Examining the Influence of Near Wall Hydraulics on the Regeneration and Mobilization of Discolouration Material in a Drinking Water Distribution Laboratory
Potable water in Canada leaves treatment facilities in pristine quality and excellent condition for both drinking and sanitation. However, customer concerns related to discoloured drinking water continue to serve as a worldwide issue in urban drinking water distribution systems (DWDS). Fundamentally, water discolouration is a result of the long-term accumulation of particulate material which is subsequently mobilized due to sudden changes in hydraulic conditions. Field and laboratory studies have shown that cohesive layers on the pipe wall are adaptive to the respective environmental and hydrodynamic conditions. The most readily used approach to manage the risk of water discolouration is unidirectional flushing of watermains. The imposition of an increased hydraulic shear stress erodes these cohesive layers from the pipe wall into the bulk water. To examine the regeneration and mobilization of discolouration material a full-scale laboratory was designed to simulate the operation of a DWDS. The laboratory consists of two identical pipe loops comprised of 108 mm diameter PVC pipes, each with a length of 198 m. All components of the laboratory are located within a climate-controlled chamber to simulate seasonal temperature variation. The laboratory is fitted with instrumentation to monitor turbidity, flow rate, pressure, and temperature in a real time manner. Three experiments of duration 40, 80 and 120 days allowed for the growth of cohesive layers under steady-state flow conditions. Each growth phase was followed by 3 successive 15-minute flushing intervals to erode the layers. Grab samples for TSS, metals composition and particle size distribution were scheduled throughout each experiment. Results found that cohesive layers of various strength characteristics developed with an approximate linear increase in turbidity response with increased growth duration. The strength of cohesive layers was observed to increase with increased growth duration. The conditioning velocity during each growth phase had a negligible effect on both material accumulation and layer strength. Turbidity was determined to be a good indicator of total suspended solids and iron in the water.
URI for this recordhttp://hdl.handle.net/1974/24957
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