Most public libraries accept donations of books from the public on the condition that they are free to do as they see best with them. They may keep the encyclopedias or sell them to someone and use the proceeds to buy needed books.
State libraries may accept donations of encyclopedias as well. There are other organizations that accept donations, such as Books For Africa, which distributes books to people in need in Africa.
Books that are very damaged or unusable are likely to be disposed of. There are some encyclopedias for which there is such an abundant supply and/or the information contained within is so out of date that they no longer serve any useful purpose.