Circular developments of maritime industrial ports in Europe: a semi-systematic review of the current situation

Our current approaches to resource management are not sustainable. Businesses typically follow a linear approach where resources are not well utilized. Maritime ports are part of the problem, as they need to optimize the use of resources and generate negative externalities. However, they can also be important drivers of sustainability if they effectively transition to Circular Economy (CE). In this study, eight principles of CE and ten CBMs, are discussed and used to analyze ports in three areas of intervention. This paper analyzes current CE practices in European ports and the potential to adopt Circular Business Models (CBMs) to create value for port stakeholders and contribute to the United Nations Sustainable Development Goals (SDGs). Drivers and barriers to CE were analyzed, and the level of development was assessed. The ports studied are in Europe and are generally regarded as Maritime Industrial Ports (MIP). The methodology includes a Semi-Systematic Literature Review (SSLR) and a SWOT analysis to examine CE practices in maritime ports. This methodology helped enhance the analysis of Drivers and Barriers to CE transition. This study concludes that ports are developing circular practices and business models on the technical and biological flows, but the level of implementation is moderated to low. Six drivers for adopting CE principles were identified, including European ports’ experience in circular activities and the Quality & Environmental Management System (EMS). In addition, seven barriers to CE were highlighted, including the diversity of port characteristics and the different interests and ambitions of port stakeholders that make it difficult to standardize measurements and transition to circularity. Circular development goals in ports should be integrated, and development must balance social, economic, and environmental sustainability. The findings and implications of this study will help Port Authorities (PA) in the strategy, policy development, and implementation of CBMs.


Introduction
Our life systems work circular.There are no landfills; material flows, and one species' waste is another's food (EMF 2014).The sun provides energy, things grow and die, and nutrients return to the soil, and it works (Taylor 2020).If the living circular model works, can the way people think and work be changed to operate in a more circular and sustainable way?Using nature as an industry model, humans can use fewer resources and regenerate our planet (Raworth 2018), thus becoming more sustainable (Environment, Social and Economic).Waste is a human creation, and the more we have, the less we are sustainable.
The most commonly accepted definition of sustainability has its origin in the Brundtland Report of 1987 (Kuhlman & Farrington 2010), "Sustainable development is the development that meets the needs of the present without compromising the ability of future generations to meet their own needs" (WCED 1987a(WCED , 1987b)).The concept has evolved to include three pillars: Social, Economic, and Environmental (Kuhlman & Farrington 2010) and environmental sustainability is the cornerstone.Today, people are compromising the existence of future generations due to the linear modus operandi of industries and societies.
Under the traditional Linear Economy (LE) approach, when virgin materials are turned into products for usage or consumption and then disposed of, excessive waste and pollution are generated (Rabaina et al. 2020), and(EMF 2019), and resource management is not optimal.LE is destroying our planet, aligning with capitalist ideas of "more is better" (Bonciu, 2021).For example, one can imagine a company that produces disposable plastic water bottles.The company extracts petroleum to make the plastic, uses energy to manufacture and transport the bottles, and sells them to consumers.After use, the bottles are typically discarded and end up in landfills or oceans as waste, which can take hundreds of years to decompose and harm animal species (United Nations, 2018).
The Circular Economy (CE) is today's essential alternative to Linear Economy (LE).It promotes sustainable practices by efficiently using resources, minimizing waste, and reducing environmental harm (EMF 2019;Velenturf & Purnell 2017).Industries, communities, and ecosystems can achieve long-term sustainability by adopting a CE approach.For instance, instead of disposing of plastic water bottles, CE allows for their collection, cleaning, and transformation into new bottles or other products through upcycling (McDonough and Braungart 2002).Alternatively, pyrolysis can convert plastic into fuel (Ghodke 2022).These are just a few examples of material flows within the CE model (refer to Fig. 2).
Maritime Ports play a vital role in global trade, transportation and economic development (UNCTAD 2020).As such, ports can be important drivers of change in many different ways, from facilitating global trade and connecting markets to promoting economic growth, driving innovation, and fostering sustainable development (Ghisellini et al. 2016).If large ports implement circular practices effectively, vast volumes of waste could be reduced, reused, recycled, upcycled, or cascaded.Large ports in Europe and elsewhere typically settle shipping, chemical & petrochemical, oil & gas, waste management, aluminum, steel, and other heavy industries.All these organizational practices generate much pollution due to their nature and processes (World Bank 2018).
This study investigates current CE practices of Maritime Industrial Ports (MIP) in Europe that contributes to a more resilient and sustainable ports.A MIP is a logistic and industrial node in global supply chains with a solid maritime character and a functional and spatial clustering of activities directly or indirectly linked to transportation, transformation, and information processes within global supply chains (Notteboom et al. 2022).Large industry clusters are located in these ports, such as chemical & petrochemical, steel, aluminum, manufacturing, and logistics (Sohar port 2023).There is a potential to develop symbiosis with a circular mindset (Monios & Woxenius 2020).
CE principles in port operations promote resource efficiency, waste reduction, and material reuse.This resource efficiency includes recycling, renewable energy use, and greenhouse gas emission reduction (Ghisellini et al. 2016).By embracing circular practices, ports can foster innovation through new technologies, business models, and partnerships (LOOP Ports 2018).Using circular practices can also create economic benefits such as cost savings, increased efficiency, and new business opportunities (Pieroni et al. 2018).Circular approaches also mitigate the environmental impact and minimize waste, pollution, and energy consumption, thereby protecting ecosystems, reducing carbon emissions, and enhancing sustainability (Greenport 2022).Additionally, adopting circular practices enhances port resilience to climate change, economic downturns, and supply chain disruptions, which aids in diversifying resources and improving adaptability (ESPO 2021).Ports are crucial in driving the transition to a CE by promoting circular practices across their operations and supply chains and harnessing innovation in areas like digitalization, automation, and smart ports (Philipp 2020), (Heikkila et al. 2022).
While numerous studies have investigated sustainability and circular economy (CE) in various industries, there is a lack of research specifically focusing on the application of CE in ports, particularly Maritime Industrial Ports (MIP) with industrial symbiosis.Compared to other industries, the Ellen MacArthur Foundation has conducted limited studies on ports, with one notable report titled "Completing the Picture: How the Circular Economy Tackles Climate Change" (EMF -Completing the Circle 2021).This report examines the role of CE principles in reducing greenhouse gas emissions within the maritime sector.The Ellen MacArthur Foundation is a renowned organization in the field of CE, actively promoting the adoption of CE principles across different industries, including the maritime sector (Tiana et al. 2020).

