Dependency of bulk chlorine decay rates on flow velocity in water distribution networks

2003 ◽  
Vol 3 (1-2) ◽  
pp. 209-214 ◽  
Author(s):  
J. Menaia ◽  
S.T. Coelho ◽  
A. Lopes ◽  
E. Fonte ◽  
J. Palma
Keyword(s):  
Drinking Water ◽  
Flow Velocity ◽  
Distribution Systems ◽  
Distribution Networks ◽  
Decay Rates ◽  
Decay Kinetics ◽  
Decay Rate Constant ◽  
Chlorine Residual ◽  
Chlorine Decay ◽  
Static Conditions

Understanding chlorine residual decay kinetics and the factors that influence them are essential for such current tasks as siting chlorination facilities, dosage optimisation, choice of sampling locations and frequencies, and general design and operational control of drinking water networks, increasingly accomplished with the help of simulation models. Available constants for bulk chlorine decay are typically determined under static conditions. However, as for all fast reactions in water flows, chlorine consumption rates in drinking water pipes may be influenced by the existing mixing regimes, a function of flow turbulence, which is primarily controlled by flow velocity and pipe diameter. Flow velocities vary greatly in space and time in water transmission and distribution systems; pipe diameters are seldom uniform. Although both variables are readily available in the currently available network analysis simulators that implement chlorine models, such variations are not accounted for. Instead, a single preset decay rate constant is generally used for describing chlorine residual consumption throughout an entire system. In addition to highlighting how negligible PVC pipe wall chlorine consumption is, as such, this paper presents experimental evidence of a significant correlation between pipe flow velocity and bulk chlorine decay rates, and proposes a simple but effective approach to implement this dependency in current simulators.

An experimental study for chlorine residual and trihalomethane formation with rechlorination

2007 ◽  
Vol 55 (1-2) ◽  
pp. 307-313 ◽  
Author(s):  
J. Lee ◽  
D. Lee ◽  
J. Sohn
Keyword(s):  
Distribution System ◽  
Distribution Systems ◽  
Water Distribution ◽  
Disinfection Byproducts ◽  
Correction Coefficient ◽  
Empirical Power ◽  
Chlorine Residual ◽  
Chlorine Decay ◽  
And Control ◽  
Large Distribution

Maintenance of adequate chlorine residuals and control of disinfection byproducts (DBPs) throughout water distribution systems is currently an important issue. In particular, rechlorination can be a powerful tool in controlling adequate chlorine residual in a large distribution system. The patterns of chlorine decay and formation of DBPs due to rechlorination are different from those of chlorination; chlorine decay is slower and trihalomethane (THM) formation is lower with rechlorination. The present study evaluates whether existing predictive models for chlorine residual and THM formation are applicable in the case of rechlorination. A parallel first-order decay model represents the best simulation results for chlorine decay, and an empirical power function model (modified Amy model) with an introduced correction coefficient (ϕ1, ϕ2) is more suitable to THM formation.

scholarly journals Quantification of the bacterial community of drinking water-associated biofilms under different flow velocities and changing chlorination regimes

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Z. Tsvetanova
Keyword(s):  
Drinking Water ◽  
Flow Velocity ◽  
Biofilm Formation ◽  
Distribution Systems ◽  
Water Distribution ◽  
Culturable Bacteria ◽  
Drinking Water Distribution Systems ◽  
Biomass Removal ◽  
Water Chlorination ◽  
Flow Velocities

Abstract Microbial growth in drinking water distribution systems (DWDS) depends on a great number of factors, and its control represents a great challenge for management of these engineering systems. The present case study assessed the influence that a pair of factors—water chlorination and flow velocity—had on the biofilms formed in a model DWDS in 626 days. The culturable bacteria number and biomass of the biofilms developed under the flow velocities of 0.3 m/s, 0.5 m/s, 0.7 m/s and 1 m/s were determined during three consecutively applied regimes of water chlorination to 0.05 mg/l (in 380 days), 0.42 mg/l (in 46 days) and 0.14 mg/l free chlorine (in 200 days). The results demonstrated that biofilm formation was a prolonged process directly depended on flow velocity at drinking water chlorination to 0.05 mg/l. The increase in the water chlorination to 0.42 mg/l chlorine resulted in both the reduction in culturable bacteria number and biomass removal, but the bacteria killing and the biofilm removal were distinct processes. The biocide action of chlorine was faster and more effective than its biomass removal effect. The chlorine decreasing from 0.42 to 0.14 mg/l resulted in increasing the biofilm HPC densities, although the biomass removal process was still continuing. The study carried out contributes for better understanding the biofilm behavior in DWDS and demonstrates that biofilm formation could be managed within a DWDS through operational decisions on parameters that can be changed and controlled as flow velocity and chlorination to safeguard drinking water quality.

