f grey water is generated, a separate treatment and disposal system is required. Compost toilets are most often used by persons who are, in princi- ple, concerned about conservation of natural resources, and by per- sons who live where conditions are not suitable for a conventional septic tank system. The major benefit to the environment of com- post toilet use is a reduction in the volume of household wastewater entering the soil. Although one would expect a reduction in patho- genic organisms entering the soil as well, this is not necessarily the case. Grey water has been shown to be as nasty as black water LOW-IMPACT SYSTEMS under some conditions. In general, a reduction in drain field size- one receiving only grey water-is appropriate when compost toilets are used. This could be an asset if the drain field must be installed in clay soils, on steep slopes, or where suitable land area is limited. An accompanying benefit of the use of composting toilets is a significant reduction in the amount of nitrogen entering the soil, since most of the nitrogen in wastewater comes from body wastes, both urine and fecal. This effect is most significant where nitrate levels in ground water are already high, and where dense develop- ment exists or is expected. In Scandinavia, where compost toilets originated, they are used most often in seasonally occupied homes. Such use continues in other countries as a primary application. Process Biological decomposition is the process that keeps biological waste material from piling up in the world. Fallen trees rot away and dead squirrels decompose. Mostly, bacteria and fungi are responsible for this breakdown of organic matter, but other organisms such as earthworms and insects can speed up the process. The decomposi- tion of human waste material in a compost toilet is basically the same process as the decomposition of leaves in the forest. Compost toilets are aerobic units, in which the wastes are decomposed to carbon dioxide, water, and inert solids. Aerobic conditions are required t