Separate grey and b...
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Separate grey and black water

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New Member
Joined: 6 years ago
Posts: 2
Topic starter  

Hi Wendy,

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?



Eminent Member Admin
Joined: 8 years ago
Posts: 47

Hi Luís

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!

Active Member
Joined: 7 years ago
Posts: 7

My personal experience, more than a year on, is that separating grey from black water would be the way to go. I'm dealing right now with problems with the worm container draining, which is complicated because it is in an underground room due to geography of the house. I have shower water and clothes washing machine water going separately, but the kitchen and bathroom sinks as well as dishwasher all flow in to the worms.

Our problem isn't leaves -- the organic material I use is chipped branches, so very little leaves there, but it seems like excess toilet paper that has slowed down drainage, so then the water from sinks is just keeping everything too wet. Partly now is to try to control my kids excesses in TP usage and playing in the bathroom sinks, but also I'm considering now how to re-route the sink water-- a bit complicated as where the pipes join together is under concrete now.

kit river reacted
New Member
Joined: 6 years ago
Posts: 1

Hi there...newbie here...

I'm now designing my system for a 2 person house in Alto Alentejo. I will do a 1 IBC of 1 m3 as a vermifilter but will add on top of the bottom coarse pebble a second layer of fine pebble. Blackwater together with greywater....

Then after, and because of the soil profile - don't have topsoil and can find rock (Schist) very on the surface, it will be difficult to make a soakaway trench, will install 4 half cut with coarse rock (10 cm), medium crushed rock (10 cm), sand (5 cm) and topsoil (10 cm) - bottom to surface.

Will plant aquatic plants in the top soil (Phragmites, Juncus, Scirpus and Typha).

The last step is a couple of recycled bathtubs with some azolla and watercress that will fluctuate in the water. As I have a pond that dries in the summer I will store the cleaned water in it. That pond will give water for the trees in the summer season.

Regarding winter, on the rainy season - that's my problem....

I have rain water flowing through the fields in a near surface, surface flow and discharge in a season river that passes through my property (17 ha). All fields around are abandoned and I'm the only habitant in a 4 km radius from the nearest village.

What you suggest?




Eminent Member Admin
Joined: 8 years ago
Posts: 47


What's the rationale for the fine pebble layer in the worm tank? If you're putting grey water through the tank then I'd be wary of anything likely to slow down the drainage rate or you could have problems.

I didn't quite understand what you mean by "will install 4 half cut"? Do you mean you'll use IBC tanks cut in two? It doesn't matter that you have almost no topsoil. Neither have I. I'm also on schist and I don't have problems soaking away my grey and black water. What's important is that your secondary processing area has organic material in it the same as the worm tank. It's the organic material which is the basis for the vermicomposting system and it's THIS that cleans the water. It's a living, self-regulating ecosystem. An entirely different thing from inorganic filtration materials which will not remove waste pollutants (nitrates, etc). You need a secondary level of cleaning after the worm tank to ensure the best possible standard of water exiting the system and in case anything goes wrong with the main tank, and you release dirty water from it.

I would see the bathtubs as redundant. Once the water has been through the worm tank and the secondary ecosystem, it's more than clean enough to use for irrigation. And the grey water from 2 people is unlikely to keep your pond full (unless it's very small). Likely you will lose most of the water to evaporation in the summer anyway.

So rather than introduce all these intermediate steps which may produce their own problems, I would take the water directly from the worm tank to mulch pits containing organic material uphill of each of the trees you want to irrigate. This ensures wide dispersal of the water passing through the system, adds a fertility reserve and a lot of soil life around your trees, reduces soil compaction and increases infiltration rates. The more trees you grow, the better your infiltration rates will be and therefore the less water there will be running over the surface in the winter. Desertification of the land is a huge and worsening problem in Portugal and the more water you can slow, spread and infiltrate, the better your land becomes. A series of swales (on-contour ditches) behind lines of trees rather than mulch pits behind individual trees might be even better, and in winter would catch some of that surface water runoff and soak it into the land instead.