Research purpose
This study investigates current Circular Economy (CE) developments in several European Maritime Industrial Ports (MIP) while examining potential Circular Business Models (CBMs) to implement that will make ports more resilient by maintaining material flows in circulation and regenerating the ecosystem and contributing to achieving the SDGs.The specific research objectives are: Different regions and industries worldwide, such as China, Japan, Scandinavian countries, the United States, and Europe, are actively promoting and making significant progress in implementing circular economy (CE) practices (Patwa 2021;Ellen MacArthur Foundation, 2018).However, due to the vastness of these areas, this study focuses specifically on European ports.European ports are chosen for several reasons, including the establishment of a legal framework by the EU to support the transition to a circular economy.This framework includes the Waste Framework Directive, which sets recycling and landfill diversion targets (European Parliament, 2008).Furthermore, the European Commission's Green Deal, proposed in 2019, aiming to make the EU climate-neutral by 2050 and includes the Fit for 55 package and the CE Action Plan.The Fit for 55 package proposes legislative measures to reduce greenhouse gas emissions by 55% by 2030 compared to 1990 levels, while the CE Action Plan focuses on waste reduction and promoting sustainable production (European Commission, 2015).
The ports being investigated are medium to large-sized MIPs situated in Europe, primarily following a landlord-type governance model.When these ports oversee adjacent Industrial Zones (IZs), they have the potential to foster Industrial Symbiosis (IS).The selected ports are affiliated with reputable organizations such as ESPO, Green Port Initiative, or Loop Port projects, and they actively engage in circular or sustainable practices (ESPO 2023;Green Port Initiative 2023).A range of ports from various countries were considered, and their details are presented in Table 1.
To achieve these objectives, a Semi-Systematic Literature Review (SSLR) was conducted by collecting data on 115 articles published from 1987 to 2023.More details are explained in the research methodology.
The remainder of this study is organized as follows: The "Literature Review" section presents definitions and principles of CE introduces more details about MIPs and CBMs in general, and explains some applications of CE and CBMs in ports."Methodology" outlines the scope of the study, explains how SSLR was conducted, and discusses the application of SWOT."Research findings" link the results to the research objectives."Conclusions and Discussions" summarizes the main points of the research, as it provides a detailed discussion of the results, implications, and limitations of this study.Direction for further research is also provided.

Introduction to circular economy (CE)
The CE promotes sustainability and resource efficiency by minimizing waste and maximizing the use of resources (Barros 2021).Unlike the Linear Economy (LE) with its "take-make-dispose" model, the CE aims to keep resources in use for as long as possible, reducing the reliance on finite resources (EMF on LE 2020).This involves sharing resources among industries and closing loops.See Fig. 1 for a comparison of the two models.
The Circular Economy (CE), according to the Ellen MacArthur Foundation (EMF), is based on three core principles: 1) Designing out waste and pollution, 2) Keeping products and materials in use, and 3) Regenerating natural systems (EMF 2019).However, other studies have identified additional principles to address the complexity of the topic (Geissdoerfer et al. 2016;Kirchherr et al., 2017).Table 2 presents eight CE principles that any industry aspiring to embrace CE practices should consider.
The CE approach requires a shift in the way we think about production and consumption and a redesign of business models, products, and services.This approach is for the port industry and any business, from car manufacturing to airplanes to retailing (EMF 2014).
CE has been implemented in ports since the 1990s in Industrial Zones (eco-industrial parks) such as the Kalundborg in Denmark, Stockholm Symbiosis in Sweden, and Kawasaki in Japan.These synergies allow the optimization of resources used and better cooperation in developing Industrial Symbiosis (IS) (Guillaume 2013).Developing IS waste of one company becomes the input of other closing loops."The goods of today are the resources of tomorrow at yesterday's resource prices" (UNCTAD 2019).Different countries are developing IS in Europe, including Germany, Belgium, Denmark, France, Italy, Netherlands, Portugal, Spain, and the UK.(Massard, 2013).The potential for IS is still ongoing in existing cases, and there is still a wide range of opportunities for its application in businesses.
The concept of the Circular Economy (CE) traces back to industrialist Walter Stahel's idea of "closed loop" production systems in the 1970s (Stahel 2008).However, it was in the 1990s that the term gained broader recognition in Europe as a response to concerns about resource scarcity, waste, and environmental degradation.The Ellen MacArthur Foundation, established in 2009, played a crucial role in promoting and popularizing the CE through research and advocacy efforts.This has led businesses and governments worldwide to adopt CE principles widely.Today, numerous countries, cities, and companies across various sectors are actively pursuing circular economy strategies and practices.
Since the early 2000s, the Circular Economy (CE) has gained momentum in response to concerns about resource depletion and environmental degradation.It aligns with the United Nations Sustainable Development Goals (SDGs), particularly SDG 12 (Schroder & Raes 2021).In Europe, the CE is integral to the EU's Green Deal and the CE Action Plan 2020, aiming for a climate-neutral Europe by 2050 (European Commission 2020).The CE offers benefits such as reduced environmental impact and new business opportunities (Barros 2021).The Ellen MacArthur Foundation and its network of partners promote CE practices (EMF -Completing the Circle 2021).Transitioning to a CE requires collaboration, innovation, changes in consumer behavior, and supportive government policies.
Transitioning to a Circular Economy (CE) necessitates systemic and cultural changes, collaboration, and innovation across sectors (Ghisellini et al. 2016).It involves shifting mindsets and behaviors from the linear model to a sustainable and regenerative system.This requires redesigning products, adopting resource-efficient business models, and addressing policy and market barriers.Infrastructure investments are also essential, including recycling facilities, waste management systems, and transportation networks.
Despite the challenges, the CE offers compelling benefits such as reduced environmental impact, enhanced resource security, and new business opportunities.To ensure inclusivity and equity, access, affordability, and participation must be  2019), is a widely recognized representation of the CE system.It offers a simple and intuitive visualization of the CE concept, serving as a valuable tool for policymakers, businesses, and stakeholders.The butterfly's body represents the convergence of the biological and technical cycles, fostering innovation and collaboration for developing new products and processes that integrate both cycles.This framework minimizes material leakage and reduces negative externalities (Korhonen et al. 2016).
According to a study published in the journal of sustainability in 2020, there were over 2.5 million peer-reviewed articles on sustainability between 2000 and 2019 (Giampietro et al. 2020).A search in the Scopus database for articles published between 2000 and 2021 using the term "circular economy" yielded over 6,000 peer-reviewed articles on the topic (Scopus 2021).However, when narrowed down to the context of ports, only 48 articles were found, suggesting limited information in this specific industry.While the Circular Economy is a relatively new concept, there is a growing body of literature exploring its potential benefits, challenges, and implementation strategies in various sectors.

