Implementation of Blockchain Technology in Waste Management

: Implementing blockchain technology in waste management is a novel approach to environmental sustainability and accountability challenges in our modern world. Blockchain, a technology that enables decentralized and immutable ledgers, is now being re-imagined as a tool to revolutionize waste management. This innovative approach aims to improve waste management transparency, traceability, and efﬁciency, resulting in signiﬁcant environmental and economic beneﬁts. In traditional waste management systems, the tracking and disposal of waste materials are not transparent and can be vulnerable to fraud, mismanagement, and inefﬁciency. Blockchain technology provides a secure and transparent platform for recording every step in the waste management lifecycle, from waste generation to collection, transportation, recycling, or disposal. Every transaction in the blockchain is recorded in a tamper-proof manner, enabling real-time monitoring and veriﬁcation of waste-related data. This paper introduces the concept of using blockchain technology in waste management. The main goal of this work is to show the implementation of blockchain technology in an existing waste management company, using smart contracts in the recycling process to provide transparency. Also, the digital product passport was redeﬁned in terms of circular economy and waste recycling.


Introduction
Efficient waste management has become a pressing global concern in an era of increasing urbanization and rapid population growth [1].Over the past decade, cities around the world have produced more and more waste, with negative impacts on both human health and the environment.It is estimated that the annual amount of solid waste generated worldwide will increase to 2.2 billion tonnes per year by 2025.On average, each individual generates between 0.11 and 4.54 kg of solid waste per day.Alarmingly, reports show that 33% of solid waste generated in urban areas is not disposed of in an environmentally friendly and safe manner [2].
Traditional waste management systems struggle to keep up with increasing waste volumes, so innovative solutions are needed to address this pressing issue.Moreover, waste management has faced various challenges, including difficult consumer behavior, errors in waste sorting, insufficient facilities, recycling, and data protection policy [3].
Various countries have implemented innovative strategies and initiatives to improve waste management.Japan is known for its meticulous waste separation system.Citizens are required to separate their waste into categories such as burnable, non-burnable, and recyclables [4].South Korea implemented a pay-as-you-throw system, where citizens are charged based on the amount of waste they generate.This incentivizes waste reduction and recycling [5].Due to limited land space, Singapore has invested heavily in waste-toenergy plants.These facilities incinerate solid waste to generate electricity, reducing the volume of waste in landfills [6].Germany has a successful dual system for packaging waste.Manufacturers are responsible for collecting and recycling their packaging materials.Yellow bins are provided for packaging waste, and citizens are actively involved in sorting [7].Sweden has been successful in using waste incineration not only for waste reduction but also for heat and power generation.This approach has significantly reduced the country's reliance on fossil fuels [8].Norway has a successful bottle recycling program where consumers pay a small deposit on beverage containers.Returning these containers to special reverse vending machines provides a financial incentive for recycling [9].South Australia implemented a successful container deposit scheme, where consumers receive a refund for returning beverage containers.This has led to increased recycling rates and reduced littering [10].Moreover, it is also worth following the progress of the NEOM project, which can become a global model for the cities of the future.The NEOM project, a vision of the future of the city in Saudi Arabia, aims to create a place that will lead the way in terms of sustainable development by combining advanced technologies with adherence to the principles of a circular economy [11].The use of blockchain technology can revolutionize the management of resources, enabling complete transparency and tracking of the product life cycle-from raw materials to recycling.The blockchain can also improve the exchange and verification of emissions and waste data, which ensures reliability and strengthens trust in the NEOM ecosystem.
Waste management's disposal chain is a complex system involving many stakeholders.Typical waste transfers involve citizens and industries; municipalities; outsourced entities that collect and manage the bins; different centers that deal with collection, disposal, and recycling; and producers of recycled waste materials that put new products on the market [12].
The monitoring and recording of waste collection data plays a crucial role in ensuring compliance with applicable laws and regulations.It also has the potential to provide valuable insights that could influence future legislation and ultimately prevent the inefficient disposal of waste through methods such as landfilling or incineration.However, the process of tracking waste and monitoring ownership to generate these important data are inherently complicated.Challenges can arise from a variety of sources, such as products breaking down into smaller components, existing laws such as extended producer responsibility, which requires manufacturers to dispose of the subsequent waste from their products, and the problem of the abandonment of ownership through littering or dumping.Tracking waste and monitoring its owners currently requires more pragmatic solutions than those currently in widespread use [13].
Waste management systems can be changed by using the advantages of blockchain technology, which is a decentralized system for immutably recording data [14].In this context, blockchain technology has emerged as a transformative force, offering new approaches to improve the efficiency and sustainability of waste management [15].From secure and transparent transaction records to facilitating waste recycling, the opportunities the blockchain offers are both profound and far-reaching.
The main advantages of implementing blockchain technology are that it can guarantee safety and authenticity, verify that products are environmentally friendly, and help reduce resource consumption and improve recycling performance [16].Blockchain can potentially affect the supply chain and enable quick and efficient information exchange between parties [17].Adopting a blockchain can be a game changer for the supply chain, removing the traditional system's flaws and inefficiencies.
This work has four fundamental objectives: (a) to present the prerequisites for the use of blockchain technology in a circular economy, (b) to describe how a blockchain can be used in the automation of processes related to waste management, (c) to detail the necessary steps in the implementation of blockchain technology for transparent waste management, and (d) to explain how blockchain technology can be used in the creation of digital product passports.

