Personally, I think immolation – burning – is an elegant way of returning something to the world without taking space or requiring much effort. I know people have an aversion to burning books, bit I think the difference is similar to that difference between burying a loved one after they pass and burying an enemy alive.
If your city offers industrial composting, I’d compost your books.
Lastly, you can do any of these, including throwing books in the trash with a statement of gratitude. Mari Kondo advises that we thank or belongings for their service and then throw them in the trash.