In Métabolismes urbains, Roberto D’Arienzo publishes the results of his PhD thesis (defended in 2015), retracing 120 years of waste treatment in Naples, from the advent of hygienism in 1884 (to eradicate a cholera epidemic) to the rise of urban recycling in 2004 (when the city adopted a “zero hectare”  plan aimed at “recycling” the urban space within its boundaries). One of the book’s points of entry into this subject is the waste crisis in southern Italy, which received international media attention at its peak in 2007.
Without mobilizing the conceptual framework of socio-ecological transitions (Fischer-Kowalski and Rotmans 2009), the author reconstructs the social and ecological trajectory of the relationships between an urban space—its users, its material artifacts, its functions—and its environment, by observing the material rejections it produces. It uncovers, without explaining it in these terms, the foundations of a circular economy for the production and management of urban waste. This economy is itself based on the development of close relations between the actors of these sectors, and between the different territories that their actions affect (Bahers et al. 2017). These close relationships must be understood over long periods of time, taking into account the evolution of lifestyles (Dittmar and Tastevin 2016) and taking into account the orientations of urban planning.
The author thus approaches the materiality of urban spaces from a historical perspective, and takes an interesting look at the socio-ecological transition that recent political debates reflect. This multidisciplinary work combines architecture and urban engineering with elements of history, philosophy, anthropology and social economy, as evidenced by the book’s bibliography.
From the waste crisis to analysis of the metabolism of urban leftovers
The origins of the waste crisis have already been attributed to fatality or the result of a failure of public action to address the imperatives of the Camorra (Giuliani 2009). By situating it in the long history of the city, the author explains its socio-ecological foundations. The book studies waste production and management in Naples between 1884 and 2004 based on the notion of urban metabolism, which makes it possible to examine the relationships between the urban site, society and its physical environment. The analysis of the flow of materials into and out of the city defines this metabolism. Naples, like any other urban site, has an initial material stock that is insufficient for the sustainability of the human settlement. To compensate for this, this territory takes and imports materials from the biosphere or other territories, as well as rejects and exports these materials (or others) to third spaces (Barles 2007). The result is a more or less looped cycle operation, depending on whether the incoming flows are recycled within the urban system or, on the contrary, exported (see Figure 1).
Source: Sabine Bognon, 2018.
Waste constitutes a part of urban (or territorial, when processed on a larger scale) metabolism, the analysis of which is based on two types of methods, sometimes combined: those that study the quantities of matter involved (material balances, substance balances, etc.) and those that examine the system of actors and the governance that allows a space to operate metabolically. Roberto D’Arienzo examines the changes in certain uses and functions of the city by explaining the interplay of actors behind these transformations, based on the case of urban waste management.
In the first part (from the end of the 19th century to the end of the fascist period), the demonstration is structured around two points. On the one hand, Neapolitan metabolism gradually becomes linear (Barles 2007), i.e. the quantity of incoming and outgoing flows is increased, while recycling is reduced. On the other hand, urban planning is becoming hygienic and rationalist, which leads to the networking of a large number of flows, including waste flows.
The rise of a linear metabolism
In the first part of the book (from the end of the 19th century to the end of the fascist period), the demonstration is structured around two points. On the one hand, Neapolitan metabolism gradually becomes linear (Barles 2007), i.e. the quantity of incoming and outgoing flows is increased, while recycling is reduced. On the other hand, urban planning is becoming hygienic and rationalist, which leads to the networking of a large number of flows, including waste flows.
Thus, as in Paris during this period (Barles 2005), Naples underwent a “metamorphosis of the superfluous” (p. 51): a wide variety of professions involved in the recovery and transformation of urban leftovers testify to this. In the following decades, urban planning entered a phase of moral and regulatory hygiene, with the adoption of new disposal techniques and the modernization of municipal waste treatment services. The author thus describes the emergence of urban planning as practical and technical: the city is seen as a body that must be maintained healthy; public policies advocate the loosening and fluidification of traffic. As industrialization (commercial port and its logistical dependencies, agri-food and pharmaceutical industries) and intra-urban agricultural decline progress, planning documents are being drafted to accompany the “adaptation of the ancient city to contemporary requirements” (p. 87). Even if the world wars implied a certain material sobriety and economies in terms of land and real estate, the fascist period reinforced two complementary trends. On the one hand, waste treatment becomes a technical service in its own right, is networked and thus made invisible in the urban landscape. On the other hand, urban expansion and growth are marked and associated with the functional enhancement of the remaining agricultural areas as “wartime vegetable gardens” (p. 158). Overall, this first period confirms the beginning of a linearization of Neapolitan metabolism: the material relations between the city (its geographical site, population, institutions) and its wider environment follow an open and linear circuit (input—use—output), and are less and less “closed” (reduced recycling).