Maritime industrial ports (MIP)
A MIP (Maritime Industrial Port) is a strategic hub for logistics, distribution, and industrial activities, offering excellent accessibility by sea, road, rail, and pipeline (Port of Rotterdam 2023).MIPs provide comprehensive facilities and expertise for loading, unloading, storage, transshipment, and processing of goods, catering to the specific needs of each company (Calvo 2018).They serve as nodes for industrial activities, such as manufacturing plants, refineries, chemical clusters, and warehouses, taking advantage of the port's location and transportation infrastructure (Calvo 2018).Additionally, MIPs play a role in renewable energy generation, waste management, and ship decommissioning (WSP, 2020).Ports can also support other economic sectors like tourism, fishing, and recreation (Port of Rotterdam 2023).
MIPs are predominantly governed by a landlord port model, where the Port Authority (PA) acts as a regulatory body and landlord, while private companies handle port operations (The World Bank, 2022).Examples of landlord ports include Rotterdam, Antwerp, New York, and Singapore.In this model, private companies lease infrastructure from the PA and are responsible for maintaining their own equipment and employing dock labor.Some ports have expanded their role as developers and operators of adjacent Industrial Zones or Free Zones (Langen, Henrik, & Hallworth, 2020).Successful Business Models (BMs) are crucial for MIPs to thrive in a dynamic market (The World Bank, 2022).

Circular business models (CBMs)
A business model (BM) is a plan or strategy that outlines how a company creates, delivers, and captures value in the marketplace (Baden-Fuller 2010).It is essential for any business to have a well-defined and effective business model in order to be successful.These models can be based on the principles of the CE, which seeks to create a closedloop system in which resources are used and reused in a continuous cycle, and these are conceptualize as Circular Business Models (CBMs).
Reducing a company's environmental footprint, trimming operational waste, and using expensive resources more efficiently is a necessity, and certainly appealing to top management.However, creating a CBM is challenging, and taking the wrong approa can be expensive (Harvard Business Review 2021).Success depends on many factors, but perhaps the most important is choosing a strategy that aligns with the company's capabilities and resources and addresses the constraints on its operations.Different general CBMs were identified in the literature and are summarized in Table 3 below.
Not all CBM are new.The concepts of recycling, reuse, and repair have existed for some time now (Awan & Sroufe 2022).The sharing of under-utilized household possessions also has a long history, and the provision of access to products, rather than ownership of them, is not so different from traditional product leasing.What is new is the growing diversity and sophistication of some CBMs, the way people are re-thinking business operations, as well as the range of sectors that adopt them (OECD 2019).The overall goal of these new CBMs is to lessen an organization's dependence on new resources.

Research methods
This study aims to explore the current CE developments in main European MIPs and potential CBMs to implement.A SSLR was conducted to collect data from a range of sources, including academic databases, grey literature, and online sites, using a predetermined search strategy.Following the literature review, a thematic analysis was conducted to identify key themes and patterns in the data.By looking into diverse data sources, this study offers valuable insights into the experiences of different European ports in the planning and implementation of circular projects and provides a basis for future research and circular practices implementation.

Scope of the study
This study involves mainly MIPs, represented in Fig. 2, where the Port Authority (PA) is a public entity that manages, operates and develops the port and industrial area.The PA makes sure there is infrastructure for public or private organizations to develop superstructure and operate.They acts as enabler and facilitator of sustainable growth, and it is a regulator (Port of Rotterdam, 2022), (Port of Antwerp, 2020).
These ports contribute largely to the economy and social development of the country and have the potential to generate closed loop economy models with major impact The principle of cascading, the sequential and consecutive use of resources, is a potential method to create added value in circular economy (CE) practices.
Cascading can be applied for other sectors such as food by-product or wood, textiles, coffee grounds and tyres (cascading) Bioenergy, Biomass and Biochemical Production (BBB) Industrial ports explore production of energy with non-fossil fuels.This vision will require intensive research in energy storage systems.As for the materials and biochemical sector, cutting-edge technologies need to be developed and employed to convert biomass and agricultural by-products to high-value commodities such as bioplastics, fibers and pharmaceuticals.(Bio-feedstock, anaerobic digestion, regeneration) when implementing Industrial Symbiosis (IS).Industrial port effectively can balance public interest of the society and private interests of shareholders and can be an important driver of circularity.IS refers to the collaboration and resource sharing between companies in order to create a closed-loop system and reduce waste (Neves, Godina, Azevedo, & Matias, 2019).Around the world, there are a number of wellknown instances of IS.Some examples are presented in the below Table 4.These are a few examples of IS in Europe, and there are similar initiatives taking place across the continent.Overall, the trend towards industrial symbiosis is expected to continue as more companies and governments recognize the environmental and economic benefits of adopting CE practices.The following Fig. 3 illustrates the Maritime Industrial Port (MIP) system where they collaborate or manage the Industrial parks (Eco-parks).
In a landlord port model, the port infrastructure is typically owned by the port authority or the government entity responsible for managing the port.These ports often have waste reception facilities and industrial zones adjacent to the port, which are managed by the port authority.The presence of these facilities attracts a diverse range of large ships, tailored to the needs of the companies operating within the port or industrial zones.This model promotes economic growth, environmental protection, and efficient maritime operations.

