A $17million upgrade of the Helensville Wastewater Treatment Plant has vastly improved the quality of the treated wastewater and means the plant is better able to cope with peak flows in wet weather.
The upgrade includes New Zealand’s first installation of a ‘membrane aerated biofilm reactor’ – relatively new technology
for the biological treatment of wastewater.
Our technology innovation manager Kevan Brian says the old plant, which had featured an oxidation pond and ultra-filtration, wasn't consistently meeting consent requirements for the level of ammonia in the discharge. An abatement notice was issued by Auckland Council in late 2021.
“We needed to change something and we needed to do it quickly,” he says. “We’d been trialling a membrane aerated biofilm reactor (MABR) at our innovation centre at the Māngere Wastewater Treatment Plant, so while it hadn’t been done before in New Zealand, we already had the data to give us confidence that it was the right solution for Helensville.”
Inside the MABR tanks is an army of bugs that eats the carbon in liquid wastewater and reduces the amount of organic compounds and ammonia nitrogen.
“These bugs need oxygen to survive, so we pump air in to keep them happy and healthy. In the MABR, membranes hang down inside the tank like spaghetti – and the bugs cling to the membrane surface. We pump air in, and oxygen diffuses through the membrane surface. Because it diffuses oxygen, it uses about four or five times less energy from pumping than a traditional aerated bioreactor.”
The technology went into service in April and has been closely monitored as part of the commissioning process.
Brian says the MABR’s performance is exceeding expectations.
“It’s significantly outperforming the design standards, which is excellent to see,” he says. “We’d targeted a reduction of ammonia to 10mg/L, which is still below our consent requirements, but its actual performance sees ammonia levels in the treated wastewater about 1.4mg/L. Ultimately it means we’re now discharging much higher quality treated wastewater to the Kaipara River.
“The technology also has other benefits – it's much cheaper than a membrane bioreactor would have been, it's quieter, it has a smaller footprint and it reduces the greenhouse gas emissions from the biological treatment process by up to 50%.
“I think there’s a strong case for further rollouts of this technology around the country, as it’s particularly suited to small treatment plants where oxidation ponds are not consistently meeting the necessary standards.”
The treatment plant’s upgrade also included additional ultra-filtration capacity, the installation of a standby generator to keep the plant running during power outages or surges and work to strengthen and restore the capacity in the oxidation ponds by reinforcing the embankments.
Our project manager Tony Morley says the urgency of the project meant a different approach was needed.
“Because we were fast-tracking this project, the designer, contractor, and supplier had to work together to agree who could most efficiently detail the design. This resulted in our contractor detailing up elements of the design to maintain the tight construction programme. In this case it worked well, because we had a lot of expertise in-house, with Kevan and our operations team working closely with our contractors, suppliers and consultants.
“We used off-site fabrication to speed up the pace of construction, with the construction team focussed on the on-site works,” Morley says.
“The two MABR tanks were built off-site and installed in just one day – with no concrete platform and no piles. This worked really well because the site has very little space, being squeezed between the Kaipara River and the oxidation ponds.
“We’d like to sincerely thank all of our partners for helping us deliver this project on time and under budget – particularly our design partners Beca, delivery partner Brian Perry Civil and Veolia, who supplied the MABR technology that’s working so well.”
The plant treats wastewater from about 1600 homes and businesses in Helensville and Parakai.