At least one pig farmer in our area is benefitting from a waste product from Greek yogurt making: whey. This farmer mentioned to me recently that a local yogurt producer will haul over some whey (which the pigs apparently love to drink up) whenever she wants.
But I didn't realize the volume problem that the yogurt makers are encountering until I saw this NPR article about it. One whey disposal option, involving Cornell researchers, would turn it into biogas fuel. Until then, it goes to wastewater treatment plants, farmers who use it as a fertilizer component, and a few lucky pigs.