A new sludge minimization facility (SMF) proposed for Wellington takes a step further today, following the unanimous approval of the business case by the mayor and councilors of the City of Wellington.

The new facility is an important and critical investment in Wellington’s future. It will reduce the massive flow of sewage sludge to landfill by more than 80% and help the Council meet its targets of halving its emissions by 2030 and becoming a net zero carbon capital by 2050.

Infrastructure Manager Siobhan Procter says the current sludge management process is unsustainable and a new solution is imperative.

“Existing permits at the South Landfill expire in June 2026, and a new sludge management solution is required to support the approval of the new landfill extension.

“If we don’t provide a sludge treatment solution in Wellington, we will have to truck the raw sludge to the Bonny Glen landfill in Manawatū. This would significantly increase the environmental impact due to resulting odors and carbon emissions, as well as the increased environmental risk associated with loss of containment during transport.

SMF Project Technical Director Chris French says the Council carried out a rigorous options assessment and economic analysis before arriving at a preferred option – a thermal hydrolysis, digestion and thermal drying plant located at Moa Point.

“We engaged independent technical experts to identify a long list of 25 potential options, which were then shortlisted from the remaining four options. A multi-criteria analysis was conducted to compare function, whenua mana values, complexity, environment, and cost. The shortlisted options were then subjected to a cost-benefit analysis and were evaluated based on their strategic fit, community and business needs, value for money, affordability and whenua mana values.

“The thermal hydrolysis, digestion and thermal drying process works by using heat to break down large molecules. This is followed by anaerobic digestion, which reduces the total mass of sludge to a stable product that is easier to dewater or dry.

“The process mimics a process of accelerated natural decomposition of waste. The result is what is known as a Grade A biosolid product, which contains few pathogens and offers multiple opportunities for reuse in a circular economy. It also produces biogas which is captured for bioenergy production.

Wellington City Council has worked with Crown Infrastructure Partners (CIP) to roll out a new funding tool made available to local authorities under the Infrastructure Finance and Finance Act 2020. The financing tool is administered by the CIP and makes it possible to raise private capital for new infrastructures. .

The SMF project will return to the Board in December 2022 for final funding approval.

The Council is now preparing to file the necessary resource permits, after which the public will have an opportunity to comment on the facility. The Council will also host a walk-in public session, where community members can talk to the project team.

Physical site works are expected to be underway in early 2023.

Learn more about: www.wellington.govt.nz/sludge

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