The best way to dispose of old books is by keeping them in circulation. There are a number of places to donate, buy, and sell used books in Philadelphia. Some of these resources sell used books to the general public, while others donate books to places that need them like public school libraries. In essence, the less books in the landfill the better.
Philadelphia Resources for Book Reuse
Philadelphia area Goodwills are always a good bet for donating many different items, such as books.
All Philadelphia Libraries accept book donations across the greater metropolitan area.
Locate a Salvation Army to donate your used books.