Introduction: Composting Toilet

By NaturTrauM
About: With a Master in robot engineering i'm very interested in open source technology and the developpment of simple and local energy sources. Besides that I'm a nature lover, wilderness guide and vision quest tuto…

A composting toilet is a simple, watersaving and logical alternative to the water closet we know. No need for a water supply, no sewers and no sewage treatment necessary.

For me it's even a very practical way to become a part again in the ecological live-cycle of soil-plant-food-digestion-soil.

The idea for this toilet comes from the german leaflet "Das Kompostklo" you can order under:

http://www.packpapierverlag.de/?p=574

I don't provide here all the construction details of my particular toilet, but rather the principle and the materials and measures I used for our toilet which is operational for more than a year now. Our toilet is very compact, and the 200 liter barrel is enough for 1 person yearround use.

If you need all the 3D CAD SolidWorks files, pease contact me.

Step 1: The Principle

This toilet works similar to an oven: The barrel has a grid about 15cm from the bottom, on which the composting material collects. Underneath the grid is an opening through which, ideally pre-heated, the air flows into the barrel, through the composting material and out through the air exhaust tube at the top, which is ideally heated too to improve the air flow. Heating is done through south-faced windows and black paint. (There's also solutions to further improve air-flow with a wind-driven ventilator at the top of the exhaust).

On top of the barrel you put a Board with a hole as you know from a normal shithouse. The holes is closed by a nicely fitting lid to make sure the air flows out through the exhaust. The air flow is to for heating with solar energy on one side, but mainly to keep the compost heap dry, especially if there's a lot of urine input.

Through the opening at the bottom you can take out finished compost. If there's too much fluid, a little drain tube at the bottom of the barrel makes sense, which leads to a bucket underneath the toilet. This almost odorless brown fluid is very potent fertilizer, which can be used, diluted 1:10, on fruit trees and shrubs or high veggies like tomatoes or eggplant.

The measures published here are for a small toilet with 200 liter barrel, which serves one person year-round or more with breaks. Especially in winter rotting goes slower. The toilet I built is constructed modular, such as to allow to take it apart easily and to be aple to orient the door west or north instead of east without much changes. The choice of materials and how exactly you solve the details I leave up to you. I used paletts for the walls and otherwise mostly what recycled wood and other materials I had around.

Attachments

Step 2: Materials

  • A composting compartment (our 200 liter barrel is not quite enough for the two of us). Ideally plastic, metal works too but rusts.
  • Metal bars or angle steel or similar for the grid
  • Wooden planks for the house (i used large pallets), some larger pieces of plywood come in handy for the floors. The house in my case was very small, only 80x120cm, which is just enough to turn inside ;-)
  • some 5mm plywood for covers
  • A suitable roof, e.g. corrugated sheet
  • Some wood treatment for the outside (I used linseed oil and ferrite powder (as they use in sweden for their wooden houses))
  • A glass window (double layered) with frame for the southside of the barrel
  • Pieces of glass or plexi for the southside of the air exhaust tube
  • Black paint
  • A tube of about 100mm Diameter with a bend (chimney pipe or ventilation pipe, maybe flexible?)
  • Four good hinges for the door and the southern window
  • Optional: piece of sheet metal, to but before the opening of the barrel at the bottom to improve air pre-heating

Attachments

Step 3: Construction Details

See some of the construction details described in the Pictures. I'm sorry the pictures were made after one year of use because i lost the ones i made while constructing.

The grid you see in the third picture can be made of any material as long as it can hold 100kg of compost, and should have clearings of around 5cm. In my case i fixed it by just drilling four holes into the barrel sides and pushing the metal bars through.

Make sure to cover up the air inlet and outlet with fly sheet to avoid flys and the like.

Insulation all around the barrel helps keep it warm for faster rotting. I used straw.

I cut the hole with an 15° inclined jigsaw. This I could use the inside piece, with some sealing tape around it, as a perfectly fitting lid.

As i described, I made the whole construction modular. This means I made two pieces of wall 80x220cm, two pieces of wall 80x250cm with slanted top, and one wall 80x220cm including the windows for the southside. These can be assembled as necessary to have the door facing north, east or west.

Step 4: Instructions of Use

This toilet lets everything rot inside the barrel and you just remove the finished compost through the lower opening. If there's too much material (as in our case ;-), you can always shovel out some and compost it somwhere outside. Just make sure to properly cover it up with other material and let it rot for at least a year. The compost, as the fluid fertilizer, you can use to fertilize trees, shrubs and high vegetable plants like tomatoes, peppers and the like.

The use of the toilet is simple: Do your business, put some drops of EM (effective microorganisms) if you have, to support the composting, then cover it with some hands full of wood shavings, straw, hay or leaves and close the lid. Ideally, don't pee too much into the toilet (do it somewhere outside if possible) or make a urine separation or a little urinal. Otherwise you get more fluid in the bucket underneath and need to empty it regularly. And too much fluid slows the rotting process and when the material gets too wet and sticky, air flow is diminished.

Important:

  • Before the first use, put some little twigs and some straw or hay on the grid, as well as some well-matured compost to have a good foundation for your compost.

  • For more than one Person year-round you should probably take a bigger compartment

  • Use enough wood shavings, straw, hay, leaves etc. especially in winter when rotting slows down due to cold. This avoids odor and makes sure all the fluid is absorbed and the air flow is always maintained.

  • EM (effective microorganisms) help against odors, especially in the case of too much fluid and thus anaerobic rotting.