by Selwyn Manning

A $450 million sewage clarifier project is now underway at Manukau’s Mangere Sewage Purification Works.

The upgrade is designed to biologically remove organic and chemical nutrients from the raw sewage generated by over a million Aucklanders after treatment in new screening and settling tanks.

Six reactor clarifiers are expected to be more efficient than the current four tanks which work on a less efficient fixed-growth-reactor system.

Eventually there will be nine new reactor clarifiers at the site. This will be able to extract up to four times the wet sludge that the fixed-growth-reactors are currently capable of processing.

Watercare Services says the new treatment plant will go a long way towards improving the quality of the treatment effluent discharged into the Manukau Harbour.

To date, Aucklanders produce up to 285,000 tonnes of sewage a day. Once the upgrade is complete, effluent will be treated by the new reactor clarifiers, then it will be filtered by ultra-violet light to kill organisms, bacteria and viruses. It will then run to a point near Puketutu Island in the Manukau Harbour, where it will be released into the harbour twice a day at a rate of 25 tonnes a second.

The new upgrade should be fully operational by 2002.

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