(Portland, OR)  --  Portland will be using gas from sewage to power city vehicles.  City commissioners voted unanimously yesterday to convert the methane released from the city's wastewater plant into compressed natural gas.  It's expected to produce enough to power more than 150 large trucks every year.  The 15-million-dollar project will create a system to do the conversion that should get the vehicles running by the end of next year.  Officials say it should save taxpayers money in the long run while improving air quality.