Waste Management Hybridization and Social Mechanisms: The Unpredictable Effects of a Socio-Technical Assemblage

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper investigates a hybrid model of waste management that combines door-to-door (DtD) and street collection (SC) systems and has been implemented in several municipalities in Piedmont, Italy. The study evaluates the economic, environmental and social impacts of this innovation using a quasi-experimental design. The results show that although the hybrid model led to a reduction in overall waste generation, it did not significantly improve the quality of waste collection, especially for recyclable materials. Economic performance also deteriorated in the treated municipalities. The authors use a theoretical framework that integrates socio-technical systems (STS) and analytical sociology to explain these unexpected results. Below is a detailed review and comments on various aspects of the manuscript:

• The terminology employed, such as "socio-technical systems," "hybrid waste collection," and "idealtypical models," may appear intimidating to certain readers; however, it is suitable for an academic audience. To enhance accessibility for a broader readership, it would be beneficial to provide concise definitions of these terms, particularly in the theoretical background section.
• While the advantages and disadvantages of DtD and SC models are addressed in the introduction, the manuscript would be enhanced by a clearer formulation of the research gap. Although hybrid models are presented, it is not sufficiently explained how your study fills a specific gap in the existing literature. Emphasizing this aspect would highlight the originality of your research and its potential significance.
• The introduction effectively integrates Socio-Technical Systems Theory with Analytical Sociology, providing a robust foundation for the research. However, elucidating the connection between this theoretical framework and the research questions would significantly enhance clarity, allowing readers to better understand how these theories underpin the exploration of hybrid waste management models.
• The authors have conducted a thorough analysis of the economic implications; nonetheless, the policy recommendations could benefit from further elaboration. It is essential to consider how municipalities might effectively manage the rising costs associated with waste collection.
• While the hypotheses are articulated clearly, the authors acknowledge the need for further empirical validation. It would be advantageous to specify methodologies or studies that could be employed to test these hypotheses.
• The observed decline in the quality of waste separation for certain materials, notably plastics and metals, indicates a shortcoming in the optimization of the hybrid system for enhanced recycling quality. Identifying targeted modifications to improve waste separation quality, especially for these materials, within the hybrid framework is crucial.
• It would be helpful for the authors to clarify the accessibility of the dataset for other researchers, including any specific conditions or procedures for obtaining it.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Acceptable

Author Response

 

Thank you for your comments, criticisms and suggestions, which have helped us to improve the article. Here is a timely response:

• The terminology employed, such as "socio-technical systems," "hybrid waste collection," and "idealtypical models," may appear intimidating to certain readers; however, it is suitable for an academic audience. To enhance accessibility for a broader readership, it would be beneficial to provide concise definitions of these terms, particularly in the theoretical background section. 

Thanks for this comment. We added a brief definition of the socio-technical system and hybridization in the introduction. In particular, we emphasized the networked and multi-agent nuance of the socio-technical system concept and justified the use of "hybrid"  to describe a collection model in which Door-to-Door and Street Collection not merely co-exist within the same urban context (namely “mixed systems” in the academic literature) but are merged into a new integrated waste collection system. We removed the reference to Weber’s concept “idealtype” because it was too abstract and was not necessary to describe DtD and SC as collection model with peculiar characteristics. Here find tracked the changes:

Waste management is a socio-technical system (STS) a conceptual framework widely adopted in social science to investigate technological innovation pathways. At a glance, STS scientists look at technological innovation as a process shaped by the  co-evolution of technologies, infrastructures, regulations, markets, cultural norms, and user practices that collectively shape innovation pathways and results [3,4]. Like other socio-technical systems, such as energy [5], urban waste management is characterized by institutional divergence [6]: while overarching objectives—such as reducing waste generation or increasing recycling rates—are broadly shared, the pathways to achieve these goals remain contested due to differing regulatory frameworks, market structures, and socio-cultural factors (Lines 41 - 48)

