I want to talk about composting toilets and greywater systems from the standpoint of the chemicals involved, how likely they are to grow mold, the costs, and the benefits for someone with MCS to being semi (or totally) off the grid.
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1. First Generation Composting Toilets
I had the SunMar Spacesaver in my tiny house because it’s the smallest indoor self-contained composting toilet I could find at the time of building in my area, and the only one that would fit in my tiny bathroom.
It was also the best-priced unit at the time. I absolutely do not recommend this toilet as it completely fails at handling liquids. Here are a few of the other challenges followed by some recommended brands.
Toxic Additives in Composting Toilets?
I had a bad chemical reaction to the additives. I didn’t know that the toilet requires a significant amount of input in terms of additives (and money).
There are three things you need to add regularly: 1) an enzyme spray which smelled fine to me, like a very light non-toxic soap might smell, 2) a bulking material of hemp, peat moss…. and maybe sawdust. This material could be problematic for those extremely sensitive to mold.
You could definitely make/source your own bulking material to make sure it’s safe for you.
And 3) the microbes that you add to speed up the compost and keep it “odorless”.
I had such an acute reaction to the microbe mix. It smells somewhat like a urinal cake. Everything online said it was non-toxic and natural… hmm. I called them to ask what is in it and they said citronella.
Citronella contains methyl eugenol which repels bugs and is a possible health concern needing more studies to confirm its safety. There are a few essential oils I consider to be harmful for MCSers and citronella is definitely one of them.
I had to figure out what kinds of microbes were needed for the toilet and I found out that EMBokashi will work just as well and doesn’t have fragrance added.
After using the toilet for a few months, I can say that the enzyme spray is not necessary. You could just use the Bokashi or Bokashi and a bulking material.
However, I am not happy with this model at all. The upkeep is very smelly work and it often overflows with only one person using it.
Dealing with the overflow is horrible. Even before it overflows the system is such that liquid accumulates below the tray where it becomes very smelly, and moldy.
One person using this toilet full time requires that it overflows into a septic system or blackwater system. Not very self-contained at all.
Offgassing the Unit
Another chemical issue is with the unit itself. It needed some offgassing outside to get rid of the plastic and glue smells. I left it outside for a week. A month would have been ideal. I was extremely sensitive at that time.
Necessary Hook-Ups for the Compost Toilet
There is some installation necessary that ideally would be contemplated before building the bathroom of a new house!
A vent has to go through the wall, outside, and above the roofline. An emergency overflow valve needs to go through the floor and out to…. somewhere (a bucket)… or to the septic or sewage drain if you are on the grid.
You do not need to have water as an input for this type of unit or bolt it down in any way.
There are electric and non-electric self-contained units. The Spacesaver is electric. It does have a small fan which creates negative pressure, though it can easily be overpowered by a bath fan – pulling the odors back out.
There is a need for a special outdoor compost for self-contained indoor composting toilets; they say the humus the toilets produce is totally benign but there is no way it is in there long enough to be benign.
Benefits of Having a Composting Toilet
There is a huge benefit to being off the septic system and that is the freedom to put your tiny house/yurt/dome on any piece of land with some extra amps to spare & a freshwater hose (and of course you could get totally off the grid with solar panels and rainwater collection).
Challenges of Having a Composting Toilet
If you are comparing the initial cost and cost of (ongoing) inputs to just hooking up to a city sewage line, then the self-contained composting toilets are going to seem expensive.
If you are comparing the cost to installing a rural septic tank and the maintenance of that septic tank, then it starts to seem like a really good deal.
If you are extremely sensitive you’re going to want to make sure you can source some tolerable bulking material before you start.
A lot of the maintenance also includes some strong smells of excrement so you have to be able to tolerate that. It you don’t want things to start festering and producing bacteria and mold you have to empty this often, possibly every day.
I have seen some mold growing in the finishing drawer.
Another challenge for people who are disabled is that there is some work – there is the buying of the additives and maintenance. Maintenance involves turning a crank every second day for a minute.
Unclogging the mesh screen if that ever clogs up, checking to see if the system has overloaded via the emergency drain and other troubleshooting if anything goes wrong.
There is a fair amount of troubleshooting so far for me. The fan will have to be replaced or fixed if and when it stops working.
You also empty out the bottom drawer of humus every few weeks.
I’m having trouble with the Spacesaver as I don’t think it has enough capacity for one person let alone two. The tray is filling up too fast, which can be a major problem if you don’t have somewhere safe to dump it and it overflows liquids.
I don’t recommend this one as it does not handle liquids well. A urine separator would be the next type to consider.
2. Urine Separating Composting Toilets
Those who live in tiny houses began switching over to urine seperator toilets to get around the problem of the first generation of composting toilets.
What’s different about these is they separate the urine out to a separate collector.
This is crucial. It is the reason the Sunmar was overflowing and going moldy in the tray for me. I would go with one of these for sure when I replace the Sunmar.
3. Dry Flush Composting Toilets
The other type that is popular now and is even more suitable for the chemically sensitive is the dry flush self-contained.
A dry flush self-contained uses bags to contain the human waste. It’s much cleaner and much easier.
The bags are somewhat expensive and you have to carry them out to a trash bin.
Some people are really happy with this and it eliminates a lot of problems with smells and mold with the other ones.
4. Incinerating Toilets
Incinerating toilets like the Cinderella are making a bit of a comeback. Some chemically sensitive folks have chosen this option for ease of use.
No human waste to collect, no bags to throw out.
Folks who are chemically sensitive can often tolerate the smoke but you will have to decide if that is right for you.
Those primarily mold sensitive may like this option.
5. Bucket and Bag Set up
Other Types of Composting Toilets
This post deals with indoor self-contained units but other types of composting toilets include: an outdoor bucket system, an outdoor dug out (outhouse), indoor central flush, central dry, and indoor bucket systems.
6. Greywater Recycling
Being off the septic system means you also need to safely recycle your greywater – which is the water that comes out of the kitchen sink, bathroom sink and shower.
These contain more bacteria than you think via raw meat and the bacteria on your body etc.
There are a lot of different types of systems and for more detailed instruction this book is super user-friendly and outlines the simplest options depending on the number of people you have on the system.
You need both some kind of filter and water dispersion. We tried just burying the pipe so that the water would simply drain into the ground but the water could not absorb fast enough and it backed up through the house. Gross, yes.
We dug a small pit and it still backed up. Right now I have a larger pit but it still has no filter on it, it worked fine for years with little upkeep. (Note it’s not technically safe to have the water drain above ground, but this did work fine for me).
Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.
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