Pahiatua Wastewater Treatment Plant Upgrade and Wetlands

Background

Tararua District Council is upgrading the Pahiatua Wastewater Treatment Plant and constructing new wetlands to improve the quality of treated water before it’s discharged into the environment.

These projects are essential to ensure Council meets its wastewater discharge consent conditions set by Horizons Regional Council (the consenting authority under the Resource Management Act) and continues to protect the health of local waterways. Together, the upgraded treatment plant and new wetlands will create a more sustainable and environmentally responsible wastewater system for Pahiatua.

After years of careful planning, consultation, and collaboration with our iwi partners and stakeholders, the construction phase has now begun.

Why are we doing this?

Following a decision by the Environment Court and in line with consent conditions set by Horizons Regional Council, Tararua District Council have been directed to upgrade the Pahiatua Wastewater Treatment Plant to meet current and future consent standards. To comply with these conditions — which focus on reducing nitrates, phosphorus, ammonia, and suspended solids — a new Dissolved Air Flotation (DAF) plant and constructed wetland system will be built.

The wetland will work alongside the new DAF system, using natural processes to further remove nutrients before the treated water is released. This will significantly improve water quality and provide additional environmental and biodiversity benefits.

Once completed, the upgraded treatment system and wetlands will:

  • Improve the quality of treated wastewater entering local waterways.
  • Support biodiversity through the creation of wetland habitat.
  • Help ensure long-term compliance with environmental standards.
  • Contribute to a more sustainable and resilient wastewater network for Pahiatua.

About Dissolved Air Flotation (DAF)

The Dissolved Air Flotation (DAF) plant is a key part of the upgrade to Pahiatua’s wastewater treatment system. It improves how solids and nutrients are removed from wastewater before it enters the wetland for further treatment.

The DAF system works by dissolving air into the wastewater under pressure. When the pressure is released, tiny air bubbles form and attach to fine particles and suspended solids, causing them to float to the surface. These are then skimmed off, leaving much cleaner water behind.

This process is especially effective at removing:

  • Suspended solids
  • Phosphorus
  • Organic material
  • E.coli

About the wetland

The Pahiatua wetland system will include:

  • A Vertical Flow Wetland (VFW) – designed to remove ammonia from the treated water.
  • A Surface Flow Wetland (SFW) – which reduces nitrate levels and provides habitat for native plants and wildlife.
  • A biodiversity wetland area – enhancing local ecosystems and contributing to Council’s environmental sustainability goals.

Together, these components will create a more natural, resilient, and effective wastewater treatment process.

What to expect during construction

You may notice an increase in heavy vehicle movements around the site during earthworks and construction. Council and contractors will work to minimise disruption where possible, and any temporary road closures or access restrictions will be communicated in advance.

Health, safety, and environmental protection are top priorities throughout construction.

Stay informed

We’ll continue to share updates as the project moves forward.
Keep an eye on this page and follow Tararua District Council’s Facebook page for project news and key milestones.

Project milestones (subject to change)

  • October 2025 – Beginning of construction of wetlands and DAF
  • November 2025 – Beginning of Vertical Flow Wetland and Surface Flow Wetland construction
  • February 2026 – Wetlands completed
  • May 2026 – Planting of wetland
  • October 2026 – Commissioning of DAF and wetland

Frequently Asked Questions (FAQs)

The current treatment plant no longer meets modern environmental standards. To comply with wastewater discharge consent conditions set by Horizons Regional Council, Council needs to upgrade the system to improve the quality of treated water before it’s released into the environment.

The upgrade will reduce nutrients such as nitrogen and phosphorus, along with suspended solids and E.coli, helping protect local waterways and ecosystems.

DAF stands for Dissolved Air Flotation — a treatment process that removes fine solids and nutrients from wastewater. Tiny air bubbles are mixed into the water, causing impurities to float to the surface, where they’re removed.
This produces much cleaner water, which then passes through the wetland for final treatment before discharge.

Following a decision by the Environment Court and in line with consent conditions set by Horizons Regional Council, Tararua District Council have been directed to construct a Vertical Flow Wetland (VFW) and a Surface Flow Wetland (SFW) at the Pahiatua Wastewater Treatment Plant. A Biodiversity Wetland will also be constructed as the third and final step. The constructed wetlands use natural processes to further clean, and filter treated wastewater. They remove nutrients like ammonia and nitrates, improve water clarity, and create habitat for native plants and wildlife.

Wetlands are a sustainable, low-energy solution that compliment mechanical treatment systems like the DAF, providing additional environmental and biodiversity benefits.

The resource consents for the Pahiatua Wastewater Treatment Plant and wetland projects are managed by Tararua District Council and approved by Horizons Regional Council, which oversees compliance with regional water quality standards.

Once complete, the upgraded treatment system and wetlands will:

  • Improve the quality of treated water entering local waterways.
  • Help meet regional and national environmental standards.
  • Enhance local biodiversity and provide new wetland habitat.
  • Support a more sustainable and resilient wastewater system for the future.
  • Enable greater control of wastewater pond levels providing a necessary buffer for peak rainfall events.
  • Ensures a stable treatment process that is designed for urban growth which will benefit Pahiatua for decades.

Funding for the Pahiatua Wastewater Treatment Plant upgrade and wetland construction comes from Tararua District Council’s long-term plan and associated budgets for wastewater infrastructure.
The investment reflects Council’s commitment to maintaining essential services and meeting environmental obligations.

This project is a current consent requirement set by Horizons Regional Council and must be completed regardless of future changes to water services. Completing it now ensures Pahiatua meets environmental standards and provides a modern, compliant system that will transition smoothly to the new Water Services Organisation once it’s established.

No, wastewater treatment will not be affected while the upgrade takes place. The new Dissolved Air Flotation (DAF) system and wetlands are being added to the end of the existing treatment process, so the plant will continue to operate as normal during construction.

  • October 2025 – Beginning of construction of wetlands and DAF
  • November 2025 – Beginning of Vertical Flow Wetland and Surface Flow Wetland construction
  • February 2026 – Wetlands completed
  • May 2026 – Planting of wetland
  • October 2026 – Commissioning of DAF and wetland