Investigation of the Physical Mechanisms Behind the Deposition and Mobilization of Iron Oxide Particles on PVC Drinking Water Pipes

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Sass Braga, Artur
Discolouration , Iron Oxide Particles , Particle Deposition , Drinking Water Pipes , Physical Mechanism
Material deposits, including metals and biofilms, are known to progressively accumulate inside drinking water distribution systems. Such accumulation increases the risk of drinking water contamination. Research suggests that iron oxide particles are the major component of material accumulation that are usually sourced by the corrosion of iron components in a distribution network and carried from the flow to other parts of the network. Despite the significant advances in identifying sediments and mitigating large discolouration events, the physical mechanisms of particle deposition and mobilization are still poorly understood, especially considering PVC pipe material. In this thesis, a series of controlled experiments using a full-scale drinking water distribution laboratory with PVC pipes are proposed to investigate the attachment and mobilization of iron oxide particles on PVC pipe walls of the system. Through the experiments, new monitoring techniques were designed to assess the fate of iron oxide particles within the pipes, including a method for direct quantification of iron oxide particles on the surface of undisturbed pipe wall samples using automated brightfield microscopy and image analysis. Experimental results produced new insights about: 1) the mechanisms behind the attachment of iron oxide particles to PVC pipe walls, which was dominant at the invert position of pipes and affected by the particles size, fluid velocity, and pipe wall roughness; 2) the origins of the shear strength of inorganic particle accumulation, that depends on the settling of particles in roughness “valleys” of the pipe wall roughness assisted by particle weight, and 3) particle mobilization dynamics during discolouration events, where the flow acceleration stage during flushing was observed to produce the dominant detachment of particulate materials. The research results have contributed to improving the understanding of early stages of particulate sediment accumulation on PVC drinking water pipes – a finding that might be key to developing proactive strategies to control the long-term buildup of sediment materials in operational networks and improve drinking water safety.
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