Auckland residents subjected to bad smells from sewage treatment plant and pipes

Bacterial problems at the Māngere sewage treatment plant in Auckland have caused bad smells for the nearby community. Photo / Martin Sykes

Hillsborough residents are the latest Aucklanders to kick up a stink about foul air, and wastewater managers are blaming the hot, dry summer.

The plight of the suburb on the northern shore of the Manukau Harbour, vented this week on social media, follows the pong on the south produced since early February by digestion problems at the Māngere Wastewater Treatment Plant.

"Was so strong this morning," wrote one member of a Hillsborough community page.

A Māngere resident told the Herald last month the foul smell had persisted for about a month.

"It stinks. We can't open the house and windows," the man said.

Watercare Services, which manages the treatment plant and the region's sewers, said the bad smells wafting outside the plant were caused by an upset in the balance of the various types of bacteria in the eight digesters. Bacteria break down solid waste in the digesters.

Asked today about progress in fixing the problem, a Watercare spokeswoman said the digesters are "continuing to return to normal operations". She referred the Herald to a statement on the Watercare website dated April 5 which indicated Māngere Bridge was in for "some odour" early this week, based on predicted winds.

Offensive odours drifting beyond the plant's boundary is contrary to its resource consents. It was a common problem before the large oxidation ponds in the harbour were decommissioned in a major, $450 million upgrading of the plant more than 15 years ago.

In respect of Hillsborough, Watercare's head of service delivery, Simon Porter, said there was a "slight odour" today.

The source was thought to be a wastewater "siphon" - a structure where the sewer dips down under the harbour before rising on the far side - at Hoskins Ave.

A siphon needs a vent. The foul air that comes out is put through a biological filter containing bark, scoria and earth. The filter media must be damp to work properly and relies on rainfall plus irrigation.

"As you will recall," Porter said, "it has been a long, dry, hot summer and steps have been taken to reduce odour levels by increasing irrigation at the siphon site.

"Further investigations are continuing in the coming weeks."