Council continuing to work on Wanganui plant's odour issues

The city's water treatment plant. Photo / Stuart Munro

Wanganui District Council is continuing work on odour issues at its troubled wastewater treatment plant while plans are developed for an upgrade.

Infrastructure Manager Mark Hughes said the odour was still affecting parts of the district at times, although the frequency and duration had reduced. He said odour emissions are not constant but vary due to several factors, the main one being the amount and make-up of waste that industries send.

The atomiser fence system has been upgraded with around 250 extra nozzles added to the original system and more planned over the next two weeks.

"While the atomiser fence is working well to reduce odour, it is set to cope with the level of waste we expect to receive. If additional, unexpected waste is received, as happened this week, the atomisers are not always able to reduce the odour sufficiently," Mr Hughes said.

In addition to six venturi-type aerators from the Central Hawke's Bay District Council, WDC has purchased and installed five new venturi-type aerators and refurbished two of the original aerators and installed them as well, making a total of 13 aerators running continuously on the inlet side of the aerated lagoon.

"This made a big improvement on the dissolved oxygen levels and helps to control the odour being produced and released by the sludge in this part of the plant," he said.

Dosing equipment had also been installed at the Beach Rd pump station to be able to add hydrogen peroxide to the influent to reduce unwanted odours in the incoming wastewater from reaching the plant.

"We have completed a third sludge survey of the wastewater treatment plant sludge levels and quality. The data from the two most recent surveys will be used to calculate how much sludge needs to be removed from the plant. We are in the process of generating all the necessary documentation and contracts to put this work out to tender next month with a view to commence sludge removal by September."

Development of the concept design is progressing to plan and Mr Hughes said the council expected to communicate an update in August.