Past and Future Trajectories of Human Excreta Management Systems: Paris in the Nineteenth to Twenty-First Centuries

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: 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. 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 agro-systems 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.

Trajectories of the Seine River Basin

“…The impact of the Paris conurbation on this section of the river is present in almost all the following chapters (see, e.g. [37,40]). The basin output is considered at the Poses station (Fig.…”

“…The urbanized part of the basin has been growing over the past two centuries. Paris megacity increased from 75 km 2 in the 1850s (Paris area) to 2,850 km 2 today [37]. In 2015, it was home to 12.4 million (M) of the 16.7 M inhabitants (inhab.)…”

“…The urban pollution generated by the city of Paris, and later by the Parisian conurbation, which impacts the lower Seine and the estuary has been a major concern of the authorities for over a century [37][38][39]. Water quality has been severely degraded in terms of oxygen levels, ammonia, and nitrite concentrations, as well as the occurrence of faecal bacteria over a section of river extending from 100 to 250 km downstream from Paris [40].…”

Séparation à la source et valorisation des excrétas humains du Grand Paris : des filières émergentes

“…À Paris, aujourd'hui, seulement 4 % de l'azote et 41 % du phosphore des excrétats humains font l'objet d'une valorisation agricole, à travers les boues d'épuration épandues ou compostées [ESCULIER et al, 2018]. Ce ne fut pas toujours le cas : au début du XX e siècle, les taux de recyclage agricole de l'azote et du phosphore des excrétats humains de l'agglomération parisienne étaient respectivement ainsi d'environ 50% et 70%, alors que l'agglomération comptait déjà plus de 3 millions d'habitants [ESCULIER et BARLES, 2019]. La nécessité d'une transition écologique de notre mode de gestion des excrétats humains invite donc à 5 Sources : OMS, 2012 ;FRIEDLER et al, 2013 ;ANSES, 2015 ;ESCULIER et al, 2018. Les valeurs présentées correspondent à des données collectées dans la période 2010 -2015 et sont des valeurs de référence susceptibles de variations importantes selon les contextes.…”

Nitrogen biogeochemistry of water-agro-food systems: the example of the Seine land-to-sea continuum

“…Animal protein intake has increased considerably in proportion, reaching 70% of the total protein ingestion in the beginning of the 21st century, and has slowly decreased in recent years (Le Noë et al, 2018). Human excreta in the 19 th century was considered a useful fertilizing resource, collected in cesspools, and then through sewer networks (Barles, 2005;Esculier & Barles, 2019). It is currently treated in wastewater purification plants, which eliminate about 57% of N in excreta as atmospheric dinitrogen through an energetically expensive process of denitrification (using methanol as an electron donor), recover 4% as sludge, only a small part of which is recycled in agriculture, and discharge the remaining part (39%) to surface water (Esculier et al, 2018).…”