While it’s not on the scale of the largest wastewater treatment plant in the world – that honour belongs to Egypt’s Guinness record holding Bahr El Baqar – the Pukekohe Wastewater Treatment Plant is NZ’s most sophisticated wastewater treatment plant to date.
The project converts the WWTP from a batch process using Sequence Batch Reactors (SBRs) to a Continuous Flow Facility, doubling the capacity of the plant within the confines of the existing plant. For the sake of sustainability and cost efficiency, the plant’s design re-used as much of the existing infrastructure as possible, including taking the plant’s existing two main SBR tanks offline and then refurbishing them as continuous flow reactors with new dividers. Rather than a ‘filling, treating, emptying’ regime of a SBR-based plant, the new plant takes flow continuously through a new inlet works and Activated Sludge Reactors (ASRs) before the effluent to be discharged is separated from the solids by a new membrane facility. The clever design is also sustainable, utilising membranes from another water plant to reduce the project costs.
McConnell Dowell and Heb Construction constructed the Pukekohe Wastewater Treatment Plant for Watercare Services. As part of their approach, the MCD HEB JV undertook extensive value engineering, which saved $2M prior to construction. The team then continued their drive for efficiency throughout delivery. This included applying experience from the team’s successful delivery of the Mangere Biological Nutrient Removal facility to change the pipe methodology during construction.
The original design specified FRP pipe and gate valves, however the JV had already successfully used large diameter PE pipework on Mangere BNR and while more technically challenging than the FDR pipework, the team was confident they could deliver this solution for Pukekohe WWTP.
During construction, the team also saw the opportunity to change the specified valves to knife gate valves – providing an appropriate solution that was ultimately cheaper with a much lower carbon footprint. The overall result was a more robust, reliable and streamlined solution for the treatment plant and Watercare Services Ltd. When asked what is at the heart of Pukekohe’s success, Construction Project Manager Pete Hodgson says: “The biggest challenge on any project is getting the right people with the right team ethos working together from day one. In a large multi-discipline project the real magic in terms of innovation, efficiency, and quality happens when you’ve not only got the right technical skills, but when you’ve got all parties – the client, designer and constructor - in it together. That results in being willingly to listen to each other, willingly to be open and transparent, and willingly to examine ideas and concepts that may not initially have been considered.”
Both Pukekohe Wastewater Treatment facility and the Mangere Biological Nutrient Facility are great examples of our MCD HEB teamwork and collaboration and demonstrate the value we achieve for our clients and ratepayers through the right technical experience and a genuine passion and skill for working together. Starting in 2015 at the detailed design stage, we completed the first separable portion (comprising 85% of Pukekohe works) back in Jan 2021. We’re on track to deliver the project’s Sep Portion 2 in June 2022.
Learn more about the project here.
