ELI5: How do compost toilets work

[lindabarzini]

(Explain like I am 5)

How do these compost toilets that are self-contained work? What about odor? Are these considered an upgrade from a jabsco marine head?

I can't see dumping and rinsing the bottom receptacle. Do people just purchase several empties?

[lonesoldier0408]

The information on most composting units, use only the supplied receptacle, storage of spares would not be practical on a vessel. Many sites state that, "Periodically washing out the receptacle is ok, but not required, as the residue from previous compost, kick starts the next batch."
Dump while at sea or bag and dumpster drop at the marina.

The higher end models have ventilation fans, as part of the process to dry the compost.


Still surrounded by anchors.

[moepitman]

The two most prevalent seem to be the Air Head and Nature's Head. I've been looking into these, as I recently acquired a '70's vintage boat with the original plumbing (direct to the through hulls). The old head was damaged and unusable. I still haven't decided whether to go with one of these or build my own, as they are quite expensive.

As to how they work, they explain it rather well on their websites:

Air Head is here, and Nature's Head here.

I've spoken to several people who like them, and one who's not a fan. Since I work in health care, the "gross-out" factor probably doesn't affect me so much, so I'm willing to try it. It seems to me that the potential for disaster is minimized, with no through-hulls in use and no tank full of sewage under my bed. It's all confined to the head compartment.

[vjm]

"Composting" toilets separate urine and feces, and the feces goes in a receptacle filled with a dessicating medium which dries out any dampness. This keeps the feces portion from smelling. Most users describe the only odor from a properly used and set up composter as earthy, like a bag of soil you get at the garden shop. After the contents have sat for six months, they can be spread as compost, although most sources advise not putting it on food crops from an abundance of caution.

The urine goes in a separate receptacle, which has to be emptied more frequently than the feces receptacle. There can be some odor with the urine, but there are various things you can add to the urine receptacle that knock it out.

So, properly installed and used, no objectionable odors, and dead simple.

What you do with the contents depends on where you are and your own priorities. If you have a garden, you can take the feces receptacle contents home and let them continue composting. If you are far enough offshore, the contents of both receptacles can be pitched overboard. If you are in a marina or have shore access you can dispose of the feces receptacle contents in a garbage dumpster and pour the urine down the restroom toilet. If you need to wait, you can put a lid on the feces container and just let it keep composting aboard. You can also cap the urine jug and wait to dispose of it. Obviously, multiple containers would be needed for this strategy.

Rinsing the feces bucket usually is not necessary or recommended, but you can if you need to. Rinsing the urine container is a good idea.

The only problems I have heard of are bugs, which can be taken care of with a handful of diatomaceous earth in the feces receptacle, and needing more air circulation to encourage dessication, which can be easily dealt with by installing a vent hose and fan.

There are some accounts of folks who just can't seem to get the hang of keeping the urine and feces separate. This is just operator error. Lots of people, men and women and kids and guests, do just fine with composters as their only toilet.

There is a huge thread on the topic that is worth reading and multiple other threads as well. The manufacturer's websites are also helpful, so check out Nature's Head, AirHead, C-Head, and Ecovita.

I would consider a composter a huge upgrade from an traditional marine head system, but opinions differ.

[boatster]

Do composting heads have to be vented or can they be self-contained like a porta potty?

[AJ_n_Audrey]

I own an early 80's boat with original head, which I have already re-built once. The head is now starting to exhibit signs that it will need to be repaired / re-built again, and I am considering an Airhead replacement. As I understand the composting feature, peat is added to aid in composting, but regardless of the process, I like the idea of no holding tank (reclaimed storage space), one less thru-hull, and no pump-out or discharge at sea. I have done a lot of gardening, so I understand composting, and I'm not fussy about how waste gets handled, so I am pretty sure a composting toilet is in my future. Having to periodically empty the urine container is no big deal to me, and emptying the number 2 container is something I have promised my wife I will never ask her to do, so she's on board (so to speak).

[Chuck Hawley]

On a related topic: I've often wondered if urine can be dumped overboard anytime, even within three miles of shore. The argument would be that it doesn't contain coliform bacteria, so is not regulated. Putting it another way, the effluent, if pumped out, would show zero % of the substance that the MDS laws are based upon. Plus, I believe it's sterile.

