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Fertilizer Obtained From Composting Latrines

Human waste contains organic matter and several nutrients that are essential for plant growth. The most important of these are Nitrogen, Phosphorous and Potassium. The reuse of composted waste in agriculture keeps these essential nutrients in the system, creating a closed loop system. Closed loops are necessary for the establishment of sustainable systems.

The bulk of the nutrients are contained in the urine, as shown in the table below. Separation of feces and urine is therefore, an important consideration. Urine separation will reduce the total nutrient levels in the composted humus. However, if the urine is collected separately it may also be used on crops. It is important of dilute collected urine to 4-5 times its volume to avoid “burning” the crops with excess nutrients.

Nutrient amounts excreted by an adult human per year

Nitrogen (kg)Phosphate (kg)Potassium (kg)Carbon (kg)
Urine3-50.40.7 -0.93.0
Feces0.7 - 1.00.30.28.8
Total3.7 - 6.00.70.9 - 1.111.8

Composting reduces the level of nutrients available in the humus, especially nitrogen. Typical annual nutrient amount in feces after composting are 0.1 kg nitrogen, 0.2 kg phosphate, and 0.2 kg potassium per adult. The reduced fertilizer benefits are the cost associated with improved sanitary conditions. It is important to realize that composting latrines that combine urine and feces will also result in a lower total nutrient level of the humus. If maximum nutrient cycling is to be obtained, the urine and feces must be separated. (In general, the composting system will function more efficiently this way too). Separation has the additional benefit of having urine nutrients available for immediate use, where the composting feces are only available for field use at the end of the incubation period (possibly a year later).

Additional Information

Basic Fertilizer Information
Fornyet Energi Composting Toilet - Gives a detailed table of nutrients found in composted feces.
Composting Council of Canada - A report on the use of municiplal solid waste compost