Characteristics of Blockchain Technology
The prevailing data processing systems are mainly based on centralized architectures within organizational units or cloud technology [18].When a business process requires interaction between multiple entities, communication solutions are added to enable these interactions through specific communication mechanisms.However, centralization also has drawbacks, such as potential points of failure, vulnerability to cyberattacks, and data inconsistency [19].This approach can drive up costs and complicate systems.Participants must rely on trusted intermediaries to act as arbiters and approve transactions or verify the origin and accuracy of data.
Blockchain is a system based on a database network that allows all participants to record, disseminate, and store information effectively, securely, and equally [20].Moreover, it is a system that operates without a central administrator or manager, in which all data history is available at all times and in which information, once stored, cannot be changed.In other words, it is a system designed so that the information stored and transmitted over the network has a high level of credibility and security, and network participants have transparent access to a common, trusted source of information [21].
A blockchain database can be defined as a sequence of data blocks that are tightly linked (Figure 1).Each block contains elements such as data, a block identifier (hash), and the identifier of the previous block [22].Any change in data in a block is immediately detected due to inconsistencies in the structure of the entire chain.The chain's integrity is constantly monitored by all network users [23].In an operational sense, the blockchain is a distributed multi-user database managed by a network of computers operating according to a specific blockchain protocol [24].Each network node has its own copy of the database, operates it with equal rights, and can initiate and verify changes.Everyone has access to the database, but no one controls it, and consensus enforced by the protocol makes all changes.The main features of the blockchain are its immutability and transparency.Network participants immediately detect and reject any attempt to interfere with previously stored data [25].
Finally, it is important to emphasize that the distributed environment means that each participant owns a complete copy of the blockchain (Figure 2).This makes the system resistant to failures and attempts to centralize control.All changes are made based on consensus among network participants.Thus, the blockchain provides a reliable and transparent source of truth for all participants [26].

Types of Blockchain Technology
Blockchain technology can be used for public registers available to the gen Although encryption techniques may protect certain data in this registry, its o ifiable from available records.To inspect this data, there are tools such as a explorer or dedicated data extraction and analysis software [27].
When choosing blockchain technology for a specific application, it is cruc mine the appropriate blockchain type.There are three basic types: Public Blockchain: This is characterized by an open structure that anyone can It operates in a decentralized and autonomous manner, not subject to the co central entity.Decisions regarding its development are made democratically community.Private Blockchain: This is a dedicated solution, most often created for a spec zation or consortium of enterprises.Access is strictly limited, and the network under the supervision of a designated unit or group.Hybrid Blockchain: This combines features of both types above.It is a specifi private blockchain with a defined management policy.However, some parts o the public network infrastructure, for example, to make settlements between p Although originally created as the basis for cryptocurrencies, blockchain has the potential to revolutionize many sectors of the economy.By ensuring parency and immutability, the blockchain can help trace the origin of produc particularly important in the food, clothing, and pharmaceutical industries.F in the healthcare space, the blockchain can store and share patients' medical ensuring their privacy and security.In the energy sector, this technology can