These analyses clearly highlight the strengths and weaknesses of Door-to-Door (DtD) and Street Collection (SC) systems.  However, in most urban contexts, including small and medium-sized cities, “mixed” waste collection systems are commonly found (16, 17, 20), where regulatory and technological elements from both models coexist within the same setting. For instance, it is not uncommon for municipalities to implement DtD collection for certain waste fractions while relying on SC for others or to adopt different models across different areas of the city and different user categories. Several studies have examined the economic and environmental sustainability of these models in various European cities (16, 17, 18, 19). However, they have rarely focused on cases where the collection system was not merely a combination of DtD and SC, but rather an innovative model stemming for the integration of regulations and technologies from both systems. In this paper we refer to these mixed waste collection models.as “hybrid models” (Lines 70 - 82)

• While the advantages and disadvantages of DtD and SC models are addressed in the introduction, the manuscript would be enhanced by a clearer formulation of the research gap. Although hybrid models are presented, it is not sufficiently explained how your study fills a specific gap in the existing literature. Emphasizing this aspect would highlight the originality of your research and its potential significance.

In the current version, we have put more emphasis on the originality and utility of our study in relation to the literature on the strengths and weaknesses of DtD and SC, and also in relation to literature that focused on  hybrid/mixed cases. Furthermore, we emphasised the usefulness of a theoretical approach rooted in the sociology of innovation processes, in order to better understand what determines the greater or lesser sustainability of collection systems, and in particular, the co-determination relationship between norms, technologies and social behaviour. We attach the new paragraph in the Introduction:

Several studies have examined the economic and environmental sustainability of these models in various European cities (16, 17, 18, 19). However, they have rarely focused on cases where the collection system was not merely a combination of DtD and SC, but rather a true hybrid—an innovative model characterized by the overlap of regulations and technologies from both systems.A prime example of such hybrid models is the implementation of smart bins (20), which are street containers accessible only via an identification card and equipped with opening mechanisms designed to incentivize users to reduce waste volume, particularly for residual and organic waste. These models have a significant economic and environmental impact, which requires further study to better inform urban policy decisions. Moreover, they offer a valuable opportunity from a scientific perspective, as they illustrate how variations in regulations and technologies influence individual behaviors, and how the aggregation of these behaviors creates the conditions for innovation. This represents a challenge that allows sociological disciplines to collaborate with STEM fields not only in understanding but also in modeling waste collection systems oriented toward sustainability (Lines 71 - 92). 

• The introduction effectively integrates Socio-Technical Systems Theory with Analytical Sociology, providing a robust foundation for the research. However, elucidating the connection between this theoretical framework and the research questions would significantly enhance clarity, allowing readers to better understand how these theories underpin the exploration of hybrid waste management models.

Thanks for the comment, it’s true that a clear link between research questions and theoretical framework was missing. We tried to address the issue by two main changes. First, we updated the questions as follows (Lines 123 - 133):

(1) Has the introduction of the DtD mechanism - the locking of containers for mixed, or-ganic waste and paper with magnetic cards and the tracking of the delivery of these types of waste. - achieved meaningful results in terms of sustainability? 

(2) How did this hybridization reconfigure user practices within a changing context resulting from the interactions between new rules and technologies? 

(3) What mechanisms triggered by this reconfiguration might explain the results of the hybridization?

Second, we added a few lines at the beginning of the theoretical section that we hope help in clarifying the connection (Lines 142 - 154):

The research questions address two main dynamics: the aggregate effect of the innovation introduced in waste collection and management (question 1), and the ways changes at the level of individual users appear to produce such an effect (questions 2 and 3). To capture these dynamics, we developed a theoretical framework by combining two well-established traditions of social science research: Socio-technical Systems and Ana-lytical Sociology. The latter provides conceptual tools to link the different levels of a so-cial system by considering the actions and interactions of individual agents as affected by and influencing the environment in which they are embedded, and highlights the rele-vance of hypothesising mechanisms to explain such reciprocal micro-macro dynamics. The former provides useful conceptual tools to support the identification of these mech-anisms, by conceiving them as the result of the combination of the hardware and soft-ware components of social systems, i.e. the technologies and the social settings (rules, behaviours, cultures...) with which they interact.

• The authors have conducted a thorough analysis of the economic implications; nonetheless, the policy recommendations could benefit from further elaboration. It is essential to consider how municipalities might effectively manage the rising costs associated with waste collection.

