Abstract: International audience ; The use of sewers to transport human excreta away from inhabited zones now causes particularly acute problems in megacities. Given the major global changes faced by wastewater management systems, these huge population centres highlight the limitations of the traditional sanitation management model. Apart from the frequent overloads on centralised wastewater management systems, there is their deep footprint in terms of energy expenditure, greenhouse gas emissions and continuing frequent pollution of aquatic environments. Yet managed separately, these excreta could be used as fertiliser: their agricultural application would represent a move away from the waste remediation model and an opportunity for mutual benefit between urban and agricultural zones, supplying the latter with lasting, local and nonfossil fertilising materials. Focusing on the case of the Paris conurbation, we provide a crosscutting analysis of the current opportunities for implementing source separation systems in a highly concentrated population centre. More specifically, we examine the technical, organisational and economic obstacles and drivers around the production of fertilisers from human excreta, in particular from urine, under good sanitary and agronomic conditions. We show the buildup of evidence about the incoherence of the current wastewater management system and the need for a paradigm shift. Nonetheless, pilot projects remain difficult to implement (due to political, sociocultural, economic, regulatory and technical obstacles, which are particularly tough in the case of a megacity). Despite this, there has been a recent shift in the dynamics, with projects emerging on the margins of urban planning. A key factor in their success is adaptation to different territorial configurations. Backed by individuals and groups with specific priorities, these projects offer a glimpse of the possibility of devising new sociotechnical systems for managing human waste.
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