I think you have to make some attempts to communicate with him regarding unacceptable behaviour.
What you would do with a child with standard comprehension - and they usually bite too quick to catch them ijn the act! - is to turn him to you, make eye contact, and say "NO! loudly and shake your head. Then take him a\way from the person he has bitten and make him stay apart for a few minutes. I really don;t know if he is able to understand the concept of apology - that is something you need to discuss with your health or social worker.
I realy do feel for you - and you need to get some expert help on this, for everyone's sake.