We added, in the conclusion, a paragraph where we expose some proposals for policy maker that are connected with research results (891 - 916):

The research results ultimately allow for the provision of some operational proposals to local decision-makers regarding a possible revision of waste collection systems. The use of an individual waste tracking system and the adoption of containers with smaller openings for non-recyclable waste have shown encouraging results in reducing this type of material. This approach should be maintained and extended to other types of waste, particularly plastic and metals, and accompanied by a communication campaign aimed at informing citizens precisely on how to separate waste correctly. Indeed, these are the best strategies to address the issue of declining quality in waste intended for recovery.Even more significant reductions in non-recyclable waste could be achieved with the implementation of the PAYT (Pay-As-You-Throw) system. Although effective, the incentive—or rather, the "fear of financial penalties" induced by the tracking device on non-recyclable waste—may not be long-lasting. To consolidate this result, users must see their higher or lower compliance with the service reflected on their waste collection bills.Similarly, the distribution of service costs should be more closely based on the performance of individual municipalities. As highlighted in previous sections, the municipalities involved in the study have experienced increased collection and treatment costs because they funded the investment in new technological devices. However, they have not benefited from the cost reductions resulting from lower non-recyclable waste disposal. This is because ACEA distributes treatment costs among all member municipalities based on criteria that are not exclusively linked to the amount of non-recyclable waste produced. The adoption of a tariff system more accurately reflecting the reality of waste flows in each municipality will lead to a rebalancing of overall costs (in particular, an increase in treatment costs for municipalities not involved in the system and a decrease for those that are). This, in turn, will make the expansion of the initiative across the entire territory more urgent.

• While the hypotheses are articulated clearly, the authors acknowledge the need for further empirical validation. It would be advantageous to specify methodologies or studies that could be employed to test these hypotheses. 

Thanks for highlighting the need of identifying proper tools and methods to get reliable data and information in order for the hypothesis to be teste. Actually, we are already in the process of designing a mixed-methods fieldwork (survey and focus groups) only focused on the treated group and aimed at getting more detailed info about waste collection practices and attitudes and identifying the motivations behind. In the first version we thought it was not the case, while discussing the main understanding and research perspective, to get into methodological detail. But of course should you deem relevant we can include a short description about the next (foreseen) steps.

• The observed decline in the quality of waste separation for certain materials, notably plastics and metals, indicates a shortcoming in the optimization of the hybrid system for enhanced recycling quality. Identifying targeted modifications to improve waste separation quality, especially for these materials, within the hybrid framework is crucial.

Thank you for this suggestion. As previously mentioned, we have included a recommendation in the conclusions on how to address the issue. Specifically: i) Implementing access control with a card system for plastic and metal bins, as is already the case for organic waste and paper.
ii) Launching a communication campaign explicitly focused on distinguishing between residual waste, plastic, and paper, as well as clarifying the materials that are most commonly confused.

 

• It would be helpful for the authors to clarify the accessibility of the dataset for other researchers, including any specific conditions or procedures for obtaining it. 

In 3.2 we reported the data we used in the analysis

1. Demography - Residents by age at municipal level (Source: ISTAT – Italian national Institute of statistics)
2. Income, - Income per capita at municipal level (Source: Italian Ministry of Finance)
3. Economic structure – Labor forces and Local Units by economic sector at municipal level (Source: ASIA –Registry of Italian active enterprises)
4. Waste collection - Quantity of waste collected by type and by municipality, years 2019-2023 – (Source: ACEA) 
5. Waste service - Economic flows (costs and gains) generated by the service, years 2019 -2023 – (Source: ACEA)

 

They belong to two categories of data: publicly available (1,2,3) and owned by Acea (4,5). Access to the latter is of course upon request to the owner. We added in the Data Avaliablity Statement at the end the following:

This paper uses two categories of data listed in par 3.2: A) Data publicly available that support the socio-economic description of the 2 groups of municipalities reported in table 1 B) Data available upon request from Acea that support the operationalization of the DID

Reviewer 2 Report

Comments and Suggestions for Authors

This study investigates the hybridization of waste management models by integrating door-to-door (DtD) and street collection (SC) systems in small and medium-sized municipalities in Piedmont, Italy. The research employs a quasi-experimental approach to assess the environmental and economic impacts of this hybrid system. The Socio-Technical System (STS) framework and Analytical Sociology are used to explore macro-micro interactions influencing waste management performance. The study is theoretically grounded and methodologically rigorous, providing an important contribution to the debate on waste management optimization. However, several scientific, methodological, and clarity-related issues need to be addressed before publication.

