I have a biodigester. After reading about Vermi toilets I am starting to get regret! ha ha!
So, I currently have a 3000 litre tank that is in the ground already so retrofitting it into a Vermi toilet doesn't seem practical. I do have some questions that you can maybe help with in regards to a green filter or soak away which I don't currently have as the biodigester produces liquid effluent that runs into the city sewer. I am wanting to return the water & nutrients to the soil but I am concerned about pathogens and nitrates. A biodigester is obviously anaerobic so pathogens are a problem but as I understand the bacteria also take care of 90% of heavy metals and many of the pathogens.
(the biodigester does not receive grey water)
So I am thinking:
Create a vermicompost container as a second stage for the effluent. Feed it with food scraps, etc. and run my biodigestor effluent through that. This will provide an aerobic composting stage to really clean out any pathogens. I can then run the water/tea/effluent from that into a green filter soak away as you guys prescribe on this website. (Without being concerned about nitrates and pathogens making it into the ground water.
Take the biodigestor effluent straight into an aerobic (soil-based) soak away or greenfilter? You explain your green filter as:
"greenfilters...are filled with the same organic material as is used in the worm tank. This encourages the development of the same ecosystem within a loose-textured, well-aerated matrix, so similar rapid percolation rates can be expected within the organic layer of the greenfilter as are seen in the worm tank."
So it seems as If that would kind of achieve the same purpose as option A?
Interesting project! Where are you and how many people/animals are contributing to the biodigester? This might determine whether or not it's worth thinking seriously about a retrofit vermicomposting system? There are ways ...
As for your A or B options, A is likely a 'safer' and more robust option in that the vermicomposting system is contained and there's no danger of your worms wandering off somewhere else, which they're free to do in an uncontained environment. The food scraps may be important as I don't know how well anaerobic biodigester effluent will be tolerated by an aerobic system. I would suspect only as a small percentage mixed with other food sources. The last thing you want is to risk turning your system anaerobic.
This study might be useful.