Abstract This chapter addresses the fate of nutrients in agro-food systems after
their ingestion by humans. Depending on how human urine and faeces are managed,
they can become a source of pollution to the environment, or they can be used as a
resource, notably as fertilisers, thus contributing to closing the loop of nutrients.
Taking the city of Paris as a case study from the nineteenth to the twenty-first
century, we analyse the fate of human excreta through the evaluation of
corresponding nitrogen and phosphorus mass flows. We put forward two major
phases concerning the management of human excreta:
1. The circularisation phase (1800s to 1900s): human excreta management is
characterised by increasing circularity which peaks in the 1900s with around
50% of human excreta nutrients being recycled.
2. The linearisation phase (1900s–today): human excreta management is
characterised by increasing linearity, i.e. a decrease in recycling rates of nutrients.
Generalisation and improvement of wastewater treatment have led to decreasing
pollution but also confirm the linearisation process (e.g. 5% recycling of human
excreta nitrogen).
This increase in linearity came together with increased dependency of agrosystems on fossil resources. Ongoing climate change is also putting the current
system under pressure since the dilution capacity of the Seine River is decreasing,
while the population of Paris is increasing. We therefore analyse three scenarios of
future human excreta management (incineration, end-of-pipe recycling and source
separation) and show that source separation of human excreta may offer the perspective of a sustainable human excreta management system.
Keywords Biogeochemical cycles, Circularity, Human excreta, Nitrogen,
Phosphorus, Pollution, Socioecological trajectories, Source separation, Urban
metabolism, Urine, Wastewater
1 Introduction
1.1 Context
“Flush and forget” toilets are so deeply rooted in the Western way of life that little
attention is paid to the fate of our daily excreta. However, raising awareness of the
disastrous ecological state to which the development model of Western countries has
led, be it eutrophication, climate change or biodiversity loss – to quote only three
major transgressions of planetary boundaries [1] – prompts us to question all aspects
of the Western way of life. Conventional human excreta management is therefore
currently being reconsidered by numerous research projects and innovative
implementations, especially in Northern Europe [2] and also more recently in France
[3], notably in the OCAPI programme (www.leesu.fr/ocapi) and the PIREN-Seine.
On the other hand, past human excreta management has been carefully analysed for
Paris in previous studies conducted within the PIREN-Seine programme. It has been
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F. Esculier and S. Barles
their ingestion by humans. Depending on how human urine and faeces are managed,
they can become a source of pollution to the environment, or they can be used as a
resource, notably as fertilisers, thus contributing to closing the loop of nutrients.
Taking the city of Paris as a case study from the nineteenth to the twenty-first
century, we analyse the fate of human excreta through the evaluation of
corresponding nitrogen and phosphorus mass flows. We put forward two major
phases concerning the management of human excreta:
1. The circularisation phase (1800s to 1900s): human excreta management is
characterised by increasing circularity which peaks in the 1900s with around
50% of human excreta nutrients being recycled.
2. The linearisation phase (1900s–today): human excreta management is
characterised by increasing linearity, i.e. a decrease in recycling rates of nutrients.
Generalisation and improvement of wastewater treatment have led to decreasing
pollution but also confirm the linearisation process (e.g. 5% recycling of human
excreta nitrogen).
This increase in linearity came together with increased dependency of agrosystems on fossil resources. Ongoing climate change is also putting the current
system under pressure since the dilution capacity of the Seine River is decreasing,
while the population of Paris is increasing. We therefore analyse three scenarios of
future human excreta management (incineration, end-of-pipe recycling and source
separation) and show that source separation of human excreta may offer the perspective of a sustainable human excreta management system.
Keywords Biogeochemical cycles, Circularity, Human excreta, Nitrogen,
Phosphorus, Pollution, Socioecological trajectories, Source separation, Urban
metabolism, Urine, Wastewater
1 Introduction
1.1 Context
“Flush and forget” toilets are so deeply rooted in the Western way of life that little
attention is paid to the fate of our daily excreta. However, raising awareness of the
disastrous ecological state to which the development model of Western countries has
led, be it eutrophication, climate change or biodiversity loss – to quote only three
major transgressions of planetary boundaries [1] – prompts us to question all aspects
of the Western way of life. Conventional human excreta management is therefore
currently being reconsidered by numerous research projects and innovative
implementations, especially in Northern Europe [2] and also more recently in France
[3], notably in the OCAPI programme (www.leesu.fr/ocapi) and the PIREN-Seine.
On the other hand, past human excreta management has been carefully analysed for
Paris in previous studies conducted within the PIREN-Seine programme. It has been
118
F. Esculier and S. Barles