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Sathasivan A.,Curtin University Australia | Fisher I.,Watervale Systems Pty. Ltd. | Kastl G.,MWH Australia
Journal / American Water Works Association | Year: 2010

Microbial acceleration of chloramine decay (including nitrification) exacerbates the difficulty of maintaining an adequate disinfectant residual in chloraminated systems with long retention times. An adaptive management strategy based on the microbial decay factor (Fn) was developed to improve chloramine residual in a service reservoir (tank). The reservoir studied has a capacity of 404 ML and is not mechanically mixed. It undergoes continuous chemical, physical, and microbial stratification in summer but in winter is only microbially stratified. At the end of summer 2002-03 (southern hemisphere), signs of severe nitrification were observed. After careful consideration of control options, serial dilution was adopted, particularly in winter. The F m value resulting from this serial dilution was predictable from previous measurement of Fm in the reservoir and its inflow. Subsequently, an adaptive control strategy to maintain low Fm ensured that the reservoir was clear of severe nitrification for the next two years of evaluation.


Fisher I.,Watervale Systems Pty Ltd | Kastl G.,Level 3 Communications | Sathasivan A.,Curtin University Australia
Water Research | Year: 2011

Maintaining the chlorine residual is a major disinfection goal for many water distribution systems. A suitable general chlorine bulk-decay model is required for simulation of chlorine profiles in networks to assist disinfection planning/management efficiently. The first-order model is unsuitable due to inaccuracy and inability to represent rechlorination. Three potentially suitable, simple, reactant models were compared. The single-reactant model was found to be unsuitable, as it was inaccurate when restricted to using a single set of invariant parameters. The two-reactant model was more suitable than the variable-rate-coefficient model, although both models were accurate under the same restriction. The two-reactant model was then calibrated against datasets consisting of multiple decay tests for five distinctly different waters. It accurately predicted data reserved for validation over the chlorine concentration range of 0-6 mg/L, using a single set of invariant parameters, and is therefore the simplest, generally suitable model for simulating chlorine profiles in distribution system networks. © 2011 Elsevier Ltd.


Fisher I.,Watervale Systems Pty Ltd. | Kastl G.,MWH Australia | Sathasivan A.,Curtin University Australia | Jegatheesan V.,Deakin University
Critical Reviews in Environmental Science and Technology | Year: 2011

Effective disinfection planning and management in large, complex water distribution systems requires an accurate network water quality model. This model should be based on reaction kinetics, which describes disinfectant loss from bulk water over time, within experimental error. Models in the literature were reviewed for their ability to meet this requirement in real networks. Essential features were identified as accuracy, simplicity, computational efficiency, and ability to describe consistently the effects of initial chlorine dose, temperature variation, and successive rechlorinations. A reaction scheme of two organic constituents reacting with free chlorine was found to be necessary and sufficient to provide the required features. Recent release of the multispecies extension (MSX) to EPANET and MWH Soft's H2OMap Water MSX network software enables users to implement this and other multiple-reactant bulk decay models in real system simulations. © 2011 Taylor & Francis Group, LLC.


Fisher I.,Watervale Systems Pty Ltd | Kastl G.,Level Inc | Sathasivan A.,Curtin University Australia
Water Research | Year: 2012

Maintaining a chlorine residual is a major disinfection goal in many water distribution systems. A suitable general model of chlorine decay in the transported bulk water is an essential component for efficiently modelling chlorine concentration in distribution systems. The two-reactant model meets basic suitability criteria, including accurate prediction of chlorine residual over hundreds of hours, commencing with chlorine concentration 0-4 mg/L. This model was augmented with an equation that increases the decay coefficients with temperature according to Arrhenius theory. The augmented model was calibrated against decay-test data sets to obtain a single invariant set of parameters for each water. Model estimates of chlorine residuals over time closely matched decay-test data, over the usual operating ranges of initial chlorine concentration (1-4 mg/L) and temperature (3.5-28 °C). When the augmented model was fitted to partial data sets, it also predicted the data reserved for validation very well, suggesting that this model can accurately predict the combined effect of initial chlorine concentration and temperature on chlorine bulk decay in distribution systems, using a single set of invariant parameters for a given source water. © 2012 Elsevier Ltd.


