There is a caveat to biodigestion. The microorganisms involved require warm temperatures. Warmer than we have here in North America during the half of the year. So you have to provide some heat source to warm the digester, and this somewhat lessens the benefit. They use this method extensively in India where the temperatures are somewhat warmer year-round.
Now, if we only had some source of low level waste heat to do that. Hmm…..