It’s methane fermentation, so methane is the only carbon/energy source. Depending on processing, you end up with something similar to brewers yeast you find at some grocery stores or a more purified protein powder. For animal feed it would likely be the former. Inputs are methane, salts, water and electricity to the run the bioreactors. I assume there’s some amount of pure oxygen or nitrogen supplementation to reach the most efficient ratios.