Improving sludge management in water treatment

Image: North Pine Water Treatment Plant
Image: North Pine Water Treatment Plant

The North Pine Water Treatment Plant provides clean, safe drinking water for the northern Brisbane and Moreton Bay regions. When the plant required a sludge residue handling upgrade, local water utility Seqwater engaged Zinfra as its principal contractor for the design and construct job. Having consistently worked with the utility since 2013, Zinfra has a strong understanding of Seqwater’s needs and requirements, and was able to offer several innovative solutions, delivering project efficiencies and numerous savings for the bulk water authority.

The North Pine Water Treatment Plant project centred around the provision of two new centrifuges to dewater sludge extracted during the water treatment process. The centrifuges are located within a specialised dewatering building that also houses chemical dosing, solids storage, and water and air services, all of which are powered and controlled by the new Motor Control Cubical (MCC) for the facility.

In addition to the dewatering building and equipment, Zinfra upgraded the existing clarifiers and constructed a centrifuge feed tank, along with new pipework, electrical and control supply to all equipment, and road upgrades.

Efficiencies and strong collaboration result in limited operational impacts

All upgrade projects require some element of tie-in to the existing system that may result in significant impacts to plant operation.
Zinfra Project Manager, Spencer Walmsley, said that the majority of clients, particularly when it is a key asset such as the North Pine Water Treatment Plant, request limited interruptions to their daily operations.

“The project required six typical tie-ins, including high voltage power supply, service water, sludge inlet, sludge overflow, sludge disposal area (SDA) transfer pipeline and a final fibre optic/control integration. These were coordinated during existing planned shutdowns or completed with temporary bypasses. This resulted in limited operational impacts, in addition to all tie-ins being completed successfully and within the designated time frame,” Mr Walmsley said.

Zinfra also proposed a two-storey design for the dewatering building, where Seqwater had originally considered a split level building with significantly long conveyors (25m plus). This reduced the overall construction footprint, including reducing the amount of access roads and new fencing required.

Ensuring proactive and effective stakeholder management

Mr Walmsley highlighted that construction on any brownfield operational plant always brings challenges, but proactive and effective reporting and communication during the design and construction phases identified several unforeseen challenges early on.

“Zinfra involves delivery staff during design phases early in the process to ensure construction limitations, time periods, and most importantly safety are considered and form part of the solution. This helps facilitate the right design outcomes, saves time, reduces safety issues, and can highlight and resolve operational or access restrictions and issues early.

“Specific to the North Pine project, we established clear and transparent reporting along with routine progress meetings and numerous design workshops. In setting up these reviews and meetings to discuss and resolve issues being encountered or likely to be encountered, all parties were involved in the resolution strategies, culminating in the delivery of a successful project.”

Mitigating risks through consistent communication and robust procedures

Prior to site works commencing, progress meetings identified excavation and the potential presence of asbestos as two of the higher construction risks. To mitigate these risks, Zinfra and Seqwater developed a site specific excavation procedure to reduce the potential of damage to existing known and unknown buried services, utilising Non Destructive Digging (NDD) techniques to verify the perimeter of excavations deemed to be in high risk areas prior to mechanical excavation activities commencing.

While a review of the site’s asbestos register identified that workers were not likely to encounter asbestos, the potential risk was still highlighted and site testing was carried out during initial decommissioning and tank refurbishment works.

According to Mr Walmsley, 11 of the 12 samples taken during drying bed demolition works confirmed the existence of asbestos piping which was uncovered prior to demolition commencing.

“The area was demarcated and barricaded off, and on confirmation of the results, a licensed asbestos contractor was arranged to remove all Asbestos Containing Materials (ACM), with work re-commencing following issue of a clearance certificate,” Mr Walmsley said.

Overall, Zinfra showed strong alignment of its core values and safety non-negotiables with Seqwater’s policies and procedures, delivering exceptional project outcomes for the North Pine Water Treatment Plant.

We acknowledge the Traditional Owners of the lands upon which we operate and recognise their continuing connection to land, waters, and culture. We pay our respects to their Elders past and present.

Pictured: Artwork by Aboriginal artist Chern’ee Sutton from Mount Isa for our Group’s Reconciliation Action Plan.