1. The introduction should provide a stronger comparative discussion of previous hybridization efforts in waste management. Are similar models already studied in other regions or countries? If so, what is unique about this case?
2. The rationale behind integrating DtD and SC should be better justified with quantitative or qualitative arguments. Why were this approach chosen over improving existing models?
3. The introduction of magnetic card-based tracking is interesting but needs further technical details on how it was implemented and how compliance was ensured.
4. The economic feasibility of this hybrid model should be discussed in the context of long-term sustainability.
5. The study employs a quasi-experimental design with difference-in-differences (DID) analysis, which is a strength. However, the validity of the control group needs stronger justification. Were matching techniques used to ensure comparability between treated (T) and non-treated (NT) municipalities?
6. The 17 performance indicators used to evaluate environmental and economic impacts are well-defined, but their relative importance should be weighted.
7. Contradictory effects of the hybridization model (e.g., reduction in total waste but no improvement in waste separation efficiency) need a stronger causal explanation.
8. The decline in material quality for recyclables suggests behavioral shifts that are not fully explained.
9. The Coleman Boat framework is an interesting addition, but the link between micro-level behavior and macro-level systemic effects should be better demonstrated with data.
10. The assumption that economic incentives influenced behavior needs empirical validation.
11. The study should compare its findings with existing policy targets, such as EU waste management directives or the circular economy action plan.
12. The abstract should clearly state the research gap and the main unexpected findings rather than focusing too much on theoretical frameworks.
13. Figure 1 is missing.
14. The visualization of Figure 2 is useful, but the scaling and labeling should be improved to highlight key trends.
15. The DID values in Table 4a should be explained in simpler terms for clarity.
16. Consider adding a summary column in Table 4b that highlights whether each change was positive or negative for sustainability goals.

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Thanks for all your comments. They give us the opportunity to strengthen the overall robustness of the theoretical and methodological framework and to improve a lot the reflections and lessons learnt. Before going in details through all of them, as a general remark we would like to stress that this paper, and the analysis behind, is the first of three steps of a research design aimed at investigating the complex socio-technical processes which shape the innovation pathways in the field of waste collection and management with the ambition of explaining the dynamics affecting its economic and environmental performance. As we write in the introduction (lines 100-108): the research design focuses on the innovation represented by the hybrid model is therefore structured as follows: (1) description of the effects of the innovation on the waste management system performance and formulation of causal hypothesis to explain the generative micro-macro dynamics behind such effects; (2) qualitative and quantitative insights to test causal hypothesis and build a middle range theory able to bridge innovation pathways and environmental performance in waste management; (3) scenarios analysis based on the operationalization of the theory (given the micro-macro approach the most suitable are microfunded modelling technques such as Agent Based models). This paper covers the 1st step therefore the main aim is to identify hypothesis to be tested in next steps.

• The introduction should provide a stronger comparative discussion of previous hybridization efforts in waste management. Are similar models already studied in other regions or countries? If so, what is unique about this case?

Thank you for the suggestion. In the current version, we have put more emphasis on the originality and utility of our study in relation to the literature on the strengths and weaknesses of DtD and SC, and also in relation to literature that focused on “hybrid” cases. Furthermore, we emphasised the usefulness of a theoretical approach rooted in the sociology of innovation processes, in order to better understand what determines the greater or lesser sustainability of collection systems, and in particular, the co-determination relationship between norms, technologies and social behaviour. We attach the new paragraph in the Introduction (lines 70 - 93):

