As you may remember black water is all of the waste water generated by your household that is too contaminated to be considered gray water. Here, contamination does not mean loaded with chemicals, but rather has unacceptable levels of pathogens making it unsuitable for drinking water or irrigation (loaded with feces in our case).
Our sources of black water are the two toilets we are planning to install. Some definitions of black water also include laundry and kitchen sink water due to the possibility of cleaning dirty diapers and the suspended solids contained in them respectively. The reality is that the level of pathogens in these gray water sources is minimal compared to toilet water, and proper gray water treatment is all that is required to handle these nutrient-rich gray water sources. See Create an Oasis with Greywater for a detailed discussion of the pros and cons of various gray water sources.
My initial position for our black water was that we would use a typical toilet hooked to a standard septic installation. I was worried about smell, a messy cleaning job, other people’s perception of our toilet … (need I go on).
Sandra surprised me by telling me that she was considering a composting toilet. Not willing to be left off of the green bandwagon (I am the family composter after all … and the kids know what sheep manure means to me), we started researching this topic. We have now talked to numerous people who use composting toilets and checked them out in action. I have been converted … we are now planning to install two composting toilets!
Our investigation of manufacturers is limited to date, I have been looking exclusively at the Sun-Mar line of composting toilets. Unless another product catches my attention I plan to use their specifications in my house design. Sun-Mar is a Canadian manufacturer (which means I’m
supporting a local manufacturer … who ironically is setup in Ontario while I am in BC), that has been around for a while and gets good reviews of their products. Down the road if I find another suitable manufacturer I may switch my alliegances.
Which Model to Choose?
A quick perusal of the Sun-Mar website led me to the CENTREX 3000 AC/DC central flush model or a combination of two of the Excel AC/DC stand alone units.
My initial selection of the CENTREX 3000 AC/DC model was based on a simple constraint, its ability to handle the volume of black water generated by a family of five. The central unit
allows multiple toilet connections and it processes the black water centrally, hopefully making it impossible to overload the system. The drawback is that the central unit needs to be installed below the toilets so that gravity and a little water flushes them. This is a problem in an earthship as I will not have a convenient basement to install this unit in. I believe that I can accomodate this unit in a crawlspace underneath one of the toilets. However, this implies digging and building a crawlspace, adding cost and complexity to the design.
I would prefer to install two seperate stand-alone units to minimize cost and system complexity but these stand alone units do not have the capicity required for five full time users. Two stand
alone units installed together do have the required capicity, but how would I ensure that both stand alone units were being used equally, and one was not being overloaded? I can just see myself policing the kids toilet use …
Chris: Alright Katie which toilet did you just use? (reaching for my clipboard to add notes on monthly loads)
Katie (unhappily): The one in the utility room …
Chris: And what did you do?
And the kids are only getting older …
For now I am planning on installing two stand-alone units. Hopefully, their pattern of use will balance out on its own and I will not have to resort to charting the volumes flushed down each one. I think this is the simple option and will prove to be more cost-effective in the long run.
The Plumbing Required
The unit I have selected has connections for a 2″ fan assisted stack vent that is used with AC or DC electricity to vent the unit, and a 4″ stack vent that allows the unit to be operated without electricity. Given that I always plan to have electricity (at worst 12 volts supplied by a solar system), do I need to install the 4″ stack? Can I just make do with the 2″ stack vent? For the time being I am assuming that I must install the unit with the 2″ stack and the 4″ stack.
The unit also has a 1″ drain that is required for overflow control. Sun-Mar claims that this overflow is a precautionary measure in case the system is overloaded on a short term basis (Helen’s next birthday party with 9 girls and parents?), and will not be used very often.
The drain needs to go to an existing septic field or approved recycling bed. My initial thoughts are to connect it to the existing septic system we have on site, and possibly provide a septic drain line out to an area that could eventually be used as a recycling bed.
The first thing I did was sketch out one of these toilets and discover that it was significantly bigger than a standard flush toilet. This meant laying out the bathroom yet again, and while I was in the middle of
doing that I came up with the bathroom layout of the decade. I had visions of CAD students whispering about the brilliance of this layout during Drafting 101! Unfortunately, Sandra did NOT think my new layout
was brilliant. She did not like it, and dashed my hopes of having my name enshrined right next to Crapper … thank you Sandra!
It did force us to re-think our bathroom layout and we decided to move the second bathroom closer to the living room and put a shower in it. There were multiple reasons for this decision:
- the two gray water planters now get their incoming water from adjacant plumbing
fixtures, eliminating the need to move water between the two planters,
- the bathroom across the hallway from the main bathroom would have required moving gray water under the adjacent hallway,
- Sandra and I both like the idea of a bathroom close to our bedroom that does not have kids in it.
I have updated some of the pages on my plans page to reflect these changes.
I am still concerned about composting toilets from an aesthetic perspective.
I read in one of the Earthship books that if you consider your composting toilet to be like an indoor outhouse you will not be disappointed.
This is not exactly a blanket endorsement. I am relying on the improvements that have been made to composting toilets since Mike Reynolds wrote about them, as I have seen them and read about them.