Laurelin poops. She does so quite regularly—a sign of health. That must be why she thought it a waste to just throw all that hearty poop away, as if it wasn’t worth a thing. Enter her homemade composting toilet, where all that treasure is collected, in a rather substantial bucket.

Here, you can see the frame with the bucket, but, as of then (in November 2017), without a s**thole.

A composting toilet is a natural signpost on her journey of becoming full-fledged permaculture hippie. How else would she ever get close to closing the nutrient cycle? There’s only so much shit you can do to keep your outputs from exceeding your inputs. If you keep flushing your outputs into the ocean, your soil won’t thank you, and neither will this grumpy marine biologist; all that nitrogen will wreak havoc (like algal blooms) all the way downstream, via estuaries, in the sea.

Keep your nitrogen near

We’ve been living in nitrogen-flooded times, since the availability of cheap artifical fertilizers revolutionized agriculture around a half-century ago. One of the casualties of this revolution have been the quality of our surface water. Ground water quality has also been affected.

This is not Laurelin and my mother their main concern. Their main house is connected to a sceptic tank, not to the sewer. And although it’s a shit, old sceptic tank (contrary to what they were told when Annemarie bought the property), that does mean that their outputs don’t end up somewhere downstream.

But, I am ranting. They’re not about to start using artificial fertilizers. Their main priority is keeping nutrients in their system, not so much to keep these nutrients out of other systems.

At the end of Februari, an egg-shaped hole had materialized. (You can also see the nice flushing job that Laurelin has done on the stone wall.)
Even without the final finishing touches (such as the flap that Laurelin wants to use to connect the shit bucket to the top board) the composting toilet has already served the residents while the turd of a toilet in the main house was being replaced. And it does look neat with the smooth, wooden seat. All it really needed were some fresh feces and urine.

Shit safety

Some poop pathogens are a bit scary. Among the scarier critters are soil-transmitted helminths. Helminthiasis—worm infection—is largely confined to tropical regions, but that is hardly reassuring when WWOOF delivers a dirty dreadlock hippie from Who Knows Which Shit Country at the doorstep.

Not as scary as the worms are the bacteria. Most strains of Escherichia coli—a particularly well-studied species—are harmless and a part of every healthy person’s gut flora, although some strains are serious turd troublemakers. Dispite there only being relatively few pathogenic strains of E. coli (such as E. coli O157:H), its ubiquitousness in human feces and its popularity as a model organism in the life sciences makes it the go-to indicator organism for fecal contamination of soils and surface waters. Thus, typically, an E. coli test will be employed to make sure that the dreaded dready hippie’s worms don’t end up in the salad.

E. coli tests are already cheap, and cheaper, simpler tests such as E. coli test strips are underway. Still, the hassle of testing the home-made humanure for contamination can be by-passed by being somewhat conscious about the composting process and application.

Process-wise, it should already be sufficiently clear that defecating directly in the lettuce bed is a bad idea. So, Laurelin collects the compost in an open compost pile, where the sawdust (that they apply between bowel movements) should provide for the aerobic growing conditions (40–60 °C = 104–140 °F) needed by the thermophilic composting bacteria that oxidize the waste while generating temperatures high enough to kill even helminth eggs, the hardiest of all poop pathogens.

Duration Temperature Source
2 weeks 55 °C Berger, W. (2011) Technology review of composting toilets – Basic overview of composting toilets (with or without urine diversion)
1 week 60 °C
1 hour 62 °C Composting Chamber, in The Online Compendium of Sanitation Systems and Technologies
1 day 50 °C
1 week 46 °C
1 month 43 °C

Because there’s no unanimous agreement on the temperatures and durations needed to kill all shit scariness and because Laurelin doesn’t feel like tracking the temperature of her humanure heap with a thermometer, even after composting for a year, she won’t apply her humanure to the vegetable patches. Instead, the compost will be used to kickstart the many nut trees after they’ve been transplanted from the tree nursery.

The humanure heap is open to the air, but almost closed to small rodents who might be tempted to scitter around with poop pathogens on them, although the interface between the bricks and the mesh wire still needs to be tightened. The grass shows that it has been a while since the last bowel movement was moved onto this pile.
Sawdust, picked up for free at a local sawmill, and applied after each new layer of excrement, absorbs the moisture and keeps the dry composting toilet dry. As long as the muck bucket stays dry, the odours stay at acceptable levels. And the sawdust loosens the structure, which helps to avoid smelly anaerobic processes.

If all this got you excited to recycle you own poop and you want to learn more, there’s an article on composting toilets on Wikipedia. And, if you want to go all official, ISO standard 24521:2016 is in the making.