Wastewater treatment ahead of capacity thanks to upgrades

As Mangawhai’s population continues to grow, including possible extra housing to be consented for Mangawhai Central, there is debate around the ability of the local wastewater plant to cope with the projected extra load. JULIA WADE was invited on a tour of the facility.

Operators and consultants for Mangwhai Wastewater Treatment Plant, along with Kaipara District Council GM Infrastructure Services Jim Sephton, want to reassure the community, saying ‘the plant is doing its job and will continue to do its job for the future’.

Kaipara mayor Dr Jason Smith and Kaiwaka-Mangawhai Ward councillor Peter Wethey joined the technicians recently on a tour of the plant, discreetly located behind the bushlands of Mangawhai Activity Zone.

Collecting sewage and grey water from 2000 local connections stretching from the Heads to the Domain, the state-of-the-art surprisingly odourless treatment plant, which is said to produce some of the best recycled reticulated water in New Zealand, efficiently turns 600 cubic metres of waste per day into clean product suitable for pasture irrigation and garden use.

WSP 3 Waters work group manager, Eros Foschieri, says 20 years ago when houses were on septic tanks ‘the harbour was polluted from discharge’ leaving it not fit for swimming.

“Then the plant was built and ten years later Mangawhai has grown and the harbour is clear… this plant is doing its job and we’re planning to keep growing it for the future,” he says. “A recent aeration upgrade gave Mangawhai an additional 1000 connections so the plant has a lot more capacity to serve more homes. We are also running a number of studies on catchment and other ways of disposal in the long-term with a key item being community engagement.”

Options for treated wastewater
By 2043 projected growth estimates the plant will eventually accommodate three times the current population, with 6000 connections hooked up to the system.

The aeration upgrade also expanded the dispersal field at Browns Road Farm to 65 hectares Sephton says, which puts the plant in ‘a very good place to keep providing the growing community with a clean environment’.

“In terms of the dispersal field, we’re actually on the cusp of switching from having to worry about how we get rid of the water to having a lot of people looking for good irrigation water… there are conversations taking place within the community such as the golf club and farmers who are keen to find a way to address the drought,” he says. “At the moment we’re developing a long-term plan and within that there a number of projects which will help the capacity of the plant to grow.”

Councillor Wethey says he understands the golf club is keen to look at the possibility of using the treated waste water.

“They can take advantage of the residual nitrogen, potassium and phosphorus in the treated water and diminish the artificial fertiliser they use several times a year… it’s a win-win.”

Sephton says the plant provides real opportunity ‘to have a lot of win-win situations’.

“The circular economy is a big part of infrastructure strategy going forward. Where the pipelines have been laid connecting the plant to Browns Road, there are a lot of farms and if we get the right conditions we can help with irrigation, which ties in with the work done around Kaipara Kai regarding land productivity,” he says. “It’s starting to come together really well.”

Capacity for Mangawhai Central
The prospect of a thousand new houses built at the Mangawhai Central (MC) development means some residents are concerned they might see history repeat by having to fork out for another new treatment plant in the years to come. Jim Sephton says ‘the timing of the plant’s improvements are always one step ahead of the growth’.

“We have always planned for the growth around Mangwhai Central, which was included in the district plan,” he says. “Every three years we review our long-term plan, introducing new efficiencies… and work with MC developers or any developers on introducing technology on how to keep waste in the pipe network a bit longer so that it can be controlled in terms of when it comes to the plant.”

Funding for the growth will come out of development contributions and the ‘user pays principle’ by way of targeted rates.

Wastewater technician Mike Jackson, who has worked at the plant for three years, says the plant can grow with Mangawhai.

“Studies show through long-term flow monitoring and population modelling that the volume of wastewater coming into the plant is going to significantly increase beyond the plant’s current capacity in the coming years, which we all know,” he says. “However the treatment plant is modular, meaning that the plant can simply be added on to.”

“The timing of the plant’s improvements are always one step ahead of the growth.”

- Jim Sephton

Mangawhai’s waste is in good hands. From left, waste water technician Mike Jackson, KDC GM Infrastructure Services Jim Sephton, WSP/OPUS team Eros Foschieri and Andrew Springer, Kaipara mayor Dr Jason Smith and councillor Peter Wethey, 3 Waters senior treatment manager Terry Roche, Civil Infrastructure NZ general manager Wendy Edwards, 3 Waters contract manager Johan Guy and waste water technician Dave Allan.

Clear waters of the Mangawhai’s state-of-the-art treatment plant; the waste water treatment team are confident that ‘the plant is doing its job and will continue to do its job for the future'.