Due to single-compartment structures in some toilets, solid waste hasn’t had time to mature when it is time to empty the toilet and the waste must be stored in a separate outdoor compost for 2 to 3 years prior to use as fertilizer.
To improve ventilation and to reduce moisture one must always sprinkle bark or saw dust or other substances on the waste after use.
The liquids are not biologically cleansed and should not therefore be treated as normal household wastewater (grey water).
In some models, the liquid is evaporated by electricity, which consumes vast amounts of energy and causes acid rain. In some cases, the liquid separator in the toilet seat might be blocked.
Also, flies and other insects might have free access to the toilet; additionally, the composters often have holes and small niches where the eggs laid by flies can’t be destroyed.