Welcome to bird world. No matter how hard you try, you are always going to have at least some waste due to the fact that birds are such messy eaters.
I think the best you can probably do is some kind of feeder that has a pan underneath to help catch the wasted feed, so you can try to recycle it if its clean and dry enough.
I put a big washbasin type plastic bin I got at the dollar store underneath my hanging feeder, weighted with a big rock. It is about 24" in diameter and about 5" deep, and it does a pretty good job at catching most of what they waste. Even though the birds stand in it, and once in a while get a little poo in it, I find that most of the spilled feed stays clean and I can reuse it.
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