Types of Blockchain Technology
Blockchain technology can be used for public registers available to the general public.Although encryption techniques may protect certain data in this registry, its origin is verifiable from available records.To inspect this data, there are tools such as a blockchain explorer or dedicated data extraction and analysis software [27].
When choosing blockchain technology for a specific application, it is crucial to determine the appropriate blockchain type.There are three basic types: Public Blockchain: This is characterized by an open structure that anyone can connect to.It operates in a decentralized and autonomous manner, not subject to the control of any central entity.Decisions regarding its development are made democratically by the user community.Private Blockchain: This is a dedicated solution, most often created for a specific organization or consortium of enterprises.Access is strictly limited, and the network is managed under the supervision of a designated unit or group.Hybrid Blockchain: This combines features of both types above.It is a specific form of a private blockchain with a defined management policy.However, some parts of it can use the public network infrastructure, for example, to make settlements between participants.
Although originally created as the basis for cryptocurrencies, blockchain technology has the potential to revolutionize many sectors of the economy.By ensuring data transparency and immutability, the blockchain can help trace the origin of products, which is particularly important in the food, clothing, and pharmaceutical industries.For example, in the healthcare space, the blockchain can store and share patients' medical data while ensuring their privacy and security.In the energy sector, this technology can support the development of so-called microgrids, enable more effective energy exchange between users, and support the entire process related to a circular economy [28].The unique properties of blockchain technology mean that it can play a key role in shaping the future of many sectors of the economy (Figure 3).

European Green Deal
The European Green Deal outlines a vision for a sustainable EU economy, encompassing measures across sectors like clean energy, industry, infrastructure, and finance.It notably addresses plastic and packaging waste through various initiatives.For instance, the key component of the Circular Economy Action Plan targets resource-intensive sectors, including plastics.It sets a goal of achieving 100% reusable or recyclable packaging throughout the EU by 2030, introduces a regulatory framework for biodegradable and bio-based plastics, and sets out measures to be implemented concerning single-use plastics.
The Green Deal's 'Farm to Fork' strategy emphasizes sustainable agriculture and food production to reduce the environmental impact of packaging and food waste.This strategy is expected to address the issue of excessive plastic packaging driven by food safety concerns.
Furthermore, the Commission sees non-recycled plastic packaging waste as a potential revenue source to support climate objectives in the budget.The Green Deal envisions a significant role for the private sector in financing the transition to a greener economy.This is achieved by adopting a clearer classification of environmentally sustainable business activities, integrating sustainability into corporate governance, and enhancing disclosure norms for climate and environmental data applicable to companies and financial institutions.Such measures could impact companies' obligations to disclose information regarding their sustainability efforts to reduce plastic usage [30].

A Circular System as One of the Policies of the Green Deal
The circular economy is a key element of the Green Deal, which aims to create a system in which resources are used optimally and minimize waste and consumption of raw materials.The circular economy promotes the idea that products should be designed to be durable, easy to repair and reuse, and fully recyclable.In the Green Deal, the circular economy is considered one of the main mechanisms for achieving sustainable development, reducing greenhouse gas emissions, and protecting biodiversity.It also supports innovation and job creation in recycling and the circular economy sectors.
The circular economy offers an alternative to the linear economic model outlined by Demestichas and Daskalakis [31].This alternative model includes:

European Green Deal
The European Green Deal outlines a vision for a sustainable EU economy, encompassing measures across sectors like clean energy, industry, infrastructure, and finance.It notably addresses plastic and packaging waste through various initiatives.For instance, the key component of the Circular Economy Action Plan targets resource-intensive sectors, including plastics.It sets a goal of achieving 100% reusable or recyclable packaging throughout the EU by 2030, introduces a regulatory framework for biodegradable and bio-based plastics, and sets out measures to be implemented concerning single-use plastics.
The Green Deal's 'Farm to Fork' strategy emphasizes sustainable agriculture and food production to reduce the environmental impact of packaging and food waste.This strategy is expected to address the issue of excessive plastic packaging driven by food safety concerns.
Furthermore, the Commission sees non-recycled plastic packaging waste as a potential revenue source to support climate objectives in the budget.The Green Deal envisions a significant role for the private sector in financing the transition to a greener economy.This is achieved by adopting a clearer classification of environmentally sustainable business activities, integrating sustainability into corporate governance, and enhancing disclosure norms for climate and environmental data applicable to companies and financial institutions.Such measures could impact companies' obligations to disclose information regarding their sustainability efforts to reduce plastic usage [30].

