Optimisation of Gold Coast City’s chlorine dosing system for the southern region distribution network

Chamberlain, Michael (2007) Optimisation of Gold Coast City’s chlorine dosing system for the southern region distribution network. [USQ Project]


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[Executive Summary]: Gold Coast Water (GCW) have identified that the existing chlorine disinfection system is not effectively servicing the extremities of the city’s water distribution network. This study was
required by GCW in a bid to resolve the issue.

The purpose of this study was to provide a recommendation on a near optimal disinfection solution for Gold Coast City’s Southern Regional potable water network based on the hydraulic behaviour of the system. Disinfection options were designed according to GCW’s internal product
specifications outlined in the Desired Standards of Service (DSS) water quality criteria.

Literature of the subject matter were extensively reviewed to determine how the two most widely used disinfectants, chlorine and chloramine, function in a distribution network as well as to determine the best approach to water quality network analysis and system design. Technical
studies for four common phases of chlorine network modelling were discussed in detail, these include the distribution of chlorine through a network, factors affecting chlorine decay, optimal selection of chlorine booster stations, and chlorine scheduling.

“H2ONET Analyser”, developed by MWH Soft, Inc. (1996-2003), was the chosen hydraulic modelling software for this study. GCW’s Hydraulic Network Model was last updated by Cardno MBK in October 2006. However, the model required further revision to incorporate more recent changes
including the Pressure and Leakage Management Project (PLMP).

In attempt to calibrate the model, field data was extracted from pressure loggers and online PLMP
monitors in PRV chambers. The outcome of the calibration indicated that model pipe friction coefficients did not require changing. The model was surprisingly accurate in simulating real time pressure and exhibited an average model error well below +10% over all field locations. This was verified with an alternative data set that also demonstrated an error well below +10%. A
sensitivity analysis undertaken on the Global Demand Factor (GDF) revealed that it was relatively
insensitive to small changes but did produce a better field curve when a GDF of 1 was adopted. An
Average Day demand was adopted for the model design runs.

The Tugun Desalinisation Plant, pipeline and off takes were incorporated into the model for all
design runs. Desalinisation will be activated late 2008 and will supply south of and including Burleigh and Reedy Creek Water Supply Districts (WSD). The model therefore needed to include Desalinisation to represent the future operating regime of the network.

Initial network analysis was undertaken using the future operating conditions to compare the distribution of chlorine and chloramine through the distribution system. It was found that chloramine survived much longer where a residual ≥ 0.2 mg/L could be achieved in 73.1% of the study area during a 2007 AD demand scenario. This equated to almost a 500% increase over chlorine distribution.

Design runs for chlorine and chloramine were undertaken for the study after analysing the system flows and determining the best locations for potential disinfectant booster stations. Boosters were located at storage reservoirs, where possible, to utilise their mixing capabilities. The design runs included continued disinfectant dosing at Molendinar and Mudgeeraba water treatment facilities and the Tugun Desalinisation Plant. It was found that chlorine required an additional 11 rechlorination stations while chloramine required only a single booster station.

The results of the project present sufficient evidence that conventional chlorine dosing does not
provide effective disinfection for Gold Coast City’s Southern Regional water distribution network.
Two solutions have been provided in this report that mitigate the existing disinfection deficiency
to an appropriate level. The number of booster sources required for Option 1 is not practical from
an operational and maintenance perspective even though ongoing costs were slightly lower. The initial capital costs for Option 2 are also much more practical. Therefore it is recommended that Option 2 be further investigated for future disinfection of the Southern Region potable water network. Given the future South East Queensland Potable water operating strategy (transfer of
water to and from Brisbane/Logan) and that Brisbane Water disinfect with chloramine, Option 2 appears to be a valid proposal.

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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: 17 Jun 2008 00:43
Last Modified: 02 Jul 2013 23:03
Uncontrolled Keywords: Gold Coast Water; Gold Coast City; chlorine disinfection system; southern region water distribution network
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
URI: https://sear.unisq.edu.au/id/eprint/4208

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