The dynamics of biofilm detachment from the pipe walls of drinking water distribution systems was investigated through experiments in a full-scale pipe loop laboratory system. Biofilms grown under steady-state and transitory flow rates were compared. Flow cytometry was used to quantify the microbial cells of the biofilms, and biofilm shear strength was evaluated based on their capacity to resist mobilization when subjected to elevated flushing flow rates. The results suggest that biofilms grown under transitory flow regimes may develop stronger adhesion strength to the pipe wall. This paper contributes to the enhanced understanding of biofilm behaviour in drinking water systems and its potential impacts on water quality.

Excessive accumulation of particulate material and biofilms on the inner walls of drinking water pipes increases the risk of water discoloration events, known to be the major cause of customer complaints worldwide. As a result, water utilities use pipe flushing operations to mobilize material deposits from ‘dirty sections’ of their pipe networks. Nevertheless, the development of preventative strategies is still limited by the lack of knowledge about the material accumulation process and the behaviour of resuspended particles during flushing. The goal of this paper is to investigate the behaviour of insoluble iron oxide particles during controlled accumulation and flushing processes in PVC drinking water pipes. A set of four experiments was completed where water with a known concentration of iron oxide particles was introduced into a full-scale pipe loop laboratory system under steady flow conditions producing the accumulation of particles along half the pipe length. The system was then flushed using two sequential velocities (0.7 and 1.2 m s⁻¹) and the direction of flush was changed between each independent flushing stage. During the flushing operations, it was found that a small number of mobilized particles can reattach to downstream sections pipes, and resist mobilization to elevated wall shear stresses of 1.2 Pa. Furthermore, even after successive flushes in one direction, a subsequent flush of equal velocity in the opposite direction was able to mobilize new particles from the pipe wall surface. These findings revealed a new mechanism of particle resistance to mobilization that is independent of the WSS. These results may assist water utilities in improving flushing strategies for DWDSs and managing accumulated material in their networks.

Biofilms facilitated the attachment of iron oxide particles on PVC pipes. Biofilms increased particles resistance to mobilization through flushing.

This research explores the microbial ecology within drinking water distribution systems (DWDS). The aim of the paper was to examine the impact of small-amplitude transients on the bacterial composition in bulk water and biofilms. The findings highlight the dominance of Proteobacteria and the significant transformation of microbial communities in response to changes in environmental conditions. The study underscores the complex interplay between operational strategies and microbial dynamics in DWDS and emphasizes the necessity for ongoing research to enhance water quality management amidst climate change challenges.

Moderate hydraulic transients (∼20 kPa) enhanced biofilm growth/adhesion; stronger ones caused detachment but created resilient films. Small transients shaped biofilm distribution in water pipes, proving flow variability drives microbial stability.