A Circular System as One of the Policies of the Green Deal
The circular economy is a key element of the Green Deal, which aims to create a system in which resources are used optimally and minimize waste and consumption of raw materials.The circular economy promotes the idea that products should be designed to be durable, easy to repair and reuse, and fully recyclable.In the Green Deal, the circular economy is considered one of the main mechanisms for achieving sustainable development, reducing greenhouse gas emissions, and protecting biodiversity.It also supports innovation and job creation in recycling and the circular economy sectors.
The circular economy offers an alternative to the linear economic model outlined by Demestichas and Daskalakis [31].This alternative model includes: (1) Smart product manufacturing that maximizes the efficient use of energy, materials, and resources while actively avoiding waste and pollution.It also includes concerted action to minimize dependence on new and non-renewable resources.(2) Extension of the life of products and their components to maintain their highest value for as long as possible.This includes giving them multiple "lives" and optimizing their use not only in their first life cycle but also in subsequent iterations.
(3) Harnessing the potential of materials once considered waste by regenerating natural resources and restoring finite materials for later reuse.
In March 2020, the European Commission presented a new action plan for the circular economy [32].The Council responded to the plan in its conclusions of December 2020.It also highlighted the role of the circular economy in ensuring a green recovery from the COVID-19 pandemic.The plan proposes over 30 actions related to sustainable product design, circularity in production processes, and empowerment of consumers and public purchasers.Activities will cover sectors such as electronics and IT, batteries, packaging, plastics, textiles, construction and buildings, and food.
The European Commission has recognized the circular economy as a key element of the European sustainable development strategy.It adopted a package of measures to accelerate Europe's transition to a circular economy [33].One of the main elements of this action plan is to reduce waste, i.e., the amount of waste generated in Europe, by promoting the recycling and reuse of materials and supporting the sustainable design of products so that they are durable, easy to repair and, at the end of their life, recyclable.The key action is to reduce the amount of single-use waste, especially plastic waste, by limiting the production and use of disposable items.Other actions include promoting alternative waste management methods, such as composting, recycling and energy recovery, and reducing waste sent to landfills.
The circular economy is a production and consumption model in which existing materials and products are shared and leased.However, the original design specifications of a product can be used to facilitate different R-strategies like reuse, repair, or recycling for as long as possible [34].In this way, the life cycle of products is extended.In practice, this means that waste is reduced to a minimum.When a product reaches the end of its life, its materials are left on the market whenever possible.These can be used productively, again and again, creating further value.
In February 2021, the Parliament passed a resolution endorsing the new Circular Economy Action Plan (CEAP) [35].This calls for additional measures to pave the way to a carbon-neutral, environmentally friendly, toxin-free, and fully circular economy by 2050.These measures include implementing stricter recycling rules and setting binding targets for materials' use and consumption by 2030.
In March 2022, the Commission took an important step by presenting the first set of measures to accelerate the transition to a circular economy under the CEAP.These proposals include initiatives to promote sustainable products, empower consumers to make a green transition, re-evaluate regulations for construction products, and formulate a strategy for sustainable textiles.
At the same time, the spread of digitalization has an ever-increasing impact on our personal and professional lives.It has seamlessly integrated into almost every aspect of daily life.In the Fourth Industrial Revolution (IR 4.0), the digitization of product information will be pivotal.Blockchain technology is proving to be an important enabler for the advancement of IR 4.0, and its application can create an ecosystem that connects the Internet of Things (IoT) to the monitoring of product lifecycles and certification [36].
Currently, however, the lack of consistent and accurate information about resources, products, and processes makes it impossible to quantify circular initiatives in many cases.At the same time, discussions are ongoing about the transparency and information sharing required to achieve a circular economy.Effective digitization of product and process information to capture an entire product lifecycle is a hurdle that must be overcome to close the gap between the conception of a circular economy and its practical implementation [37].
In addition, product-specific information requirements will ensure that consumers are aware of the environmental impact of their purchases.All regulated products will be provided with digital product passports.This will make repairing or recycling products easier and track substances of concern along the supply chain.Labelling may also be introduced.The proposal also includes measures to end the destruction of unsold consumer goods, expand green public procurement, and incentivize sustainable products.

