Adding redworms to a desiccating toilet system
Update 2/7/2010: Just so you know, there are some graphic pictures below. If you aren’t interested in viewing humanure, please don’t read further.
Last week I had an interesting meeting with Mike, an official at a local state park. They have a desiccating toilet that just isn’t working as well as they had hoped. Here’s a picture of the toilet system from the outside.
Eldorado Canyon State Park Bathrooms
Below is a picture of the system from the inside. They have two large plastic vaults that have air flowing from the outside into them. The feces and toilet paper are held up via a metal trough, and air flow drys them out. Wood shavings are regularly spread in the system, which is supposed to help control odor (I think). Finally, the entire mass of poop is regularly sprayed with fresh water (on a timer). That is supposed to help decomposition. (I don’t understand how the water spraying and the air drying work together, and neither did Mike.)
Eldorado Canyon Desiccating Toilet System
Below is a picture of inside the system. Yup, that’s human feces and toilet paper. I visited during the winter, and the level was not high. Mike said that the entire mass freezes solid during the winter. The white horizontal line in the middle of the picture is a tool that lets someone distribute wood chips or move poop.
Inside Eldorado Canyon Toilet Vault
The primary issue with the toilet is a high pH leachate that accumulates at the bottom of the system, below the trough. Eventually that liquid gets so high that the system needs to be pumped. You can read his description of the issues; he goes into far more detail about what has been tried. He also summarizes what we discussed and the plan moving forward:
- I’ll build a compost bin, in the basement with the vaults, loaded with worms.
- I’ll get the worms started with food scraps from the office.
- I’ll make some experimental sections in the worm bin, and try adding some of the, er, material from the devap toilets, and maybe try soaking a different section with the excess water. The idea is to see what the worms like and thrive on.
- If the wigglers like human waste, but not the bilge water, then I’ll leave the vaults unmodified, add worms, and let ‘em go to town this summer.
- If the wigglers like human waste AND the bilge water, I’ll add worms to the vaults, and scale up by periodically pumping some of the waste water up into the stack.
- Worms will crawl and explore, but they also like dark and quiet. It’s highly unlikely that they’ll crawl up to the main floor.
- If the worms are successful, they’ll probably die off every winter in the cold vaults. The warm, freestanding compost pile will have to be maintained during the winters.
- It’ll be interesting to see what happens with the odor.
- I’m totally rooting for the worms. It would be phenomenally cool if worms could thrive on the wood chips, waste, and wastewater.
It will be interesting to see how the worms adapt to a diet of human waste. I found some links that indicate that they should do alright (thanks, Google Scholar!). Here’s one on a worm composting outhouse, which discusses some of the unique aspects of vermicomposting human waste (as opposed to the more typical feedstocks of yard and kitchen waste):
The worm bin should be operated like any worm bin. The moisture, temperature and aeration needs are the same. One difference is that human waste has a Carbon to Nitrogen ratio of 20:1 and so it needs a high carbon material added to decompose best.
Here’s another article discussing using vermicomposting to stabilize sewage sludge. Here’s an article about redworms reducing pathogens (a topic I reviewed last year). This is an interesting article on how feedstock affects E. Foetida weight and length (pdf). And here’s an interesting abstract for an article on the effects of stocking density and feeding rate on biosolid vermicomposting that is worth excerpting:
Specifically, the focus of this study was to investigate and establish an optimal stocking density and an optimal feeding rate for the vermicomposting of biosolids, with paper mulch provided as bedding. A stocking density of 1.60 kg-worms/m2 (0.33 lb-worms/ft2) and a feeding rate of 1.25 kg-feed/kg-worm/day resulted in the highest bioconversion of the substrate into earthworm biomass. The best vermicompost was obtained at the same stocking density and a feeding rate of 0.75 kg-feed/kg-worm/day.
Based on reviewing these articles, a key component of this system will be adding enough carbon to keep the worms happy. The main source of carbon currently is wood shavings, but they are purchased. I think that shredded paper and/or leaves would be good alternatives. Some calculations should be made to determine how much bedding substance to add.
In addition, redworms need a pH between 5 and 9, and I believe the leachate was well above that (update 2/7/2010: per a conversation with Mike, the pH of the leachate is 8.5 or 9). I don’t think the worms will be able to process or reduce that liquid directly. However, the source of the leachate seems at first blush to be the fresh water spraying, so if the worms process the waste and help maintain humidity, less spraying may be needed, and thus less leachate may be created. Even if the same amount of spraying is required, the worm castings may retain more of the water, and reduce leachate in that manner.
I’m a huge fan of Mike’s plan to start small (with a 55 gallon drum) and see how the redworms react to waste and/or leachate. This experimentation will be cheaper and easier to control, as well as giving Mike a chance to become familiar with worm keeping.
11 comments February 2nd, 2010
