So use your regular fixer without bad consious. A "bio"-fix does NOT and can NOT exist. Proper disposal and re-using the toxic and expensive silver is the only way that makes sense, for us AND the environment.
I'm really getting tired answering this question: salt does NOT work as a fixer. No matter how often it is claimed. This is a myth coming from the 19th century!!!
Important update, see next post: Fixer 2. I don't delete this post, it's part of my own Caffenol history.