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Capalaba Water Treatment Plant: Case Study

Zinfra Navigates Challenging Waters in Queensland

One of Australia’s largest water businesses Seqwater recently contracted Zinfra to complete three separate contracts at their Capalaba Water Treatment Plant. Initially winning the contract to upgrade and automate their Powder Activated Carbon (PAC) dosing plant, Seqwater awarded Zinfra further contracts to undertake two major upgrades as part of their Renewal and Refurbishment (R&R) program.

The water treatment plant at Capalaba, in the suburbs between Brisbane and the Gold Coast, Queensland, required the upgrade work to their established infrastructure to maintain compliance with ever-improving environmental and water quality standards, and to ensure the safe operation of their facility.

With the most geographically spread and diverse asset base of any capital city water authority, Seqwater’s operations extend from the New South Wales border to the base of the Toowoomba ranges and north to Gympie.

The main challenge facing Zinfra when delivering the works was the brownfield nature of the plant. Normal construction techniques had to be changed and shutdown methodologies developed to ensure limited impact to the normal day to day operation of the plant.

Zinfra Project Manager, Spencer Walmsley, commented “it has been great to be part of a project that increases the efficiency of the treatment plant and further enhances the water quality for the local Redlands community.”


“Developing methods and strategies to deliver our services, while limiting impact to operations has been at times a difficult task but has made the project more rewarding,” said Mr Walmsley.

In order to reduce shutdown times from over a week to just three days, and ensure Seqwater could continue to meet customer demand, temporary isolations at the inlet and outlets to the raw water pumps allowed time to install, align and pre-commission the new pumps prior to introducing them to plant operation.

By isolating one of the two operating clarifiers and filters, a significant portion of the scope of works could be completed while the system was still operating, including the DN700 replacement interconnecting pipework to connect both clarifiers to a single filter. Taking the filter and clarifier offline also allowed for the removal of the filter’s media and refurbishment of the internal walls and equipment within the filter prior to re-installing the replacement filter media.

With one filter taken offline a method was also developed to allow for the installation of the new filter outlet and below ground works, including removal and replacement of the filter building to house two new UV reactors (duty/standby). By taking a staged approach to the work, only two single shutdowns were required to allow for pipework replacement at the downstream chemical dosing chamber.

While this work was undertaken, the operational filter could temporarily maintain the magflow and ultrasonic flow meters including pH, pressure differential and turbidity instrumentation operation to ensure water quality and the accuracy of fluoride and chlorine chemical dosing could be effectively monitored by the Seqwater Operations team.

Due to the age and various prior upgrades over the years, the site has an assortment of equipment and pipework within it. One of the major challenges for Zinfra involved accessing and determining correct flange sizes, and verifying flange orientations and alignments, along with actual pipework sizes. Many variables were found when completing this important verification process which ensured that Zinfra was able to fabricate, order and change its equipment and methodologies to adapt to these variances.


Clients like Seqwater rely on service providers to bring innovative solutions and specialised knowledge to bear on their projects and operations. Zinfra has delivered a number of cost and time savings to the client through smart thinking and clever, collaborative problem solving.

During the tender process, Zinfra suggested reducing the depth of the new clear water storage tank scour line required to connect two tanks together. The design depth of the line was on average 2.5-3.0 metres deep, but by reducing this depth Seqwater benefited in the form of cost savings from increased productivity, and Zinfra reduced their exposure to high risk activities posed by trenches deeper than 1.5 metres.

Zinfra also identified the proposed design alignment required for the removal of a number of significant eucalypt trees, which would need relevant local government approvals. After investigation, Zinfra altered the design, reducing the overall length of the service from 140 metres to 115 metres and also aligned with an existing road, removing the need for tree removal.

The projects incorporated a number of chemical dosing system upgrades including alum dosing, polymer, sodium hydroxide and lime. The upgrades, to make the plant more efficient, moved the current dosing points to new locations or through the in-pipe static mixers, installed as part of the works.

Zinfra identified an opportunity to reduce the footprint of a new polymer dosing system that was to be installed in the old PAC dosing storage building, by providing a tank-on-tank batching system, coupled with the three off-dosing skids. This concept change provided Seqwater with a designated area for an emerging works project, either an acid flush system for lime or an upgrade to its service water system.

Off the back of these innovative solutions, Seqwater charged Zinfra with designing a new service water system, controlled by a pressure loop for the plant, to ensure that a 3.5-6.0 bar water pressure is maintained to service the plant’s existing service water needs as well as the increased demand of the polymer system, thereby resolving some existing lime and chlorine batching and dosing issues.

Delivery of the three projects at Seqwater’s Capalaba Water Treatment Plant represented a significant opportunity for Zinfra to showcase their capability in the water treatment plant sector.  As well as their ability to engage collaboratively with clients to deliver a high standard of work, Zinfra has shown they can problem solve and work nimbly to produce cost effective, safe outcomes for their clients.

Mr Walmsley attributed the success of the project to “a strong working relationship with Seqwater. Their onsite operators are easy to deal with and extremely helpful,” he said.