24 Jan 2018

The life and times of wastewater

From Jesse Mulligan, 1–4pm, 1:16 pm on 24 January 2018

A passport of a man seeking asylum is just one of the valuable items that have made their way to Mangere's wastewater treatment plant. The water that carries it there is itself an undervalued resource, says Watercare's Shane Morgan.

Mangere Water Treatment Plant

Mangere Water Treatment Plant Photo: Supplied

The wastewater that disappears down Auckland sinks and toilets first travels through a small PVC pipe to a central point at the property boundary, then passes through a collector sewer and a trunk sewer on its way to the Mangere plant – a journey that takes from 2 to 20 hours depending on location.

While most of the wastewater that goes to Mangere comes from houses, about 15 to 20 percent comes from commercial or industrial buildings, Shane says.

Once the water reaches the plant, Watercare's job is to cost-efficiently treat it so it's safe to be re-used as water or energy.

The first step in the process is sifting out 'debris', i.e. non-organic stuff such as passports that shouldn't go down the toilet, Shane says.

"There are a large number of small toys, false teeth – we had a gentleman come into the treatment plant trying to reclaim his false teeth once, wallets..."

Then the water is sterilised and pasteurised and good bacteria extracted for reuse in the treatment process or conversion into energy.

"We're farmers, essentially. We farm bacteria.

"We generate about 65 percent of our total energy needs from wastewater."

The solid material produced at the end of the treatment process – known as biosolids – is full of nitrogen and phosphorus and can be a great soil conditioner, Shane says.

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