In the last 10–15 years in some German drinking water reservoirs an increase in the NOM (natural organic matter) content has occurred. The impact of such a change on the drinking water quality was almost unknown. A research project was carried out at several drinking water reservoirs and water works concerning the change in the NOM quality and the nutrient situation. The results indicate that the NOM increase in the reservoir is predominately caused by an increasing input of high and intermediate molecular weight humic substances from the catchment area into the reservoir. The fractions of the polysaccharides and the high molecular weight humic substances are significantly reduced in the treatment process. In contrast, the elimination rate for the substances with an intermediate and low molecular weight was low. Due to the low elimination rate particularly of the intermediate humic fraction, the NOM content of the treated water increased with the change in the raw water. Furthermore, the BDOC of the treated water increased with the NOM content. For the AOC of the treated water no relationship was found with the NOM content. However, the change of this parameter was affected by the snowmelt and the circulation in the reservoir.
Investigations into distribution systems (DS) working without or with low disinfectant residuals showed that the main process for the bacteria change in such systems is the release of bacteria from the biofilm, whereas the growth of bacteria in the water can be neglected. Important for the quality are short-term increases of bacteria release connected to an increase of bacteria growth on the inner pipe surface as a result of changes in the concentration of biodegradable organic matter (BOM) in the water. A model to describe the bacterial water quality change was developed on the basis of investigations. In contrast to other models, a consideration of the formation of BOM as a result of NOM oxidation by disinfectant residuals as well as the decreasing effect of inactivation of released bacteria by the decreasing disinfectant residual concentration, were necessary.
The Taihu (Tai lake) region is one of the most economically prospering areas of China. Due to its location within this district of high anthropogenic activities, Taihu represents a drastic example of water pollution with nutrients (nitrogen, phosphate), organic contaminants and heavy metals. High nutrient levels combined with very shallow water create large eutrophication problems, threatening the drinking water supply of the surrounding cities. Within the international research project SIGN (SinoGerman Water Supply Network, www.water-sign.de), funded by the German Federal Ministry of Education and Research (BMBF), a powerful consortium of fifteen German partners is working on the overall aim of assuring good water quality from the source to the tap by taking the whole water cycle into account: The diverse research topics range from future proof strategies for urban catchment, innovative monitoring and early warning approaches for lake and drinking water, control and use of biological degradation processes, efficient water treatment technologies, adapted water distribution up to promoting sector policy by good governance. The implementation in China is warranted, since the leading Chinese research institutes as well as the most important local stakeholders, e.g. water suppliers, are involved.
Worldwide, surface waters like lakes and reservoirs are one of the major sources for drinking water production, especially in regions with water scarcity. In the last decades, they have undergone significant changes due to climate change. This includes not only an increase of the water temperature but also microbiological changes. In recent years, increased numbers of coliform bacteria have been observed in these surface waters. In our monitoring study we analyzed two drinking water reservoirs (Klingenberg and Kleine Kinzig Reservoir) over a two-year period in 2018 and 2019. We detected high numbers of coliform bacteria up to 2.4 x 10^4 bacteria per 100 ml during summer months, representing an increase of four orders of magnitude compared to winter. Diversity decreased to one or two species that dominated the entire water body, namely Enterobacter asburiae and Lelliottia spp., depending on the reservoir. Interestingly, the same, very closely related strains have been found in several reservoirs from different regions. Fecal indicator bacteria Escherichia coli and enterococci could only be detected in low concentrations. Furthermore, fecal marker genes were not detected in the reservoir, indicating that high concentrations of coliform bacteria were not due to fecal contamination. Microbial community revealed Frankiales and Burkholderiales as dominant orders. Enterobacterales, however, only had a frequency of 0.04% within the microbial community, which is not significantly affected by the extreme change in coliform bacteria number. Redundancy analysis revealed water temperature, oxygen as well as nutrients and metals (phosphate, manganese) as factors affecting the dominant species. We conclude that this sudden increase of coliform bacteria is an autochthonic process that can be considered as a mass proliferation or ‘coliform bloom’ within the reservoir. It is correlated to higher water temperatures in summer and is therefore expected to occur more frequently in the near future, challenging drinking water production.
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