Sathasivan A.,Curtin University Australia | Kastl G.,MWH Pty. Ltd. | Fisher I.,Watervale Systems Pty. Ltd. | Krishna K.C.B.,Curtin University Australia | Sarker D.,Curtin University Australia
Water Quality Technology Conference and Exposition 2011 | Year: 2011

Chloramine is widely practiced as a secondary disinfectant in many utilities, including that in Australia and US. Utilities face challenges in maintaining adequate disinfectant residual. Usually, nitrification is thought to be responsible for instability of residual and hence mostly measurement targets nitrification indicators. To prove/disprove this belief, the authors analyzed two different types of samples using the microbial decay factor (Fm) method: mildly and severely nitrifying samples. Microbial decay in mildly nitrifying samples was heavily dependent on total chlorine residual rather than nitrite levels in the sample and it took place without any signs of nitrification. In severely nitrifying samples suspected soluble microbial products accelerated chloramine decay much more than the process of nitrification, i.e. production of nitrite or subsequent drop in pH. Therefore, other processes were found to be more significant in accelerating chloramine decay than the nitrification process. For proper control of chloramine residual, measurement of chloramine decay characteristics is recommended. 2011 © American Water Works Association AWWA WQTC Conference Proceedings All Rights Reserved.


Sathasivan A.,Curtin University Australia | Bal Krishna K.C.,Curtin University Australia | Fisher I.,Watervale Systems Pty. Ltd.
Water Research | Year: 2010

Service reservoirs play an important role in maintaining water quality in distribution systems. Several factors affect the reservoir water quality, including bulk water reactions, stratification, sediment accumulation and wall reactions. It is generally thought that biofilm and sediments can harbour microorganisms, especially in chloraminated reservoirs, but their impact on disinfectant loss on disinfectant loss has not been quantified. Hence, debate exists as to the extent of the problem. To quantify the impact, the reservoir acceleration factor (FRa) is defined. This factor represents the acceleration of chloramine decay arising from all causes, including changes in retention time, assuming that the reservoir is completely mixed. Such an approach quantifies the impact of factors, other than chemical reactions, in the bulk water. Data from three full-scale chloraminated service reservoirs in distribution systems of Sydney, Australia, were analysed to demonstrate the generality of the method. Results showed that in two large service reservoirs (404 × 103 m3 and 82 × 103 m3) there was minimal impact from biofilm/sediment. However, in a small reservoir (3 × 103 m3), the biofilm/sediment had significant impact. In both small and large reservoirs, the effect of stratification was significant. © 2010 Elsevier Ltd.


PubMed | Watervale Systems Pty Ltd
Type: Journal Article | Journal: Water research | Year: 2012

Maintaining a chlorine residual is a major disinfection goal in many water distribution systems. A suitable general model of chlorine decay in the transported bulk water is an essential component for efficiently modelling chlorine concentration in distribution systems. The two-reactant model meets basic suitability criteria, including accurate prediction of chlorine residual over hundreds of hours, commencing with chlorine concentration 0-4 mg/L. This model was augmented with an equation that increases the decay coefficients with temperature according to Arrhenius theory. The augmented model was calibrated against decay-test data sets to obtain a single invariant set of parameters for each water. Model estimates of chlorine residuals over time closely matched decay-test data, over the usual operating ranges of initial chlorine concentration (1-4 mg/L) and temperature (3.5-28 C). When the augmented model was fitted to partial data sets, it also predicted the data reserved for validation very well, suggesting that this model can accurately predict the combined effect of initial chlorine concentration and temperature on chlorine bulk decay in distribution systems, using a single set of invariant parameters for a given source water.


PubMed | Watervale Systems Pty Ltd
Type: Journal Article | Journal: Water research | Year: 2011

Maintaining the chlorine residual is a major disinfection goal for many water distribution systems. A suitable general chlorine bulk-decay model is required for simulation of chlorine profiles in networks to assist disinfection planning/management efficiently. The first-order model is unsuitable due to inaccuracy and inability to represent rechlorination. Three potentially suitable, simple, reactant models were compared. The single-reactant model was found to be unsuitable, as it was inaccurate when restricted to using a single set of invariant parameters. The two-reactant model was more suitable than the variable-rate-coefficient model, although both models were accurate under the same restriction. The two-reactant model was then calibrated against datasets consisting of multiple decay tests for five distinctly different waters. It accurately predicted data reserved for validation over the chlorine concentration range of 0-6mg/L, using a single set of invariant parameters, and is therefore the simplest, generally suitable model for simulating chlorine profiles in distribution system networks.

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