Slice of Heaven in a Can (SOHIAC) is my project to develop an inexpensive, minimalist solution to the issue of homelessness due to disaster or societal conditions, by reusing surplus ISO shipping containers as a basic construction module.  

Since Roman times, and perhaps before, water systems have been used to carry away human waste. A significant infrastructure to deal with sewage is part of every major city’s operations and budget, and most of them rely on water transport through a system of sewer pipes to deliver the sewage (or Blackwater, as it is also known) to a large scale plant for neutralizing the health hazards and turning it into a safe sludge that can be recycled as agricultural fertilizer.  

When that infrastructure is not in place, or when it is not functional, things can get quite horrendous very quickly, as witnessed by Emily K. Troutman, in this firsthand account from Port Au Prince, Haiti: http://www.aolnews.com/world/article/sanitation-in-haiti-is-really-in-the-pits/19591460 

Off the grid, we have to deal with sewage without the urban infrastructure, so what to do? In the illustration at the top I depict what is probably the most radical, and almost certainly the most controversial aspect of my SOHIAC design. Some readers, predictably, will not make it through this entire article. What you see above is the entire SOHIAC bathroom… a composting toilet inside a shower stall.

Let’s look at the toilet first. Everybody poops, everybody pees. What do you do with it? With a standard American water closet you push the handle and a couple of gallons of water flush it all down into the sewer system (aka “Flush & Forget”). This is the largest single use of water in a typical American household, and the average American flushes away about 7,750 gallons a year. In rural areas, the septic tank and field are the norm for disposal, but still using that same amount of flushed water, which must be dispersed safely, somehow. First I’ll discuss the traditional septic system, and then explain how a newer “Divide & Conquer” approach is more ecologically sound.

What happens in a septic tank is that the water is separated from the solids, which begin being digested by anaerobic bacteria and settle to the bottom. The excess liquid overflows into a second tank, in which further digestion and settling occur. The relatively clear water overflowing from the second tanks flows out to an absorption field, commonly known as a leach field.

In the leach field, the liquid flows through perforated pipes into gravel filled troughs, and from there leaches out into the surrounding soil where it is taken up by plants and trees. As Erma Bombeck famously wrote, “the grass is always greener over the septic tank,” because it is receiving underground water and fertilization from the leach field.

The settling tank in the septic system fills up eventually, and must be promptly pumped out, or the solids will overflow into the leach field and ruin it. And there must be adequate clear ground and a reasonable percolation rate (absorption rate of the soil) for it to work. Absent either, the next choice is a cesspool, in which waste is merely stored until it can be pumped out. A PortaPotty is essentially a portable cesspool. Absent a cesspool, you are back to digging a hole in the ground, and covering it over when full, an even more smelly and unhealthy alternative.

Composting toilets are a relatively new development in which that whole process is compacted into a single appliance. Waste goes in, and dry, odorless composted fertilizer comes out. Canadians and Scandinavians have taken to composting toilets in larger numbers than Americans to date. Ecological activist and actor Ed Begley, Jr. is probably the best known user, endorsing the Envirolet composting toilets which are installed in his Beverly Hills home, and fertilizing his lush rose garden with the output.

Of the three most widely available brands in the US, Envirolet is the Cadillac. It’s also the largest unit, and the most expensive, and has the most options.

Biolet is a little smaller, a little less expensive. But both are about twice the size and 50-100% more expensive than the unit I’ve chosen for this project, the Nature’s Head.

It’s so called because it was designed as a “zero discharge” head (toilet) to be used in the confined quarters of a boat, and it’s a US Coast Guard Approved Class III device. It’s also American made, whereas the Envirolet is Canadian and the Biolet is European. It is manually operated, except for a small exhaust fan. I'll use a solar powered fan for this application. 

I’ve compiled the most pertinent details below, and you can find out more about all of them on the internet. A European brand, Separett, has an innovative design that would make the cut if it were more readily available in the US; however at this writing its US website is down and I can’t get any current info on it.

Brand, Price,  Shipping (to Hawai’i), Volume Occupied cu/ft,  Notes

Envirolet Basic Plus, $2,099 , $290, 11.9 cu ft ,Water flush models, vacuum extraction, remote storage, you name it, great if your budget is unlimited

Biolet NE, $1,300, ~$250 , 6.6 cu ft , Good quality, good reviews, but seems to have a serious customer service issue, based on internet comments.

Nature’s Head, $885 , $150 , 3.3 cu ft , Ships direct from Ohio factory. Simple, effective, fits in smallest space.  Dual waste system.

Comparison made on non-electric base models with comparable features, with capacity for 2 adults in full time usage.

Single Stream or Divided Stream? – Water based sewage systems are “Single Stream,” with all waste being combined in one sewer pipe system. It’s efficient for large scale urban systems, less so for rural systems, because the first step in the process is to separate liquids from solids. An old idea, Divided Stream Waste, used in Queen Victoria’s royal toilet, has been reinvented for Ecosan purposes.

The principle is simple. Solid waste (the poo, if you’re having trouble following this) needs to be liquid free, merely damp, in order to compost aerobically and thus destroy disease causing organisms. Urine, on the other hand, is inherently sterile, and in addition is a safe, nitrogen rich fertilizer when diluted. (See the book “Liquid Gold” for details.)

Conventional composting toilets are single stream, combining liquid and solid waste, primarily using fans to dry the waste to proper composting moisture levels. Dual stream composting toilets separate the urine at the source, for disposal in a simple “greywater” system designed to disperse shower and sink wastewater. Properly designed, this can be used advantageously for garden irrigation. And once the solid waste is fully composted, it is an odorless, nearly dry soil amendment for rich lawns and flower beds. It can also be added to a conventional compost pile where it works as a starter and accelerant.  

Now, back to the mini-bathroom concept. In a 160 sq ft efficiency apartment, it’s important not to devote too much space to the bathroom, and combining the toilet and shower in one 3’ x 4’ stall is about as compact as I can make it and still retain utility. Having a shower head on a flexible hose and a floor drain in the middle means that cleaning up the entire bathroom space is simple and easy. And having a seat and a grab bar in a shower stall is extremely practical, allowing seated showers, easy grooming of legs and feet, and good safe access for the disabled and elderly.

The sink, since you were wondering, is just outside the bathroom stall in the galley area. For such a compact and inexpensive living space, eliminating the duplication of a second sink only a few feet away makes good practical sense.

Love, David

SOHIAC illustrations and text © 2010 David Kinne.

Search on SOHIAC for other posts in this series. 

Photos courtesy their respective manufacturers. Septic tank and leach field illustrations © Daniel Friedman

www.envirolet.com

www.biolet.com

www.natureshead.net