Circular economy, varieties of capitalism and technology diffusion: Anaerobic digestion in Sweden and Paran ´ a

The transition to a circular economy relies on systems that facilitate waste recovery and recirculation of resources. These systems are based on certain enabling technologies. The aim of this paper is to explain how socio-economic structures influence the diffusion of such technologies. It applies a framework built on societal embedding and varieties of capitalism to compare the diffusion of anaerobic digestion (AD) in Sweden in northern Europe and Paran ´ a in southern Brazil. Both Sweden and Paran ´ a have experienced accelerated diffusion of AD, but there are significant differences in the respective diffusion patterns. The comparative analysis points to a tradeoff between system complexity and speed of diffusion. It illustrates how AD can be presented as a solution to various problems, and it further shows how the specific problems that gain attention shape diffusion patterns. By showing how socio-economic structures influence the appointment of problem owners, their agency, and legitimate forms of institutional support, the analysis demonstrates how economic systems condition technology diffusion.


Introduction
Recovery of waste to enable recirculation of resources is a fundamental building block for circular economies.Such recirculation lessens the need to extract virgin resources and prevents pollution by turning waste into useful resources.The system diagram presented by Webster (2017) shows how circular economies rely on two different material loops that facilitate such recirculation: one that consists of finite materials and another loop with renewable resources.In the renewable loop, which often is denoted 'the circular bioeconomy' (Salvador et al., 2021), anaerobic digestion (AD) of organic matter is a key enabling technology (Pan et al., 2015).By means of AD, it is possible to address multiple environmental problems, including organic waste management, wastewater treatment, air quality, eutrophication, and greenhouse gas emissions (Börjesson and Berglund, 2007).This, however, assumes a controlled utilization of the biogas and digestates produced through AD, using the digestates as biofertilizers and the biogas as an energy carrier.
To manage the collection of substrates for AD, as well as an efficient use of the resulting biogas and biofertilizers, it is necessary to gather stakeholders from different sectors such as energy, waste management, sanitation, agriculture, and food production.Previous studies of such emerging socio-technical systems have preferred national demarcations, analyzing single-case studies in individual countries (De Oliveira and Negro, 2019;Lönnqvist et al., 2018;Ottosson et al., 2020).Moreover, several studies have zoomed in on specific cities or regions (D'Adamo et al., 2021;Fallde and Eklund, 2015;Lönnqvist et al., 2015;Patrizio et al., 2015).While some studies have compared AD adoption and policies in different countries (Gustafsson and Anderberg, 2021;Nevzorova and Karakaya, 2020), comparative analyses of diffusion processes are less common.Raven and Geels (2010) and Tigabu et al. (2015) are two exceptions that compare two European and two African states, respectively.Both these studies explain technology diffusion by pointing to the inner dynamics of the emerging socio-technical systems.However, such inward-oriented analyses provide a limited understanding of how societal contexts influence technology diffusion (Markard et al., 2015;Markard and Truffer, 2008).
Comparative studies are useful to understand how technologies become embedded into surrounding societies.According to Kanger et al. (2019), societal embedding implies that technology is co-constructed with society in a process influenced by socio-economic structures.In this paper, we refer to varieties of capitalism (Hall and Soskice, 2001) to distinguish such structures.The paper compares the diffusion of AD in Sweden in northern Europe and Paraná in southern Brazil.The number of inhabitants of Sweden and Paraná is similar, and both have experienced accelerated diffusion of AD.However, the respective diffusion patterns differ.The paper compares how the surrounding socio-economic structures have shaped the diffusion patterns.The aim is to explain how socio-economic structures influence the diffusion of key enabling technologies for circular economies.
After this introductory section, a theoretical framework section elaborates on societal embedding and varieties of capitalism.Thereafter, a methods section presents the rationale for case selection and comments on the data sources and analysis.The subsequent two sections present the cases.Next, a comparative analysis elucidates contrasting patterns in terms of societal embedding and varieties of capitalism.A concluding section summarizes the main findings.

