Podcast transcript: urban metabolism, at the heart of the matter

Clément Dillenseger: I am a geographer, having completed my doctoral research at the EVS Laboratory in Lyon, focusing on urban and environmental geography. My work investigates how the circulation of clean and dirty materials impacts urban environments at multiple scales.

Pierre Desvaux: I am a postdoctoral researcher at the ESO laboratory in Nantes and also affiliated with the EVS laboratory in Lyon. My research explores how societies regulate the materiality they require to function. In 2019, we established the Metabolism Studio at the Lyon Urban School, a structure dedicated to scientific discourse on metabolism through meetings, study days, and conferences.

Stream Voices: what is urban metabolism?

Clément Dillenseger: Metabolism, in its broadest sense, describes the material exchanges between societies and the biosphere. It is often analyzed at the urban scale, giving rise to the term “urban metabolism,” though it can also be studied at the scale of a building or an entire region. This approach allows us to track material flows and their interactions with social and political structures.

Pierre Desvaux: When considering metabolism, the notion of boundaries becomes complex. A city, viewed through a metabolic lens, depends on materials sourced externally for its construction and functioning, as well as the disposal of waste, whether solid, atmospheric, or aquatic. This makes defining clear-cut boundaries nearly impossible. Ultimately, urban metabolism ties into the planetary system, yet within this global framework, we can isolate specific objects of study, defining them spatially or thematically to facilitate analysis.

Clément Dillenseger: Studying metabolism also intersects with political ecology. Ecological processes within cities or other territories are inherently political because they affect people differently. The choices made regarding material circulation and management reflect power structures and social priorities.

Stream Voices: what is the history behind the concept of metabolism?

Clément Dillenseger: The term “metabolism” was first formalized by the German chemist Justus von Liebig in the 19th century, who coined the term Stoffwechsel, meaning “change of matter.” Karl Marx, a contemporary of Liebig, was influenced by his ideas and incorporated the notion of metabolism into his analysis of labor. For Marx, metabolism symbolized the transfer of materials from nature to society, with labor being the process through which this transformation occurs.

Pierre Desvaux: The use of metaphors in social sciences can be risky, particularly when drawing from biological concepts. Unlike biological cells, human societies are structured by power relations, justice, and inequality. If we are not careful, the metaphor of metabolism can naturalize socio-political processes, making them seem inevitable rather than constructed. However, metaphors remain powerful tools for communication, making complex concepts more accessible to broader audiences.

Clément Dillenseger: In biology, metabolism involves chemical reactions that generate energy for cellular function, drawing from environmental flows such as nutrients or solar energy. Similarly, we can analyze the invisible material flows that sustain cities, especially in a globalized world where supply chains are increasingly remote.

Pierre Desvaux: Material flows include food, waste, energy, and digital infrastructures, all of which have environmental and social consequences. Some researchers even incorporate financial flows into metabolic analyses. While the metaphor can sometimes be stretched, the study of these flows helps reveal the power structures and dependencies embedded in urban systems.

Clément Dillenseger: Tourism, for instance, disrupts local metabolisms seasonally by increasing material consumption and waste production. Geographers analyze material flows in spatial and territorial terms, seeking to understand their origins and destinations. The globalization of supply chains makes it increasingly difficult to trace these flows, highlighting the need for a more localized and spatialized approach to metabolism.

Stream Voices: you have conducted field studies in Lyon, Cairo, and Vienna, focusing on waste management as a lens to examine urban metabolism.

Pierre Desvaux: In Cairo, waste management is a complex system involving both formal and informal actors. Government-led waste collection services coexist with independent waste pickers, such as the Zabaleen community, who historically managed much of the city’s waste. Their ability to raise pigs allowed them to process organic waste efficiently. However, as Cairo’s population expanded, the waste system became more fragmented, with different groups vying for control over valuable recyclable materials.

Clément Dillenseger: Across all cities, waste collection and processing exist, but the narratives surrounding them differ. In Vienna, for example, waste management is highly visible and integrated into public life. The city promotes awareness of its waste-to-energy processes, with two-thirds of households heated through urban waste incineration. This transparency fosters a sense of ecological responsibility but also serves as a self-congratulatory narrative that conceals the city’s reliance on external sites for hazardous waste disposal.

Pierre Desvaux: The discourse around the circular economy suggests a closed-loop system where waste is continuously repurposed. However, unlike ecosystems where organic waste becomes nutrients for new life, human waste management relies heavily on energy-intensive and often inefficient recycling processes. For instance, only 4-5% of plastics are effectively recycled. The idea of complete material recovery is largely a myth, often depoliticized through misleading ecological analogies.

Stream Voices: the management of material flows is often made invisible, except in Vienna, where waste processes are staged as part of urban life. Yet, a closer examination reveals similarities between metabolic studies and concepts of care and maintenance.

Pierre Desvaux: Urban metabolism depends on infrastructure and human labor. Whether in formal employment or informal arrangements, countless workers—waste collectors, street sweepers, volunteers—enable the circulation and transformation of materials. However, cultural perceptions of cleanliness and dirtiness often push these activities out of sight.

Clément Dillenseger: Societies define themselves through notions of cleanliness, distancing themselves from waste and those who handle it. Yet, the growing involvement of volunteers in waste collection suggests a shifting perception, recognizing waste as a persistent issue rather than something that simply “disappears.” Some materials, like plastic, are more readily reintegrated into circulation due to their cleanliness, whereas organic and bodily waste remain deeply stigmatized.

Stream Voices: Clément Dillenseger and Pierre Desvaux have compiled their research into Metabolism: Matter in Circulation, Matter in Transformation, published by E205 Editions. Based on discussions within the Metabolism Studio at the Lyon Urban School, the book aims to make these reflections accessible to a wider audience.

Pierre Desvaux: Our goal is to provide analytical tools that help people critically examine the material flows shaping their environments. By understanding the socio-political dimensions of metabolism, we can challenge dominant narratives and rethink urban sustainability.

Interview conducted by Jasmine Leonardon, Head of Research and Scientific content at PCA-STREAM, sound by Lucie Wix and editing by Milan Rivet.