Characterisation of the Physical Composition and Microbial Community Structure of Biofilms within a Model Full-Scale Drinking Water Distribution System

Abstract

Within drinking water distribution systems (DWDS), microorganisms form multi-species biofilms on internal pipe surfaces. A matrix of extracellular polymeric substances (EPS) is produced by the attached community and provides structure and stability for the biofilm. If the EPS adhesive strength deteriorates or is overcome by external shear forces, biofilm is mobilised into the water potentially leading to degradation of water quality. However, little is known about the EPS within DWDS biofilms or how this is influenced by community composition or environmental parameters, because of the complications in obtaining biofilm samples and the difficulties in analysing EPS. Additionally, although biofilms may contain various microbial groups, research commonly focuses solely upon bacteria. This research applies an EPS analysis method based upon fluorescent confocal laser scanning microscopy (CLSM) in combination with digital image analysis (DIA), to concurrently characterize cells and EPS (carbohydrates and proteins) within drinking water biofilms from a full-scale DWDS experimental pipe loop facility with representative hydraulic conditions. Application of the EPS analysis method, alongside DNA fingerprinting of bacterial, archaeal and fungal communities, was demonstrated for biofilms sampled from different positions around the pipeline, after 28 days growth within the DWDS experimental facility. The volume of EPS was 4.9 times greater than that of the cells within biofilms, with carbohydrates present as the dominant component. Additionally, the greatest proportion of EPS was located above that of the cells. Fungi and archaea were established as important components of the biofilm community, although bacteria were more diverse. Moreover, biofilms from different positions were similar with respect to community structure and the quantity, composition and three-dimensional distribution of cells and EPS, indicating that active colonisation of the pipe wall is an important driver in material accumulation within the DWDS.

Assessing biofilm development in drinking water distribution systems by Machine Learning methods

“…Thus, obtaining representative biofilm samples of the spatial, temporal and physicochemical variation of real DWDSs is highly challenging [121]. Sampling just the flowing water is not an option.…”

“…Indeed, much of the current understanding about DWDS biofilm is based on studies from pilot or bench-top scale experimental models of drinking water systems [121].…”

“…It is highly challenging to acquire biofilm samples that are representative of the spatial, temporal and physico-chemical variation of real DWDSs since communities comprised in the functioning of buried infrastructures are alive [121]. In the limited cases that biofilm in situ samplings are carried out, due to the cost and complexity of the process, sampling is normally based on availability, due to maintenance operations of the network, and not as part of a structured survey.…”

“…There is no single accepted method to quantify biofilm cells [121]. The most commonly used biofilm quantification techniques are presented below.…”

“…All biofilm samples were collected without draining the system, limiting the impact of sampling upon biofilm accumulation, and replacement sterile coupons were immediately inserted into the pipe [121]. Inserts and outer coupons were separated aseptically (Figure 4.19).…”