A semi-systematic literature review (SSLR)
A Semi-Systematic Literature Review (SSLR) wasconducted to analyze the CE models approach and its current application in MIPs.This method was selected because the topic of CE is conceptualized differently and studied by various groups of researchers

Kalundborg Symbiosis
The symbiosis involves a network of companies that share resources and byproducts in order to reduce waste and improve resource efficiency

Kwinana Industrial Area
The area is home to several companies that collaborate to reduce waste and promote sustainability, including a cement company that uses waste from a nearby nickel refinery as a raw material

Port of Rotterdam
The has implemented several industrial symbiosis initiatives, including the Rotterdam Heat Grid, which uses waste heat from local industries to heat homes and buildings

Symbiosis Center Denmark
The organization connects companies across Denmark and helps them find opportunities for collaboration and resource sharing

Port of Amsterdam
The port connects companies and organizations in the port area to exchange resources such as energy, water, and waste.For example, residual heat from wasteto-energy plants is used to heat greenhouses, and steam from industrial processes is used to generate electricity Kemi-Tornio Industrial Park In this port the waste heat from a stainless steel plant is used to dry wood chips, which are then used as fuel in a bioenergy plant Symbiosis in Güssing, Austria The town has a biogas plant, which produces electricity and heat from agricultural waste and organic materials.The heat generated by the biogas plant is used to heat buildings and greenhouses, and excess electricity is sold to the national grid Høje-Taastrup, Denmark The municipality of Høje-Taastrup in Denmark has implemented an industrial symbiosis program, which connects companies to exchange resources such as energy, water, and waste.Example, Waste heat from a brewery is used to heat a swimming pool, and excess water from a pharmaceutical plant is used for irrigation with diverse disciplines, and may hinder a full systematic review process (Wong 2013).While a systematic review follows a predefined and reproducible search strategy to identify and select relevant studies, a semi-systematic review may have a more flexible search strategy and may include a wider range of literature sources (Snyder, Literature review as a research method, 2019).Application of CE was investigated in different sectors beside the ports as well.This SSLR approach included search methods, inclusion and exclusion criteria, data extraction, and synthesis following the guidelines of (Petticrew and Roberts 2006) to have accurate, precise and trustworthy background information.An effective SSLR research method creates a firm foundation for advancing knowledge and facilitating theory development (Webster and Watson 2002).By integrating findings and perspectives from many empirical findings, a literature review can address research questions with a power that no single study has (Snyder 2019).
In this study, the researchers reviewed studies published after 1987 when the Brundtland Commission developed guiding principles for sustainable development, as it is generally understood today.This was an important milestone in port and shipping sustainability and part of the literature reviewed in this report.The research terms were a combination of: "Sustainability and port sustainability", "Circular Economy or Circular Economy in ports" OR "circular transition in ports", "Circular Business Models (CBM)", and "Industrial Symbiosis (IS)".Search for titles and keywords was done in broad databases such as ISI, Science Direct, directory of open access journal, Web of Science, Elsevier Science, IEEE Explore, complementary index, Library Database and EBSCO.
The research was limited to studies in English or Spanish language.The review includes academic peer-reviewed paper, grey literature such as conference proceedings, latest news, book chapters, and technical reports from port stakeholders, in addition to selected international and regional reports, projects, and studies.The grey literature was included to ensure diversity of views particularly due to lack of coverage of some concepts in academic literature.The total number of studies initially identified from different disciplines and ports were 780.However, relevance in information is pursued rather than quantity of literature.Limiting the scope to what is necessary was ensured by establishing the following inclusion and exclusion criteria which is futher explained in Table 5.
1. Criterion one: Provided a guideline on the type of peer reviewed and grey literature included in the synthesis, details presented in Fig. 4. 2. Criterion two: Is judgmental, it restricts the number of studies included to select the most relevant to the research topic.Therefore, a test-retest process was performed, i.e. researchers conduct a second extraction process from a random selection of pri-  The inclusion and exclusion criteria are demonstrated through the filtering process shown in Fig. 4. Following-up references using a snowballing approach added 18 articles.The final total number of studies included is 83.The majority of studies found are in the topic of sustainability.In addition, in CE more than 300 peer reviewed articles were identified but a search for CE in ports revealed less than 100 publications, showing limited research on the topic.
After the review of 115 studies, qualitative data of European ports, good CE practices, barriers and drivers, and levels of development are collected.IS on different ports are documented due to their importance in CE exponential development and sustainability.Together with the SSLR, a SWOT analysis is elaborated to help design effective strategies for ports transitioning to a CE.

SWOT analysis
A SWOT analysis tool is elaborated to document internal strengths (S) and weaknesses (W) of European MIP CE implementation, as well as external opportunities (O) and threats (T).The analysis is used to find drivers and barriers to circular practices in MIP.PA could use the information to set goals on circularity and strengthen competitive advantage of industrial ports aiming to benefit in the long term from their sustainable and circular commitments.Table 10 shows the SWOT analysis applied in ports.

Research outcomes
The foundation for CE is based on eight principles, and the application in ports is explained in point 4.1.Tables 6, 7, and 8 identify current CE practices of main MIPs in Europe based on these CE principles.Circular practices need to be implemented more in MIPs by applying different CBMs.Circular practices will help ports reduce gas emissions and substantially support planet Earth's regeneration.Ports already accommodate industries that are actively involved in waste treatment, collection, and shipment.Many of these wastes are highly polluting materials, mainly metals, plastic, construction, and biomass (Loop Port 2018).This makes ports ideal locations to implement circular practices to reduce worldwide emissions of GHG and other types of waste and increase energy efficiency with a high impact on a region and country (Biwei et al. 2012).The following are CE practices of the main MIP in Europe based on the CE principles.

