Whanganui District Council still grappling with odour issues at wastewater treatment plant

The wastewater treatment plant near Whanganui Airport. Photo / NZME

Odour continues to escape from the city’s wastewater treatment plant despite continued mitigation efforts by the Whanganui District Council.

A report from the council’s senior wastewater engineer, Tony Hooper, acknowledged the impacts of the odour on nearby businesses, particularly Mid West Helicopters - the plant’s nearest neighbour.

He told the council’s operations and performance committee the feeling had always been that the plant’s dryer and primary pond were the sources of the odour.

The dryer was recently shut down for two weeks after correspondence with its maker, German company Haarsleev.

“We looked at the air circulation system and found two significant issues,” Hooper said.

“They have been corrected and I’m pleased to report that it’s made the environment in that dryer building, I would estimate, 70% to 80% better than it was beforehand.”

Hooper said 17 small holes in the plant’s primary pond cover had been identified after “a guy from Taranaki came down with a fancy camera”.

He said AEL (Aspect Environmental Lining), the maker of the cover, visited the site this week and would return in a few weeks to fix them.

Last year there were 14 odour complaints - 12 of which came from Mid West Helicopters.

Hooper’s report said media in the dryer’s biofilter was replaced last year but, while airflow had improved, it had not translated into less foul air escaping the dryer.

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

In March this year, rubber seals around the dryer doors were replaced to prevent steam and air from entering the building environment but that had very little effect.

There is funding in the council’s budget for odour treatment in the 2025/26 financial year.

Whanganui district councillor Charlie Anderson. Photo / NZME

Councillor Charlie Anderson said the odour was a serious health and safety issue and asked if the smell would continue until then.

Hooper said the worst case scenario was “we would have to purchase a unit that could treat the air and is designed to do that”.

“I’m hopeful that just installing a small-scale filtering system in the ducting means we won’t have to.

“We are going ahead with that in the next few weeks.”

Hooper said purpose-built odour treatment equipment - a scrubber - would cost between $100,000 and $200,000.

His report said staff had recently found only one other belt dryer in the country - operated by the Christchurch City Council.

“I have contacted them and am very keen to organise a day trip [with two of our operators] to have a look at their operation and see if they have similar issues to ours and, if so, how they overcome them.”

Staff were planning to shut down the dryer for a month in September/October and “go through every aspect”.

“We are confident that once the issue is accurately understood the matter will be resolved,” the report said.

“The challenge is in getting to that point, which ultimately requires a ‘trial and error’ approach.”

Councillor Rob Vinsen said the dryer “wasn’t an uncontroversial purchase” when the plant was being built.

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

“Some engineers said you don’t need it,” Vinsen said.

“Have you actually considered not operating the dryer? Would there be an advantage?”

Hooper said putting sludge through the dryer reduced it by five or six times.

“The fact we put it through a dryer and it goes through those heat extremes means you can do more with it as a finished product as well.

“When you put [sludge] through a decanter and you’re just removing some water, you’re not actually treating any bacteria in there.”

Mike Tweed is a 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.