Smart Contracts
A key element of blockchain technology is smart contracts, which sometimes digitally mirror real-world contracts.Smart contracts contain codes for agreements between parties, monitor terms, and perform embedded functions.Smart contracts replace traditional legal third parties with network consensus.They can increase efficiency and reduce transaction costs because they automatically execute when certain conditions are met and maintain digital records of rules and business logic.Smart contracts can also be used for supply-chain process management and reengineering [38].These contracts are created jointly by participants in a network.They serve the purpose of facilitating peerto-peer transactions or remittances, as described by Wang et al. [39].After a transaction is completed, a corresponding block is generated and distributed across the network nodes.Online merchants involved in the process can verify the transaction details to ensure the integrity of the transaction data.Smart contracts function as programmable code that can be executed automatically and as active participants.They can respond immediately to the information received and carefully record and retain the value of the transaction.
Smart contracts adhere rigorously to predefined rules through the consistent monitoring of trigger conditions.They execute the corresponding code when conditions are met and record the generated data onto the blockchain.In energy transactions, smart contracts play a pivotal role in receiving and processing transaction information.They can temporarily hold energy assets from buyers and sellers during transactions and carry out operations based on pre-established transaction rules agreed upon by the involved parties.Serving as fundamental and integral components of regional energy trading models, smart contracts are poised to remain a prominent subject of interest in both blockchain and energy research [40].
In waste management, smart contracts could play many key roles, such as automatic verification and rewards.If a waste management system offers rewards for recycling, a smart contract could automatically verify that a particular person is separating waste correctly and provide them with appropriate rewards [41].Smart contracts could also trace the origins of waste, helping to identify and eliminate sources of pollution.They could provide transparency in the recycling process, ensuring that waste goes to the appropriate treatment sites and is not disposed of in unauthorized locations [42].To help accomplish this, wastes produced in various locations (e.g., factories, households, restaurants) can be "tagged" on the blockchain system with a unique identifier.This identifier is immutable and can be assigned to a specific waste source.As the waste passes through various stagesfrom production to transport to processing-these activities are recorded on the blockchain.Additionally, to optimize the entire process, a smart contract could be integrated with other systems, such as fleet management systems for waste collection vehicles, allowing route optimization and more effective resource management [43].