Application of CE principles in MIP
Over 80 percent of all product-related environmental impacts are determined during the design phase (European Commission 2020).MIPs need to work with eco-design of equipment, packaging, building infrastructure, and superstructures to reduce the environmental impact of materials, including energy consumption, through their complete life cycle.→ Designing our waste and pollution in ports.
MIP need to provide and keep improving port waste reception facilities and promote IS in their facilities to optimize the resources used.Ports need to reduce the time for handling abandoned cargo so items can be in circulation faster.It is more relevant for   MIP can build resilience through diversity due to the availability of resources and ecosystems that can be regenerated by the actions of ports (water, forests, wildlife, and birds).Ports must contribute to developing the ecosystem around them.Denmark or Rotterdam, for example, and planting trees and protecting wildlife.Regenerating natural systems.
Renewable energy is a crucial aspect of producing circular products and resources; ports have to consider how the components of renewable plants are designed, manufactured, built, and managed.CE has to be baked into the energy transition by design to ensure the world has a sustainable supply of raw materials.Green design will take concerted action from companies and regulators.The shift to green hydrogen and carbon capture for energy purposes should be an essential strategy for different ports, and alliances must be made to benefit other ports and communities.Green hydrogen and carbon capture will considerably reduce CO2 emissions.→ Shift to renewable energy sources.
An economy can get more excellent value from diversity by sharing strengths and having a large pool of resources to draw on; such a system can also bounce back from the shock of events.By implementing circular practices, a port is resilient, continuing to Source: By the author  carry out its mission in the face of adversity because it closes loops with materials.If we maintain products and materials in circulation, redesign products to be more easily upgraded, and design out waste, we contribute to resilient production.Being circular will also translate into a resilient SC discussed extensively during the Covid19 pandemic.→ Build resilience through diversity.
Cascading maximizes resource effectiveness by using biomass in products that create economic value over multiple lifetimes.This approach to production and consumption states that energy recovery should be the last option only after all higher-value products and services have been exhausted.This concept is often associated with the forestry sector, food, and wealth.Industries in IZ with such clusters need to promote cascades.This is linked to building resilience and keeping products and materials in use.→ Applied cascades.
To innovate is a worldwide general principle that aims to enhance productivity and be sustainable.In the last years, all the renewable energies and CCUS developed in port facilities have been due to innovative ideas.Now is the time to use more technology in waste management.→ Re-think and innovate.
A CE is not about one firm or port changing one product or service; it is about many actors working together to create adequate flows of materials and information, with everything increasingly powered by renewable energy.When we think about systems, we see the connection between people, places, and ideas.By applying system thinking in ports and eco-parks, we begin to see how we can create opportunities to generate economic, environmental, and societal gains, and we create a balance.→ Think integrated (System Thinking).
CE implemented in industrial ports significantly impacts sustainability due to their large size of operations, influence in Industrial Zones (IZ), energy use, logistics activities, and variety of stakeholders interacting.Already different circular activities are undergoing in industrial ports around Europe, such as green hydrogen or biofuel production or upcycling of materials generating CBMs such as Design for Recycling (DFR) or Resource  Recovery, Recycle and Upcycle (RRU).However, there is more to be done to make a change in the regeneration of planet Earth.

CE implementation and alignment with the CE system model
Three main areas of port intervention are identified to encourage CE implementation and developing CBMs (Loop Port 2018).These areas are: 1. Circular assets and equipment of industrial ports Through maintenance and smarter use, ports can optimize the capacity and lifetime of existing port equipment and infrastructure and facilitate the transition to a CE.These assets and equipment include cranes, conveyor systems, container handling equipment, tugs and pilot boats, mooring equipment, berthing equipment, buoys, grid, OPS, and more.2. Circular flows within industrial ports Waste generated by port activities is another area where ports can facilitate the transition to CE.These will allow better use of internal resources of the port, Industrial zones, and transport network converging in the port.Industrial Symbiosis fits in this area of intervention.3. Industrial ports and circular markets Ports can also enable other industries to be more circular by developing new activities connecting supply and demand for resources and materials moving through the port.These will support the development of a circular approach to Supply Chains and transport networks.Industrial Symbiosis is applied in this intervention area when ports manage industrial parks.
Tables 6, 7, and 8 show different CE practices in European ports, the type of material flow, and CBMs, in these three different areas of intervention.CE practices include initiatives (proposed projects and feasibility studies), projects, or ongoing operations.

Circular assets and equipment of industrial ports
Table 6 shows that renewable and sustainable energy investments are predominant in some large ports.Regulations to stimulate the transition to more circular activities are essential.It also shows that ports are starting to use more innovative technology, but CE in maintenance needs to be better documented in CE or sustainable article topics.OPS terminal operators and shipping companies are joining forces to increase clean and costefficient energy access.

Circular flows within ports
Table 7 shows that Ports are crossroads of different kinds of waste generated due to their operations or by stakeholders.More examples need to be documented as good practices.

Ports and circular markets
Table 8 highlights the potential of ports as key drivers of circular and sustainable projects by connecting stakeholders and providing incentives.Notable examples include the financial benefits derived from sustainable practices promoted by Germany, Sweden and other Scandinavian countries and the extension of the lifespan of car parts through effective collaboration between ports and other stakeholders.An illustrative case is the port of Aberdeen in Scotland, which aims to establish itself as a decommissioning hub, generating employment opportunities while promoting circular economy principles.The port intends to maximize material reuse, repurposing, and recycling during the decommissioning process (Greenport 2022).

SWOT analysis
The following are Strengths, Weaknesses, Opportunities, and Threats affecting a better transition to a CE, summarized in the following SWOT in Table 9.These are essential inputs for Drivers and Barriers to CE implementation.

Drivers and barriers to circular implementation
To identify the main Drivers and Barriers to CE, more than 115 articles were reviewed, and the SWOT analyzed.This Drivers and Barriers can help managers of other ports identify opportunities for improvement, develop strategies to address the barriers and leverage the drivers to achieve the desired outcomes.

