Per person:


Grey water
Sewage water after purification1
Volume, l/p*yr
Nutrients, Kg/ year
N: 4.116

P: 0.592
N: 0.742

P: 0.117
N: 0.442

P: 0.148
N: 3.96

P: 0.06
N-conc. (mg/l)
P-conc. (mg/l)
N/P rate9
High risk for pathogens. High dry mass
concentration of pollutants
Risk for viruses and nitrogen pollution

1) Here, 93.25% P and 25% N purification is assumed. The P purification figure is calculated from the figures actually reported from the larger, so-called A-type, purification plants in Sweden [19]. With the improvement of the Swedish sewage plants, the removal of nitrogen can be increased to 50% or 75%. The nitrogen effluent from the sewage plants would then decrease to 2.64 and 1.32 kg N/persons*year, respectively, and the average concentration of nitrogen in the effluent water would decrease to 18.3 mg/l and 9.1 mg/l, respectively. Still, all these figures are higher than the content of the grey water.

2) This figure is an average from the estimations of [14, 4, 12 and 15].

3) This figure is an average of the estimations of [14, 4, 12 and 15].

4) According to the statistics from VAV [20], 173 litres/person*day is used in households. Statistics Sweden [16] uses a somewhat higher figure, 185 litres. In the calculations, an intermediate figure, 179 l/p*d is used..

5) In order to attain consistence with the numbers actually reported from 23 of the largest sewage plants (A-plants) in Sweden, serving 40% of the population [19], one have to assume an average extra flux of water of about 217 litres per person per day to the sewage pipes from drainage water or leakage. The total amount of water actually purified is about 400 litres per person per day in the plants studied.

6) Astonishingly, figures regarding the content of ordinary human urine and faeces are rare. This figure is an average from the estimations of [14, 4, 12 and 15].

7) This figure is an average from the estimations of [14, 4, 12 and 15]., combined with an investigation of the food habits of the Swedish population[2].

8) This figure is calculated from the total use of phosphorus På svenska detergents reported 1994 [10] divided by the inhabitants of Sweden. However, in this figure is included the industrial use of detergents. The household use of detergents containing phosphorus have declined the last decade.

9) For the nutrients to be taken up by plants, the ratio N/P should be around 10. If this figure is below 10, nitrogen is the limiting substance, leading to a sub-optimal phosphorus uptake unless the plants can get nitrogen from other sources. If the ratio is far above 10, the reverse is accurate.