10 diluted plate count agar, 20 degrees C, 14 d) in the fresh water was increasing along the distribution line. Initially there were counts around 1 CFU ml-1 and after 12 km between 120 and 1100 CFU ml-1. Water taken from house tabs showed higher colony counts than water taken after reservoirs. After a stagnating time of 14 d all 40 water samples showed aftergrowth from 10(3) up to 10(4) CFU ml-1. Water from the two sampling locations with the longest distance from the treatment plant showed less regrowth tendency. Epifluorescence microscopy and the INT-method for determining the electron transport system positive bacteria (ETS+) were less useful for monitoring bacterial regrowth. However, in the stagnating water there occurred a significantly higher percentage of ETS+ units as compared to the colony forming units (CFU) with growing distance from the treatment plant.

[Bacterial regrowth in drinking water. I. The upgrading of drinking water]. / Bakterielle Wieder-Verkeimung im Trinkwasser. I. Mitteilung: Trinkwasseraufbereitung.

Seven dead-end water pipes were installed after each treatment step in a drinking water plant. During a period of 7 weeks the bacterial load of freshwater and stagnating water was investigated with different methods. A modified surface spread plate count (Plate Count Agar, 10-fold diluted, 14 days incubation at 20 degrees C) proved to be more effective than the traditional pour plate method, because it gave consistently higher colony counts and had a lower level of detection (0.001 CFU ml-1). The enumerating of electron-transport-system positive bacteria yielded higher numbers than the colony count methods, but is not recommended when recently oxidized water samples are to be investigated. Highest cell counts were attained when using epifluorescence microscopic counting, yet bacterial regrowth could not be monitored thus. The tendency of bacterial regrowth was highest in freshly ozonized water. In stagnating lake water no regrowth occurred after 1 and 3 weeks because of the balance of bacteria and their predators.