In calf farms (for meat production) during life time of one calf, so per calf per life time:
1) 2220 KWh (Kilo Watt hour) energy in the form of dung produced, comes in fermentor.
2) Comes out from fermentor (intermediate is BIOGAS):
465 KWh electricity
370 KWh heat
3) Heat needed for fermentor it self 320 KWh
This is good news! Moreover calfs are sometimes in the meadow too, and sometimes in the cowshed, where the dung actual is collected.
In Holland (my country) there is a surplus of cow dung (manure). There is not enough land and meadows to spread the manure as fertilizer for plant growth. Not even when the fermentor has done its work, so derrie comes in, (also) derrie and biogas comes out. Manure is rich in nitrates and phosphates, there is already to much phosphate and nitrate in the soil, this also tends to leak to the underground drinking water storage (so storage in the soil). However the good news is this is a local Dutch problem only, all other countries, or lets say most countries, do not have this problem, there is more than enough land in the world to spread the fermentor treated manure as fertilizer, no phosphate and nitrate problem in the world.