Just asking.

This would essentially mean you could dump urine without fear of repercussions.

Cheers,

Chuck

[vjm]

Originally Posted by boatster

Do composting heads have to be vented or can they be self-contained like a porta potty?

Most do, some don't, and I believe I saw one vented into an interior storage space somewhere on the net. It's really about moisture evaporation not venting head smell so much.

Please don't use peat! It's an environmental issue and not really renewable. Coconut coir works great and is available at pet stores and on Amazon. Some brands work better than others, and there are different techniques to break off a chunk and rehydrate it slightly before use. As far as I know the environmental concerns with peat are not true for coir.

[AJ_n_Audrey]

Chuck, the other option on dumping urine is to put the container in a bag and carry it to the marina restroom. But with regard to pollution, I have no evidence to substantiate this, but I believe swimmers sometimes pee in the ocean....and then of course, there are whales........;-) But yes, urine is mostly sterile.

vjm, good info on coconut coir, and that's good news for me from a re-supply standpoint, because there are many coconut trees in my intended cruising areas.

[jcdexter]

We've been using an Airhead on Tribute for 6 years. We have the fan and have zero odor. Ours is a two head boat. I've had to rebuild the Raritan which is also 6 years old twice and replace the hoses once because they became completely clogged with salt. The Airhead has required zero maintenence. I wish both my toilets were Airheads. Two Airheads would allow two people to go 60 days without emptying. With the help of Geoff at Airhead, I plumbed the urine container into my holding tank with a simple foot pump. Works great!

[PeteHalstedc]

For our project we purchased ours from C-Head portable composting toilet system. We haven't put it to use yet, but did a lot of research before purchasing and as others have mentioned most report the only possible smell being an "earthy" smell. One of the keys to the smell is the separation of urine and Feces. It is when the two mix that all of the "really bad smell" happens.

First I will say Sandy at C-head was great and worked through the process with us and did some customization and recommendations for our specific installation. I would definitely recommend looking at C-Head as well as Natures Head and Air Head, especially if cost is a deciding factor or you are thinking of building your own.

As I said we haven't put it in place yet, but I can say it was very satisfying removing a bunch of stinky hoses, a holding tank, and next time we do a haul out, 2 thru-hulls will be removed as well.

[captlloyd]

My favorite reply: go on ''YouTube'' and learn all about it. Just type in ''Composting toilet''. "YouTube '' is great !!

[AD28]

sigh.

been discussed ad nauseum

[oldragbaggers]

Originally Posted by lindabarzini

(Explain like I am 5)

How do these compost toilets that are self-contained work? What about odor? Are these considered an upgrade from a jabsco marine head?

I can't see dumping and rinsing the bottom receptacle. Do people just purchase several empties?

These two RVers have videos that give the clearest explanations I've ever seen and answer all the questions. Check these videos and you'll know all you ever needed to know.

https://www.youtube.com/watch?v=_E2xOoNov9s

https://www.youtube.com/watch?v=5CdnVZkCKXU

[Minggat]

How do they work?

Very very well. Non issue.
Think cat box without the smell.

Cat boxes smell because there is no urine separation.

I once had a crew dump the urine in the solids bin. The result was ammonia smell. The fix was to dump that batch and start a new one. So easy.

The most helpful thing to remember is that they are only called composting toilets. I imagine that is because land based units really do try to compost. As has been mentioned, their real function is to dehydrate.

As for "kick starting" batches, again, this sounds like someone has not let go of the idea that they don't really compost.

As for venting, there is no smell to worry about. None. The venting then is an aid to removing humidity as a part of dehydrating.

As for the 2 manufacturers mentioned. I'm glad that I waited and did not buy one of them.

C Head. Give them a look. Could not be more simple to use.

Back to the "cat box" principle.
Life got even more simple once I started treating it like a cat box. For any more details than that, just think about what it takes to make that work, minus the smell. I have not changed out a batch in well over a year. I Just top it up.

I use coconut coir simply because you can buy it in compressed bricks. Sawdust works very well.