It would unfortunately have to come directly from the producers or manufacturers, due to the possibility of tampering.
If this were cost-effective then it would already be happening since the conglomerates with both human and animal divisions would be eager to harvest the benefits and would have the economy of scale to work with.
Yep, you'd have to have a system in place where the food waste was picked up daily and delivered directly to the processing plant and then processed in a timely manner. It could be done but the logistics of it all would be difficult.
I doubt it could even be done at all.
To take my job in the deli as an example,
The first thing I will do tomorrow morning when I get in is check dates on the lunchmeat and cheese. I will pull out the ones that marked for that day and set them aside in a particular place on the counter -- still in all their wrappings, both the manufacturer's plastic wrap and our cling wrap, and with their adhesive paper tags.
I and others will also go through the items on the shelves and pull dates for sandwiches, deli salads, cheese trays, etc. and put them into a cart, again still in all their wrappings, that will be shoved into a corner until someone has time to deal with them.
I will then do other prep tasks for the day that are more urgent than scanning out unsalable meat and cheese -- cleaning, filling personal shopper orders, making party trays, etc. Eventually I'll weigh that stuff out and toss it into the trash with all the other trash.
During the day waste meat and cheese accumulates in a bucket next to the slicer, to be weighed out at the end of the day. Some of that meat will have been there in that bucket on the counter from as early as 6 am all the way up to 9pm.
During the day we will also peel and/or seed fruits and vegetables for various reasons, discard the heel ends of bread, drop random bits of stuff on the floor, etc. It all goes in the same trash. Even if we tried to separate it, there are still plastic adhesive labels on the fruit peels, and it would be a massive waste of time and effort for me to take my piece of parchment paper that I've used as a clean worksurface to prepare your pinwheel tray over to one can, shake the trimmings into that can, and then put the paper and my dirty gloves into a different can.
Real world, I scoop up everything inside the paper, trash it, dump my used gloves after it, and move immediately to my next task. I'm paid to make salable products and serve customers, not to sort trash.
To get all the waste from just the fresh foods department -- Produce, Deli, Bakery, and Meat -- you'd probably need at least two additional employees daily who did nothing but collect waste and they'd have to be ready to swoop in behind me and get those pinwheel trimmings before I bundled them out of the way so it wouldn't interfere with production.
I made friends with one of the ladies, whose Dad owns the supermarket I shop at. She has no problem giving me veggies that no one will buy anymore because they are iffy looking.
This is something that can be done on a very small scale in a high-trust community. It's quite impossible on a large scale.
The nature of human nature is that the worst employee makes the rules for everyone else. If we opened up the door for people to take the discards there would certainly be dishonest employees creating extra discards by falsifying dates so that they could sell them out the back door.
And someone would fake getting sick and sue the company for "allowing" an employee to engage in that dishonest practice.
