The Value of Human Faeces

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Elements (g/ppd) Urine Faeces Urine + faeces
Nitrogen 11.0 1.5 12.5
Phosphorous 1.0 0.5 1.5
Potassium 2.5 1.0 3.5
Organic carbon 6.6 21.4 30
Wet weight 1,200 70-140 1,200-1,400
Dry weight 60 35 95

The following is from Closing the loop in wastewater management and sanitation (source)

Resource value of human excreta

Human excreta are comprised of two basic components, urine and faeces. When urine and faeces are kept apart, they have different properties, are produced in different quantities, and require different care in processing. Published figures indicate that more than 1 kg of urine is produced daily, while less than 150 g of faeces, including moisture, is produced daily.11 These figures, of course, vary by type of diet, location, age, activity and health status.

Urine contains nearly 80% of the total nitrogen found in excreta (Table 1). Urine also contains two-thirds of the excreted phosphorous and potassium. The majority of the carbon excreted, up to 70%, is found in faeces. The quantities shown above may suggest that excreta contain few nutrients. Each person urinates annually about 4 kg of nitrogen, 0.4 kg of phosphorous, and nearly 1 kg of potassium; total excretion is 4.5 kg of nitrogen, more than a half kg of phosphorous, and 1.2 kg of potassium. In an urban setting of 10 million people, this equates to 45 million kg of nitrogen, nearly 6 million kg of phosphorous, and more than 12 million kg of potassium. It also represents 10 million litres of nutrient rich and mostly sterile water that is excreted. The water that is not flushed by 10 million people equates to 0.15 km3 of water saved by using ecological sanitation, fresh water that could be used for other purposes, such as food production, without risk of infection. Other elements, such as calcium and magnesium, are excreted in nearly equal amounts in urine and faeces. There are many other nutrients found in human excreta, but they are not shown above. Although using only urine is valuable, both urine and faeces should be recovered and recycled to avoid long term depletion of soils.

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