Hello Marcos
I built a composting toilet for the family farm about 40 years ago based on a little book published by McGill University of how to build a Clivus Multrum type composting toilet from concrete blocks. We had a rather large family so it was too! I built it 6' wide and 8' high and about 8' long! Amazingly, it worked (without EVER being emptied) for almost 25 years with regular daily use by 8 to 12 people and holiday use by up to 50 people.
I can no longer find a link to McGill's little book but you can see how they work here at the Clivus Multrum site :
http://www.clivusmultrum.com/science-technology.php
You can see that building it from other materials is also possible.
I also built the same type of toilet - just not as large - about 35 years ago, in a float home I built on the west coast. I welded it in while I was building the barge and made it the right size to fit in the space under the stairs. I made the clean out door in the side instead of the end so it could be emptied from outside the float home for use in the flower boxes. I used sheet steel, painted on the outside and coated on the inside with coal tar epoxy (which I have since decided is NOT environmentally friendly). I do believe that ferro-cement would have been a better choice and might have built it from that if it had not been built in a floating structure.
The original Clivus Multrum was originally built with an additional 'Input tube' from the kitchen for vegetable scraps. I noticed that they have now stopped doing that and assume that it is because of of fruit fly population explosions that we had happen on the farm.
If you have adequate dry materials to add after every use, then urine buildup will not happen, but if you can divert the urine, you can use it sooner and you will have an easier time maintaining the desired aerobic action.
More recently I retrofit a house that seemed unsuitable for a Clivis Multrum type toilet to have a simple plastic 45 gallon drum type composting toilet. I used it for about 6 years but found that even when switched out the barrels for normal sized plastic garbage cans, to accumulate the waste in, they became very heavy and required quite a lot of yard space - as well as taking almost a year to break down (due to chilly winters). And those were the fast ones! The ones that I made the mistake of using yellow cedar planer shavings in are still working hard trying to decompose the yellow cedar! (Which really should have occurred to me because we used the yellow cedar to build and repair boats BECAUSE it does not rot easily!)
Here is what I have learned. Red wriggler worms help a lot to speed composting up! So when setting up a new empty container for use, I add a shovel full of almost completely decomposed material (loaded with worms) from a previous bucket (that I also added worms to). Then I also add a fair amount of shredded paper or cardboard or other dry absorbent material to the bottom of the container as well. The worms especially appreciate reasonably thick layers of cardboard or newspaper and seem to go there to mate or rest.
I now use a wider variety of materials for my covering material. Peat moss, recycled potting soil, leaf mold from composted grass or leaves, coffee grounds, straw, dried grass, dried seaweed, chopped up weeds, etc all work well but ANY absorbent material that worms enjoy eating and you have access to is also fine. Most carbon based organic material is fine, just NOT fir, or red or yellow cedar sawdust or shavings if you want the compost to be ready in any reasonable length of time!
I guess the most important lesson I have learned with this smaller container composting toilet, is that the bigger stationary composting toilets are best - even if it seems to be quite a lot of work and in some cases may take up space in a basement or require angling the chute from the toilet to the tank out through a wall away from an existing house and then digging a big hole in the ground, to install the large compost chamber outside the house. It really is worth it!
It is both nicer and safer to live with the Clivus Multrum type composting toilet. Nicer because you are not regularly wrestling with heavy containers and safer because those same containers are full of potentially dangerous bacteria and other pathogens since they are too small to allow the compost to be matured before they have to be moved! The large stationary toilet also makes it easier to keep flies and animals out of the composting manure through the use of screened vents and better latching or locking lids on the clean out chamber. This is quite important because I have had both high winds and animals (like raccoons and bears) knock the lids off the smaller compost containers allowing rainwater to flood them and REALLY make a mess!
When planning a new house design I often work the toilet position into the layout very early and try to keep the storage chamber in a fairy central and very warm area (like next to a wood fired stove or furnace). I do this for a couple of reasons. One is that the compost will break down much faster in a nice warm environment and the other is that during a cold winter the compost will continue to break down at the same speed which it will not do if the temperature drops past a critical point! In a cold climate the additional warmth radiating out in all directions from the compost container in the warm space is an added benefit, allowing you to recover what would otherwise be wasted heat.
If possible I do like to extend the chamber so the clean out door is outside the home - preferably inside a greenhouse or even a woodshed where it is still warm but where it easier to get your wheelbarrow close enough to make emptying the chamber as easy as possible.
Hope this gives you some good ideas:-)
Nancy
