Impact of hydraulic interventions on chronic and acute material loading and discolouration risk in drinking water distribution systems

Abstract

This paper presents results from an intensive long term investigation in three comparable trunk mains and downstream impact of non-invasive, in-service flow conditioning to manage discolouration risk.Findings show that flow conditioning, the careful regular increase in flows to mobilise small amounts of material from cohesive layers formed at the pipe wall, provides immediate risk mitigation and system resilience benefits. Evidence is presented showing longer term risk reduction in the trunk mains and a 25% discolouration risk reduction in the downstream networks. Whilst the flow conditioning produced an acute but short duration controlled mobilisation of material from the trunk main, longer term downstream monitoring showed reduced chronic or background material loading.It is proposed this change is due to altering the material exchange behaviour and volumes bound within cohesive layers that develop on bulk water / infrastructure interfaces. The paper provides evidence that flow conditioning is an efficient strategy to manage discolouration risk and improve consumer water quality throughout water distribution systems.

The interplay of suspended sediment concentration, particle size and fluid velocity on the rapid deposition of suspended iron oxide particles in PVC drinking water pipes

“…The experiments performed mimicked the acute loading of suspended particles from an upstream turbidity event ( Sunny et al., 2020 ), in a downstream pipe under more normal daily conditions. The experiments used simplified steady state conditions, while daily demand patterns are known to have an impact on material accumulation ( Husband et al., 2008 ), these experiments were arguably performed under the highest daily peak flow which was greater than the self-cleaning velocities ( Blokker et al., 2011 ).…”

“…This paper aims to examine the dynamics of acute particulate attachment on pipe walls ( Sunny et al., 2020 ) following the rapid release and travel of a concentrated plume of iron oxide particles immediately following a simulated discolouration event in controlled experiments completed in a full-scale PVC pipe loop laboratory. The specific objectives of the experiments were to: (1) estimate the average rate of iron oxide particle deposition on PVC pipes immediately after the rapid release, and during the passage of, a highly-concentrated plume of iron oxide particles that typifies discolouration events in real systems; (2) determine whether previously deposited particles on the pipe wall from the passage of previous iron oxide particle plumes affect the average rate of iron oxide deposition and attachment to the pipe wall, and (3) examine the specific mechanisms involved in the particle settling phenomenon for drinking water pipes, and the effect of particle size distribution of sediments in suspension on the formation of material deposits on the pipe wall.…”

Dynamic Hydraulics in a Drinking Water Distribution System Influence Suspended Particles and Turbidity, But Not Microbiology

“…Recently, flow conditioning has been proposed as a mitigation strategy to limit material loading in pipes and brown water complaints. The careful regular increase of flow in trunk mains enables to mobilize small amounts of material from cohesive layers from the pipe walls and to reduce loading of downstream distribution pipes [32].…”

The microbial ecology of a Mediterranean chlorinated drinking water distribution systems in the city of Valencia (Spain)

“…Extensive fieldwork, bench top trials and full scale laboratory pipe research have all highlighted particulate material continually present in the fluid phase accumulating on DWDS surfaces as layers with distinct shear strength characteristics (Choi & Morgenroth, 2003;Douterelo et al, 2013;Sunny et al, 2020). This DWDS phenomena is experienced worldwide, and a unifying feature facilitating wall attachment is the endemic presence of biofilms.…”

“…Flow conditioning in trunk mains applies this concept to incrementally remove network material, mitigating risks and increasing resilience without any loss of water and at minimal cost . The mobilisation of these layers does create short-term, but managed, low-level turbidity responses; however, flow conditioning has shown additional benefits including a reduction in material loading that reduces downstream asset deterioration and disinfection decay rates (Sunny et al, 2020). A consequence of the continual particulate loading in bulk flow, measurable as background turbidity, is that when flows approach quiescence, gravitational settling may occur.…”