Prediction of chlorine and trihalomethanes concentration profile in bulk drinking water distribution systems from laboratory data

2003 ◽  
Vol 3 (1-2) ◽  
pp. 239-246 ◽  
Author(s):  
G. Kastl ◽  
I. Fisher ◽  
V. Jegatheesan ◽  
J. Chandy ◽  
K. Clarkson
Keyword(s):  
Drinking Water ◽  
Distribution System ◽  
Distribution Systems ◽  
Water Distribution ◽  
Laboratory Data ◽  
Water Distribution Systems ◽  
Optimum Level ◽  
Drinking Water Distribution Systems ◽  
Drinking Water Distribution ◽  
Chlorine Decay

Nearly all drinking water distribution systems experience a “natural” reduction of disinfection residuals. The most frequently used disinfectant is chlorine, which can decay due to reactions with organic and inorganic compounds in the water and by liquid/solids reaction with the biofilm, pipe walls and sediments. Usually levels of 0.2-0.5 mg/L of free chlorine are required at the point of consumption to maintain bacteriological safety. Higher concentrations are not desirable as they present the problems of taste and odour and increase formation of disinfection by-products. It is usually a considerable concern for the operators of drinking water distribution systems to manage chlorine residuals at the “optimum level”, considering all these issues. This paper describes how the chlorine profile in a drinking water distribution system can be modelled and optimised on the basis of readily and inexpensively available laboratory data. Methods are presented for deriving the laboratory data, fitting a chlorine decay model of bulk water to the data and applying the model, in conjunction with a simplified hydraulic model, to obtain the chlorine profile in a distribution system at steady flow conditions. Two case studies are used to demonstrate the utility of the technique. Melbourne’s Greenvale-Sydenham distribution system is unfiltered and uses chlorination as its only treatment. The chlorine model developed from laboratory data was applied to the whole system and the chlorine profile was shown to be accurately simulated. Biofilm was not found to critically affect chlorine decay. In the other case study, Sydney Water’s Nepean system was modelled from limited hydraulic data. Chlorine decay and trihalomethane (THM) formation in raw and treated water were measured in a laboratory, and a chlorine decay and THM model was derived on the basis of these data. Simulated chlorine and THM profiles agree well with the measured values available. Various applications of this modelling approach are also briefly discussed.

scholarly journals Modeling particle transport and discoloration risk in drinking water distribution networks

2017 ◽  
Vol 10 (2) ◽  
pp. 99-107 ◽  
Author(s):  
Joost van Summeren ◽  
Mirjam Blokker
Keyword(s):  
Drinking Water ◽  
Particle Transport ◽  
Distribution Systems ◽  
Water Distribution ◽  
Field Measurements ◽  
Distribution Networks ◽  
Particulate Material ◽  
Turbulent Pipe Flow ◽  
Shear Stresses ◽  
Drinking Water Distribution

Abstract. Discoloration of drinking water is a worldwide phenomenon caused by accumulation and subsequent remobilization of particulate matter in drinking water distribution systems (DWDSs). It contributes a substantial fraction of customer complaints to water utilities. Accurate discoloration risk predictions could improve system operation by allowing for more effective programs on cleaning and prevention actions and field measurements, but are challenged by incomplete understanding on the origins and properties of particles and a complex and not fully understood interplay of processes in distribution networks. In this paper, we assess and describe relevant hydraulic processes that govern particle transport in turbulent pipe flow, including gravitational settling, bed-load transport, and particle entrainment into suspension. We assess which transport mechanisms are dominant for a range of bulk flow velocities, particle diameters, and particle mass densities, which includes common conditions for DWDSs in the Netherlands, the UK, and Australia. Our analysis shows that the theoretically predicted particle settling velocity and threshold shear stresses for incipient particle motion are in the same range as, but more variable than, previous estimates from lab experiments, field measurements, and modeling. The presented material will be used in the future development of a numerical modeling tool to determine and predict the spatial distribution of particulate material and discoloration risk in DWDSs. Our approach is aimed at understanding specific causalities and processes, which can complement data-driven approaches.

scholarly journals Accumulation and modeling of particles in drinking water pipe fittings

2012 ◽  
Vol 5 (1) ◽  
pp. 47-57 ◽  
Author(s):  
K. Neilands ◽  
M. Bernats ◽  
J. Rubulis
Keyword(s):  
Drinking Water ◽  
Distribution Systems ◽  
Water Distribution ◽  
Distribution Networks ◽  
Particle Accumulation ◽  
Catchment Areas ◽  
Drinking Water Distribution ◽  
Online Measurements ◽  
Pipe Fittings ◽  
Pipe Geometry