Societal embedding
Societal embedding (SE) was introduced as a complement for models that describe technology diffusion as a linear process that engages different adopter categoriesinnovators, early adopters, early majority, late majority, and laggardsin a stepwise process (Rogers, 2003).SE describes the formation of socio-technical systems through the co-construction of technology and context (Rip and Kemp, 1998).It suggests that new technology must be integrated into businesses and markets, admissible according to regulations and standards, accepted by the wide society, and aligned with user practices (Geels and Johnson, 2018).SE implies that technology diffusion is full of choices and struggles (Kanger et al., 2019), which requires articulation and collective action (Geels et al., 2007).In contrast to technology-centered approaches that usually treat context as a series of opportunities or barriers, socio-technical perspectives admit that technology can at least in parts shape social systems and vice versa (Geels and Johnson, 2018).Deuten et al. (1997) first introduced three dimensions of SE: business, regulatory, and cultural environment.Later studies added user environment as a fourth dimension (Geels and Johnson, 2018).User environment involves the incorporation of new technologies into user practices (Geels and Johnson, 2018).Interactions between users and technological diffusion go beyond purchase experience and individual adopters, and it may also include other actors affected by the adoption of the new technology.Business environment refers to business procedures, strategies, and markets (Deuten et al., 1997).The emergence and diffusion of new technologies may lead to changes in the ways business is carried out or even cause the collapse of incumbent industries (Kanger et al., 2019).The regulatory environment concerns rules, laws, regulations, standards, and policies that influence production, distribution, and use (Kanger et al., 2019).For emerging socio-technical systems, it is particularly hard to navigate the regulatory environment since appropriate policies and standards may not exist at first (Deuten et al., 1997).New technologies also need to be accepted in the cultural environment.Failure in considering this may cause backlashes in the diffusion process (Markard et al., 2016).Therefore, it is necessary to articulate and negotiate pros and cons to create legitimacy and social acceptance.

Varieties of capitalism
Focusing the analyst's attention on institutional structures, Varieties of Capitalism (VofC) provides a tool for the comparison of political economies (Hall and Soskice, 2001).VofC divides developed countries into liberal market economies (LMEs) and coordinated market economies (CMEs) according to how firms resolve coordination issues.Institutions support particular sets of coordination mechanisms, thus dictating how firms coordinate relations and develop capabilities.Hall and Soskice's (2001) original framework set the analytical boundaries around the national state.However, there is a growing debate on how the national level influences local developments and how much room it leaves for diversity (Eriksson et al., 2020) since firms are affected by institutions at different geographical scales, from local to global.
After the second world war, the Nordic countries developed strong features of CMEs where coordination through networks are vital complements to market arrangements.In the Nordic countries, national and municipal levels of governance are quite strong, while intermediary levels are weak (Eriksson et al., 2020).This allows local actors to have a strong agency, which is necessary to implement national policies.Moreover, in EU members such as Sweden, not only institutions below the national level are important but also above it as their membership in the European Union adds a governance layer.
Overall, immature economies neither fit LMEs nor CMEs because they may depend on foreign investment, have a strong state presence, or lack network structures to arbitrate conflicts (Hall, 2015).Schneider (2009) proposes a third category, hierarchical market economies (HMEs), that allows the categorization of Latin American countries according to VofC.In HMEs, the state retains a strong presence and influence.Although HMEs present characteristics of both LMEs and CMEs, it is not a mixture since the types of interactions are unique.
Countries tend to develop complementary institutional structures in different domains.However, these are not always positive as some countries can get stuck in cycles that are detrimental to development (Schneider, 2009).Brazilian institutional structures have blocked growth beyond commodity exports, locking the country in low-skill sectors and stalling wealth distribution (Morgan et al., 2020).Brazil presents a high degree of informal social coordination based on the similar class background between public authorities and large domestic enterprises (Nölke, 2010), in contrast with CMEs, where non-market relations are provided by formal institutions.The Brazilian nation is fragmented, formed by the union, the Federal District (Brasília), 26 member states and municipalities, all of which have political autonomy and shared competences according to the Federal constitution.

Theoretical synthesis
Whereas SE understands technology diffusion as a co-evolving and multidimensional process, VofC explains how institutions impact interactions and knowledge flows.According to SE, market success goes beyond the technology itself.Contextual characteristics are essential; they may stimulate or block technology diffusion, and they may open certain ways of adopting the technology while hindering others.Showing how economies are built on institutions, the literature on VofC offers a scheme of classification that is helpful to distinguish how socioeconomic structures may affect adoption.The scheme, putting the firm at the core of the analysis, runs across all the contextual dimensions incorporated in SE.It is particularly useful for analysing cases of professional markets, where the technology adopters are firms.These firms operate in different user, business, regulatory and cultural environments at different geographical scales.VofC admits that institutions change over time, but VofC analyses rarely address such changes.In this sense, SE and VofC complement each other by highlighting the dynamic features of technology diffusion while still acknowledging the stability of economic systems.

