Wastewater Aeration Basin to go Offline

The upgrade of the New Plymouth Wastewater Treatment Plant reaches a milestone next week when the first aeration basin goes offline on Monday (12 November).

One of the plant’s two aeration basins will be out of service for four months so that it can be emptied and upgraded as part of the Wai Taatari (‘Filtered Water’) project, which will enable the plant to meet the district’s needs for nearly 30 years.

“This stage of the upgrade will affect users of the sea in the area of the Waiwhakaiho outfall during these four months,” says Manager Water and Wastes Mark Hall. “We encourage people to take a precautionary approach to swimming or eating shellfish from this area.”

The basin needs to be taken offline so that it can be emptied, have its concrete structure modified, and have pipework and 2,500 diffusers installed.

During these four months only half of the incoming wastewater to the plant will be fully treated as usual. The other half will be screened to remove material that is larger than 3mm, disinfected, then mixed with the treated effluent before being discharged to sea via the Waiwhakaiho outfall.

“The mix of treated and disinfected effluent will be diluted rapidly by the sea, however there might be a slightly higher risk of skin irritation and illness among swimmers and other water users in the area,” says Mr Hall.

“There will also be a slightly higher risk of illness among those who eat shellfish from this area – we’re erecting warning signs at Fitzroy and Bell Block beaches recommending no shellfish be collected during this time.”

During the first week of the shutdown there might be odour issues from the treatment plant while solid material at the bottom of the aeration basin is dug up and removed.

“There is 20 years of accumulation in those basins – much of it seeds which we don’t digest and which have settled on the basins’ floor.

“Whether there is any odour will depend on the weather conditions and air temperature, how long the job takes and the amount of material we have to remove. We apologise in advance if there is any odour.”

While the basin is scheduled to go offline on Monday, the start could be postponed if there is a delay in the arrival of necessary equipment.

The second aeration basin will be taken offline next year once the upgrade of the first basin is completed and it is operational again.