Cement Mixer Composting Toilet?

[miscrms]

So, I don't know if this will go anywhere but I thought I'd put the idea out there. Should I end up actually building it I'll document the process and learnings here.

So, I'm feeling frustrated by the composting toilet options available and thinking about a DIY build. The nature's head unit seems well liked, but doesn't really compost and seems likely to be on the small side for a family of 5 planning to full time off grid as much as possible. And it seems expensive for what it is. The "real" composting toilets are ridiculously expensive for what they are, generally don't rate very well, and are not really configured in a convenient layout for Skoolie use. And the all in one units still may not be big enough for our family. The idea may end up being completely impractical but we'll see where it goes.

So if we go this route, the design spec may be a little different than most. I love many of the low cost designs folks have come up with, but if I can stay under the cost of the Natures Head ($1000) and have something that work and fits our needs better, that would be a win. It would also be somewhat driven by the specific layout of our soon to be bus, which has a side emergency door directly over a belly storage bin.



I still need to read up more on the specifics (get the humanure book), but here's my basic understanding from using a Sun-Mar at my parents camp and having a compost tumbler at home. As I understand, effective composting takes heat, time, aeration and mixing, as well as the basic balancing of nitrogen, carbon and moisture to promote digestion. Time in this case means several stages of "finishing" and sufficient storage volume in each stage to let time pass before material is moved to the next stage. Adding an external heat source, air circulation, and mechanical mixing can all help accelerate the process and reduce the time / storage volume required. Since space is a premium on a bus, and we won't have an off site storage option, maximizing these acceleration factors seems key.

One of the main things most commercial composting (or desiccating) toilets seem to have that most DIY's don't is the mixing / aeration component unless it's done manually. Air circulation and heat are relatively straight forward, but mixing less so. Which brings me to the cement mixer idea ;) There are a number of upright style designs that might work, but I'm leaning toward these externally driven side dump type designs at the moment. Harbor freight has two sizes, a 1.25 cuft. (9.4 gallon) for $160, and a 3.5 cuft. (26.2 gallon) for $210.

https://www.harborfreight.com/1-14-C...xer-61931.html
https://www.harborfreight.com/3-12-C...xer-61932.html

Turns out I'm not quite so clever as I thought, as their are numerous examples on the internet of folks using old cement mixers as composters.

My initial though is to build a relatively air/bug tight box over the upright mixer, which would be shortened by modifying the legs below the crossbar. Ideally the inside of the box would be water tight as well, maybe shower polywall or something, to contain any inevitable spillage. The box would then have a top hole and toilet seat, and heat source / ventilation like most more traditional DIY units to accelerate composting and help control odor. The mixer could either just be manually run every so often, or perhaps put on a timer to run at regular intervals.

From there I have two thoughts. One is the bottom of the box becomes the first finishing tray stage. When the mixer drum gets to a certain fullness, it would just be dumped into the tray below. Then the drum is ready for the next load, and the first load has time to mature. Ideally this tray would be designed in a way that it could be pulled out through the open emergency door for disposal. Or, designed to slide out and dump into a second slide out tray / bin located directly below in the belly bin for storage and more finishing. Alternatively the whole mixer drum assembly could be designed to slide out the emergency door and dump directly into the belly storage bin.

Thought / comments welcome!

Rob

[Rusty]

Originally Posted by miscrms

One of the main things most commercial composting (or desiccating) toilets seem to have that most DIY's don't is the mixing / aeration component unless it's done manually. Air circulation and heat are relatively straight forward, but mixing less so. Which brings me to the cement mixer idea ;)

Thought / comments welcome!

Rob

There is a build on here... or youtube.... but he had the usual 5-gallon bucket, but he installed a motor under the bus that had a shaft that protruded up into the bucket. He put a paddle on it and it mixed the excrement to aerate. I forget where he took the motor off off... an old microwave turntable or better: a BBQ rotisserie motor would work.

Somebody chime-in and help me remember whose video.

[Njsurf73]

I seem to remember the same, but not exactly who. I have a couple old bbq motors you can have! I have never used the rotisserie function!

Sent from my XT1254 using Tapatalk

[Rusty]

Originally Posted by Njsurf73

I seem to remember the same, but not exactly who. I have a couple old bbq motors you can have!

Thanks , NJ. I just want to 'borrow' them, I will return them when done.

Guy was on youtube- pretty big build, some neat ideas- was a tall bus.

[Doktari]

Bumped this thread. Ive spent the better part of this afternoon mulling over toilet options. I wondered about cement and mortar mixers then I stumbled on these meat mixers. I like stainless steel. I don’t care if it doesn’t look like a toilet as long as it works well. I see there are meat mixers of all sizes up to a huge family size electric powered beast like this one:
https://www.amazon.com/Hakka®-Electr...%2C321&sr=8-14
I’m single and don’t know what size I’d need. But about half the size of the biggest one. Maybe 60 lb? Some of them tilt and dump. Wheels could be attached to the legs so they roll under a counter? Maybe they could be accessed by a hatch on the outside of the bus and then dumped into a cart or just a hole in the garden or a composting pile? Modifications would be needed to the lid for a seat and vent. A medium size mixer would cost about one third the price of a Natures head composting toilet and possibly be better?