Introduction to anaerobic digestion
Anaerobic digestion (AD) means the degradation of organic matter in the absence of oxygen, resulting in the production of biogas (incl.methane) and digestate.The role of AD is multifaceted as it can be used for hygienization and treatment of waste, production of a renewable energy carrier (methane), and production of biofertilizer (digestate) (Börjesson and Berglund, 2007).Competing waste management technologies rarely combine energy and nutrient recovery but focus on one T. Magnusson et al. of the two: energy recovery (incineration, landfills) or nutrient recovery (composting) (Börjesson and Berglund, 2007;Murphy and Power, 2006).For wastewater treatment, the choice of anaerobic instead of aerobic treatment will imply both the production of a renewable energy carrier and reduced energy consumption for the treatment process (Meyer and Edwards, 2014).
Common substrates used for AD are sorted household waste, sewage sludge, food waste, industrial waste (e.g., stillage from ethanol production and wastewaters from breweries and pulp and paper mills), manure, and other agricultural residues.Substrates can be digested solely, but often different substrates are combined in co-digestion processes.Specific choices of substrates, technology, and parameters such as temperature and treatment time will impact the amount and quality of the biogas and digestate (Sarker et al., 2019).
Biogas mainly consists of methane and carbon dioxide but can also contain smaller amounts of water, nitrogen, oxygen, hydrogen sulfides, and other trace gases.It can be used to generate heat, electricity, or motive power (e.g., vehicle fuel).Depending on the quality of the gas and its intended use, further refinement may be needed.To be used as vehicle fuel, the biogas must be upgraded to biomethane (>95% methane content), meaning that the gas is cleaned from carbon dioxide and impurities (Gustafsson et al., 2020).The digestate can be used as a biofertilizer, replacing mineral fertilizers, facilitating the recirculation of nutrients, and increasing the possibility for organic farming (Drosg et al., 2015).

Case selection
The selection of the two cases, Paraná and Sweden, is based on theoretical sampling (Eisenhardt and Graebner, 2007), with the intention to learn about AD diffusion in geographical settings characterized by differing socio-economic structures.Following Nilsson et al. (2012), we consider the supra-national EU level in the Swedish case analogous with the Brazilian federal level in the case of Paraná.
Sweden had just over 10 million inhabitants by the end of 2020 (SCB, 2021), being the seventh-largest economy among the EU-member states in 2020 (World Bank, 2021).It is an industrialized nation with a large, export-oriented, and knowledge-intensive manufacturing industry.The significance of the agricultural sector has declined steadily during the last century and in 2018, it represented only one percent of the gross domestic product (GDP) (UI, 2021).In 2020, the food import was about 50% higher than the export (JV, 2021).Sweden occupies about 450 000 km 2 and has 290 municipalities (SCB, 2021).As an industrialized nation, Sweden has a well-established public infrastructure that provides access to energy, transport, sanitation, and waste management.The municipalities have extensive responsibility for waste management and sanitation services.For this reason, municipalities operate utility firms, which obtain business directives from municipal boards (i.e., local city governments) and incomes from fees that citizens pay for the services.The municipalities share the responsibility for public transport with the regions, which are intermediary governance structures.
With estimated 11,5 million inhabitants in 2020, Paraná is the sixthmost populous Brazilian state and was the fifth-largest economy in 2018 (IBGE, 2021).Paraná has a diversified economy with strong service and industry sector.Yet, with a highly productive livestock sector, extensive grain production and food industry, the agribusiness sector generates around 33% of Paraná's GDP (IPARDES, 2020).The state was the third-largest food exporter in Brazil in 2020, whereas most of the food consumed by Paraná inhabitants is produced locally (AGROSTAT, 2021).Across its almost 200 000 km 2 , Paraná has 399 municipalities (IBGE, 2021).Paraná presents good sanitation and urban solid waste management conditions compared to the rest of Brazil, as 214 municipalities provided access to sewage networks in 2017 (IBGE, 2021), and 208 offered selective waste collection in 2008 (SIDRA, 2013).

Data sources and analysis
The research relied on multiple data sources.We retrieved quantitative data from annual statistics on biogas production and the use of digestates and biogas.In the case of Sweden, the Swedish Energy Agency (SEA) publishes the data.In the case of Paraná, CIBiogása science and technology institution dedicated to developing the biogas value chainpresents the data.For a broader contextual understanding, we complemented the quantitative with qualitative data from interviews and workshops.Table 1 summarizes the data used and the Appendix presents detailed information about the data sources for the respective cases.
The data sets on biogas production and use in Sweden and Paraná are not directly comparable because different units are used.Whereas the Swedish data refers to energy content (GWh), the Paraná data refers to total gas volume (Nm 3 ).Since the energy content of the gas produced at different AD facilities can vary depending on the methane content (e.g., between 5 and 8.5 kWh/Nm 3 ; Sarker et al., 2019), it is difficult to convert to one unit. 1Still, it is possible to compare the development trajectories of the respective cases.For both cases, quantitative data is available from 2005 until 2019.In the Paraná case, this gives a complete picture of the accelerated diffusion, whereas the diffusion started earlier in Sweden.We use qualitative and literature sources to comment on the preceding years in Sweden.
In terms of categorization of production facilities and biogas use, the data sets correspond to each other with three minor reservations.Firstly, the Swedish data contains "flaring" as a use category, while flared biogas is not included in the Paraná data.Secondly, the Paraná data is incomplete with regards to biogas production from sewage treatment plants.Thirdly, "mechanical" is a use category in the Paraná data, which refers to the use of biogas to generate motive power that can drive such things as pumps and compressors.The corresponding category in the Swedish data is "industrial", which is a broader category as it incorporates the use of biogas in all types of industrial processes.
For the comparative analysis, we use four dimensions of societal embedding: user, business, regulatory, and cultural (see section 2.1).The user environment explores the reasoning behind AD adoption and the preferred use of biogas.The business environment investigates the development of the AD value chain structures and business models.The regulatory environment looks at policies that influence the adoption of AD and the use of biogas and the digestate.The cultural environment examines public acceptance.Moreover, we use varieties of capitalism (see section 2.2) to explain the observed differences.

