Paihia Wastewater Treatment Plant

The Paihia WWTP upgrade exemplifies our joint commitment to preserve the habitat of the endangered Northland Mudfish in the culturally significant Waitangi Wetland

What is the Paihia WWTP?

Paihia Wastewater Treatment Plant (WWTP) was originally constructed as a wastewater treatment pond, nestled between the Waitangi Forest and Waitangi Wetland to serve several Bay of Islands communities.

The plant is owned and operated by The Far North District Council (FNDC) and serves approximately 5,000 residents in the communities of Paihia, Waitangi, Opua and Haruru. In summer, this number can exceed more than twice that – nearly 11,000 people.

Since the 1980s, treated effluent from the ponds would discharge into the local stream and from there into the Waitangi Wetland, home to the endangered Waikaka (Northland Mudfish), a Māori taonga. The discharged effluent from the pond was threatening the health of the wetland and its habitats.

Given the threat to the native wildlife, the FNDC made it a priority to upgrade the Paihia WWTP in order to protect the taonga of the area.

Location

Northland, New Zealand

Client

Far North District Council (FNDC)

Project Value

Project value

Project Status

Complete

Client Goals

The FNDC had two main priorities: to protect the wetland and its valued ecosystem, and to meet resource consent in order to maintain stringent water quality standards. These standards are much stricter than what is possible to achieve through a historical pond design.

The project also faced landownership, topography and spatial, and affordability constraints with challenges from environmental and cultural considerations.

In addition, the exceptionally high compliance standards required specialist technology, which required extra consideration.

With the existing pond system achieving 40 mg/l ammonia in the effluent and a conventional upgrade priced at over $25M to achieve the challenging 2 mg/l ammonia consent standard, WSP and FNDC worked with Marshall Projects Ltd to deliver an innovative solution to achieve high effluent quality and for a lower budget.

WSP Solutions

Several technical options were considered, including conversion to an activated sludge plant, in-pond treatment with aquamats, construction of a new treatment plant, tertiary nitrifying treatment (a trial gave inconclusive results), and floating wetlands (which had insufficient local track record at the time of evaluation).

After careful consideration of the needs of the surrounding ecosystem and the requirements of FNDC, we adopted an innovative US-developed ‘Bioshell®’ technology, our team achieved this standard – plus other quality improvements – for $6.5M.

What if we safeguarded cultural treasures through kaitiakitanga and manaakitanga principles?

It was important to the project partners and the community that the cultural and ecological significance of the pond was not lost during the necessary upgrades. We were able to use the principles of kaitiakitanga and manaakitanga in order to safeguard the taonga unique to the whenua.

The result is conditions of consent providing robust protection to the Waitangi Wetland habitat of the Waikaka (Northland Mudfish).

What if we could breathe new life into New Zealand’s waterways? 

Together, WSP, Marshall Projects Ltd and FNDC cross-examined options that would ultimately achieve the highest environmental reward.

The alternative solutions to the Bioshell®’ technology was a new treatment plant on an alternative site. Our approach not only saw a cost reduction of over $20m but also a 70% reduction in embodied carbon. The Paihia WWTP is a great example of the success of a project when we prioritise wai and tāngata.

What if we cared for our water like we care for our whānau?

Keeping the Paihia community involved was crucial to the success of the project, so communication was a chief priority for the project team. Key milestones were set at contract award and communicated with the local community and iwi, Ngati Rahiri, and Ngāti kawa.

Benefits include

- Improved effluent quality protecting the local environment
- Long-term sustainable solutions, suitable for future growth
-Lower rates for the community
- Protection of the threatened Northland Mudfish population
- Affordable plant upgrades

What if by encouraging collaboration, we increase innovation?

The Paihia WWTP constraints (reusing existing assets, limited footprint, and low affordability) are common among many New Zealand communities. Commercially-available conventional technology was unable to provide a solution that fit the projects constraints and challenges - while also reducing nutrient levels in an existing pond system. Some innovative in-pond systems were considered, but these systems were not proven to achieve the level of ammonia removal required, nor perform at the consistency needed.

In order to craft the best solution, FNDC made the decision to encourage innovation from the supply chain. To achieve this, the project was open tendered with a non-prescriptive specification, with clear outcomes and sufficient flexibility to consider non-traditional methodologies.

The targeted requirements allowed the project team to develop the best solution possible while also providing fluidity in the project process. The specifications included desired project outcomes, core general standards for materials, asset life, electrical and control systems, but did not identify a specific solution. The result is that the chosen approach demonstrates excellence in procurement and encourages supplier innovation, while achieving above and beyond project requirements.

The Paihia WWTP upgrade exceeded our expectations to the delight of Council, Regional Council, and our communities. The innovative Bioshells have not only removed more ammonia but also removed total nitrogen, Biochemical Oxygen Demand suspended solids, and E coli in the discharge to the wetlands. The project was delivered to tight timescales committed to Regional Council and completed two months ahead of programme due to the approach adopted.

Tanya Proctor Manager Infrastructure Programme Delivery