An automatic deodorising system has been added to the arsenal of actions employed to defeat the smell from Wanganui's wastewater treatment plant.
Yesterday in a press release Wanganui Mayor Annette Main acknowledged while the odour from the wastewater treatment plant is decreasing, it is still causing problems in some areas.
``I am pleased that the effort being put into addressing the odour from the plant is reducing the intensity, but we do know that there were still problems caused on Christmas Day in some urban areas.
``I thank everyone for their huge tolerance and support, especially those who are ensuring the message to visitors is consistent and positive about the temporary nature of the smell.''
Ms Main said she understood the ``timing of this has been very upsetting over a time when so many family and friends are visiting''.
In an update, Wanganui District Council infrastructure manager Mark Hughes said the main lagoon (pond) was relatively stable and had not given any significant issues of concern over the last two days.
``Oxygain lines have been raised and both the Oxygain treatment and bio-augmentation is continuing.
``This is being further supplemented by light sodium nitrate treatment introduced at Beach Road pumping station.''
The black scum production is decreasing and will be removed by sucker truck.
The main aerators are still switched off as the recently received waste is settling to the bottom of this pond and switching them on would tend to bring it back to the surface and potentially cause significant odour.
The oxygenating effect of the aerators is being replaced by the Oxygain and nitrate treatments.
However, the settling lagoon (pond) is not yet stable and ``continues to discharge some odour, but with a decreasing intensity and reducing frequency than over the previous weekend. The Oxygain lines have been raised and both the Oxygain treatment and bio-augmentation is continuing.''
Manual addition of sodium nitrate through the transfer from the main pond occurs twice a day every day.
Further treatment is added by boat when any adverse change is detected.
Mr Hughes said an automatic deodorising system has been installed at the transfer to the UV plant to reduce the odour from the UV plant and outfall.
``Both the transfer from the main lagoon and to the UV plant is being manually controlled and is currently set at 150 l/sec (25 per cent) to try and establish a steady state across the pond and help the recently received waste to settle.''
He said any changes to flow into the plant are being buffered by the main pond and scum is still forming and will be removed.
There were no new problems at the UV plant.
He said the inspection of the outfall was complete and did not show any structural problems. Some debris was removed during the inspection.