Implementation of Blockchain Technology in Waste Management
In combination with the Internet of Things (IoT), the blockchain can bring many benefits.The IoT consists of physical devices, ranging from simple sensors and cameras to advanced machines and devices, that communicate with each other via the Internet; this allows the collection, analysis, and exchange of data in real time [44].The main advantage of IoT is the ability to automate and optimize processes, which leads to increased efficiency, reduced costs, and improved quality of life [45].Examples of IoT applications include smart homes, health monitoring, advanced production systems, and vehicle fleet management.
Thanks to IoT, devices can collect data in real time and make decisions automatically.The blockchain, in turn, ensures the security and immutability of this data, which is crucial for many applications such as supply chain monitoring [46], asset management [47], or product certification [48].
The blockchain can be used as a communication bus to enable the creation of digital services and products and provide the necessary tools to create solutions.There are many blockchain solutions on the market that can be used in various scenarios.For example, IoTeX combines fast, secure blockchain technology with the IoT [49].VeChain blockchain specializes in enterprise-class solutions.Thanks to its stability and integration possibilities, it is used to build solutions based on the supply chain and data integrity [50].SkeyNetwork blockchain provides technology that connects IoT devices to the blockchain.SkeyNetwork's Non-Fungible Tokens (NFTs) are proof of ownership due to smart objects in a network having their unique token.
Applying blockchain technology to waste management can be observed as part of the development of smart cities.These cities embody a conceptual urban development model based on the utilization of human, collective, and technological capital to enhance development and prosperity in urban agglomerations [51].Despite the widespread use of technology in smart cities, they can have problems with waste management [52].These cities generate domestic, commercial, medical, agricultural, and industrial waste.This waste can be classified into various categories, including liquid and solid household waste, medical waste, hazardous waste, recyclables, green waste, and electronic waste (e-waste).It is often sent to landfills, waste recycling facilities, composters, and waste-to-energy generation plants [53].Including traceability and tracking capabilities is of great value in validating the legitimacy of data on waste collection, processing, and transportation in smart cities.These features enable real-time monitoring of the location and condition of waste throughout its journey, i.e., from collection to sorting, transportation, treatment, and disposal or recycling.Unlike current centralized waste data management systems that are vulnerable to intentional or accidental tampering, these tracking capabilities improve the integrity of the process [28].Traceability is invaluable in facilitating identifying, storing, and comprehensively managing data on activities and outcomes within waste management processes.Key data points typically recorded during waste disposal include details such as waste type, volume, pickup location, route information, updated transit times, and details about the people involved in each waste disposal phase.Thus, blockchain technology has great potential to replace the slow manual systems used in waste management in many smart cities [54].
One of the ways that the blockchain can improve waste management is by creating digital asset tokens (e.g., security tokens) associated with smart cities' waste for tracking and tracing purposes [55].These tokens play a pivotal role in tracking recycled waste materials.They significantly assist government agencies in reducing waste management costs and streamlining business operations.Traceability ensures that waste generated in smart cities is managed by established waste management guidelines to protect the environment from pollution.It also enables users to monitor the lifecycle of smart city waste efficiently [56].
Blockchain technology can identify the specific type of healthcare waste processed at recycling facilities and then reused to manufacture medical devices and equipment [57].The increased transparency in asset traceability enabled by the blockchain increases the value of the waste supply chain.It minimizes the costs associated with waste management processes such as collection, sorting, transportation, and processing [58].
Industries can use the blockchain to identify the origin and transportation route of food scraps and waste to recycling facilities for fertilizer production [59].Using these data, they can build new fertilizer production facilities near waste sources to reduce transportation costs.
The blockchain's tracking capability allows users to record the location of trucks transporting smart city waste in real-time, providing additional information such as optimal routes and waste weight [60].These data on the location of waste shipments ensure that trucks drive in accordance with designated garbage collection points.This is especially important when waste comes from different areas and communities.To increase human safety, the blockchain can use sensors attached to garbage bags to verify that hazardous waste remains separate from non-hazardous waste during transport [61].
The blockchain's transparency and immutability make it useful for tracking the amount of waste shipped, received, and recycled at recycling facilities, detailing the credentials and actions of waste handlers, and recording where waste is stored during the separation, sorting, recycling, or disposal process.This identifier can be assigned to a specific waste source.As waste passes through various stages-from production to transportation to processing-all these activities are recorded in the blockchain [62].Such an identifier for waste in the blockchain system could take different forms depending on the needs and specificity of a particular system.It could take the form of a QR code or a special Radio Frequency Identification/Near Field Communication (RFID/NFC) chip.Using a two-dimensional code, which can be easily scanned with a smartphone or a special reader, it is possible to store large amounts of information and easily print it on various materials.A QR code can be placed on product packaging that, when scanned, directs the user to a blockchain record with information about the origin of the waste [63].Regarding RFID/NFC, items can be tracked remotely using radio waves [64].The tracking process is automatic, the solution is weatherproof, and the data can be stored directly on the chip and connected to the blockchain as an NFT token.The choice of a particular identifier depends on many factors, such as the type of waste, available infrastructure, cost, and security requirements.Different identification technologies can also be combined, depending on the needs of a particular waste management system.
