As to recycling by restaurants, the US Army was one of the first to do this as a general practice, many decades ago. Many, if not all, Army Mess Halls had separate "garbage cans" marked "EDIBLE" and "INEDIBLE" and the orts were quite carefully separated. The Mess Hall was permitted/encouraged to SELL the "EDIBLES" to livestock feeders (mainly hog farmers), and could retain most of the proceeds to "augment" their official budget.

The practice was threatened some time ago by Dept of Agriculture rules that, in the US at least, required that all "hog food" be thoroughly cooked before serving, but appeared to survive that "new" demand, despite the requirement that the buyers certify their uses.

It may have been done in by the newer regulations on animal feed that have come into play due to "mad cow" and some other threats. It's more likely to have faded due to the increasing use of "contractor services" for many such functions (although I don't know that Blackwater has offered this particular one).

I don't know that it remains common now, although it appeared to be a net profit situation for the Mess Halls.

John