Chemical Composition of Human Dejecta

Source: Composting: Sanitary Disposal and Reclamation of Organic Wastes, by Harold B. Gotaas, monograph under WHO auspices, 1956, p. 35

Human faeces material without urine
Approximate quantity:	150 to 270 g (0.3 - 0.6 lb.) per capita per day moist weight
Approximate composition:	Moisture content	66 - 80 %
	Organic matter (dry basis)	88 - 97 %
	Nitrogen (dry basis)	5.0 - 7.0 %
	Phosphorus (P₂O₅) (dry basis)	3.0 - 5.4 %
	Potassium (K₂O) (dry basis)	1.0 - 2.5 %
	Carbon (dry basis)	40 - 55 %
	Calcium (CaO) (dry basis)	4.0 - 5.0 %
	C/N Ratio	5.0 - 10.0

Human urine
Approximate quantity:	Volume: 1.0 to 1.3 litres (1¾ - 2¼ pints) per capita per day
	Dry solids: 50 to 70 g (0.12 – 0.16 lb.) per capita per day
Approximate composition:	Moisture content	93 - 96 %
	Organic matter (dry basis)	65 - 85 %
	Nitrogen (dry basis)	15 - 19 %
	Phosphorus (P₂O₅) (dry basis)	2.5 - 5.0 %
	Potassium (K₂O) (dry basis)	3.0 - 4.5 %
	Carbon (dry basis)	11 - 17 %
	Calcium (CaO) (dry basis)	4.5 - 6.0 %

From the above data, we can estimate the average nitrogen and phosphorus content of human dejecta. For this, we first determine the maximum and minimum limits within which these values are found. These limits define both extremes in the characteristics of the dejecta produced by vegetarians / frugal eaters on the one hand, and carnivores / intensive eaters on the other.

Faeces

Nitrogen. The minimum value can be estimated from 40g of dry matter containing 5% nitrogen (N). This represents 2g of N per day per person, equivalent to 0.73kg per year. The maximum is at 81g of dry matter containing 7% N, which makes for 5.67g of N per day per person, or 2.07kg per year.

Phosphorus. The minimum is 3% of 40g, equal to 1.2g of phosphorus pentoxide (P₂O₅) per day per person, or 0.438kg per year. The maximum is 5.4% of 81g, equal to 4.374g of P₂O₅ per day per person, or 1.597kg per year.

Urine

Nitrogen. The minimum value can be estimated from 50g of dry matter containing 15% nitrogen (N). This represents 7.5g of N per day per person, equivalent to 2.738 kg per year. The maximum is at 70g of dry matter containing 19% N, which makes for 13.3g of N per day per person, or 4.855kg per year.

Phosphorus. The minimum is 2.5% of 50g, equal to 1.25g of phosphorus pentoxide (P₂O₅) per day per person, or 0.456kg per year. The maximum is 5 % of 70g, equal to 3.5g of (P₂O₅) per day per person, or 1.277kg per year.

Determining the total content of nitrogen and phosphorus

Nitrogen and Phosphorus Content [kg per person per year]
	Nitrogen [N]	Phosphorus [P₂O₅]
Faecal matter	0.73 to 2.07	0.438 to 1.597
Urine	2.738 to 4.855	0.456 to 1.277
Total average production	5.20 kg N	1.884 P₂O₅ = 0.823 kg P

Concerning nitrogen, we have a total of (0.73+2.738) = 3.468 (minimum) to (2.07+4.855) = 6.925kg (maximum) of nitrogen produced per year per person, in the form of precious organic compounds. The average value of nitrogen is therefore (3.468+6.925)/2 = 5.1965 rounded out at 5.20kg of N per year per person. As this is an estimated average, the real value will be situated somewhere between the minimum and maximum limits.

Concerning phosphorus, we have a total of (0.438+0.456)= 0.894 (minimum) to (1.597+1.277)= 2.874kg (maximum) of (P₂O₅) produced per year per person, again in the form of precious organic compounds. The average value of phosphorus is therefore (0.894+2.874)/2 = 1.884kg of (P₂O₅), equivalent to 0.823kg of phosphorus (P) per year per person. Again, the real value will be situated somewhere between the minimum and maximum limits.

According to these estimates, urine contains about 73% of the nitrogen contained in human dejecta. This is close to the 80% ratio usually cited in most technical literature. The discrepancy likely depends on the nature of the population sampled. The chemical compostion of human dejecta can vary quite a lot depending on people’s food habits.

To continue reading, go to chapter on Composting human dejecta.

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