Next time you flush a toilet in Whangarei, you could be helping to save ratepayer money and enlighten local farmers to a better way of dealing with effluent.
A new unit at the city's wastewater treatment plant will use methane - a byproduct of the sewage treatment process - to generate electricity. This power would be used to run other processes at the plant, said Whangarei District Council waste and drainage operations engineer Adam Twose.
The unit would also serve as a demonstration project for Northland farmers wanting to put similar technology to use with animal effluent.
"The electricity produced won't be enough to export to the grid because this site [the treatment plant] uses about 250 to 300 kilowatts all the time," Mr Twose said. "This process is only going to generate about 70 kilowatts, but that will save the council about $60,000 worth of electricity a year."
The WDC's Kioreroa Rd plant would soon see the installation of a General Motors 8-litre V8 en
gine next to its sewage digestors. The engine is similar to what can be found inside many American muscle cars and would form the basis of a co-generation unit, which produces useful electricity as well as the heat needed to "cook" sewage sludge as part of the treatment process.
"We cook the sludge at 37C for about 30 days, allowing the solids to break down," Mr Twose said. After this, the sewage sludge was dried and taken to landfill.
Mr Twose said sludge was now cooked using boilers, which ran off the methane this process produced - a self-contained process.