The impact of sample line biofilms on drinking water quality and microbial compliance

A combination of laboratory tests and fieldwork using bespoke full-scale sample line testing rigs (recreating physical, chemical, and biological conditions of operational systems) is envisioned to ensure understanding is transferable. Sample line biofilm formation, characteristics (microbiome, EPS, physical structure) and mobilisation will be monitored (via the analysis of removable surfaces), alongside bulk-water quality and planktonic microbiome, under different design, operational and sampling hydraulic regimes. Installation of sample line rigs in The University of Sheffield (UoS) temperature-controlled pipe loop facility will provide laboratory level control to determine the impact of variables such as sample line material/connections, tap cleaning strategies, hydraulic operation (stagnation/flowing) and shear stress during sample collection (flushing regimes). The UoS setup would also facilitate spike tests with non-pathogenic coliforms and comparison of sample line biofilms to those forming in network pipes. Understanding and quantifying the impact of final water characteristics such as biocide concentration and nutrient loads (in combination with hydraulics) on sample line biofilm growth rate and stability will be key to informing optimal sample line design and management. Thus, lab work will be complemented by installation of sample line rigs at water treatment works, with one (or more) water company sponsors. A subset of hydraulic regimes will be tested across a wide range of treated water types and qualities; seasonality and/or location (kiosk vs. room) could be explored via a longitudinal study. A typical experiment is anticipated to involve developing biofilms under a particular environmental condition, exposing the biofilms to different hydraulic disturbances (flushing) as occurs during sampling, allowing the biofilms to regrow and then repeating the flushing regime. Regular biofilm and bulk-water samples (online and discrete) will be collected to characterise cell concentrations, cell viability, microbiome composition (particularly bacteria and coliforms) and targeted analysis of biofilm physical structure (EPS). The understanding gained from the experimental programme will be validated by exploration of the correlation between the identified important environmental factors and bacteriological exceedance through analysis of historic bacteriological exceedance datasets.