The city of Ft. Worth, TX, has signed a contract with one of the state’s new competitive energy suppliers that will save it an average of $1.1 million a year over a 20-year period.

TXU Energy Services (Dallas, TX) will operate and maintain a pair of 5.2-MW generators at the city’s Village Creek wastewater treatment plant, which treats 166 million gal per day. The turbines will use a “free” fuel source — the methane produced at the plant — to generate about half the electricity needed to operate the facility. Eventually, when power demand at the plant is low, it could sell electricity back to the local electric utility. A key element to the deal is that Village Creek is one of the few wastewater treatment plants in the nation able to interconnect with a transmission system.

The turbines replace 40-year-old internal combustion engines that had supplied about 30% of the plant’s power needs. TXU Energy Services, which will manage the new generators, guarantees that the turbines will operate 96% of the time.