Urban air quality as a problem that triggered acceleration
In Sweden, sewage plants have used AD as a process technology since

Table 1
Summary of data sources.the 1960s, using the resulting biogas internally at the plants or flaring it.However, in the mid-1990s, a few pioneering municipalities started developing and building systems to facilitate biogas as a fuel for city buses (Olsson and Fallde, 2015).The prime reason for this was that the exhaust emissions from the existing diesel-fueled buses caused air quality problems in city centers.Buses running on natural gas could help solving this problem.However, since Sweden does not have any elaborate national infrastructure for compressed natural gas (CNG), locally produced biogas became a preferred option.To make it possible to use buses originally designed for CNG, it was necessary to upgrade the biogas to biomethane.Moreover, it was necessary to install gas compressors, local pipelines for gas distribution, and filling stations at bus depots.Municipalities, to extend the biogas production capacity, complemented existing AD facilities at sewage treatment plants with new co-digestion plants, which could use various substrates as inputs.Organic wastes from slaughterhouses, households, and manure from livestock were directed to these plants.This necessitated new waste management practices, and the municipalities had to involve holders of waste to develop and implement systems and routines for organic waste separation.
The use of biomethane in city buses depended on close user/producer interaction, with municipal utility firms representing the producer side and local public transport authorities representing the user side (Fallde and Eklund, 2015).Having the local public transport authority as a partner meant that demand for biogas could be guaranteed.The local citizens would enjoy the benefits when breathing cleaner air and using public transport services.Municipalities referred to this in information campaigns to motivate citizens to engage in household waste sorting.Altogether, the alleged benefits for the local society and the close collaboration between municipalities and public transport authorities made it possible to justify the requisite investments.Moreover, the collaboration made it possible to solve problems jointly and plan supply and demand on a long-term basis so that expansions in production volume could be matched with increased demand.The use of digestates as biofertilizers in local organic farming was an added benefit, but this was not a prime motive for building the systems.

Increased co-digestion, upgrading, and use of biomethane as a vehicle fuel
Until the early 2000s, the co-digestion of organic wastes for vehicle fuel production was confined to a few pioneering cities such as Linköping and Uppsala.However, ever-stricter national and European restrictions against organic waste disposal in landfills prompted municipalities to search for alternative ways of managing this waste.Whereas composting or incineration are simpler options, these technologies do not bring the multiple benefits of AD.Moreover, as part of its national climate policies, the Swedish government implemented fuel tax exemptions for renewable fuels.Since vehicle fuel taxes are high in Sweden, the fuel tax exemption increased the possibilities for producers and distributors to compete with fossil fuels on price and still profit from biomethane sales.The late 2000s and early 2010s saw a rapid expansion of co-digestion, with several new plants being established.Between 2006 and 2019, there was a more than a five-fold increase in production volume from co-digestion, much due to establishing new plants (Figs. 1  and 2).As much as 87% of the biogas from the co-digestion plants was upgraded to biomethane in 2017 (SEA, 2018).When considering the number of plants, sewage treatment outnumbers co-digestion, but co-digestion dominates production volume.
A corresponding increase in the number of registered gas-fueled buses in Sweden (TransportAnalysis, 2020) indicates that a primary intention with the co-digestion was to supply biomethane for public transport. 2To extend the market, producers and distributors have also supplied biomethane to other vehicles such as cars, light trucks, and refuse trucks, but data on vehicle gas supply shows that public transport has remained the prime user category (Statistics Sweden, 2020)).
The share of the total volume of nationally produced biogas upgraded to biomethane has increased steadily over the last 15 years, reaching 69% in 2019, and the main part (about 87%) of the biomethane was used as a vehicle fuel (SEA, 2020)).Of the total production volume, 15% was used to generate heat, and 10% was flared.While the amount of flared biogas has been relatively constant over the last 15 years, the biogas used for heat generation has decreased in favor of upgrading.Other applications are minor (Fig. 3).
In 2019, 52% of the nationally produced biogas (excluding landfill gas) came from co-digestion, and 37% came from sewage.Only 7% came from industrial facilities (food and pulp & paper), and 3% from farmbased production (SEA, 2020)).There was a five-fold increase in the amount of digested manure between 2009 and 2019, much due to a special subsidy scheme implemented by the Swedish government.However, two-thirds of this is digested at co-digestion plants.Since co-digestion plants use mixes of substrates, sewage sludge is still the dominant substrate, with 34% of the national biogas production being based on sludge.This is followed by household waste (22%), manure (11%), slaughterhouse waste (9%), food industry waste (6%), industrial sludge (5%), energy crops (2%), and a residual category.
Municipal utility firms operate all sewage plants, and until 2009,  2 The correlation coefficient (R) between biogas production from co-digestion (GWh/year) and the number of gas-fueled buses in Sweden between 2005 and 2019 is 0.97.
they also operated all co-digestion plants.However, since 2010, private enterprises have taken control over a substantial part of the co-digestion by acquiring existing plants and establishing new ones.Private firms now control most larger plants, and about 60% of the national codigestion production comes from these plants. 3he digestates must fulfil certain criteria to qualify for use as biofertilizers in organic agriculture.The intention is to ensure a certain quality level and reduce the risk of contaminants being disseminated.In 2019, all digestates from the Swedish co-digestion plants were used as biofertilizers, but this does not generate any substantial revenues for the producers.Only 41% of the digestates from sewage plants were used in this way, and the remaining part was used in construction work or for covering landfills (SEA, 2020)).

