Minimal effort compost toilet

I saw something like this on a Youtube video that I can't locate now, so I adapted it, along with some other ideas, to turn it into something that I think will work for us. We're hoping to use a thrown-away HVAC duct, but if we don't find one we can maybe make it out of old dryer shells, or maybe even incorporate some washer bins towards the end of the cycle.

We visited a few intentional communities that use composting toilets and we were amazed at the fact that they just had no foul odor to them at all. I always expected at least a little outhouse fragrance but there was none! That's what really prompted me to focus on a workable composting system for our natural home.

One of the great attractions I have to permaculture is that instead of creating extra work for you, it prompts you to let the natural laws of nature do the work for you. You could spend a thousand bucks on a little Biolet or a Sun-Mar or a Nature's Head, but you still have to empty it every time it gets full and you still have to dispose of the waste frequently, because all you're really doing is pooping in a prettier box. Composting your waste should be as easy as it is ecologically sound - just using a little gravity, sunlight, and natures critters.

When I saw this guy's video I wanted to learn more but there was nothing else out there that I could find on it, so I dove into my 3D modeling programs and started designing my own.

This is basically how it works, and how the guy explained it in the video. He had 3 compartments. I made my first compartment bigger and added another because there'll be 6 of us - and we'll likely be moving the poop more often.

The poop box is indoors BTW. I took away the walls and floor on this first illustration so you could see the workings more clearly. Basically the poop hits the floor of the bins and slides downhill as it piles up, gradually pushing it aside.

Now granted - there are 6 of us - so the time frame will depend entirely on the poop-to-internal-bin-volume ratio, but I plan to make big bins. I'll just need to think on how much poop we produce in a day and do a little math before I start detailing measurements and time-frames. Not something I want to contemplate before dinner :-\

We'll be heating our house with a rocket mass heater in colder weather. Note the exhaust pipes from a rocket heater - by the time it reaches another room - would likely not be warmer than 120°

To aid in that negative air flow I applied some simple physics...

Another concept I've entertained came from Michael Reynolds' poop-cooker idea and another idea I saw on Youtube where a guy built a septic tank to appease the local authorities, then put windows over it and used it as an underground composting pit, adding PVC vent pipes, and letting the sun shine through the glass, onto the poop, thereby drying out the poop to kill off the bacteria and heating the compost so it could break down faster even in cold weather. Shoring up the sides with strawbales can help keep things warm also - and if the poop still looks too wet we can toss a few pitchforks of straw into the mix to dry it up more.

So I thought I'd incorporate that guy's solar cooking concept into this design by adding glass (maybe double-pane for better insulation) to the top of  bin #2 to help dry everything out before introducing it to the cooler, darker bins 3 and 4. Granted it won't be a pretty thing to look at, but it'll do the job.

When you're dealing with all this poop, you have to be sure your final 'product' is clean before you let it out into the world. Redundancy is a good thing. My research suggests that 2 years of composting humanure is best, so we may finish the job in another bin if it doesn't test clean and free of pathogens when it comes out of that 4th bin. So we'll be adding worms to bins #3 and #4. Vermiculture can really speed up the decomposition process and really enrich the compost with all kinds of nutrients.

One last, and hopefully redundant, course of action to make sure everything is properly re-introduced to the circle of life came from our last (2014) trip to the Mother Earth News Fair. We attended a couple of classes on the wonders of mycoremediation. Mushrooms are amazing things. They can clean the most toxic chemicals and make them harmless. We can inoculate the sawdust we initially use to cover the poop with king stropharia spawn, which devours E.coli

So the quick and dirty version is we separate the poop into 4 bins, each with small openings along their ceilings venting gasses up to the previous bin and out the warmed ventilation pipe.

• Bin #1 - fresh poop with compost-able materials being added daily, urine separated to minimize moisture content
• Bin #2 - sun dried poop, heated by the sun to jump-start the decomposition process
• Bin #3 - black soldier fly larvae to break it down further for a few more months
• Bin #4 - the oldest compost - once the previous bin is ready to move down, we empty bin #4 and test it with the Health Deartment for pathogens and decide then if it's safe add to the soil

I'd like to test each bin after 3-4 months just to see how it's coming along and whether or not I'll need to add a 5th bin. I'm guessing it'll decompose more slowly in winter, but maybe burying Bins #3 and #4 in strawbales will help. The goal is to show that the un-composted poop will never touch the ground, as the system is all self contained, unlike those little store-bought $1000 composting toilets that they actually approve of. Also that there is "minimal to no" handling of the un-composted poop, unlike those approved compost toilets. Those are the main things the health department are concerned about. If it fails, there's still the option to just have it all hauled away.

UPDATE 9/24/15
After attending Tradd Cotter's workshops at this year's Mother Earth News Fair we decided to add king stropharia spawn to the sawdust we use to initially cover our poop.

UPDATE 6/9/2016
After further research we're planning to add black soldier fly larvae to one of the chambers. They're voracious poop eaters, turning poop into castings, and when they become adults they don't eat - they just fly off, mate and make more larvae. So I'll add a screened in box over the vent so they don't leave the area, with some sponges along the chamber for them to lay their eggs, and their larvae can drop right back down into the poop.

UPDATE 6/21/2016
Per Wiki:Captive breeding has been observed in a cylindrical chamber measuring 46 cm (18 in) diameter by 56 cm (22 in) tall for 99 litres (3.5 cubic feet). "Mating under artificial light did not occur but did succeed with natural sunlight." ^[8]
I need to design a chamber to capture adults for breeding and for them to lay eggs whose hatchlings will drop back down into the compost bins.