About Composting Toilets

Thu, 10/16/2008 - 14:39 — Compost Stu

About Composting Toilets
Composting toilets fall into two categories, wet and dry. The wet types are not much good if you want to retrieve your compost so I won’t go into them in too much detail. I have a simple theory when it comes to human faecal matter: If you don’t eat, you don’t shit and if you don’t shit you die. So compost your shit and grow your food to eat and live. If you’ve got this far and you don’t know what a composting toilet is then this is for you, basically they are toilets that compost your shit and piss! Of course there are many, ways to skin a crap, so there are plenty of different types to choose from. Most work on the principal that if you get the carbon : nitrogen ratio right and aerate well, then the bum nuggets will go through a mouldering process that takes about a year and completely changes their biological makeup.

The first composting toilets probably originated when people noticed cats covering their deposits with earth or leaf litter and copied them. So maybe they were good for something after all. From then on it was no flies on ours!! The Chinese and Vietnamese were early pioneers of the modern variety. They used a double chambered vault that de-composed anaerobically (pooooohhhhyy) and separated urine. The resultant goop was then used directly on food crops. This was NOT an effective way to kill pathogens in faecal matter.
Later on the Swedish came up with the aerated vault version, on which many of todays more successful composting toilets are based. Modern dry composting toilets can be simply classified as either batch composting types or continuous reactor types. The former use a receptacle that is sealed after being filled, whilst deposits are made into another identical receptacle. The first is then given at least one year (or more where diseases are present in the community) then emptied to be used again. Continuous types simply fill from the top, allowing a minimum of 12 mths before the compost in the vestibule (receiving area) can be removed. When choosing a composting toilet for your own needs, apply the KISS (Keep It Simple Stupid) concept liberally, as many well meaning designers have over complicated an essentially simple idea. The less moving parts (preferably none), the better.

Urine Separation
Eventually, we will all be doing this, one way or the other. Urine contains plant nutrients in an ideal balance for the healthy growth of most plants, and actually contains most of the nutrients in our by-product stream. (Insert Graph, source: Ralph Otterpohl, in Water, Vol 21, 2001) Most composting toilets do not have the facility to easily separate urine from faeces. Unless they are designed with the Asian “squatter” plate, it has proven difficult to come up with a pedestal type that effectively separates urine. Although the squat is the most practical position from which to empty ones bowels (due to the extra pressure on the bowel from the closer diaphragm), many in the west are uncomfortable using the squatter. Actively choosing to urinate in a different place seems the simplest way to separate urine from faeces. Of course there will always be a small amount that is excreted along with poo. I advocate the use of a simple sawdust bucket system for urine collection. A 10L bucket should be filled with sawdust from a timber yard (moist and biologically active sawdust is best). This can be placed under a conventional toilet seat frame and used for urination. When the urine reaches the top, it can be emptied directly out onto a tree or the garden. The sawdust prevents the urine from smelling and balances out the nitrogen in the urine with carbon. My system uses a bidet which flushes the urine with a small amount of water into a dosing siphon. The nutrient rich brew then mixes with treated grey water and gravity dose irrigates about 400m2 of garden beds.

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