Is there any way to disable 'Library' feature in Lightroom 3? I don't need it and i do not want to waste my free space on it.
What features of Lightroom do you want to use then? The library is essential to the workflow of as it is where the images to be worked on are represented.
Full sized images are not stored in the library catalog file, so it is not very large in relation to them. For example the library files from a catalog with 3023 files is only 43MB after flagging and editing.
I'm assuming you mean you want to be able to use Lightroom's editing facilities (i.e. the Develop module) but on an ad-hoc basis: you want to edit a photo, save your changes and quit without having to build up a catalog.
If so, I think your only option is to create a catalog, import the photo, edit and export, then delete it from the catalog again. If that sounds like a lot of hassle it's because Lightroom really isn't designed to be used that way. For this kind of editing, Photoshop and the Camera Raw plugin might come closer to addressing your requirements. (Photoshop's equivalent to the Lightroom Library module is Adobe Bridge, but that's a completely separate application and Photoshop can easily be used without it.)
However, I'd also recommend you take another look at the Library and consider the benefits it offers you. It's an incredibly powerful (yet user-friendly) way to organise, categorise, tag and browse your photos.