1) First, You installed SH404SEF component.
2) In the folder /components/com_booklibrary create a subfolder sef_ext, like this
Now using FTP or similar, drop the file com_booklibrary.php into that sef_ext directory.
3) In Joomla Global Configuration set in SEO Search Engine Friendly URLs - NO and in sh404SEF component set Enable URL optimization - YES.
So, after that you will have such URL for example for alone category
Last version of sh404SEF plugin for Book Library - Library Management Joomla Extension you can find on our website (Tab Modules and Plugins)