Disposable products and disposable planning
From the 1960s to the 1990s, the linearization of metabolism increased. The Neapolitan urban system generates increasing material losses: waste production is always increasing, but recycling does not succeed in reducing these losses. The author even speaks of a “waste” of spatial resources in relation to the production of urban waste. As elsewhere, the globalization of the economy and increased supply facilities are transforming metabolism: the consumer society is freeing itself from the weight of permanent things in favour of the convenience of disposable goods (Chessel 2012). Naples must also absorb significant population growth. In the post-war years, delays in planning created a regulatory vacuum and gave way to abusivismo, the illegal diversion of planning. Urbanization is therefore advancing without taking into account the material capacities of the territory: the urban sprawl of agricultural areas is undermining the primary economy, the urban fabric is congesting the city centre, and new buildings are vulnerable. The municipal urban plan adopted in 1972 has little control over the social and economic difficulties caused by the decline of intra-urban and port industrial areas; land wastelands and vacancies are multiplying, and the use of mass demolition produces large quantities of leftovers.
From waste recycling to urban recycling
In the 1990s, two emblematic measures echoed the first international provisions on sustainable development: the first signs of the waste crisis led to the continuation of landfills (authorized or not) for waste, and the public authorities responded. Anticipating a national law of 1997 and the European directive of 2008,  the 1993 regulation aims, one year before “the official start of the waste crisis” (p. 245), at the separate collection and differentiated recovery of household waste. The author believes that these measures are a key to understanding the outcome of the crisis. By going further than this regulation and following the electoral promises of the municipal team elected after the crisis, Naples has been committed since 2011 to a “zero waste”  approach by 2020 (Berlingen 2014). Similarly, the rise of sustainable development is affecting the management of urban leftovers: a 1994 planning document already provided for “land reclamation” objectives, considering open spaces as “latent resources” (p. 254) and deindustrialized spaces as potential sites for urban renewal. In 2004, a new urban planning document recommended densification and “urban recycling” (p. 258), introducing a zero hectare policy in line with the zero waste approach. This greening of the management of urban leftovers also led, in 2010, to the formation of an urban renewal consortium inspired by these principles and by architectural eco-design: the author describes in detail the emblematic projects of this approach. D’Arienzo demonstrates that it is through the organization of space—and ultimately through urban planning—that the daily functioning of a city is shaped.
Towards a new socio-ecological transition for Naples’ urban metabolism?
For the most contemporary period, the book ignores some of the controversies related to the acceptability and consequences of a renewed governance of Neapolitan metabolism. This is all the more regrettable as these debates are regularly mentioned for past periods. For example, by referring to “flexible” or “reversible” urban planning (p. 283) as responses to the linear and dissipative nature of contemporary Neapolitan metabolism, the author seems to omit that the solutions he proposes are already sketched (for example, the occupation of wastelands by collective gardens or buildings on hold by ephemeral activities), and their possibly controversial consequences (for example, the strengthening of segregation dynamics). Moreover, in a context where densification and intensification dominate models of the sustainable city, the importance of the issue of urban leftovers should not prevent us from questioning the management of urban leftovers in general. Nor does the book mention the consequences of the zero waste policy that have already been proven or are expected. Although this municipal initiative offers hope for a reduction in the production of waste, it also implies fairly radical changes in the ways in which goods are distributed and consumed. While the historical analysis of waste production was accompanied by a study of its management, the possible conflicts that it caused, as well as its consequences on the material “weight” of Neapolitan metabolism, the book says nothing about the governance of “zero” policies, which circulate as pilot models for a transition to a sustainable city. To ensure that this transition does not remain incantatory and allows tangible changes in urban metabolism to occur, the book would have benefited from paying particular attention to the issues raised by the governance of waste flows resulting from these “zero” policies.
Ultimately, this account of the socio-ecological trajectory of waste production and management in Naples demonstrates the value of an approach that uses metabolism as a tool for understanding the changing ways in which an urban system functions. Furthermore, it comes at a time when the question of the place of waste in urban production seems to be (re)gaining legitimacy among political decision-makers and civil society, as well as growing interest among the general public—as illustrated, for example, by the recent exhibition at MuCEM in Marseille titled Vies d’ordures, focusing on the various “Lives of Garbage” in the cities of the Mediterranean. 
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