Eutrophication as a problem that triggered acceleration
In the frontier between Paraná and Paraguay lies Itaipu Binacional, the second-largest hydroelectric power plant in the world, owned by the Brazilian and Paraguayan governments.The Paraná River Basin covers an extensive area of western Paraná and serves the Itaipu reservoir.The region is privileged by its abundance of natural resources, rich biodiversity, and fertile soils.However, the area has suffered from the expansion of agriculture and uncontrolled growth of urban areas, which increases deforestation, soil erosion, and water pollution.During routine quality checks, Itaipu identified eutrophication of the Paraná River Basin (Lofhagen et al., 2018).The substantial amounts of fertilizers and organic matter in the river, caused by the surrounding agriculture, lead to an excess of nutrients which, in turn, caused the proliferation of algae and aquatic plants, threatening the ecological balance in the region.In 2008, Itaipu, Eletrobrás, and the United Nations Industrial Development Organization (UNIDO) signed a memorandum declaring western Paraná an international area for promotion and development of renewable energy, which triggered a series of biogas-related developments in the region.Five years later, in partnership with the State Company of Paraná (Companhia do Estado do Paraná -Copel) and the Paraná Sanitation Company (Companhia de Saneamento do Paraná -Sanepar), demonstration units were developed in three main sectors: agriculture, sanitation and waste management.Initially, the demonstration projects sold the electricity produced to the state grid operator through contracts.Later, when the National Electricity Regulatory Agency implemented the distributed generation program (Agência Nacional de Energia Elétrica -ANEEL, Resolution 482/2012), the demonstration units were among the first in the country to be registered as micro and mini generationup to 5 MW.
After a series of studies to identify the causes of poor water quality in the Paraná River Basin, the Ajuricaba micro-basin was recognized as one of the greatest contributors (Lofhagen et al., 2018).The extensive livestock activities in the region meant a large concentration of animals in a small area.Consequently, there was a high concentration of potential substrates, making the region ideal for AD.Itaipu, the local municipality, and several other state organizations came together to develop and support the implementation of the first bioenergy condominium in Brazil.Anaerobic digestors were installed, and a pipeline was built to transport the biogas to the micro thermoelectric power plant.The biogas was originally used to generate electricity and for cooking, but this was later substituted with the generation of heat to a local poultry cooperative.
The condominium model was later repeated in Entre Rios do Oeste, yet this time biogas was used to generate electricity for public buildings in the municipality.Analogous to the Ajuricaba Condominium, farms produce the biogas, feeding it into dedicated pipelines to the mini biogas power plant.The farmers receive payment according to the volume of biogas produced while the municipality can save up to 12% on their electricity bill (Biogas Analyst & Technological Development Director, Appendix B).