A product-tracking ecosystem requires a combination of advanced technologies with well-designed processes and extensive collaboration between all supply chain stakeholders [65].Using the above solution to ensure transparency in the recycling process is a key element for sustainable waste management [61].Modern societies are increasingly emphasizing the responsible use of resources, and transparency of recycling processes is one of the most important tools for gaining the trust of consumers and stakeholders.
An example of a solution implemented in some cities in Poland is the ability to monitor the filling levels and collection of trash containers.Waste24, a waste collection company, is working to achieve adequate recycling rates and make the whole waste collection process smoother.For this purpose, it uses a blockchain in software for municipal services and individual waste generators which improves the process of waste management by increasing the transparency of the whole process; this is reflected in tools such as the Waste Database.The combination of its proprietary software solution with the blockchain supports transparent waste management, as all information about each participant in the waste cycle is recorded in real-time.This allows one to accurately document what is happening to the waste that is produced at any given time.
Waste24 focuses on waste disposal automation, which is a particular problem especially for large waste producers and enterprises with many branches.In the case of the latter, waste collection is a factor that greatly affects costs.A blockchain in waste management improves control over the expenses incurred for each waste collection [56].Waste24.netsoftware is integrated with container fill sensors, informing users about any overflows.By using blockchain solutions as a communication bus, communication barriers eliminated due to time play an important role in the work of waste collection companies.Waste must be collected within a relatively short window, so garbage trucks do not obstruct other cars from moving on the streets.An indirect result of the work on a blockchain in waste management is the "Digital Key" application, whose task is to open gates and garbage shelters.This innovation significantly shortens garbage truck stops in front of properties and improves traffic throughout the city.All Waste 24 solutions are based on the use of the SkeyNetwork blockchain ecosystem.Thanks to the integration of intelligent IoT sensors, the Waste.netsystem, and the SkeyNetwork blockchain, it is possible to constantly check how much free space remains in the garbage bin of a given company, which not only makes garbage collection more efficient, but also to reduces costs.
The above example shows that the modern market requires companies not only to manage the supply chain effectively, but also to pay attention to sustainable development and ecological responsibility.In this context, technologies such as IoT and the blockchain are becoming increasingly attractive to enterprises seeking innovations in supply chain management.
With increasing environmental awareness and an emphasis on sustainable business practices, real-time, closed-loop monitoring will likely become the standard across many industries.As technology advances and the price of IoT sensors declines, the opportunities for closed-loop applications will expand, bringing benefits to both businesses and the environment.
Based on the immutable record of data and transactions, the blockchain can verify and identify any missing waste by comparing the weight of received and shipped waste [66].Blockchain platforms are preferred only if the organizations involved in a business process are heterogeneous and have competing interests.Otherwise, centralized solutions are more appropriate for implementing waste management services.Since waste management involves organizations with competing interests, blockchain technology can offer unlimited benefits to waste handlers.
Many waste materials' service life and reliability vary and depend on the composition and working environment of such equipment/products/materials.At the end of the life of such materials, they should be recycled or disposed of responsibly at approved waste recycling facilities.For example, many waste mobile phones contain expensive lithium and cobalt materials that could be reused to manufacture new products after mobile phones are discontinued [67].
Based on the food supply-chain system defined by Khan et al. [68], the process can be redefined for a waste management system: (1) Provider: In the context of waste management, this stage involves providing information regarding the origin of waste, including details about the crops, the use of pesticides and fertilizers, and the machinery involved.All transactions related to this stage are recorded on the blockchain.(2) Producer: In waste management, this phase focuses on gathering information about the waste-producing entity, which may be a farm or a similar establishment.It includes details about the farming practices, cultivation process, and weather conditions.This information is documented for transparency and accountability.(3) Processing: In waste management, this stage pertains to the processing facility where waste is handled.It includes details about the facility itself, the equipment used, and the specific processing methods employed.Transactions with waste producers and suppliers are logged on the blockchain for traceability.(4) Distribution: This phase involves managing the transportation and distribution of waste.It encompasses information about shipping, routes taken, storage conditions, and transit times at each stage of transportation.All transactions involving waste suppliers and traders are recorded on the blockchain to ensure transparency and accountability.(5) Retailer: In the waste management context, this stage involves providing information about the waste item, including its quality, quantity, expiry date, storage conditions, and shelf life.These data are crucial for the proper handling and disposal of the waste.(6) Consumer: This final stage allows the end consumer to access detailed information about the waste item using a QR code on their mobile device.This information includes the journey of the waste item from its source to the retailer, providing transparency and building consumer confidence in the waste management process.
Therefore, reliable channeling of waste materials can lead to an environmentally friendly and safe smart city.Producers of solid waste, such as scrap metal, car tires, and smartphones, are usually required to monitor these materials after they have reached the end of their useful life [69].Technologies can help ensure that waste from all materials sold is collected at waste treatment centers.The lifespan of each solid material device and the overall supply in the market can ensure that the waste of all solid materials sold is collected at waste treatment centers.Producers can collect waste through registered retailers, designated collection sites, or authorized dismantlers/recyclers.Residential waste channelization refers to the collection and processing of waste at a designated waste treatment center.Centralized waste channelization solutions are costly and less trustworthy [70].In addition, such solutions cannot provide a reliable traceability of waste channelization.Some challenges for centralized systems are complete control over waste collection data, sensor credibility, fault tolerance requirements, and low robustness due to non-replicable data.