Drivers
• Setting a CE zction plan embedded in the port environmental plan: Port Authorities should create cultural changes and governance to promote the circular mindset.They must set a circular vision and embed it in the environmental plan.From a commercial point of view, if ports want to become more attractive to customers, they need to protect the environment and inform their customers.EMS standards such as the ISO 14001, ISO 14044:2006 (Life Cycle Analysis implementation), and Eco-Management and Audit Scheme (EMAS) will help ports identify achievements and environmental improvement.Implementation of the ECOPORT tools "Port Environmental Review System (PERS)" and "Self Diagnosis Method (SDM)" is particularly effective in the pathway to an ISO or EMAS standard.• Deciding on CBM(s) to implement for business sustainability: Ports must set CBMS to be implemented.Innovative models allow ports to take advantage of changing customer demands and expectations.If ports cannot innovate and shift their business models to be more circular and sustainable, they could be displaced by other ports that are better able to meet customer needs.Innovative CBMs on value chains for products such as plastic, textiles, rubber, metals, cement, chemicals, or biomaterials will reduce high CO2 emission because these are high pollution emitting materials.• Applying disruptive technology: New technological innovations have a great capacity to enable CBMs: 1) Digital (IoT, big data, blockchain, and RFID) helps ports to track resources and monitor utilization and waste capacity.2) Physical (3D printing, robotics, energy storage and harvesting, modular design technology, and nanotechnology) helps Port Authorities and companies in the port to reduce production and material costs and reduce environmental impact.3) Biological (bio-energy, bio-based materials, biocatalysis, hydroponics, and aeroponics) help ports and companies in the port aiming to become energy hubs move away from fossil-based energy sources (Wbcsd 2015).Digitalization could assist in closing the material loops by providing accurate information on the availability, location, and condition of products.
• Providing incentive mechanisms by governments and port authorities: Rewards for the good sustainable practice of ports and CO2 emission reduction motivate shipping companies and other stakeholders to move to a more circular and sustainable way of doing business.Rewards are an essential mechanism to achieve environmental priorities such as shipping decarbonisation, shipping certifications, air quality improvements, climate change mitigation, energy efficiency, and pollution reduction.Industrial ports have access to waste, which could be used efficiently, such as creat- ing biofuel, fertilizers, and others.Suppose industrial ports are developing industrial zones (eco-parks).In that case, a multi-pronged approach must help small and growing businesses be circular and reach net zero emissions.• Enhancing partnership and collaboration: Collaborative efforts such as Private-Public-Partnership (PPPs), joint efforts among several government ministries, or ports of the network enhance the experience needed to create effective circular models and policies.To enhance competitive advantage, European ports must cooperate with port networks and stakeholders for digitalization, keep up to date with EMS, provide rewards to stakeholders protecting the environment, and convert waste into materials.It is important for an alliance of governments supported by stakeholders willing to work together, share knowledge, and advocate for the global CE transition to more sustainable management of natural resources at the political level and in multilateral fora (Migliorini, 2022).Aiming for this better government integration, the global alliance on CE and resource efficiency (GACERE) kicked off in 2021.• Implementing measuring tools that support the transition to a CE: Industrial ports should quantify the CE and environmental impacts of their activities to be more sustainable.Ports should have a sustainable port index considering CE implementation; this should be publicly available and agreed upon at the world level.A port index help prioritize investments (especially regarding public funds),, evaluate the success of the actions carried out,and provide a joint base to monitor the evolution of ports toward fulfilling the SDGs.Tools such as the Life Cycle Analysis (LCA), Circulytics (From EMF), and Circular Transition Indicators (CTI) (From the wbcsd) support industrial ports' transition towards a more circular business, regardless of complexity and size of operations.These tools are also used to assist companies, consumers, and policymakers in greening their practices and decisions.For example, LCA results can tell us if one product or service is environmentally preferable to another or what aspects of a product or process contribute most to environmental impacts.Circulytics and CTI measures terminals and companies' entire circularity achievements in a more comprehensive way.

Barriers
• Lack of awareness and organizational cultural barriers: Particularly a lack of stakeholders or consumer interest and awareness, as well as a weak company culture (integrity and ethics, respect for the environment…), are considered significant CE barriers by businesses and policymakers.Awareness of CE is vital to increase enthusiasm and support, stimulate self-mobilization and action, and mobilize local knowledge and resources.Ports must think strategically when developing circular programs, projects, or initiatives.Integration needs to be at the core of circular developments.• Absence of customers and other stakeholders' interests: In many cases, port stakeholders need to understand the concept of CE in ports and its benefits.Additionally, circular products and actions are more expensive than 'non-circular' goods.These two factors limit consumer demand for circular products or services.Customers and consumers opt to pay for less expensive products that contribute to carbon emissions.• Expensive upfront investments in new business models and taxation systems: Business transformation in ports is costly.It requires significant investments in energy production facilities, superstructure, and waste management facilities.These include high secondary product costs, and raw materials, as opposed to the often lower cost of virgin resources (partially caused by higher taxes on labor which penalizes reuse, repair, and recycling), and current taxation systems, which tend to reward linear models rather than circular models (value-added tax on upcycled products, for example, requires paying twice for the same product).Policies should promote activities that are desired by society and punish those that are not.• Shortage of green infrastructure: The key is to produce resources like electricity, steel, cement, and meat without any emissions but at the least cost.This approach requires an upgrade of infrastructure.Using more clean energy requires upgrades and suitable financial mechanisms for vehicles, buildings, and port equipment.For example, the Port Authority of Valencia (PAV) has expanded its electric vehicle fleet and added new charging points for employees and visitors (Greenport 2022).Nearly one-third of plastics are not collected by a waste management system and end up as litter in the world's lands, rivers, and oceans.According to the Washington Post, there could be more plastics than fish in the ocean by 2050 (The Washington Post, 2016).• Lack of harmonized policies to facilitate the transition to a circular economy: Effective policies can help accelerate and scale up circular actions in the economy.These policies support businesses in overcoming hurdles by stimulating innovative projects and long-term investments in circularity, facilitating collaboration and partnerships, and producing tangible results.Policies for robust standards and norms in production, expansion of circular procurement, tax relief for circular products, support for ecoindustrial parks, and awareness campaigns are essential.• The GDP as an indicator of economic activities: The GDP index does not consider social and environmental externalities, discouraging value creation in both these areas.A new economic model for measuring growth and sustainable development is needed.Policymakers could use 'resource-miser' indicators such as value-per-weight and labor-input-per-weight ratios rather than GDP or others.• Lack of better integration (system thinking): Ports and companies inside the port look more to economic sustainability than social and environmental sustainability integration.Ports think about producing biofuel but need to see the impact on the food supply.Better integration is needed.This integration is about looking for the planet's harmony and integration to work for the planet.

Level of development of CE practices
The following Table 10 shows the level of application of circular projects for each material flow, High Application (HA), Moderated application (MA) and low application (LA) based on the findings in the research.This rating provides evidence of achieving objective 2 of the research.Moving towards a more circular approach could deliver benefits such as reducing pressure on the environment, improving the security of the supply of raw materials, increasing competitiveness, stimulating innovation, and boosting economic growth.It could create approximately 580,000 jobs in the EU alone (European Commission 2019).Carbon Capture is getting much attention and can potentially create chemically identical characteristics to fossil-derived diesel and naphtha (Greenport 2022).People must move forward on CE implementation to allow future generations to meet their needs.