Increased production from industrial facilities, and use of biogas for heat and electricity
The sugarcane sector has a large biogas potential but biogas production from sugar-alcohol industry waste comes with major technical and economic challenges.Nonetheless, the state has led the development in this sector by implementing the first demonstration unit and the first commercial unit.Fig. 4 shows that there has been a remarkable growth of biogas production in Paraná during the last decade.In particular, the rapid growth in industrial facilities is striking, and this is now the dominating type of facility in terms of production volume.Most of those are slaughterhouses, starch industries, breweries, or sugar and alcohol industries.Also, the production from farm facilities has grown, and Fig. 5 shows that farm facilities now outnumber industrial facilities, but with a significantly lower production volume per unit.The adoption of AD in the food industry and at farms can be explained by the increasing attention to eutrophication problems and the consideration of AD as a potential remedy to these problems.
As evident from Fig. 6, the dominating way of using biogas in Paraná is to generate heat, followed by electricity generation.While heat is used for internal processes, biogas power plants are connected to the electricity grid through the distributed generation program.However, there have been a few smaller initiatives directed at upgrading to biomethane.In 2017, Itaipu built a demonstration plant inside the hydroelectric power plant complex.It uses substrates from different waste streams  from within the Itaipu complex, such as food waste from its restaurants, grass pruning from the green areas, and sewage.The biomethane is used to fuel up to 80 vehicles from the company's fleet, while the digestate is used in the gardens.Another biomethane demonstration unit was developed in farms in western Paraná and the municipality of Castro in cooperation with the agricultural machinery company New Holland.Until 2018, the farms used the biogas for heat and electricity generation; then, upgrading was added to facilitate use of the fuel for the tractors operating in the property.
Paraná is among few Brazilian states that has biogas-specific state legislation.In 2018, the state implemented State Policy on Biogas and Biomethane (Política Estadual do Biogás e Biometano -Law 19.500/ 2018).The policy promotes the development of biogas solutions and regulates the ground for biogas production, logistics, and use in the state, which further supports legal biogas initiatives and actors across the biogas value chain.Paraná's Gas Company (Companhia Paranaense de Gás -Compagas) also encouraged the implementation of a biogasspecific policy since it defined the limits of action of each actor, thus harmonizing the relation between biogas and the piped gas monopoly by the state company.Although the policy also mentioned a minimum percentage of biomethane in the gas grid, the state regulatory agency never regulated the proposal because of consumer resistance due to a fear of raised gas prices.Appendix B).The use of the biogas varies according to the biogas production volumes.In small plants, the biogas produced is used for heat generation to reduce the costs of the sludge thermal treatment, while in medium-scale plants, the biogas is used to generate electricity.The energy recovery models were so successful that Sanepar, in partnership with a private company, developed a large-scale codigestion plant in Curitiba that receives urban solid waste from several streams besides sewage sludge.This plant is connected to the electricity grid generating credits for the sanitation company.
The digestate from farm-based and industrial facilities can be used as fertilizer following the National Environmental Council guidelines.In these sectors, the digestate is used internally by the producer, externally through donations or agreements, or both.But it rarely generates revenues for producers.Paraná's biogas policy further elaborates the characteristics of fertilizer and biofertilizer, their sources, and their applications.In the case of digestate from sewage treatment plants, the legislation is stricter, only allowing the digestate to be used as fertilizer when it does not contact the crop (e.g., coffee, corn, and oranges).As a result, only half of the treated sludge in sewage plants is used as fertilizer, while the other half is landfilled.

Comparative analysis
Both Sweden and Paraná show an accelerated diffusion of AD.The diffusion started somewhat earlier in Sweden, while the acceleration was quicker in Paraná.Moreover, the patterns of diffusion are markedly different.Below, we compare the two cases according to the societal embedding dimensions user, business, regulatory, and cultural environments (Deuten et al., 1997;Geels and Johnson, 2018;Kanger et al., 2019).The analysis concludes by referring to varieties of capitalism (Hall and Soskice, 2001) to explain the observed differences.

User environment
In both cases, environmental problems triggered AD adoption, but the problems differ.In Paraná, the downgrading of water quality caused by indiscriminate expansion of animal husbandry paved the way for the adoption of AD across the food value chainone of the strongest industry sectors in the state.In Sweden, AD was coupled with public transport to reduce air pollution in city centers while at the same time offering a solution to local waste management problems.Later, it was also associated with climate policies.
Rural areas in Paraná suffer from power cuts, which can cause a loss in production, especially for swine and chicken farmers.Biogas-based distributed power generation is a potential solution to this problem.In addition, biogas producers with low energy demands can generate extra income from electricity generation.By contrast, being situated in a mature industrialized nation with a stable electric grid and low electricity prices, this has not been a preferred option in Sweden.
In Paraná, the common use of biogas is in industrial facilities to supply heat to internal processes, mainly in the food industry.Industrial firms are responsible for assuring the correct disposal of their residues, and they must develop and implement a solid waste management plan in compliance with the municipality's plan.The implementation of AD reduces operational costs while solving an environmental problem.In Sweden, the use of biomethane as a vehicle fuel has required more complex systems.Upgrading facilities and elaborate distribution networks are necessary to deliver biomethane to external users and match their demand with a supply.AD plants must be sufficiently large to justify the investments needed.Therefore, municipalities have capitalized on synergies with sewage treatment plants to establish central codigestion plants.

