Business Case for the New Sludge Minimisation Facility in Wellington Approved

The new facility is a huge and crucial investment in the future of Wellington. It will cut the amount of sewage sludge sent to landfills by more than 80 per cent and assist the Council in reaching its goals of halving its emissions by 2030 and becoming a net-zero carbon capital by 2050.

Chief Infrastructure Officer Siobhan Procter asserts that the current sludge management technique is unsustainable and that a new solution must be found immediately.

“The existing consents at the Southern Landfill expire in June 2026, and a new sludge management solution is required to support the consenting of the new landfill extension.

“If we don’t provide a sludge treatment solution in Wellington, we’ll have to truck raw sludge to Bonny Glen Landfill in the Manawatū. This would substantially increase the environmental impact due to the odour and carbon emissions that would result, as well as the increased environmental risk associated with loss of containment during transport.”

The Director of Technical Operations for the SMF Project, Chris French, states that the Council conducted a thorough evaluation of available choices and economic analyses before settling on the preferable option: a thermal hydrolysis, digestion, and thermal drying plant located near Moa Point.

“We engaged independent technical experts to identify a long list of 25 potential options, which was then shortlisted to four remaining options. A Multi-Criteria Analysis was conducted to compare function, mana whenua values, complexity, environment, and cost. The shortlisted options then underwent a cost-to-benefit analysis and were assessed for strategic fit, community and business needs, value for money, affordability, and mana whenua values.

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

“The process mimics an accelerated natural decomposition process of waste. It results in what is known as a Grade A biosolids product, which is low in pathogens and has multiple re-use opportunities in a circular economy. It also produces biogas, which is captured for bio-energy generation.”

Wellington City Council has collaborated with Crown Infrastructure Partners (CIP) to implement a new financial instrument made available to local governments by the Infrastructure Funding and Financing Act of 2020. CIP administers the financial instrument, which allows private funds to be mobilised for new infrastructure.

The SMF project will return to the Council for final financial approval in December 2022.

The Council is currently planning to submit the required resource consents, after which the public will be able to provide feedback on the facility. In addition, the council will organise a public drop-in session where community members can speak with the project team.

Source: Wellington City Council

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