From what I have read, the digestion approach seems to be a decent alternatiive. In many instances, the gas is burned locally for energy rather than being captured for use elsewhere. Taking care to "not let the perfect be the enemy of the good," this seems like a pretty good alternative to incineration or spreading the waste on farmland. I've heard opposition to digestion on the grounds that it will help factory farms stay in business or grow but, personally, I don't think our agenda should expand tangentially to trying to put these operations out of business because it's unrealistic and perpetuates the status quo or a worse solution.