• Suspended sediment plume produced sediment deposits on PVC drinking water pipes. • Iron oxide particles as small as 4.6 μm were rapidly deposited on pipe walls. • Self-clean velocities were insufficient to prevent fine particle deposition. • Deposition followed an exponential decay process along the length of the pipe. • Adhesion forces enhanced by gravity likely selected particles that formed deposits.

Discoloration is currently the major cause of consumer complaints worldwide, being mainly caused by the accumulation and mobilization of materials in the inner pipe walls of drinking water distribution systems. The understanding about material detachment from pipe walls is limited due to its complexity and lack of data. The purpose of this study was to examine the initial stages of material detachment from PVC pipe walls during flushing operations using a full-scale laboratory system. Experiments consisted of a material accumulation phase with periods from 40 to 120 days, followed by a material mobilization phase with wall shear stresses above 5 Pa. Results indicated that material detachment mainly occurs during the periods of velocity increase, at rates ranging from 0.5 to 14 mNTU/s. In addition, a second stage of material detachment was observed during steady flow conditions, and a fast detachment event highlighted impacts of curved sections on the mobilization phenomena.

PVC pipe wall samples were acquired from a full-scale drinking water distribution laboratory using 3D printed coupons. Brightfield microscopy and imaging processing were used to investigate iron oxide particles deposited on samples surface.

Turbidity and brightfield microscopy were used to investigate the attachment of iron oxide particles on drinking water PVC pipes. Experimental evidence motivated new insights about the physical process of particle attachment.

Experiments with synthetic iron oxide particles in a full-scale pipe system were used to investigate the material shear strength of particulate accumulation. Results highlighted the importance of the pipe wall roughness on the attachment process.

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.