Paris conurbation comprised 432 municipalities. The city of Paris accounts
for approximately one-fifth of this conurbation of approximately 10,700,000
inhabitants.
1.3 Methodology
For each decade between 1800 and 2010, we sought to estimate the degree of
circularity of human excreta management, i.e. the proportion of N and P in human
excreta that was returned to agricultural land. For this purpose, we estimated four
main parameters:
1. N-DEC is the recycling rate, calculated in terms of N, of human excreta
collected through a decentralised device, usually a cesspool, and returned to
agricultural land.
2. P-DEC is the same as N-DEC calculated in terms of P.
3. N-CENT is the recycling rate, calculated in terms of N, of human excreta
collected through a centralised device, i.e. a sewer.
4. P-CENT is the same as N-CENT calculated in terms of P.
These recycling rates were multiplied by the proportion of people connected to a
sewer (parameter SEWER) or to a decentralised device (deduced from the parameter
SEWER) to obtain the global proportion of N and P recycled in the Paris conurbation. Except for denitrification in wastewater treatment plants (WWTPs) and incineration of sludge, all N and P that is not recycled in agriculture is considered to be
transferred in a reactive form to soil, underground, air or surface water and is thus
considered as a pollution.
The data are selected to represent at best each decade: they correspond to the
average of the decade when all annual data are available, otherwise the value at the
middle of the decade. The parameter SEWER was calculated for the city of Paris on
the basis of municipal statistical data [10]. Between the 1870s and the 1910s, the
number of Parisians connected to the sewer via a filtering device called a tinette
filtrante was estimated [11], considered as a combined centralised and decentralised
system.
Outside the city of Paris, the parameter SEWER was linearly increased from 0%
in the 1890s to 33% in the 1940s [12] and extrapolated, by taking into account the
historical evolution of sewage management [13], to a total connection rate of 98%
estimated in the 2010s [14]. Until the 1940s, it was considered that the connected
population of the suburbs was equally distributed between connection to the main
sewer network of the Paris conurbation and to an independent suburban sewer
network [15].
Data from [7, 10, 13, 15, 16] enabled us to estimate the proportion of four
different fates of N and P when collected in a sewer:
Past and Future Trajectories of Human Excreta Management Systems: Paris. . .
121
for approximately one-fifth of this conurbation of approximately 10,700,000
inhabitants.
1.3 Methodology
For each decade between 1800 and 2010, we sought to estimate the degree of
circularity of human excreta management, i.e. the proportion of N and P in human
excreta that was returned to agricultural land. For this purpose, we estimated four
main parameters:
1. N-DEC is the recycling rate, calculated in terms of N, of human excreta
collected through a decentralised device, usually a cesspool, and returned to
agricultural land.
2. P-DEC is the same as N-DEC calculated in terms of P.
3. N-CENT is the recycling rate, calculated in terms of N, of human excreta
collected through a centralised device, i.e. a sewer.
4. P-CENT is the same as N-CENT calculated in terms of P.
These recycling rates were multiplied by the proportion of people connected to a
sewer (parameter SEWER) or to a decentralised device (deduced from the parameter
SEWER) to obtain the global proportion of N and P recycled in the Paris conurbation. Except for denitrification in wastewater treatment plants (WWTPs) and incineration of sludge, all N and P that is not recycled in agriculture is considered to be
transferred in a reactive form to soil, underground, air or surface water and is thus
considered as a pollution.
The data are selected to represent at best each decade: they correspond to the
average of the decade when all annual data are available, otherwise the value at the
middle of the decade. The parameter SEWER was calculated for the city of Paris on
the basis of municipal statistical data [10]. Between the 1870s and the 1910s, the
number of Parisians connected to the sewer via a filtering device called a tinette
filtrante was estimated [11], considered as a combined centralised and decentralised
system.
Outside the city of Paris, the parameter SEWER was linearly increased from 0%
in the 1890s to 33% in the 1940s [12] and extrapolated, by taking into account the
historical evolution of sewage management [13], to a total connection rate of 98%
estimated in the 2010s [14]. Until the 1940s, it was considered that the connected
population of the suburbs was equally distributed between connection to the main
sewer network of the Paris conurbation and to an independent suburban sewer
network [15].
Data from [7, 10, 13, 15, 16] enabled us to estimate the proportion of four
different fates of N and P when collected in a sewer:
Past and Future Trajectories of Human Excreta Management Systems: Paris. . .
121