KOKOMO, IN --- After months of working out problems, the city of Kokomo in Indiana is finally confident in its efforts to run some city trucks on biodiesel, the Kokomo Tribune reported. 

Back in February, the city's K-Fuel biodiesel program drew national headlines. It was a green initiative that sought to turn used restaurant cooking oil into fuel for city trucks. But the program ran into trouble when the fleet was hit by a rash of gummed-up fuel filters. By mid-June, the city had halted biodiesel production. 

The source of the problems was eventually discovered, however, by a laboratory in Ohio. Microorganisms living in the city's storage tank were the culprit. A fuel additive, similar to a fuel-injector cleaner, was applied to kill the microorganisms, and then contractors vacuumed the black sludge out of the tank once the dead microorganisms settled at the bottom. About 250 gallons of black sludge were removed. 

For the past several weeks, about 15 city vehicles have been running on a 20-percent biodiesel mixture. Since biodiesel starts to gel at a higher temperature than regular diesel, city officials said they plan to carefully monitor how much K-Fuel they add to the diesel reserve during winter months.