Biofilm monitoring in Drinking Water Distribution Systems

Water distribution systems (WDS) are an essential urban infrastructure that must be adequately monitored and managed in order to provide safe and high-quality drinking water to consumers. Many problems in WDS are primarily caused by biofilms in the water pipes (e.g., residual disinfectant decay, proliferation of pathogens, nitrification, and microbiologically influenced corrosion). Monitoring of biofilm development in WDS is essential to develop strategies for management of these problems. Currently we are investigating biofilm communities, activity, and growth rate within water distribution pipes using two different approaches: (1) offline analysis of bulk water and biofilm samples in the laboratory; and (2) online monitoring of biofilm growth rate using an in-pipe biofilm sensor.

(1) Offline biofilm analysis using molecular biological methods -- Collecting biofilm samples from operational WDS for detailed biological analyses is a substantial challenge due to limited access to the pipes during regular operations. One of the possible approaches to tackle this challenge (i.e., studying biofilms in situ in WDS) is collecting samples from a device inserted into the pipe. Accessibility to biofilms on sensors installed to the water pipes at various locations, which is the major advantage of our team, offers a unique opportunity for systematic investigation of temporal and spatial distribution/change of microbial communities and water quality within an operational WDS. Specifically, we have designed and initiated research to analyze biofilm communities colonizing in-pipe sensors of the WaterWiSe (Water Wireless Sentinel) system, which comprises wireless sensor nodes measuring hydraulics and basic physicochemical water quality parameters. Biofilms on different types of materials (sensor surface) as well as bulk water sample have been collected from tapping points of the WaterWiSe system. The samples are brought back to the laboratory for detailed molecular biological analyses to investigate the occurrence of target microbes and composition of microbial communities.

(2) Online biofilm monitoring using an in-pipe biofilm sensor -- We are about to initiate this particular research project aiming to design and integrate a sensor that can measure the rate of biofilm growth online within the water distribution network. The initial task of this project is installation of a customized biofilm sensor to selected sections of WDS and online monitoring data (i.e., quantitative measurement of biofilm growth rate) acquisition through a wireless sensor network. The performance of the in-pipe biofilm sensor will be evaluated by validating the sensor response with offline biofilm measurement, namely, laboratory analysis of microbial abundance and composition in biofilms.

The outcomes of this work will provide direct insight to explain how the development of biofilm is related to factors including i) pipe size, material and age, ii) local hydraulic conditions (operating pressures, flow rates, water age), and iii) local chemical environment and water quality (turbidity, oxidation-reduction potential [ORP], residual chlorine, microbial numbers, etc.). This will also allow us to obtain a better understanding of chronic microbial water quality issues, if any, and in situ processes in WDS (microbiological activity and associated adverse effects, such as turbidity and taste/odor problems, etc.). Online continuous measurement of biofilm growth coupled with laboratory-based offline microbial analyses will provide more comprehensive and detailed information on drinking water biofilms in this particular geographical region than was previously available to us - this can be used to guide efficient management of water quality in WDS in Singapore (disinfection, flushing regimes, etc.).