Whanganui wastewater treatment plant solves odour issues after complaints from nearby business

Senior wastewater engineer Tony Hooper says odour issues from the wastewater treatment plant usually arise when the wind is easterly or southeasterly. Photo / Bevan Conley

Whanganui wastewater treatment plant staff have identified sources of an odour that has prompted complaints this year - primarily from neighbouring Mid West Helicopters.

Whanganui District Council senior wastewater engineer Tony Hooper told a council operations and performance committee meeting two parts of the process at the plant were causing the smells.

One was venting from the building that housed the plant’s drier.

“It also appears that a small amount of foul air is escaping the primary pond cover. We suspect there is a small tear,” Hooper said.

“If you get downwind of the primary pond, in just the right location, you can detect an odour.”

Hooper said a venting system had been installed in the building after the drier unit began leaking foul air. That system discharged into the environment.

“Originally it was discharging vertically but we’ve installed a bend on it so it goes out to the side and doesn’t have so much opportunity to travel off-site.”

If that failed, an additional biofilter or carbon filter package could be built to filter the discharge from the vent.

The process of replacing the biofilter media in the dryer unit was “part way complete”, Hooper said.

That would treat the foul air and make the environment in the building much better.

Biofilter media is an organic material that absorbs biologically and degrades odorous compounds.

Hooper’s report shows 14 odour complaints in 2023 - 12 of which came from Mid West Helicopters.

A complaint from Mid West in June said “things are very pongy here this morning. The drier and another pooey smell”.

Hooper said issues usually came when the wind was easterly or southeasterly because that blew the foul air in the direction of the airport.

A reduction in complaints over the past six weeks was probably down to a lot of westerly winds, he said.

Mid West was the plant’s closest airport neighbour and an easterly wind headed “directly for their hangar doors”.

The report said an odour fence was built along part of the western fence line of the plant in response to complaints that started in late 2021.

It was designed to deodorise any odours which left the site in that direction.

“This is still in operation although it seems that it is having little impact and we are evaluating whether to turn it off.”

Councillor Charlie Anderson said Mid West Helicopters wouldn’t make complaints “just for the hell of it”.

“The smell, when they get it, is real and it can last for a long time.

“I think Tony and the team are on to it.

“We look forward to clean air from now on and thank them for their diligence and concern to sort the problem out.”

The plant, which cost $40 million, has been in full operation since February 2019.

Mike Tweed is an assistant news director and multimedia journalist at the Whanganui Chronicle. Since starting in March 2020, he has dabbled in everything from sport to music. At present his focus is local government, primarily the Whanganui District Council.