A composting toilet is a type of toilet that treats human excreta by a biological process called composting. This process leads to the decomposition of organic matter and turns human excreta into compost. It is carried out by microorganisms (mainly bacteria and fungi) under controlled aerobic conditions. Most composting toilets use no water for flushing and are therefore “dry toilets”.
In many composting toilet designs, carbon additives such as sawdust, coconut coir, or peat moss is added after each use. This practice creates air pockets in the human excreta to promote aerobic decomposition. This also improves the carbon-to-nitrogen ratio and reduces potential odor. Most composting toilet systems rely on mesophilic composting. Longer retention time in the composting chamber also facilitates pathogen die-off. The end product can also be moved to a secondary system – usually another composting step – to allow more time for mesophilic composting to further reduce pathogens.
Composting toilets, together with the secondary composting step, produce a humus-like endproduct that can be used to enrich soil if local regulations allow this. Some composting toilets have urine diversion systems in the toilet bowl to collect the urine separately and control excess moisture. A “vermifilter toilet” is a composting toilet with flushing water where earthworms are used to promote decomposition to compost.
Composting toilets do not require a connection to septic tanks or sewer systems unlike flush toilets. Common applications include national parks, remote holiday cottages, ecotourism resorts, off-grid homes and rural areas in developing countries.