Another Alternate Toilet

Last week I wrote about outhouses as a way to handle human waste if normal infrastructure fails or is unavailable. However, there are places when an outhouse just won't work:

• Locations in the mountains with very little or no soil
• Any area where you can't dig a post-hole without the use of explosives
• Locations near water where the water table is less than 3 feet below the surface (check at high tide)
• Areas below sea level (New Orleans)
• Arid or desert regions where the soil isn't stable or will suck the moisture out of the waste before it can break down
• Areas with dead or toxic soil (salt flats or polluted/contaminated soils)

In places like these, you may want to look into composting toilets. A composting toilet (CT) uses controlled aerobic digestion to break down waste, and the long retention time will destroy most of the pathogenic (disease-causing) organisms present in the waste. Proper venting will keep odors and dangerous gasses out of your living spaces, so it is feasible to put a CT inside a house. There are a few different types of CT on the market, so I'll break them down by how they work.

Slow or Cold Composting Toilets

The simplest style, a slow CT relies on longer retention time and limited use to operate. Most often found in seasonal-use locations without running water or electricity, the slow CT isn't much different than an outhouse, the main difference being that a CT will have some method of diverting the liquid wastes away from the solid waste to allow the solid waste to build up in layers.

A cold CT will take months or years to completely break down human feces, so the holding tank has to be large enough to contain the expected input. I've read of some parks that use a series of vaults arranged in a line or a circle with a mobile structure above them. When one of the vaults gets full, the structure is moved to the next vault in line and the full one is sealed and left to decompose for a few years before being emptied.

The compost from a slow CT is likely to contain some pathogens (unless you can give it a year or so to decompose), so you aren't going to want to use it to fertilize a garden. Trees, flowers, and pastures would be good uses for this type of fertilizer.

Active Composting Toilets

This is the type most commonly found in stores. They usually come with a fan to provide air to the “pile”,  and some will even have a heating element to keep the temperature of the pile at a level where decomposition will occur most rapidly. Liquid wastes may or may not be diverted depending on design, and the addition of bulking agents like sawdust or peat moss after each use will help aerate the pile for quicker action.

An active Ct will break down normal human wastes in a matter of weeks, but since they have moving parts they have more maintenance needs. They are also quite a bit more expensive than a conventional toilet (most are close to $1000), though an active CT should be seen as an investment that will pay for itself in lower water use and production of compost.

The addition of heat and moving air will help kill pathogens, so the compost from this style is normally safe to use on a garden.

Wet Composting Toilets

Sometimes called a “vermifilter” toilet, a wet CT uses a minimal water flush (a pint or two instead of gallons) like a standard toilet to move the waste into a reaction chamber where the liquids drain out through a mesh on the bottom. Red worms or some other type of earthworm (hence the “vermi” part of the name; raising worms is known as vermiculture) are kept in the reaction chamber and allowed to break down the solid waste. There will also be some naturally occurring aerobic bacteria that will help the worms break things down, and once there is a deep enough bed of material they will actually clean the water as it trickles through. The water flowing through the bed will carry oxygen to the worms and bacteria, so it is a necessary part of the process.

The resulting worm feces (castings) and undigestable wastes are considered safe to use as fertilizer on food crops. The liquid that flows through should be treated, or at least disinfected, before being used for anything.

Clivus Multrum

Actually a brand name of a design, a Clivus Multrum is a large inclined room located beneath a toilet. It provides a lengthy retention time and has few moving parts, but needs to be built into a building.

https://upload.wikimedia.org/wikipedia/commons/9/90/Clivus_Multrum_Composting_toilet.svg

If you're looking for a long-term solution and have the space and money, I'm sure one of their consultants would be glad to help you. There are similar designs out there; a search on the internet should find you more information than I have. I've never dealt with one of this style, as they're fairly new (patented in my lifetime) and they look to be marketed at larger structures like parks and campgrounds. The resulting compost should be free of pathogens and safe for use as fertilizer.

Maintenance

Other than the addition of sawdust, wood chips, or peat moss as a bulking agent, there are very few things you'll need to keep a CT running. There are various starter cultures of active bacteria on the market that you may want to use to jump-start your toilet if it has been dormant for a while; I see very little difference between the brands.

If you choose a wet CT, the earthworms will reproduce and keep the decomposition going (and may provide a source of income: think “bait shops”) but they will require a somewhat steady supply of food. Not a good choice for a remote cabin that only gets used a few days a year.

The fertilizer that you'll remove from a CT will return a huge percentage of nutrients back to the soil, making your garden grow better and last longer without the need for commercial fertilizers. For some people, that's enough of a reason to switch to a CT, but most of us aren't going to want to deal with the odors and mess unless we have to.