I have considered your question concerning a anaerobic digester, I do have a friend that has been working on designing a portable unite. If you provide your email I will pass it on. In a private message.
No the tanks are for fish rearing. my whole system collects water from a 30x60 barn and some other roofs then directs them down to the fish tanks. But if your interested in a biodigester unit I have a friend that has designed them for a few years, and he can design it for you if you want. Just give me your specifications and I will pass it on.