Operating Process
Although there are many designs, the process factors at work are the same. Rapid aerobic composting will be thermophilic decomposition in which bacteria that thrive at high temperatures (40-60 °C or 104-140 °F) oxidize (break down) the waste into its components, some of which are consumed in the process, reducing volume, and eliminating potential pathogens.
Drainage of excess liquid or leachate via a separate drain at the bottom of the composter is featured in some manufactured units, as the aerobic composting process requires moisture levels to be controlled (ideally 50±10%): too dry, and the mass decomposes slowly or not at all; too wet and anaerobic organisms thrive, creating undesirable odors (cf. Anaerobic digestion). This separated liquid may be diverted to a blackwater system or collected for other uses. Some units include a urine-separator or urine-diverting system.
Where solar heat is used, this might be called a "solar" toilet. These systems depend on desiccation to achieve sanitation safety goals features systems that make use of the separated liquid fraction for immediate area fertilization.
Urine can contain up to 90 percent of the N (nitrogen), up to 50 percent of the P (phosphorus) and up to 70 percent of the K (potassium) present in human excreta. In healthy individuals it is usually pathogen free, although undiluted it may contain levels of inorganic salts and organic compounds at levels toxic to plants.
The other requirement critical for microbial action (as well as drying) is oxygen. Commercial systems provide methods of ventilation that move air from the room, through the waste container, and out a vertical pipe, venting above the enclosure roof. This air movement (via convection or fan forced) will vent carbon dioxide and odors.
Some units require manual methods for periodic aeration of the solid mass such as rotating a drum inside the unit or working an "aerator rake" through the mass. Composting toilet brands have different provisions for emptying the "finished product," and supply a range of capacities based on volume of use. Frequency of emptying will depend on the speed of the decomposition process and capacity, from a few months (active hot composting) to years (passive, cold composting). With a properly sized and managed unit, a very small volume (about 10% of inputs) of a humus-like material results, which can be suitable as soil amendment for agriculture, depending on local public health regulations.
Composting toilets greatly reduce the volume of excreta on site through psychrophilic, thermophilic or mesophilic composting and yield a soil amendment that can be used in horticultural or agricultural applications as local regulations allow. In combination with a constructed wetland these even require only the half area.
These should not be confused with the pit latrine, arborloo or tree bog all of which are forms of less controlled decomposition, and may not protect ground water from nutrient or pathogen contamination or provide optimal nutrient recycling.
Read more about this topic: Composting Toilet
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