This technical brief describes a composting toilet that has proved to be most effective in [water-logged] areas where pit-latrines and septic tanks are inappropriate. It is a simple design that does not require electricity or great investment. Built using local materials, it is a self-contained unit that produces good compost and protects the soil and water from any contamination.
The composting toilet is built with two chambers for simplicity of construction and operation. The two chambers are used alternately; after the first chamber is filled, it is left to decompose and only emptied just prior to the other one becoming full. Each chamber has its own opening for removal of mature, non-odorous compost. Some types of composting toilet batch the waste in movable receptacles on trolleys or turntables whilst others generate the compost slowly and continuously as the material progresses through the device. Some require electricity for small heating elements (in cold climates) or fans (to ensure a positive airflow through the system). Some composting toilets combine the urine and faeces whilst others separate them. The compost formed by the combination of urine and faeces is better but these toilets are more likely to smell if used carelessly and they require much greater quantities of carbonaceous residues like sawdust and straw. Many of the more complex types require dry access under the toilet via a basement or cellar room.
The composting toilet comprises a raised slab over two chambers. The chambers are built on the ground, not in it. In very waterlogged areas, or those prone to flooding, a slightly raised plinth can be made. The chambers are plastered with cement internally in order to waterproof them and make compost removal tidier. Over each chamber there is a hole in the slab for faeces and a funnel to receive the urine.
In some toilets, in the centre of the slab, between the two chambers, there is a trough over which the anal cleansing is performed. The anal cleansing water trough and urine funnel is inter-connected and flow to an evaporative plant bed outside the latrine.
Other composting toilets may have a box with plant leaves that can be used instead.
In the simplest version, the chamber doors are closed by bricks and mud mortar, both of which can be reused to close it again. However, ferrocement, timber, marine ply or other materials may also be used where they are appropriate locally.
The chambers are designed to have an accumulation time of about nine months to allow thorough composting of the contents and elimination of pathogens. The compost produced is an almost dry, crumbly, black product having a light, pleasant, earthy odour. There is no fly nuisance or any odour problem and the toilets remain clean and pleasant to use. The plant bed needs almost no maintenance and the only requirement is to cut back excessive growth which can be chopped up and added to the compost chamber if required.