Business environment
In Sweden, biogas started as a by-product of waste treatment services offered by the municipalities and rose to its own multi-actor system.Nevertheless, municipalities remained a core actor.Urban air pollution triggered the search for innovative solutions to substitute diesel buses in the city center, and public transport authorities considered biomethane  T. Magnusson et al. a viable solution.Inbound logistics for substrates, as well as distribution networks and filling stations, and supply of biofertilizers to farmers, were essential parts of the system.The improvement of local infrastructure attracted private firms to enter the market.Consequently, AD in Sweden has evolved into local circular systems involving multiple actors.By contrast, in Paraná, AD revolves around single actors that generate the substrate for biogas production, operate the biogas plant, and use the biogas as an energy carrier and the digestate as biofertilizer.
Farm-based biogas facilities in Paraná are mostly small, and production is usually managed by the farms' own staff.Lack of qualified personnel can result in operational problems, which could discourage the adoption of AD.However, technology providers in Paraná are situated locally and build close relationships with adopters.This has helped to overcome problems and reduce uncertainties.Swedish farm-based biogas production has also increased.Yet, in contrast with Paraná, manure is mostly co-digestated at larger co-digestion facilities, allowing farmers to stick to their core business.

Regulatory environment
Regulations at both federal and state levels impact AD in Paraná.The federal government regulates the power sector, presenting a homogeneous regulatory framework across the country, which, together with grid accessibility, facilitates electricity generation from biogas.Gas markets are fragmented as they are subject to regulatory action by the states and the federation.The state monopoly on piped gas and the lack of infrastructure on the West of Paraná, where most AD plants are situated, discourage producers from entering fuel markets.Unlike other biofuels, biogas has no policy at the federal level.Yet, in 2018, the Paraná state government implemented the Biogas and Biomethane State Policy in response to the growing diffusion of AD in the region, which describes the rights and duties of each actor across the value chain.Shortly after, Paraná implemented another policy clarifying the domains of the state piped gas monopoly, leaving biogas out.These policies can be seen as an attempt to reduce fragmentation and uncertainty.Neither the EU nor Sweden have specific biogas policies.Value chain structures, coordination among actors, and quality standards are mostly left to the business realm.That said, both the EU and national regulation have supported the adoption of AD in Sweden, even if indirectly.Restriction to landfilling of organic waste pressured municipalities to find better waste management solutions such as AD.Incentives for the use of biogas in the transportation sector offered by the Swedish government further explain the preference for using biogas as a vehicle fuel as other sectors such as power and industry have received lower incentives.

Cultural environment
The adoption of AD by Swedish municipalities gradually expanded from sewage treatment to co-digestion based on wastes from food industries and farms until finally being integrated into urban solid waste treatment in a process that took decades.These changes in local waste management systems compelled citizens to adapt to new ways of sorting their waste.The municipalities engaged in information campaigns to spread awareness about sorting systems and create public engagement.A similar system in Paraná was discontinued shortly after been implemented as it experienced problems with the correct sorting of waste and low public acceptance.The municipality of Formosa do Oeste provided dedicated bins and carried out information campaigns yet could not achieve the same level of public acceptance as Swedish municipalities.
In Sweden, public transport and waste management integration allow citizens to participate in this system and visualize its advantages.Producers portray AD as an irreplaceable part of local circular systems that reduce environmental pollution, produce renewable fuel, and recycle nutrients.It creates tangible connections between waste sorting, environmental benefits, and public services.
In Paraná, state actors emphasize job creation and increased income in rural areas as vital benefits.AD is often portrayed by its supporters as a tool for regional development that can transform a liability into an asset and reduce the environmental impact of Paraná's agribusiness.This narrative is carried out through the food value chain and embraced by state actors in the power, gas, and sanitation sectors.Table 2 summarizes the comparative analysis according to the societal embedding dimensions.