These analyses clearly show the strengths and weaknesses of DtD and SC. However, they do not deal with the 'hybrid' cases, which are instead common in several cities in Italy, where features of  one model are applied to the other. For example, in DtD systems there are attempts to integrate components of the SC model, for example by providing kerbside bins or other neighborhood containers for certain types of waste (e.g. glass). Or, in the case of SC collection, a specific type of service or waste fraction is collected DtD, e.g. paper collection in blocks of flats. A detailed analysis of the impact of different types of 'hybridisation' on the economic and environmental sustainability of the waste cycle has been explored in the literature (Hannah et al., 2015). Larsons et al. (2010) presented five waste collection scenarios in the city of Aahrus, Denmark, three of which were characterised by hybrid collection models, which showed that the most environmentally and economically effective would be DtD. Yıldız-Geyhan et al. (2019) carried out a similar study in a district of Istanbul, which showed that the system with the best environmental and economic indicators is the one where separation is not carried out by citizens, but by operators downstream of the collection process. Rossi et al. (2022) reconstructed the LCA of the waste cycle of an Italian city of 16,000 inhabitants, which in just a few years went from a SC model to a DtD model to one based on smart bins, and showed that the latter system was the most sustainable. Although relevant, these studies look at the impact of collection systems on a single municipality, based on hypothetical scenarios rather than actual collection data. Moreover, the case study literature, which is characterized by the predominance of management and engineering analysis approaches, has not yet fully taken into account the co-determination mechanisms between the norms, technologies and behaviors of the various actors involved in the collection systems as explanatory factors for their environmental and economic performance, which requires the adoption of a theoretical and methodological framework closer to the sociology of innovation.

• The rationale behind integrating DtD and SC should be better justified with quantitative or qualitative arguments. Why were this approach chosen over improving existing models? 

Thank you for this comment, which allowed us to provide further clarification on the research design and the case study. In the introduction, we clarified that the choice of modelling the service with smart bins was made by the service manager, Acea, with the aim of reducing undifferentiated waste and improving the quality of differentiated waste, using typical door-to-door standards within a street collection model. This was a choice made by the manager, within the resources available to him and the political direction received from the municipalities that are his partners. Below is the integration (lines 110-122):

 

In particular, Acea has introduced "smart bins" for the collection of undifferentiated waste, organic waste and paper, containers that can be accessed by users with a magnetic card and that can track the number of deliveries. In addition, the smart bin for undifferentiated waste has been redesigned by reducing the size of the opening, so that only 30-litre bags can be inserted and the card must be used for each deposit. Acea's objectives, described by the company in various institutional documents, were to reduce the quantity of undifferentiated waste and improve the quality of differentiated waste, areas in which the previous collection model, corresponding to a "pure" SC, achieved results below the regional and national legal requirements. According to the Acea engineers who designed the new service, smart bins would have made it possible to introduce the strengths of door-to-door, such as individual tracking of deliveries, into a system that would maintain the strengths of SC, in particular a more sustainable personnel expenditure. 

• The introduction of magnetic card-based tracking is interesting but needs further technical details on how it was implemented and how compliance was ensured.

In the new version of the article, particularly in paragraph 3.1, we have added more technical details on smart bins and the strategy of communication adopted by ACEA to illustrate the new service (Lines 268-288). As we argue in the article, compliance was not totally ensured, also because of a scarce communication effort.

Specifically, in the old system, the bins for the collection of wet waste were 240 litres, side-loading, with a totally openable lid. Dumpsters for the other fractions had a volume of 1,700 to 3,200 litres, with a door that could be fully opened on both sides. In the new system, the bin with the undifferentiated waste was equipped with a 30-litre drawer opening and a cap with an electronic system for tracking the deliveries. The same type of design was adopted for the organic waste bin, but with a 20-litre drawer mouth. For all other bins, a calibrated mouth on both sides was chosen. The bins for undifferentiated waste, organic waste and paper were equipped with an electronic canopy, and each user was given an access card, which allowed the registration of each delivery. Acea delivered an illustrated brochure door-to-door with instructions on how to organise the new service and some advice on how to separate waste correctly. The distribution of the access cards to the bins was carried out door-to-door and through a number of information points located in the squares of the municipalities involved in the experiment. The communication materials trace the reasons for the innovation back to the need to improve waste separation and make a general reference to the success achieved by other municipalities in similar experiments. A home composter was also distributed to users who requested one.

• The economic feasibility of this hybrid model should be discussed in the context of long-term sustainability.

