By linking variables from different disciplines, novel insights into water system management can be obtained. This is established by the project Microbiology in Urban Water Systems (MUWS), which aims to characterise the microorganisms found in both potable water distribution systems and sewer networks and described in the latest issue of Drinking Water Engineering and Science.
Urban water systems are important for millions of people. They are major components of the water cycle and present unique challenges; the systems are large, complex, highly interconnected and dynamic with variable hydraulics, input sources and behaviour. These large infrastructure systems have a major impact on people's quality of life by preventing serious disease, protecting/enhancing the environment and reducing flood damage to other infrastructure. Their overall performance can be evaluated by physical, chemical and biological processes.
Despite the fact that modern water treatment works produce high-quality water as it enters the distribution system, the quality of the water is known to deteriorate during transportation within the system. Changes in water quality are due to distribution systems acting as large bio-chemical reactors in which many complex, dynamic and interrelated hydrodynamic and biochemical processes occur. Answers to key questions such as ‘which microorganisms are present?' are important for understanding these interactions.
The authors describe how the long-term objective of the MUWS project is to assess the impact of microorganisms on aspects of system performance within drinking water distribution systems and sewer networks. Using the research expertise of civil and biochemical engineers and molecular microbial ecologists, the MUWS project aims to address these key questions across different length scales of the urban water systems.
In the MUWS project, variations in the microbial community of drinking water distribution systems and sewer networks are characterised using molecular microbiological techniques rather than traditional culture-based techniques. The authors describe two key methods (denaturing gradient gel electrophoresis or DGGE and fluorescence in situ hybridization or FISH) which allowed them to gain insight into how a microbial community changes under different conditions at a variety of scales within urban water systems. DGGE analysis can be used to investigate mixed microbial communities from various environments. The method is based on the molecular separation of DNA fragments when migrating through a DGGE gel, which results in a specific banding pattern. FISH with rRNA (ribonucleic acid)-targeted oligonucleotide probes is used for the detection and quantification of microorganisms without prior cultivation.
DGCE results for both culture-independent and culture-dependent approaches indicate that the former technique underestimates the number of phylotypes present in the sample; in other words, microbial contamination could be present but not detected using current practice. The authors determined that when conducted in combination with relevant physical and chemical measurements, DGGE provides the opportunity to study the changes in microbial diversity in relation to conditions within the urban water system. The FISH method was used to quantify the number of bacteria within the water samples, and demonstrated the accurate detection of 90-93% of bacteria present. The authors found that the catalysed reported deposition FISH (CARDFISH) technique is very suitable for studying bacteria (and other microbes) in highly oligotrophic environments such as water distribution systems, because of their increased sensitivity and fluorescence intensity.
The article concludes by summarising the benefits of such an integrated approach: existing engineering knowledge and/or computer models can provide insight into choosing the most appropriate sampling locations; multivariate analysis of the different parameters allows future interpretation of changes in biological diversity in relation to specific environmental variables and hydraulic conditions; ‘biological' management tools can be developed that will aid system operators in achieving improved levels of environmental and public health protection; and relationships between the presence and behaviour of microbial assemblages and their potential release into the environment and water quality can be determined.