Composting toilets do not ...

Composting toilets do not compost feces.  They serve as a means of collecting feces in a manner that reduces odour by adding a bulking agent (sawdust or wood chips) to allow forced air to pass through and evaporate moisture.  By evaporating moisture and passing through oxygen with the air the bacterial action associated with odour generation is reduced.  While an advantage of composting toilets is the elimination of the need to use water to transport the fecal material to treatment and disposal, and avoiding the immediate cost of treatment and disposal, the disadvantages are considerable. Firstly, while actual composting also involves adding bulking component of wood chips, and passing air through the mixture, to actually compost and convert the wood and feces to carbon dioxide through aerobic respiration is much more involved, requiring maintaining moisture rather than evaporation, pH adjustment, mixing etc.  As a consequence the bulking material added to composting toilets increases the mass of waste that needs to be disposed of in a sanitary manner.  This leads to a second disadvantage, while true composting results in internal bed temperatures above 55 degrees C that can denature proteins and reduce pathogenic viruses, bacteria and parasites, the composting toilet does not achieve such temperatures - making the material that has to be removed from a composting toilet a health hazard.  A third disadvantage is having to remove, transport and sanitarily dispose and actually treat the collected solids.  My expectation is most composting toilet solids are buried nearby and in a cottage or other remote application could affect groundwater quality as a contamination source, and such burial would be illegal anywhere in North America. Then there is the last disadvantage I’ll mention, - Leachate.  Humans not only pass fecal matter with variable water content, but they also urinate significant quantities of liquid that exceeds the ability of the composting toilet to evaporate, which generates a highly contaminated liquid leachate at the bottom of the compost that must also be disposed in a legal and sanitary manner.  As a consequence, most health jurisdictions that permit the use of composting toilets do so only when a conventional means of sanitary disposal is already available in the firm of a permitted septic disposal system and field, or a sanitary sewer.  I design composting systems and also compost waste organic materials in my yard using very conventional methods along with routine mixing, moisture control, pH adjustment using  ground waste drywall, and temperature monitoring to achieve rapid decomposition under controlled conditions.  However, few people both to go to the trouble of composting properly and end up creating a trash pile for eventual disposal and/or use municipal green bin collection.  The chances of the average homeowner operating a composting toilet to actually compost are slim.