Sewage plant revamp returns life to harbour

By PHILIP ENGLISH

Fish are jumping and birds are busy in front of the outfall from the Mangere sewage purification works as the plant begins work after its $450 million, five-year overhaul.

Previously, it would have been unheard of for fish like kahawai or mullet to be jumping at the site. For more than 40 years smelly and sludge-filled oxidation ponds excluded the sea from the scene.

Now, with the ponds gone as a major part of the upgrade, wildlife has been returning to the area beyond the predictions of planners involved in the project.

The upgraded plant, opened on Friday by the Prime Minister, Helen Clark, includes New Zealand's biggest coastal marine restoration project.

In total, 500ha of oxidation ponds have been returned to the sea and 13km of shoreline has been returned to the Manukau Harbour.

"It's all a good news story, I have to say," says Watercare Services projects general manager Derrick Adams.

"Wonderful" is the single word a kaumatua of nearby Makaurau Marae, Maurice Wilson, uses to describe how he and his people feel about the upgrade and to be included in the project, unlike their treatment when the plant was first constructed.

"It's still effluent. It's not drinking water but the effect on the receiving environment is minimal," says Mr Adams of the 286,000 cu m of treated wastewater that passes through the plant every day.

Watercare Services believes the effluent is treated to a higher standard than any sewage-treatment plant in New Zealand can achieve.

When the original plant was opened in 1960, treatment involved primary sedimentation and disinfection by the oxidation ponds.

A second level of treatment was added later in the form of an early biological breakdown process.

Now improved sedimentation remains as the primary level of treatment, followed by a state-of-the-art biological-nutrient removal process, filtration and ultra-violet treatment of the effluent to carry out the job of the oxidation ponds.

The old plant made about 100 tonnes of sludge a day. The upgraded plant produces 300 tonnes, destined for landfill.

The new outfall discharges the treated effluent twice a day at high tide.

Mr Adams says levels of viruses, faecal coliforms and nutrients have been reduced dramatically - in some cases by up to almost half those of the old treatment process.

Watercare Services is required to meet new effluent standards by October 1. Commissioning of the plant is continuing, but Mr Adams is confident the new standards will be met by the target date.

Mr Wilson says the foreshore is still not as clean as it was before the plant was opened, but the water quality of the area is improving to the point that it is starting to resemble what it was like 40 years ago.

"Our parents were humble people. In the days when the treatment plant was built there was little consultation from the authorities," he said.

"But the old people agreed to the building of the plant and its ponds because they believed it would improve the lives of fellow Aucklanders.

"Our old people gave up their traditional fishing and shellfish gathering grounds, their local beach and the Oruarangi Creek estuary where they launched their fishing boats. "In many ways they made the biggest sacrifice of all. Now our places are coming back to us ...

"When I heard the sound of the sea rolling back in after all those years it was truly a great day."

By October 1, Watercare Services will also have to ensure that there will be no more objectionable odours from the plant at its boundary. A nearby resident of 42 years, Jan Brinkman, says locals have put up with smells, noise and midges.

He is impressed by the removal of the plant's smelly sludge lagoons and oxidation ponds.

"That is a vast improvement."

Mr Brinkman believes, though, that the plant will always smell, just as it has done at times over the past week.

Timeline

Mangere sewage-purification works open.

1991: Auckland Regional Council votes down a proposal for a treated-sewage pipeline with an outfall in Manukau Harbour and ultimately the Tasman Sea.

1993: Watercare Services begins Wastewater 2000 consultation process.

1997: Resource consents granted after what is believed to be one of the biggest consultation processes in NZ.

1998: Construction begins.

April 2003: Works open.

What it does

The Mangere sewage-purification works treats the waste of about a million people from Auckland, Manukau and Waitakere Cities and Papakura District.

The plant handles a waste stream of 286,000cu m a day on average.

The treatment cycle at the new plant is about 13 hours, compared to 21 days at the old plant.

During construction 3.5 million cu m of sludge was removed from the old oxidation ponds.

About $150 million of the $450 million budget has been spent on removing the ponds and restoring the harbour and coastline.