Socio-economic structures and system formation
The comparison suggests that there are several differences between the diffusion patterns in Paraná and Sweden.Firstly, different actors have been the most prominent adopters.In Paraná, the governmentally controlled Itaipu appears as the lead innovator, while private firms in the food industry and farmers have been early adopters.The involvement of these actors has been critical for the accelerated diffusion.Their control of the complete value chainfrom substrates via digestion to biogas use and, to a significant extent, biofertilizershas been instrumental for the rapid uptake.By contrast, in Sweden, municipalities and municipal utility firms have been innovators and early adopters, while private firms specializing in biomethane production have emerged at a later stage.Stimulated by governmental incentives, farmers have also adopted AD, but municipal utility firms and specialized biomethane producers have digested most of the manure in co-digestion plants.
Relating the contrasting diffusion patterns to varieties of capitalism makes it possible to highlight how socio-economic structures have shaped diffusion in the respective cases.Being situated in a hierarchical market economy (Schneider, 2009), the state initiated the diffusion of AD in Paraná.Initially, Itaipu was used as an instrument to accomplish this, and Itaipu has maintained its leadership through several subsequent initiatives.Notwithstanding extensive private involvement from the food industry and agriculture, the state has consistently orchestrated the diffusion.An illustration of this is the recent implementation of a specific policy to regulate the biogas value chain.
Correspondingly, the Nordic version of a coordinated market economy (Eriksson et al., 2020) is clearly visible in the Swedish case.With responsibility for sanitation and waste management and with a strong agency, municipalities have taken the initiative in AD adoption, building complex local systems that unite various stakeholders.An important foundation for these systems has been the kind of network structures that characterize coordinated market economies, relying on long-term contracts and trust-based relationships rather than competitive market-based relationships.
Consequently, varieties of capitalism (Hall and Soskice, 2001) have nurtured the formation of vastly different socio-technical systems.In Paraná, private ownership characterizes the system, with a high degree

Table 2
Societal embedding of AD in Sweden and Paraná.
of vertical integration and a considerable influence of state-level governance.By contrast, decentralized governance characterizes the Swedish system, with a mixed public/private ownership, disintegrated value chains, and bottom-up processes, and with the state acting as a supporter rather than a director.

Conclusion
Arguing that AD is a key enabling technology for the transition to a circular economy, this paper has presented a comparative case analysis to show how socio-economic structures have influenced the diffusion of this technology in Sweden and Paraná.While previous case studies in single countries, regions and cities have suggested that such influence does exist, comparative studies of diffusion processes have downplayed societal contexts and focused on the inner dynamics of emerging systems.By applying a framework built on societal embedding and varieties of capitalism in a comparative analysis, the paper has contributed to the understanding of contextual influences on technology diffusion.The analysis has shown contrasting diffusion patterns, resulting in the development of different systems with distinctive characteristics, and it has pointed to a critical tradeoff between socio-technical system complexity and speed of diffusion.
AD may be presented as a solution to a variety of problems, and our comparative analysis shows how its diffusion will depend on which problems get attention.Socio-economic structures influence the identification of problems, the appointment of problem owners and the agency that these problem owners possess.While the reference to varieties of capitalism made it possible for us to show how economic systems condition technology diffusion, the societal embedding dimensions added aspects that normally are not referred to as economic.This particularly relates to the analysis of the cultural environment, which points to importance of involving the civil society and engage citizens to facilitate recirculation of organic matter.
The results presented in this paper have important implications for both theory and practice.Studies of the potential for AD in different regions are often based on inventories of available substrates.While this obviously is a crucial factor to consider, our research suggests that analysts must incorporate the characteristics of economic systems and consider socio-economic structures in such studies.This is because such structures will be critical for technology diffusion.Frameworks that combine societal embedding with varieties of capitalism can function as guiding instruments for such studies.
This paper has presented an initial attempt to explain how socioeconomic structures influence the diffusion of key enabling technologies for the transition to a circular economy.Although the framework built on societal embedding and varieties of capitalism lends an argument for analytical generalization, additional studies are needed to further validate and elaborate on the research findings.While our analysis has focused on the role of AD in the transition to a circular economy, additional studies may look at other enabling technologies and investigate similarities and differences between the renewable loop and the finite materials loop of the circular economy.Future studies may also examine technology diffusion in regions characterized by other varieties of capitalism than the ones discussed in this paper.

Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Fig. 1 .
Fig. 1.Biogas production in Sweden according to the energy produced in different sectors.Biogas production from landfills and gasification is not included in the figure.Source: SEA (Appendix A).

Fig. 2 .
Fig. 2. Number of AD units per sector in Sweden.Source: SEA (Appendix A).

Fig. 4 .
Fig. 4. Biogas production in Paraná according to the volume produced in different sectors.Biogas produced from sewage and landfills is not included in this figure.Source: CIBiogás (Appendix B).
Most sewage plants do not show in the CIBiogás data.Still, AD is a widely used technology in this sector.According to Sanepar's Research and Development Manager (Appendix B), 215 out of their 225 sewage treatment plants use AD.In 2019, the sanitation sector in Paraná produced approximately 15 10 6 Nm 3 of biogas (Research and Development Manager, CIBiogás,