Bad-smelling gas has forced the temporary closure of Hastings' new wastewater treatment plant just six months after it opened.
The $27 million plant in Clive, about 10 kilometres from Hastings, was closed after the bacterial treatment process was found to produce greater than expected amounts of hydrogen sulphide - the gas which gives Rotorua its famous "rotten egg" smell.
The gas was produced by bacteria and other organisms in two large treatment tanks as they break down urban wastewater.
Hawke's Bay Regional Council compliance and pollution manager Bryce Lawrence said teething problems had been expected but the level of hydrogen sulphide produced was greater than anticipated.
"It is harmless at the levels being produced here, but it is quite a nuisance to those living nearby," he told The Dominion Post.
Engineers were modifying eight fans designed to suck bad odours from the tanks, and sewage would be diverted through the old treatment system in the meantime.
The plant closed on December 23 and will reopen on January 6.