We share this concern. In the Discussion section, we have added a reference to the need for a longer-term observation of the impacts of hybridization , particularly regarding collection costs. We argue that, for treatment costs, given that significant results have already been achieved—such as a reduction of over 50% in unsorted waste (UW)—it is instead possible to provide a reliable short-term assessment and to points out some contradictions and paradoxes described in the discussion. Find tracked here the changes (lines 617 - 633):

A comprehensive assessment of the economic impact of a techno-organizational innovation in a sector like waste management requires a long-term perspective while the case study allows for the observation of only the first two years. However it is reasonable to expect that, in the long run, T municipalities may experience a reduction in collection-related investment costs—primarily due to the amortization of expenses for the purchase and installation of smart bins—a long-term perspective alone cannot fully explain the dynamics of treatment costs. Given the strong environmental performance of T municipalities (-50% of UW in 2 years), such cost differences should already be apparent in the short term. Despite some partial and uncertain results, the pilot program seems to have enabled the T municipalities to achieve a significant portion of the targets set by Directive 2008/98/EC and the Circular Economy Plan ahead of schedule. The overall reduction in waste has exceeded the 15% target established by European regulations for 2025. The recycling rate has surpassed 60%, the threshold set for 2030. The decrease in unsorted waste and the adoption of a comprehensive separate collection system have already allowed T municipalities—as well as NT municipalities—to cease direct landfill disposal, instead diverting waste towards energy recovery.

1. The study employs a quasi-experimental design with difference-in-differences (DID) analysis, which is a strength. However, the validity of the control group needs stronger justification. Were matching techniques used to ensure comparability between treated (T) and non-treated (NT) municipalities?

 

Thanks for your comment, we fully agree that when applying counterfactual approaches (and more generally comparing groups) it is crucial to guarantee the maximum degree of similarity, or at least minimize the role of confunding on the outcome of interest. Actually, in order to minimize this risk, in our exercise we opted not to use any specific matching techniques for three intertwined main reasons. 

First, we are interested in the emerging aggregated effects at the territorial system level and not the effects on individual municipalities. The aim was therefore not to proceed with a one-to-one comparison among treated units and a subset of their most similar non-treated units extracted from the wider group of non-treated (e.g. via propensity score matching, nearest neighbors) Instead our interest is on getting the difference between the average values of the variables of interest (the 17 indicators) for the treated and the non-treated groups of municipalities as a whole. 

Secondly, and consequently, in the specific quasi-experimental setting we deemed relevant to consider the whole population of both the treated and non-treated groups, that although diverse in number of members accounts for roughly half of the population of the whole area  (61492 T vs 67064 NT). Therefore before proceeding with the DID we provided a comprehensive description of our groups with attention paid to some structural aspects of the observed areas that are likely to affect waste production (income, density of population and land use, economic structure in terms local unit and labor forces by sector) and their variation in the period of interest, i.e. 2018 – 2022. The results are reported in Table 1 and we found them a sufficiently robust guarantee of comparability. We paid attention not only to the average values (we actually considered the median) but also to the variance of the variables distribution (and we considered the variation coefficient in order for the different variables to be comparable). 

Third, in the treated groups there is one member that is actually out of scale, Pinerolo (and this is reflected in some of the some dimensional variables such as labor forces and population). But, as reported in the comments of the table, from the perspective of the experiment under scrutiny this does not make a great difference as the innovation was introduced (and the waste management is organized) not on the whole municipality but in 8 sub areas that can be for any purpose considered as many small municipalities

We have shortly integrated the comment to the table to reinforce the justification of the comparison 

1. The 17 performance indicators used to evaluate environmental and economic impacts are well-defined, but their relative importance should be weighted.

Thanks. Actually, we will address this point in the next steps of the research. At this stage we opted to consider all the variables as equally important for two main reasons:

1. We did not consider to derive a synthetic indicator of the groups’ performance that would have mandatorily required to assign weights to the indicators. Instead, it was a first exploratory exercise on a number of widely adopted indicators for assessing different aspects of the performance
2. To date, we don’t have enough knowledge to assign reliable weights to the different indicators as we based our analysis on secondary administrative data provided by Acea 

 

Said all that, we fully agree that the identification of the relative importance of the different indicators must be addressed and this will be on of the aspects that will be explore in the following steps through a number of focus groups with experts and stakeholders

• Contradictory effects of the hybridization model (e.g., reduction in total waste but no improvement in waste separation efficiency) need a stronger causal explanation. 

