Q: Can I PERMANENTLY DELETE a book that I purchased and no longer want on my account?

You can not delete purchases but you can hide them so they do not show on any of your devices.

iTunes Store: Hiding and unhiding purchases

You're welcome

I too am having issues - I want to delete books both from my iPad and from the Cloud.  However, it seems to be impossible.

Disappointment.  All the more so, when I was at the genius bar recently asking why I can not delete apps, the supposed "Genius" did not think to inform me this extended to EVERYTHING including books. 

Frankly despise not being in control of my accounts, my devices.... I think this is why I have been subconsciously using the iPad less and less.  And have given up the iPhone.  I appreciate convenience, but want control.