Separate grey and black water
First of all... Thanks so much for putting this site together and sharing all this great knowledge! With my partner, we are now restoring an old stone house in Les Gavarres, in Girona (90min drive from Barcelona). We are off-grid and I'm so happy to discover your open source knowledge.
I contacted a couple of Australian companies (1, 2) doing similar vermicomposting approaches, but they'd charge around 8,000$ for a tank with all the "proprietary fittings", which to be honest seem very similar to your solution. And on top of that I'd need to ship them from Australia. It doesn't sound right...
On the other hand I was also considering Aquatron (also proprietary but a reasonable price and with local distributor in Spain). They also claim that worms can be used, so the solid decomposition seems to aim for a completely aerobic approach similar to yours, but with no carbon added, which looks suspicious to me. Apart from that the approach seems reasonable (separating solids and liquids) but closer to a compost toilet.
In any case, I am quite convinced to try out your solution since I really believe in your open approach, and if I (hopefully) learn anything on my journey I would share and give back, contributing and being part of it in some way.
I have a couple of questions that would be great to clarify if you can help (don't worry otherwise!):
1) In the case of the Australian worm solutions I found, they claim that grey water (toilet sink, kitchen sink, laundry, showers and bath) can go together with black water into the system, and go through the worms. In other threads in this forum, you mentioned you are now exploring with also using your system to clean both black and grey water (together). Did your try black+grey water together through your warm system? Does it work? I basically need to decide whether I build independent drains for black vs grey water in the house, since that would affect costs. Probably having them separate gives me more flexibility (I can always join them after all), but if a combined black-grey system works out of the box, then it would simplify the solution, which is always nice (and most importantly, it would open up possibilities to retrofit existing houses without internal renovations, simply replacing their septic system). If the worms can handle the extra water, then it looks like it's only about making the greenfilter bigger (maybe double the size of what you'd calculate for only toilets, given that toilets are about 1/2 of the water usage per-person per-day in a normal house)? What is your opinion?
2) Both aquatron and the australian worm farms require a vent pipe. This is the only thing that feels necessary but your system does not include. I understand it just works without it, so no need for any 🙂 But did you try adding a vent pipe in any of your experiences? Do you think it could have any beneficial effect?
Thanks for the post here. In answer to your questions ...
1) Yes you can put grey water through the system and retrofit to existing septic systems. The installation done for our local municipality (see the Pai das Donas case study) handles grey water. The thing to be extra careful about is to make sure your organic matter is well mixed and of predominantly coarse materials which will allow the extra water load to pass through the tank fast enough to avoid accumulation. I've had a couple of reports of blockages occurring well above the filter area at the tank outlet and the primary suspect is a layer of leaves which form a mat once wet and hold the water.
2) Venting is unnecessary if the tank is not airtight. The Australian tanks are buried, so are therefore sirtight. I don't know how the Aquatron system works but if air exchange is very limited, then it will also need a vent. With this system, no part of it is anywhere near airtight so more than enough air circulates to keep the system aerobic - bear in mind worms live underground or in litter layers where oxygen is limited - so as long as air can enter the system relatively freely, it's sufficient. You could add a vent if you feel strongly about it, but I haven't found it necessary.
Good luck with your project and please keep us informed!