Lovers of old books are familiar with the musty, mildew smell that can accumulate on old volumes. Mildew is a form of mold that grows in damp, warm places. Because books are made of organic materials, they can absorb moisture from the air and harbor mildew. There's no need to dispose of musty books. Instead, take measures to freshen them up without damaging them.
Check your books for visible mold and mildew, which will appear to be a powdery substance on the pages or in the binding. To get rid of the mildew smell, start by getting rid of the mildew. Take the book outdoors and use a dry toothbrush to brush away any mold or mildew particles. Wipe affected pages with a damp cloth, and run over the covers and spine of the book gently with the cloth.
Prevent the mold and mildew from growing back by drying out the book completely. Go through a noticeably damp book page-by-page, sprinkling some corn starch onto the pages. Allow it to sit open for a few days, then brush the excess cornstarch away with a make up brush or soft, dry cloth.
Dry your book further, whether you have used the cornstarch method or not. Get a large plastic storage container. Line the bottom with a few inches of an absorbent material, such as charcoal briquettes (without lighter fluid) or clay-based kitty litter.
Get a smaller tray or container that is just big enough to hold your book while open. Lay the book open, with the pages up, on the tray. Fan out the pages. Cut small bits of card board and bend them into L-shapes, then place them every few pages to help keep the pages fanned out. This creates maximum air flow through the pages.
Lay the trays on top of the layer of charcoal or kitty litter in the large container. Do not stack the trays of books on top of each other, but if you can fit in two or three trays side-by-side, that's fine.
Cover the large plastic container. Make the container airtight by using duct tape around the lid or over any ventilation holes, or simply slide the entire container into a large plastic garbage bag and tie it up.
Allow the books to remain sealed in the container for a minimum of several days, and as long as one to two weeks. The charcoal or kitty litter pulls the moisture out of the book pages.
Take a whiff of your books. The smell should be gone. For lingering odors even after the pages are dry, you can place them in a plastic bag with a cotton ball dabbed with a couple of drops of lemon or eucalyptus essential oils. Seal the bag, and lay it so the cotton ball does not touch the book. Remove it a day or two later. Any stubborn remnants of the smell should be gone.
To keep your books fresh, prevent them from getting mildew again. Keep them in a dry place with low humidity. It is a good practice to keep a small container of charcoal or kitty litter on or near your book shelf, to attract any humidity in the room and avert it from seeping into the books. Change it every month or two, or when needed.