• The decline in material quality for recyclables suggests behavioral shifts that are not fully explained. 
• The Coleman Boat framework is an interesting addition, but the link between micro-level behavior and macro-level systemic effects should be better demonstrated with data.

Since issues are similer we reply to these three comments with a unique answer. We acknowledge the need to strengthen the empirical evidence, in particular, regarding the logic of aggregation (from micro to macro). This concern is also present in other applications of Coleman’s Boat (see Boudon, R. (1991). La place du désordre, Critique des théories du changement social, pg.74-6-79 Paris, PUF), where the aggregation logic is not always empirically verifiable as it involves mapping of thousands, if not millions, of micro-interactions and micro-actions (Ramström, G. (2018). Coleman’s Boat Revisited: Causal Sequences and the Micro-macro Link. Sociological Theory, 36(4), 368-391. https://doi.org/10.1177/0735275118813676). However, we believe we have provided a substantial amount of data to support not a thesis (which is beyond the scope of this article) but rather hypotheses—to be tested through field surveys in a second phase of the research, which is currently ongoing—regarding the most widespread micro-action pattern observed among users following the introduction of the treatment. In particular, the 17 indicators point out that in T Municipalities:

• A significant reduction in unsorted waste (UW) and waste generation overall.
• A deterioration in the quality of sorted waste (SW), without a corresponding increase in total quantities collected.

Both phenomena result from the aggregation of individual behaviors. Although there are multiple micro-level behaviors (described in the "micro-micro" logic), not all are equally prevalent. The 17 indicators suggest that:

• There is no widespread tendency among users to dispose of waste in non-traced containers in neighboring municipalities where tracking is absent.
• Correct waste separation is not prevalent, even when consumption levels remain unchanged.
• The non-traced containers (for plastic and glass) are not commonly used as a "refuge" for unsorted waste disposal.

This is because:

• There is no significant increase in UW production in municipalities neighboring the treated ones.
• The amount of dry waste (DW) in treated municipalities has not undergone major quantitative changes that could explain the reduction in UW.
• Glass is well-separated, whereas plastic, metals, paper, and cardboard are not, even though the latter is subject to tracking.

Based on these findings, we hypothesize that the dominant pattern consists of micro-actions aimed at reducing unsorted waste, primarily through the following strategies:

• Overall waste reduction, with a shift in consumption habits (due to economic incentives, social control and the effect of communication campaigns).
• Increased use of plastic and paper, as these are the waste fractions where sorting mistakes are most common—for example, food packaging with residual contamination, plastic toys, disposable razors, etc.

 

8. The assumption that economic incentives influenced behavior needs empirical validation.

Thanks for your comment. In line with the ambition of the paper, on the basis of empirical evidences about the effects of the innovation we applied our theoretical framework to identify causal hypothesis mechanisms that require to be empirically tested. Among them for sure the strength of the link among economic (perceived) incentives represented by PAYT and behavioral change must be supported by additional empirical evidences within the scope of our research in order for the hypothesis to be tested in the specific research setting. But the assumption this hypothesis relies on it seems quite well established in literature both in behavioral sciences ( just to name a few Kahneman, D. (2011). Thinking, fast and slow. Farrar, Straus and Giroux,Thaler RH (2015) Misbehaving: The Making of Behavioral Economics. W. W. Norton & Company, Shogren J. (2015) Behavioural Economics and Environmental Incentives, OECD, Rajapaksa D, Gifford R, Torgler B, et al. Do monetary and non-monetary incentives influence environmental attitudes and behavior? Evidence from an experimental analysis. Resources Conserv Recycl. 2019;149:168–176). Of course should you find it relevant we can include a list of reference to support the assumption 

9. The study should compare its findings with existing policy targets, such as EU waste management directives or the circular economy action plan.

Thanks for this comment.. Find attached a paragraph that we added, in the Discussion section, in order to evaluate the results obtained by T Municipalities in relation to objectives of European Commission’s Circular Economic Plan. 