Abstract. The effect of pipe fittings (mainly T-pieces) on particle accumulation in drinking water distribution networks were shown in this work. The online measurements of flow and turbidity for cast iron, polyethylene and polyvinyl chloride pipe sections were linked with analysis of pipe geometry. Up to 0.29 kg of the total amount mobilized in T-pieces ranging from DN 100/100–DN 250/250. The accumulated amount of particles in fittings was defined as J and introduced into the existing turbidity model PODDS (prediction of discoloration in distribution systems) proposed by Boxall et al. (2001) which describes the erosion of particles leading to discoloration events in drinking water network viz sections of straight pipes. However, this work does not interpret mobilization of particles in pipe fittings which have been considered in this article. T-pieces were the object of this study and depending of the diameter or daily flow velocity, the coefficient J varied from 1.16 to 8.02. The study showed that pipe fittings act as catchment areas for particle accumulation in drinking water networks.

Residual-chlorine concentration impacts the ecology of biofilms in drinking water pipes and their water quality response

2020 ◽  
Author(s):  
Katherine Fish ◽  
Paul Gaskin ◽  
Joby Boxall
Keyword(s):  
Water Quality ◽  
Drinking Water ◽  
Distribution Systems ◽  
Water Disinfection ◽  
Test Facility ◽  
Residual Chlorine ◽  
Internal Diameter ◽  
Shear Stresses ◽  
Chlorine Residual ◽  
The Impact

<p>Drinking water distribution systems (DWDS) are an engineered system designed to protect water quality during delivery from treatment works to consumers’ taps. Biofilms form on the vast internal surfaces of DWDS, impacting water quality by their activity and/or mobilisation into the bulk-water. Disinfection-residuals are often maintained in drinking water to mitigate planktonic microbial contamination (and associated water quality/health risks). However, the impact of residual-disinfection upon biofilms, and the subsequent unintended risk they may present to water quality, is unclear.</p> <p>To address this, an internationally-unique, temperature-controlled, full-scale DWDS test facility, fed with water from the local DWDS, was used to grow biofilms (for 28 days). The facility enables three simultaneous conditions to be run in replicate pipe loops (each ~200m long, 79mm internal diameter, PE100 pipe). Conditions studied were Low-, Medium- and High-chlorine regimes. Various water quality parameters were monitored throughout, biofilms were sampled every two weeks (n=5). Physical, chemical and molecular analyses were applied to characterise the matrix (structure and composition) and microbial communities (via analysis of bacterial 16S rRNA and fungal ITS genes) of biofilms developed under the different chlorine regimes. After growth, a “mobilisation” test was conducted simulating hydraulic changes that occur in DWDS. Biofilms from each chlorine regime were exposed to increasing shear stresses to determine any water quality degradation as a consequence of biofilm mobilisation.</p> <p>High-chlorine residual concentration during development reduced biofilm bacterial concentrations but increased inorganics and selected for unique bacterial and fungal communities. Ultimately the biofilms developed under a High-chlorine residual resulted in the greatest decrease in water quality, in response to mobilisation, and the Low-chlorine regime resulted in biofilms which had the lowest impact on water quality. These unanticipated findings suggest chlorine-boosting should be considered carefully and may actually exacerbate water quality issues. The derived understanding could impact the long-term management of DWDS water quality and biofilm, whilst challenging the current mind-set of continuous residual-disinfection control strategies.</p>

Bench scale investigations of bacterial regrowth in drinking water distribution systems

1998 ◽  
Vol 38 (8-9) ◽  
pp. 275-282 ◽  
Author(s):  
P. J. Ollos ◽  
R. M. Slawson ◽  
P. M. Huck
Keyword(s):  
Drinking Water ◽  
Ductile Iron ◽  
Distribution Systems ◽  
Water Distribution ◽  
Water Distribution Systems ◽  
Support Surface ◽  
Drinking Water Distribution Systems ◽  
Chlorine Residual ◽  
Drinking Water Distribution ◽  
The Impact

Laboratory reactors operated under conditions relevant for drinking water distribution systems were used to examine the impact of support surface, chloramine residual, biodegradable organic matter (BOM) concentration, shear, and temperature on the growth of heterotrophic microorganisms. In terms of both heterotrophic bacterial growth-supporting and corrosion characteristics, mild steel and stainless steel/polycarbonate substrata bracket metallic pipe materials, such as ductile iron. Results of gradually increasing disinfectant dosage studies suggest that a 0.5 mg/L free or combined chlorine residual on polycarbonate surfaces, and 0.5 mg/L free chlorine or 2.0 mg/L combined chlorine residual on ductile iron substrata would be needed to reduce biofilm HPC numbers to approximately 103 CFU/cm2. Regression analysis suggests low or very low correlation between biofilm and suspended HPC numbers.

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