Circular business models (CBMs) in ports
All generic CBMs identified in Table 3 can be implemented in MIP.Established MIP should regularly update their business plans, or they will need to anticipate trends and challenges ahead.As in other industries, we see continuous re-direction in strategies and innovation in the port that creates new opportunities and revenue streams.
This review identifies over 190 Circular Business Models (CBMs) implementations for various types of circular investments described in Tables 6, 7, and 8.The predominant models for MIP are BBB, RRU, GSS, SCC, and DFR, as detailed in Table 3.This demonstrates the integration between different models.

Circular assets and equipment
This review identified potentially 58 CBM implementations; the predominant models are also GSS, RRU, and SCC in this intervention area.To facilitate the transition to CE, ports can adopt maintenance and innovative asset utilization practices, reducing waste and resource consumption and promoting material reuse and recycling.The ports in Europe have taken actions such as developing sustainable energy sources, optimizing other resource usage, and embracing digitalization for more efficient and sustainable operations.Investments in waste management, clean water, air quality monitoring, and ecosystem protection infrastructure comply with existing and future regulatory requirements.
The development of sustainable energies is considered a RRU and/or BBB CBM(s).Installing solar farms in industrial ports (RRU) also enables creating GSS models when utilizing recycled panels and components.Solar power is increasingly utilized in warehouses and production facilities.A BBB model example is the production of Green Hydrogen, which can be used for manufacturing fertilizers and fuel.The BBB model complements SFA by enabling cleaner fertilizer production and RRU by applying blue hydrogen when capturing and storing CO2. Green hydrogen holds promise in replacing fossil fuels and achieving a net-zero society, the current geopolitical situation favors alternative energy sources and pushes for hydrogen adoption in Europe and other import-dependent markets.Combining energy sources, including green hydrogen, is essential for successfully transitioning to renewable energy.Sustainable energy production has transformative potential for ports and national economies, as demonstrated by Rotterdam and Antwerp's ambitions to become energy hubs through collaboration.
Investing in water monitoring to protect the ecosystem develops SCC and GSS Business Models.For instance, North Sea ports utilizes smart sensors to monitor water parameters, anticipating water quality issues continuously.Such actions contribute to circularity by regenerating ecosystems.Environmental sustainability efforts like tree planting, coastal cleaning, and bird protection restore ecosystems and mitigate climate change while generating SFA and CMW CBMs.Rotterdam, Denmark, Piombino, and Dover ports have implemented these actions and offer potential for replication in other industrial ports.Climate change is No 1 priority now and these actions are critical.
Responsible digitalization is important in accelerating the transition to a CE and achieving global climate goals by 2050.For example, the Port of Haminakotka in Finland employs Virtual 3D operating systems to streamline operations, identify damages, and improve stakeholder communication.Digitalization allows for implementing SCC, and DFR CBMs.The port can share the operating system with industries in the Mussalo industrial zone, enhancing design for durability and recycling.3D technology can significantly reduce material waste and contribute to Greener Supply Chains in any type of industry.
To support a sustainable energy transition, port environmental facility development, and digitalization, regional finance institutions like the European Investment Bank, African Development Bank, Inter-American Development Bank, and governments can provide financing for scalable technologies and adopt international regulations guided by circular principles.

Circular flows within the port
This review identified potentially 56 CBM implementations; the predominant models are GSS, RRU, and SCC in this intervention area.The ports identified in this study are recovering, recycling, or upcycling plastic, CO2, sand, sediments, old stables, methane, heat, rainwater, and shipping containers for other valuable uses (cascading or upcycling).Better management of waste generated by industrial ports is another area where ports can facilitate the transition to CE. Plastic reduction, recycling, and segregation of industrial ports (including industrial zones and ships as indicated in this project's scope) create RRU and GSS opportunities.These models work in collaboration and facilitate the adoption of other models, such as SFA, DFR, and SCC.
Amsterdam and Rotterdam have plastic recycling facilities using Magnetic Density Separation (MDS).They transform recyclable plastic into raw materials for new plastics.In contrast, non-recyclable plastics are converted into transport fuel by cooperating with other companies in the port, becoming a real circular plastic hub.At least 14 million tons of plastic end up in the ocean yearly, making up 80% of all marine debris from surface waters to deep-sea sediments (IUCN 2021).Plastic recycling facilities can allow ports to manage plastic waste flows and improve collaboration.
Critical circular developments in ports are on CCUS or CCU, which creates SCC, and RRR.Approximately 26 commercial-scale carbon capture projects are operating worldwide, with 21 more in early development and 13 in advanced development (Center for Climate and energy solution 2020).Carbon Capture infrastructure is essential for Europe climate plans.Singapore Economic Development Board recently mentioned that the island aims to realize at least 2 million tons of carbon capture potential by 2030 as part of a broader effort to make its Jurong Island oil refinery hub more sustainable (Reuters 2021).
Former waste streams from the fishing industry are being used to manufacture a range of high-value products in the nutrition and beauty industry.This approach developed cascades in the biological cycle of great interest for CE, more cascading CBMs need to be initiated and documented.Innovation is a crucial driver for circular practices.Biofuels, CCU, sustainable environment terminals, and offshore energy provision are just a few initiatives that require implementing state-of-the-art technology.If the technical flow does not considered new technologies, it is impossible to increase plastic recycling rates, maintain assets functioning for longer, or redesign products to be more durable.

