N.C. regulators have approved Piedmont Natural Gas’ agreement to allow Optima BioEnergy to connect a proposed swine-waste biogas plant in the town of Tar Heel.

The approval issued Monday by the N.C. Utilities Commission clears the way for Wilmington-based Optima to start construction on its second biogas plant in eastern North Carolina. Duke Energy Corp. (NYSE: DUK), which owns Piedmont, intends to buy the gas from the OptimaTH natural gas plants at both its utilities in the Carolinas.