Some people who are doing algae are using waste water from cattle as the feed stock for the algae. They are turning around and feeding the algae (without the oil) back to the cattle. This is a nice system from an ecology point of view. I don't know what it is from a nutrition point of view since they are extracting the oil and feeding the carbs back to the cattle so they don't get the Fatty Acids, but they would get the "green stuff".
I think what is clear is that we have single sourced our energy, we will have to change soon to multiple sources for our fuel. We need to make good choices which balance the ecology, economic, and social factors (feeding the world) it isn't going to be easy.
It's grandma, but you can call me sir.