Port and circular markets
This paper identified 84 CBM implementations for circular initiatives or projects running; the most predominant are GSS, RRU, SCC, and PLE in this intervention area.The port is critical as an engine to incentivize and force circular and sustainable practices.Ports can promote and encourage stakeholders to be more circular by developing new activities connecting supply and demand.Main initiatives and projects found to develop circular markets are establishing eco-parks and developing industrial symbiosis (IS), settling shipyards in their premises for building or decommissioning ships, sharing mechanical equipment, extending the life of parts and raw materials (for cars and other industries) by linking industries and providing logistics services, and creating upcycling factories.In addition to opening dialog with stakeholders to support environmental and circular projects, implementing several financial incentives are potent mechanisms to create circularity.
Under this area of intervention, one of the main goals should be the development of IS by developing Eco-Parks, these Eco-parks are a powerful mechanism for the sustainable use of environmental resources.It promotes the development of all CBMs, initiating with SCC.IS encompasses initiatives in which two or more industries develop mutually beneficial relationships.Other examples of synergetic cooperation include the shared utilization of specific equipment or facilities and the pooling of resources.Kalundborg, Rotterdam, and Harjavalta are some examples of Eco-parks identified.IS promotes economic growth while, at the same time, it generates environmental benefits.Implementation of IS, therefore, holds potential to unlock powerful mechanisms that foster sustainable development (Chertow 2007).
Extending the life of spare parts or materials for the car industry in Belgium adds value to customers and contributes to circularity.This life extension is possible by providing logistics services linking where products are used with where specialist knowledge is available.These develop RRU, PLE, and DFR CBMs.The replication of such practices in the port to enable car business symbiosis can be replicated in other shipping industries.Having shipbuilding and decommissions operations in industrial ports is a critical circular enabler.These industries will ensure responsible ship recycling or refurbishing, reducing energy and CO2 emissions.This business promoted RRU, and DFR CBMs.Today's value chain and its incentives in this market are reconfigured through a circular ships initiative.The industrial ports of Parema, Alveiro, Gdansk, and Palma have shipyards on their premises, also promoting sustainability.
Ships generate much waste from their large day-to-day operations; various biological wastes can be used well as biogas.Most technical waste, such as paper or aluminum, can be recycled in port facilities generating economy and environment benefits.For example, Costa Cruises projects to reduce waste by more than 70 percent by 2030.If facilities are developed in ports, CO2 from ships, equipment, or plants can be captured and stored in the port contributing positively to the climate change, priority number one of ESPO ports.
Cascading is an underexplored area; secondary materials from the sea can be used in medicine or added-value products.Cascading turns waste streams into new products and can be applied to both cycles but especially in the biological.For example not just the meat can be use from a fish, all anatomic parts could be also used for medical or skin care treatments.Ports in Finland and Germany are providing incentives to shipping companies to upgrade fuel systems to be more eco-friendly and implement sustainable practices such as reducing noise levels; this is based on the "Environmental Ships Index (ESI).These regulations enable sustainable practices and potentially create GSS and BBB CBMs.

Conclusions
This study examines circular practices in ports, identifying 53 practices aligned with CE principles.These practices can lead to the developing of 231 different circular business models (CBMs).The study highlights CBMs for three areas of intervention, including bioenergy and biomass production, resource recovery and recycling, green supply services, sharing models, and product life extension.Ports increasingly invest in clean energies like wind and solar power to reduce greenhouse gas emissions and support green supply services.Waste management infrastructure and technologies, such as recycling facilities and advanced wastewater treatment systems, are being implemented to address environmental sustainability.Recycling, reuse, and repair practices are gaining traction, promoting circular CBMs.Critical drivers for CE implementation in ports include a circular vision, disruptive technology, incentives, partnerships, and tracking measures.In contrast, barriers include organizational culture, lack of awareness, policy harmonization, and upfront investments.The study suggests moderate to low implementation levels of circular activities, highlighting the need for improvement.Adopting CE principles in ports can transform the linear model, benefiting the environment, economy, and stakeholders.Successful implementation requires collaboration, system thinking, and overcoming regulatory barriers.

•
To identify the current circular practices of several MIPs in Europe based on the CE principles.• To analyze the circular practices of these ports based on the CE system model, including their stage and level of development • To determine potential CBMs for implementation in line with current CE practices.• To analyze Drivers and Barriers to circular developments affecting an effective transition to CE.

Fig. 2
Fig. 2 CE system diagram (Butterfly) diagram representing the CE material flows.Source: The Ellen McArthur Foundation (EMF)

Fig. 3
Fig. 3 A conceptual framework of Maritime Industrial Port (MIP).Source: Elaborated by the author

Fig. 4
Fig. 4 Filtering Process on systematic and Semi-Systematic Literature Review.Source: by the author

Source:
By the author

Table 1
Ports in Europe analyzedSource: Own source Most of these ports are MIP with circular initiatives.They are logistic and industrial nodes in global supply chains with a solid maritime character and a functional and spatial clustering of activities.They have different terminals depending on the cluster activities and stakeholders.Some of these terminals are Container, automobile, dry bulk (e.g.cement, iron ore…), liquid bulk (e.g.oil, gas, chemicals.).A conceptual framework of a MIP is illustrated in Fig.3

Table 2
Principles of CESource: By author adopted, with inputs form the Ellen MacArthur Foundation and others

Principles of Circular Economy Purpose
prioritized, involving diverse stakeholders in the CE transition.Embracing the CE is worthwhile and necessary for a sustainable future.The Butterfly diagram, shown in Fig.2by the Ellen MacArthur Foundation (EMF

Table 3
Technical and Biological Circular Business Models (CBM)s Source: By author, with inputs form OECD, Harvard Business review, Bio-circular economy model, and other authors products, slow the flow of constituent materials through the economy, and reduce the rate of resource extraction and waste generation (refurbish/remanufacture) Resource Recovery, Recycle and Upcycle (RRU) Industrial ports host facilities that recover usable resources or energy from waste or by-products.Ports offer logistics capabilities as an added-value service.(recycle) Green Supply Service (GSS) Port suppliers replace traditional material inputs derived from virgin resources with bio-based, renewable, or recovered materials, reduce demand for virgin resource extraction in the long run (parts and product manufacturing/service provider/purchasing) Sustainable Food, Agriculture and Aquaculture (SFA) Organizations in the port can multiply the value of this sector with product diversification, product differentiation, high-value and premium-quality products and services, waste reduction, resource and land use efficiency improvement.Reduction of food waste should be a priority.(cascading & farming and collection) Cascading for Medical and Wellness (CMW) (by product)

Table 4
Examples of Industrial symbiosis Source: By author based on literature reviewed

Table 5
Inclusion and exclusion criteria Source: Elaborated by the author

Table 6
Circular assets and equipment

to CE flows Port Initiative/projects Ports (Examples) Technical Biological Development Stage Potential CBMs
Source: By the author

Table 7
Circular flows within ports materials and resources with short lifespans, such as food which can cause vast amounts of waste without appropriate regulations and resource recovery processes.→ Keeping

Table 8
Port and circular market

Table 9
SWOT Analysis for European Maritime Industrial Ports

Table 10
Maritime port material flows level of application as per research findings