Waterproof basements and walls below ground level. Use water-sealant paint on floors and walls. Allowing air to circulate against the walls will enable the moisture to evaporate. Freezing the moldy book may be an option for halting the spread of mold while you evaluate other methods for killing the active mold. Freezing will stop the growth, but it must still be cleaned.
Dormant mold is dry and powdery in appearence.
It may also have a musty smell. It can be removed using a vacuum cleaner and a soft brush or a brush attachment. Clean brushes and dispose of vacuum bag to prevent spreading the mold spores. Use a dry, clean rag or brush to remove mold from books and papers. Damp books are more susceptible to mold than wet volumes.