Dealing with moldy / mildewy antique books? USA

Hi all, I frequently buy antique books from estates that have not been kept in prime condition. So the books are mildewy and even moldy. I usually stick them in a plastic box with a box of soda to get rid of the smell and gently wipe the pages with a paper towel but I wonder if there is something else I need to do. Ideally something I can do myself for not a ton of money. I’m particularly concerned about mildew or whatnot spreading to other books in my collection. Thanks!