[musigenesis]

Originally Posted by Doktari

I’m single

You're probably gonna stay that way with a meat mixer for a toilet.

[Simplicity]

Best homemade composting toilet I've found:

https://youtu.be/9Xx9_f7n2b0

[Doktari]

Originally Posted by musigenesis

You're probably gonna stay that way with a meat mixer for a toilet.

Haha, could be. They don’t have to know it was a meat mixer lol.

[s2mikon]

Originally Posted by musigenesis

You're probably gonna stay that way with a meat mixer for a toilet.

With that and a good magazine you'll never leave the head.

[Doktari]

Originally Posted by Simplicity

Best homemade composting toilet I've found:

https://youtu.be/9Xx9_f7n2b0

Thanks, that looks like a decent variation of the 5 gallon bucket composter. I looked a hundreds of mixers like that cement mixer on Amazon and am still searching for options. As the OP started out asking about a cement mixer I’m working my way down to a bucket via a meat mixer lol. My personal preference is something bigger and more industrial than the small buckets. Buses are huge, why not put something bigger? But my ideas could change if it’s nit pragmatic. My concern is that a small bucket doesn’t really compost well or have time to compost. My understanding is it takes a lot of carbon material to get the 12:1 ratio so a bigger container might work better? Also high mass is going to help it seems. But if it’s heavy to move that could be a problem. Personally I like the idea of a continuous system rather than a batch system. A Clivus Multrum composter is a example. It works on gravity. Raw material goes in the top and finished compost comes out the bottom as it’s dug away. They don’t fit in a bus. Or do they? A lot of big buses have basements. Cut a hole in the floor and stack two composters? My small bus does not have a basement. The two-bin mouldering toilet is my other favorite. When one container is full it is left to moulder for a year or two while the other is used. I’m thinking of doing this method but will have to haul the full container in my trailer. I’m not pleased about that. I have two 13 gallon barrels. They are heavy when full.

[Doktari]

Wait a second. That hole in the floor and stacked composter idea might have merit?. Opening the outside hatch and emptying finished compost might be easier than doing it inside the bus? I bet it’s been done before?

[Doktari]

Originally Posted by s2mikon

With that and a good magazine you'll never leave the head.

Ha, gotta try that someday. Do people do that?

[s2mikon]

I bought the c-head that this video was copied from about 10 years ago for my other bus and just transferred it over to this bus. It works fine. I like some of the improvements that they did and have thought about it over the years. The gallon jug looks Disney but it does work and can be thrown out and replaced every time. Capacity: If I stay in the bus full time by myself I can get 2 weeks out of the pooper hopper and can push it to 3 weeks but not more. The jug? Well I was born with outdoor plumbing so it doesn't get so much use. I've been carrying a 5 gallon bucket in the storage bay and can empty in to it twice before it is full. So figure 6-7 weeks per person for the pooper hopper plus 1 5 gal bucket.

[s2mikon]

Has anybody tried the Eisenia foetida composting worms yet in their composting toilets? From what I have read on line they are used in parts of the world where they need sanitation in refugee camps and are endorsed by the UN and the Bill and Melinda gates foundation.

[Doktari]

Originally Posted by s2mikon

I bought the c-head that this video was copied from about 10 years ago for my other bus and just transferred it over to this bus. It works fine. I like some of the improvements that they did and have thought about it over the years. The gallon jug looks Disney but it does work and can be thrown out and replaced every time. Capacity: If I stay in the bus full time by myself I can get 2 weeks out of the pooper hopper and can push it to 3 weeks but not more. The jug? Well I was born with outdoor plumbing so it doesn't get so much use. I've been carrying a 5 gallon bucket in the storage bay and can empty in to it twice before it is full. So figure 6-7 weeks per person for the pooper hopper plus 1 5 gal bucket.

Thanks. That’s decent time frame I guess. I might end up going that route. Two weeks is a bit shorter than I hoped. I just watched a C-head video and he does secondary composting outside in his bins. Your extra bucket might help. I’m just looking at all options. I definitely don’t want to bag it and be continuously looking for somewhere to toss it. The small meat grinders are interesting and only $140-$200. I haven’t given up on them yet. There are 7 gallon buckets available. I’m tall and the extra height and capacity would be good.
https://www.amazon.com/40-Pound-20-L...%2C321&sr=8-17

[s2mikon]

Maybe Bill Gates wasn't paying attention and he thought somebody said operating system and replied yes they need worms in it.

[s2mikon]

There is also diesel fuel and a match. We did it in Vietnam.

[Simplicity]

Be careful when using a composting toilet. I just read about a woman that used a rustic one and a bear was below it for some reason. Nipped her in her butt!

Hmmmm, worms. Funny, I am putting together a worm composting tray, for my food scraps, as an educational experience for my friends daughters. Maybe I can poop and recycle my food scraps at the same time. Simply dump the whole bucket and start a new tray.

Per Gates and Windows, didn't seem too many worm problems, but lots of viruses!

[s2mikon]

You see bears are like politicians you can't trust them in an outhouse with a muzzle on.