Evaluation of loose deposits in distribution systems through: unidirectional flushing

Abstract

The objective of this project was to evaluate the extent of loose deposit accumulation in distribution systems in three Canadian cities to determine optimal flushing frequency. Unidirectional flushing was used to remove the deposits. The results obtained were found to be highly system‐dependant. The normalized mass of flushed deposits varied from less than 0.1 g/m (0.03 g/ft) to approximately 40 g/m (12 g/ft). For the range of velocities attained during flushing (0.65–2.3 m/s [2.1–7.6 fps]), the quantity of collected deposits was not a function of velocity. Analysis of the composition of the deposits confirmed the specificity of each water system. In all systems, the major fraction was iron corrosion compounds (38–72%), but organic matter (14–24%) and silicoaluminum compounds (7–16%) were also found to account for an important part of the deposits. Microbiological analyses revealed concentrations of total bacteria of approximately 1010 bacteria/g, but the presence of total coliforms was limited to 1.2% of the samples (n = 258).

Accumulation and modeling of particles in drinking water pipe fittings

“…The conclusion in this study was that neither flushing (0.37-2.14 m s −1 ) nor daily maximum velocity (0.02-0.39 m s −1 ) correlated with the washout mass of the particles. It should be noted that a similar conclusion about flushing velocity (0.65-2.3 m s −1 ) and washed out mass of particles has previously been observed (Carriere et al, 2005). Analyses of the impact of daily maximum velocity on washed out mass of particles normally should be done by applying a careful hydraulic analysis using a "bottom-up" demand allocation principle, e.g.…”

“…The quantities of particles in our study were higher compared to the data from literature. The mass of about 0.0001-0.04 g m −1 was found to be present in four different Canadian networks (Carriere et al, 2005). The quantity of particles described by the other authors was even smaller: 0.00008 g m −1 (Jonas and Murphy, 2002) and 0.026 g m −1 (Delanoue and McMath, 1997).…”

The use of high resolution monitoring in the management of water quality failures caused by discolouration

“…This crumbling of bulk sediment would probably be observed as sediment mobilisation without any need for an additional external shear (or hydraulic disturbance). If this is true, as suggested by the weak correlation between hydraulic disturbance and turbidity, it would then explain why discolouration risk tends to be less predictable, as desired, since the risk of quality failures still lingers even after "maintenance" by flushing or pigging as observed by previous studies (Gaffney and Boult, 2011;Carriere et al, 2005).…”

Microbial Growth in Drinking-Water Supplies: Problems, Causes, Control and Research Needs

“…First, this clouds the effective end point of a flushing when this is defined in the form of a turbidity threshold. Carriere (2005) explicitly reports a stop criterion for flushing of 1 FTU, but at several locations, values below 5 FTU could not be reached. Probably the effective removal of sediment from the pipe has stopped, but the water used for flushing has a turbidity of 5 FTU.…”

“…Although deposits are usually mostly mineral in nature, they may include variable fractions of organic matter Carrière et al 2005), and they may be heavily colonized by micro-and macroorganisms ). • shield microorganisms from disinfectants (Morin et al 1999) and exert a high disinfectant demand.…”