Mathew and I entered Metropolis magazine’s competition for “one fix that will make a positive difference in the designed environment.” They had 292 applicants this year.
We wrote up a proposal for a networked sensor platform for navigating the social and legal obstacles to locally cycling organic matter. It closes the loop between composting toilets and gardens by monitoring the composting process to verify the destruction of pathogens, reassure neighbors and eaters, and placate regulators.
Here’s the illustrations Mathew and I made for the occasion.
A year of your excrement is a very small; a nutrient-packed potential disease vector divided into roughly 1800 one-pint events over a year. A solution to it aught to match its scale and dispersion, reflect its value, and neutralize its dangers.
2) WATER
The most efficient flush toilets dilute your excrement over 30 times, turning small problems into big ones; 38% of U.S. municipalities self-reported dumping untreated wastewater into waterways in 2008. Waste treatment is energy intensive and must destroy dilute nutrients such as organic nitrogen even where nutrient recovery is attempted.
3) GARDEN
If your excrement were properly handled, its nutrients could fertilize a 50′ by 50′ garden and produce over 6000 servings of fruits and vegetables. Composting is the easiest and lowest energy way to eradicate pathogens and recover nutrients from excrement, yet deploying composting systems is considered a fringe concept. Why?
4) 
Flushing is a powerful allegory for control. Composting lacks the speed and satisfaction of flushing, and has no equivalent visual signifier of its action. One solution is to augment existing systems with a networked sensor attached to web-based visualization. Excrement is given a new destination that is more than allegorical.
5) TEMP PROBE VS OUR PROBE
On the left is how temperature is currently taken by “humanure” composters. On the right is our solution. Openly available, visualized and annotated records of pile temperature and humidity improve toilet user and pile maintainer confidence, and provide a record of decomposition for legal and safety reasons.
6) 
The rod held in our model’s hand is a functional prototype based on an inexpensive and self-calibrating sensor attached to the Arduino microcontroller. By taking measurements it automates the most frequent task of responsible excrement composting.
7) 
Pathogen abatement occurs through the digestive action of thermophilic bacteria and the heat they generate. Consistent records of temperature correspond to documented pathogen destruction times. Properly designed and managed, a 3′ x 3′ pile could batch process one week’s excrement from 150-200 people in six weeks.
Off-site composting avoids laws regarding on-site composting toilets which often prevent composted human excrement from being used for agriculture. Properly managed off-site thermophilic composting (pile rises above 55° C for at least 3 days) instead produces “Exceptional Quality Biosolids,” categorized by the EPA for sale and distribution to the public.
8) 
By focusing on information rather than specific physical instances, our system promotes variety. Every compost pile can benefit from monitoring, and monitoring creates the trust necessary to expand composting systems. Ours is a framework around which new infrastructure can be built; local, modular infrastructure fitting real conditions and expanding organically.
10) 
This relates to our business plan- introducing dry toilets in competition with portable chemical toilets in the USA rather than exclusively pursuing residential installations (such companies exist in Greece, UK, and Australia). Sawdust toilets smell only of sawdust-a significant improvement over chemical toilets. Collections are composted off-site using our sensors.
If all this crazy compost talk gets you excited, contact us at info@cloacina.org
CITATIONS:
Feces: based on 843g/week, pg 2358 Digestive Diseases and Sciences, Vol. 43, No. 11: 1998
Urine: based on 2 pintsday pg 118 Integral Urban House, Helga Olkowski et. al. Farallones Institute: 1979
Water: based on .9 gal/flush 5 flush/day Caroma dual-flush toilet, Caromausa.com: 2010
Garden: “Intensive Vegetable Production” Journal of the NewAlchemists 4 pp. 47-55. 1977.
“A Study of the Energy Efficiency of Intensive Vegetable Production” Journal of the New Alchemists 5 pp. 62-68 1979.
Sewer Overflow: “As Sewers Fill, Waste Poisons Waterways,” Charles Duhigg, NYT: Nov. 22 2009.
Composting Toilet Law: Oregon Statute 447.115
EPA Standards: Principal Biosolids Guidance (EPA/625/R-92/013): Chapter 10, pg 87
Molly,
You are right. Recycling human waste back to agriculture is the missing step in sustainable agriculture, and indirectly in cleaner water. Your visuals are outstanding.
The temperature monitoring approach is good, and necessary for dealing with public officials and regulations. But the reason small-scale composting is not trusted by health authorities is that although the center of an insulated pile can reach 55 C OK, the corners ands outer surfaces almost never do, pathogens there are not killed and could be spread with the compost. The solution, which is not technically hard, is to at some stage completely enclose the pile with insulation and ADD heat for 3+ days , and put thermocouples in the 8 corners and 6 surfaces to guarantee 55 C. Anything less is not certain. This is very promising work. Thanks. Earle Barnhart
Molly,
You should look at http://www.compostingtechnology.com/
Green Mountain Technologies. They have an”earth bin” for composting that is mechanized but is a good size for a small composting business . You should hook up with them about sensor systems, and ask if the bin could be insulated and heated up to 55 C for 4 days.
Earle Barnhart
Great graphics and succinct description of the issue. I have forwarded it to city planners in Mongolia.
My question: If a single person’s composted waste will fertilize a 50×50 garden plot, has anyone done the calculation on whether there is actually enough urban ground to make use of all that compost? That’s about 17.5 people per acre or 8, 712,000 acres in a city of 500k.
43,560 sq feet/acre divided by 50×50 = 2500 sq feet = 17.5 times 500k.
How is that an urban solution?
Where does the rest of the waste go?
Ah . . . why must we produce so much freaking fertilizer? Very good point Kent. If humanure composting was practiced through out cites city folks could finely have something worth while to offer the nearby farms: finished compost and lots of it.
At our house we created a urinal to divert urine for garden fertilization. According to the Integral Urban House at the rate we’re peeing the four of us will provide all the nitrogen our 200 square foot garden needs for the entire year in 15 days! I’ve been looking into possibly making our own struvite since struvite crystals are tiny and could be stored unlike buckets of urine. It’s made by bonding the magnesium chloride with the nitrogen and phosphorous in urine which releases a lot of ammonia (Smellllly) and bubbles. Making struvite definitely produces a serious odor (ammonia) and doesn’t resolve the problem of salt build up in the soils from urine. Any suggestions on what to do with our urine our welcome. Otherwise we’ll just be using it to decompose wood chips till we come up with a better plan.
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