Despite some challenges, the results of the pilot program have enabled the T municipalities to achieve a significant portion of the targets set by Directive 2008/98/EC and the Circular Economy Plan ahead of schedule. The overall reduction in waste has exceeded the 15% target established by European regulations for 2025. The recycling rate has surpassed 60%, the threshold set for 2030. The decrease in unsorted waste and the adoption of a comprehensive separate collection system have already allowed T municipalities—as well as NT municipalities—to cease direct landfill disposal, instead diverting waste towards energy recovery.

Moreover, although data on the capture rate of plastic packaging relative to the amount placed on the local market in T municipalities is not yet available, and despite challenges related to the financial returns recognized by Italian consortia, the quantities of separately collected plastic and metals increased between 2019 and 2023. However, these positive outcomes are not unique to the municipalities of Pinerolese. Across most of the indicators mentioned, Italy as a whole has already met—and in some cases exceeded—the targets set by the European Commission, as outlined in the ISPRA 2024 report (41).

These results are not only significant in terms of waste management indicators, but are also interesting from a sociological point of view, because behind them there is a collective behaviour that has changed thanks to the introduction of a technical-no-organisational innovation and that has produced unexpected results.

10. The abstract should clearly state the research gap and the main unexpected findings rather than focusing too much on theoretical frameworks.

We revised the abstract, inserted a more explicit reference to the two main research gaps that inspired our research: i) the analysis of the impact of ‘hybrid’ waste collection models from the point of view of environmental and economic sustainability; ii) the identification of co-determination relationships between norms, technologies and individual behaviour in these particular collection systems. We also revised the part on the theoretical framework, drying it up, but confirming that the matching between analytical sociology and STS constitutes an original contribution of ours and should be considered as one of the outcomes of the research.

 

 

 

Reviewer 3 Report

Comments and Suggestions for Authors

The  article title is original, relevant and topical.

Reading the abstract of the article, the reader gets a clear and accurate picture of the research carried out by the authors, being very comprehensive, containing essential introductory information, presenting the used working method and the obtained results.

The introduction and theoretical background clearly present the topic, clearly outlining the ideas of the research, presenting in detail what is already known about the topic. Here I would have some suggestions to make: some bibliographical sources (such as, 7, 18) should be detailed in the references section, as they cannot be found in the search. Also, Figure no.1 is missing here!!!

In the Methodology chapter, paragraph 3.1, the case study area, i.e. the 44 municipalities, I would suggest a geographical presentation of the 44 municipalities (a map) in order to be able to more easily identify the geomorphology of the settlements. The average income/inhabitant/capita is annual? (rd.191-192). I would also here suggest that in Table no.1 the data sources should be listed somewhere! The numbering of the tables does not coincide with the explanation in the text (rd.275-275), Table no.3 does not exist!!!!

The research results are presented in an appropriate way, being easy to read and understand, the relevant tables are presented in a clear and visible way. The units of measurement are adequate, the tables have titles, columns and rows labeled correctly and clearly, the categories of values are grouped accordingly. The text in the results explains the data presented in graphs and tables and does not repeat them, clearly presenting the results obtained. The results are discussed from several angles and placed in context without being over-interpreted.

The conclusions are supported by the obtained results, but also by the bibliographic references, which respond to the pursued aim.

Bibliographic references are also relevant and recent, with the authors making a correct reference, generally including appropriate key studies (with the specification that some bibliographic sources should be more detailed!!!!)

The article ” Waste Management Hybridization and social mechanisms: the unpredictable effects of a socio-technical assemblage ” developed by Claudio Marciano, Alessandro Sciullo, presents an information opportunity for future research, being a consistent article in itself and meets the proposed research objective.

Congratulations to the authors!

Author Response

Thank you very much for liking the article. We are delighted with the feedback. We have added the missing bibliographical references, figure 1, clarified the value referring to income in table 1 (it was actually referring to annual income), revised and adjusted the table numbers, and inserted a reference to the source of the data in table 1. We were not able to find a map with geomorphological surveys of the area within the time frame of the revision. However, if the paper is accepted, we will be sure to add it as soon as we receive it from the ACEA manager we requested it from.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

After the corrections that the authors made according to my comments, I recommend the manuscript to be published

 

Author Response

Thank you for this reply and for the revisions that allowed us to increase the quality of our paper.

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

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