Public libraries ususally don't want the books. They already have sets of encyclopedias and have no more room for others. Donate them to a school, church with a library, Good Will, Salvation Army, second hand book store, second hand store with assorted merchandise, flea market sale, garage sale. Give them to a neighborhood child less fortunate, take them to a charity that distributes to the needy. Don't throw them away. Someone somewhere would be glad to take them off your hands.

I sold mine but had to include the book case with sliding glass doors otherwise nobody wanted them. And, they go CHEAP.