Dallas – Researchers at the airport here are examining the best way to use garbage as a power source. Officials are looking at three concepts from four different companies as a means to make use of Dallas Fort Worth International Airport’s 190 tons of garbage generated per day. One includes building a power plant, the other two propose using a natural-gas turbine engine or building a fuel cell, which would convert hydrogen into electricity. At $200 million, the natural-gas engine is the least expensive. The Dallas Fort Worth area has until 2007 to meet federal clean air mandates.