Wastewater treatment plant turns waste to watts

The Village Creek wastewater treatment plant (WWTP) in Fort Worth, Texas, is on track to be completely powered by the waste it processes. The plant has been partially powered by its wastewater biosolids for the past 40 years. Through anaerobic digestion, the biosolids produce enough methane to supply about 30 percent of the plant’s electricity. A couple of years ago, the staff at the city’s water department realized the plant could produce more electricity by burning the methane more efficiently.

Staff members replaced the plant’s reciprocating engines with turbines, which are much more efficient at converting the methane into energy. Now the turbines are providing 20 percent more power to the plant than the reciprocating engines afforded.

In December 2000, McMillon signed a contract with Dallas-based TXU Energy Services to operate and maintain the turbines. The company also handles energy procurement — buying electricity from the grid or buying landfill gas — for the plant.

“The original idea was that we would install [the gas turbines], operate them and maintain them with our own forces. But we’ve always looked for opportunities to outsource non-core business functions in our water department,” says Robert McMillon, assistant water director, Fort Worth Water Department.

The primary goal at the plant is to be 100 percent self-sufficient. Village Creek has 10,000 kilowatts worth of gas turbine capacity, but it only has enough methane gas to produce about 5,000 kilowatts of energy. The city is hoping to tap methane gas at a nearby landfill for another 5,000 kilowatts, which would allow the plant to exceed its energy requirements.

Having excess energy to sell to the grid is the department’s secondary goal. The plant requires about two or three megawatts of energy at low demand periods and about seven or eight megawatts at peak periods. Theoretically, the plant would always have some energy to sell to the grid, thus supplying extra revenue to the city. By producing its own energy rather than having to buy it, the WWTP can avoid increasing rates.

McMillon says that he envisions savings of about half a million dollars annually. He expects that the $10 million project will pay for itself in 20 years. The city funded the project with a loan from the Texas Water Development Board.