Investigation on the adequacy of disinfection in Toowoomba's water supply network

Huston, Thomas Clifford (2008) Investigation on the adequacy of disinfection in Toowoomba's water supply network. [USQ Project]


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[Abstract]: Toowoomba Regional Council (TRC) maintains a distribution network in the city of Toowoomba that provides drinking quality water to over 90,000 people. The quality of water throughout this network must be maintained to high standards according to TRC’s water guidelines. Adhering to these guidelines minimises the risk of harmful waterborne pathogens and microbial contamination within the water distribution network. Water quality monitoring is an everyday task of the TRC ground staff. Manual tests at set locations within each pressure zone are conducted on a regular basis to ensure that water quality is at an adequate standard. TRC have identified that the testing data obtained from these manual tests only give an indication of the chlorine residual levels at one location at one point in time. The only feasible method to analyse chlorine residual throughout an entire network is to construct a hydraulic model which enables chlorine residuals to be modelled at every point within the distribution system at all times of the day. The purpose of this study was to construct a hydraulic model that was able to identify low and high chlorine residual levels within the Platz pressure zone and the Trunk mains system based on the hydraulic behaviour of both areas. Options to rectify the problem areas that were identified were recommended to keep chlorine residual levels within the guidelines specified by TRC. “Pipes++”, developed by Watercom Pty. Ltd. (1990-2001), was the chosen hydraulic modelling software for this study. TRC’s Hydraulic Network Models for Platz pressure zone and the Trunk mains system were last updated in November 2000 and April 2001 respectively. The models required revision to incorporate more recent changes within the distribution network.

In attempt to calibrate the models, field data were extracted from SCADA data and pressure loggers within the Platz and Trunk main systems. The Platz model was accurate in simulating real time reservoir levels and exhibited an average model error well below ±10% over all reservoir heights. The Trunk mains model was accurate regarding modelled reservoir height levels and booster pump running times when modelled against field SCADA data. Chlorine calibration was achieved within the Platz model and was accurate to ±0.1 mg/L. The Trunk mains model was unable to be calibrated for residual chlorine due to the chlorinated bore water that is contributed to sections of the trunk mains system. An analysis of the existing water quality testing locations has been undertaken to identify the impact of the set water restrictions that are in place within the Toowoomba city during these times of drought conditions. Chlorine residual manual testing data results have been obtained from the time periods between 2000-2001 and 2007-2008. The data has been compared by analysing the bore, reservoir and consumer tap results of these 2 time periods to find the impact of the present low demand of the city. Literature of the subject matter was extensively reviewed to determine how chlorine, as the most widely used disinfectant, functions within a distribution network. Technical studies concerning the parameters that affect chlorine decay and modelling and software were also analysed and reported on accordingly. Design runs for chlorine were undertaken to analyse both the Platz and Trunk systems. Average day demand scenarios were used with initial chlorine residual levels ranging from the minimum of 0.4 mg/L to the maximum allowable chlorine residual of 2.5 mg/L. In doing this, plausible scenarios were able to be modelled and analysed. The Platz pressure model was found to have areas of both permanent and temporary low chlorine residuals. A booster chlorination facility was modelled to rectify the problem areas. The Trunk mains model was found to have no chlorine residual issues throughout the network.

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Item Type: USQ Project
Refereed: No
Item Status: Live Archive
Faculty/School / Institute/Centre: Historic - Faculty of Engineering and Surveying - Department of Agricultural, Civil and Environmental Engineering (Up to 30 Jun 2013)
Date Deposited: 12 Oct 2009 06:09
Last Modified: 02 Jul 2013 23:26
Uncontrolled Keywords: Toowoomba, Queensland; water quality; water quality improvement; chlorine disinfection system
Fields of Research (2008): 09 Engineering > 0905 Civil Engineering > 090508 Water Quality Engineering
Fields of Research (2020): 40 ENGINEERING > 4004 Chemical engineering > 400499 Chemical engineering not elsewhere classified

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