The latest measures taken by the Wanganui District Council to suppress the stench coming from the city's malfunctioning wastewater treatment plant appear to be working - at least in part.

Council infrastructure manager Mark Hughes said about 14 tonnes of lime slurry was applied to the ponds on Wednesday and yesterday an application of about 35 tonnes was dropped.

Mr Hughes said the lime was mixed in a slurry truck and applied by helicopter.

"As the lime works down through the ponds, it takes some of the suspended solids down to the sludge layer. It then settles on top of the sludge and prevents hydrogen sulphide gas from bubbling up through the liquid layer of the pond and releasing odour into the air. The lime dissipates after about 10 days with no long-term adverse effects."

Hydrogen sulphide is the gas that gives the ponds its rotten egg smell.

Mr Hughes said further work was being done at Beach Road pumping station to increase the amount of oxygen in the wastewater and to help take the pond's solid down to the bottom layer.

"There is still an odour but we believe all the measures are suppressing some of the smell," Mr Hughes said.

Meanwhile, next week new aerators will be installed, which Mr Hughes said would also help increase the level of oxygen in the upper layer of the pond.

Further lime drops would continue next week, he said.

- WANGANUI CHRONICLE