Snells Beach Wastewater Treatment Plant sets new benchmark for Auckland’s wastewater infrastructure

Watercare has officially opened the Snells Beach Wastewater Treatment Plant (WWTP), a landmark project that sets a new standard for wastewater management in New Zealand. The opening marks a major milestone in Watercare’s NZ$450 million programme to transform wastewater services for the communities in Warkworth, Snells Beach and Algies Bay.

Mott MacDonald’s multidisciplinary team played a crucial role in the design and build of the new plant that was designed to accommodate population growth over the next 35 years. The state-of-the-art facility is treating the community’s wastewater using a new advanced membrane bioreactor (MBR) system, a high-efficiency treatment system that uses a membrane filtration system to produce higher quality effluent compared to traditional systems.

Delivering comprehensive engineering services across structural, process, mechanical, geotechnical, civil, architectural, electrical and building services engineering, as well as construction monitoring throughout construction phase, Mott MacDonald were a key part of the project’s success.

A collaborative effort between Watercare, Mott MacDonald and contractors meant the construction progressed while design was still underway ‒ all while enhancing environmental outcomes. As part of the detailed design phase, Mott MacDonald worked with Watercare to identify embodied carbon hotpots on the project, and design these out, leading to significant reductions in greenhouse gas emissions.

Embodied carbon was then tracked throughout the design process using Mott MacDonald’s Carbon Portal solution. This data allowed carbon to be factored into the decision making alongside the cost and programme drivers, resulting in an approximately 20% reduction in carbon emissions.

A key consideration was to design for scalability to meet the needs of the growing population in the area. The plant is expected to begin full operations later in 2025 and will process all Warkworth’s existing wastewater. Capacity upgrades will be timed with future population growth. This approach defers construction and equipment costs, and reduces passive wear and maintenance on unused equipment, improving long-term operational efficiency.

Nick Dempsey, Mott MacDonald project principal and technical director for water said: “The Snells Beach WWTP project showcases the depth of expertise across Mott MacDonald. From process and electrical design to civil and structural engineering, the team brought together multiple disciplines to deliver a truly integrated solution for the local community. Congratulations to the whole team for all your hard work over the last five years.”