 GreenHunter Energy, Inc. has begun commercial operations at its biodiesel refinery in Houston, Texas, that can produce of biodiesel.That production capacity makes it the largest biodiesel refinery in the United States, barely beating out the biodiesel refinery built by Imperium Renewables in Washington.For comparison, the total U.S. production capacity for biodiesel reached in 2007, although poor market conditions held 2007 production to about , according to the National Biodiesel Board (NBB).