N and P pollution started to be addressed with the 1978 Paris Convention
(becoming the OSPAR convention in 1992) and with the European Urban Waste
Water Treatment Directive (UWWTD) in 1991. The transfer of N and P from Paris’s
excreta via the Seine and the English Channel to neighbouring countries led these
countries in 1981 to request that the quantity of N and P released by the Seine River
basin be divided by two between 1985 and 1995 (PARCOM recommendation 88/2).
Similarly, the UWWTD required elimination of 70% of N and 80% of P from
wastewater by 1998. In 2013, 25 years after the PARCOM recommendation and
15 years after the UWWTD deadline, just as France was about to be fined by the
European Union for noncompliance, compatible N and P treatment were finally
implemented in the Paris conurbation.
However, in this new human excreta management system, circularity is not the
prevailing concern. Like C, N is mainly lost by transfer to the atmosphere. Denitrification consists in the conversion of reactive nitrogen into the non-reactive form N 2 ,
the opposite of the Haber-Bosch process. On one hand, chemical N fertilisers are
produced from N 2 using fossil resources. On the other hand, human N contained in
excreta is converted to N 2 using fossil resources. The N imprint of Paris and the
industrial world in general is thus considered unsustainable [14]. Today, one-third of
the N of the Paris conurbation excreta is still discharged to the rivers, mainly in the
form of nitrates. Two new forms of pollution also appear: nitrous oxide (N 2 O)
gaseous emissions in the treatment process and nitrite (NO 2
À ) discharged into the
river. The global recycling rate of human N in Paris today is 5%, the same value as
with the inefficient dry management methods of the beginning of the nineteenth
century.
The situation for P is ambiguous. Since it is possible to fix P in sludge via
precipitation, P pollution treatment can simultaneously lead to increased P recycling.
However, in Paris, incineration of sludge has been gradually implemented in the new
WWTPs. P contained in ash is not recovered, and, in the 2010s, a remarkable 84%
treatment rate of P in WWTPs only leads to a 40% recycling rate, mostly because of
sludge incineration [14] (Fig. 13).
4 Future Human Excreta Management Scenarios
4.1 Lock-In and Opportunities
Progressive adoption of the “toilet–sewer–wastewater treatment plant” combination
since the end of the nineteenth century has created a sociotechnical lock-in in human
excreta management. Modern comfort is associated with the disconnection of the
population with their excreta and consumption of large volumes of water. With
respect to human excreta management, the debate gradually shifted from the best
possible management of human excreta itself to the management of mixed sewage
water, then to the management of sludge and finally to the management of ash from
incinerated sludge [7]. Nutrient pollution of the rivers has only been very recently
Past and Future Trajectories of Human Excreta Management Systems: Paris. . .
133
(becoming the OSPAR convention in 1992) and with the European Urban Waste
Water Treatment Directive (UWWTD) in 1991. The transfer of N and P from Paris’s
excreta via the Seine and the English Channel to neighbouring countries led these
countries in 1981 to request that the quantity of N and P released by the Seine River
basin be divided by two between 1985 and 1995 (PARCOM recommendation 88/2).
Similarly, the UWWTD required elimination of 70% of N and 80% of P from
wastewater by 1998. In 2013, 25 years after the PARCOM recommendation and
15 years after the UWWTD deadline, just as France was about to be fined by the
European Union for noncompliance, compatible N and P treatment were finally
implemented in the Paris conurbation.
However, in this new human excreta management system, circularity is not the
prevailing concern. Like C, N is mainly lost by transfer to the atmosphere. Denitrification consists in the conversion of reactive nitrogen into the non-reactive form N 2 ,
the opposite of the Haber-Bosch process. On one hand, chemical N fertilisers are
produced from N 2 using fossil resources. On the other hand, human N contained in
excreta is converted to N 2 using fossil resources. The N imprint of Paris and the
industrial world in general is thus considered unsustainable [14]. Today, one-third of
the N of the Paris conurbation excreta is still discharged to the rivers, mainly in the
form of nitrates. Two new forms of pollution also appear: nitrous oxide (N 2 O)
gaseous emissions in the treatment process and nitrite (NO 2
À ) discharged into the
river. The global recycling rate of human N in Paris today is 5%, the same value as
with the inefficient dry management methods of the beginning of the nineteenth
century.
The situation for P is ambiguous. Since it is possible to fix P in sludge via
precipitation, P pollution treatment can simultaneously lead to increased P recycling.
However, in Paris, incineration of sludge has been gradually implemented in the new
WWTPs. P contained in ash is not recovered, and, in the 2010s, a remarkable 84%
treatment rate of P in WWTPs only leads to a 40% recycling rate, mostly because of
sludge incineration [14] (Fig. 13).
4 Future Human Excreta Management Scenarios
4.1 Lock-In and Opportunities
Progressive adoption of the “toilet–sewer–wastewater treatment plant” combination
since the end of the nineteenth century has created a sociotechnical lock-in in human
excreta management. Modern comfort is associated with the disconnection of the
population with their excreta and consumption of large volumes of water. With
respect to human excreta management, the debate gradually shifted from the best
possible management of human excreta itself to the management of mixed sewage
water, then to the management of sludge and finally to the management of ash from
incinerated sludge [7]. Nutrient pollution of the rivers has only been very recently
Past and Future Trajectories of Human Excreta Management Systems: Paris. . .
133