Digital Product Passport
Digital Product Passport (DPP) is a blockchain-based end-to-end provenance and traceability solution that allows companies to digitally record and share information about the product to prove the product's origin and sustainability.The solution provides easy access to transparent product information for supply chain participants, supporting objectives of circular economy goals provided by UE.Digital Product Passports can be linked to the real world via innovative QR codes, NFC, and RFID, which are printed or placed on the products.The Digital Product Passport concept revolves around the collection and dissemination of product-related data throughout the lifecycle of a product.Its main objective is to equip all stakeholders involved in the life cycle of a product with the necessary information to enable the implementation of a sustainable circular economy effectively.Various types of DPPs are currently being developed, many of which are tailored to specific sectors.However, it is worth noting that there is no universally accepted standard defining a DPP's exact format and structure [71].
The main objectives of the DPP are to improve the circularity of products and to promote the transparency and traceability of products, materials, and components.To achieve these goals, a DPP will likely include the following information, as outlined by Jansen et al. [72]: (1) Manufacturing data, including details about the composition of a product, the materials used in each component, details about the manufacturing process (e.g., joining techniques, binders), and the physical and chemical properties of the materials used.
In addition, they may include information on whether these materials pose nonhazardous or hazardous risks to human health or the environment.(2) Usage data, i.e., the documentation of all product parts that have been replaced or repaired during its service life.(3) End-of-life data include documentation of the collection, sorting and treatment processes during the end-of-life phase of a product.(4) Lifecycle data, such as the sales volume of a product.These data can be used to predict the expected waste generation at a given time and estimate the amount of resources that can be recycled.
The DPP offers key benefits for the circular economy: Transparency: DPP provides complete information on raw material origin, production, usage, and recycling.This grants both customers and businesses access to vital product data.Enhanced recycling: With DPP, recycling processes become more efficient.Understanding a product's composition and materials aids in selecting appropriate recycling methods.Reduced raw material waste: DPP aids in better raw material management, minimizing waste by offering precise information on materials and quantities used.Circular economy support: DPP facilitates the shift from a linear to a circular model, focusing on reuse, repair, and recycling rather than the make-use-dispose model.Consumer confidence: Customers can verify product origin, environmental impact, and disposal methods, influencing their purchasing choices.
Manufacturer incentives: Access to full product lifecycle data encourages companies to create more durable and recyclable products.
In summary, DPP is a catalyst for transitioning towards a circular economy, ensuring comprehensive transparency in product information for more sustainable consumer and business decisions.
Implementing a digital product passport system holds promise in revolutionizing plastic waste management.However, adopting a circular economy model for plastics faces several challenges, including efficient sorting by polymer type, robust waste tracking, and accurate records of prior uses (both food and non-food).Moreover, economic, regulatory, and collaborative barriers further impede progress.To advance towards a circular economy for plastics, it is imperative to redesign plastic products, incorporate vital information for downstream use, and invest in technical developments to streamline waste management.
The integration of blockchain technology is poised to play a pivotal role in achieving circular economy objectives.Through deploying smart contracts and tokenization capabilities, the blockchain enhances the system's efficiency.Embracing molecular tagging in the redesign of plastics, complemented by the seamless integration of the blockchain and circular economy principles, presents a promising pathway towards more effective solutions for combatting plastic pollution [73].
Table 1 shows areas of waste management in which blockchain technology is applied.This technology is used across various waste management domains to enhance transparency, efficiency, and accountability.For plastic waste, it facilitates direct and transparent financial transactions, incentivizes recycling through cryptocurrency rewards, ensures accurate waste tracking, and automates logistics via smart contracts.In the realm of e-waste, the blockchain enables smart contract modules for supply chain stakeholder interactions, ensures appropriate transactions through automated checks, and tracks the lifecycle of electronic devices for responsible disposal.The domain of textile waste benefits from decentralized transaction confirmation, immutable ledgers for traceability, and transparent transactions to prevent illegal dumping.In medical waste management, the blockchain supports the real-time recording and sharing of information, transparent stakeholder data, easy waste tracking, and prevention of forgery and tampering.As for hazardous waste management, the blockchain is employed for the control of information sharing, tracing of transactions through hash values, and real-time supervision of the waste transfer process, ensuring compliance and environmental protection.Overall, the blockchain is emerging as a transformative tool in waste management, optimizing processes and fostering sustainable practices for managing diverse types of waste.

Type of Waste
Applications of Blockchain Technology in Waste Management Ref.

Plastic waste
(1) New payment methods: Enable direct and transparent financial transactions for waste management services, incentivizing stakeholders to participate in sustainable practices.(2) Reuse and recycling rewards: Offer a tangible and immediate incentive for individuals and companies that recycle and reuse plastic, with rewards distributed as cryptocurrency.(3) Monitoring and tracking waste: Utilize blockchain's transparent and immutable ledger system to accurately track plastic waste from its source through recycling, ensuring accountability and reducing contamination.(4) Smart contract implementation: Automate aspects of waste management logistics, such as payment disbursal upon completion of recycling milestones, through self-executing contracts with the terms directly written into code. [68] Table 1.Cont.

Type of Waste Applications of Blockchain Technology in Waste Management
Ref.

E-waste
(1) Smart contract modules for stakeholder interaction: Blockchain can be used to create a framework where interactions between stakeholders in the e-waste supply chain are monitored.Each smart contract module could be responsible for a different part of the chain, such as collection, processing, or resale.(2) Ensuring appropriate transactions: By having all smart contract modules interact, the system can be designed to automatically check and balance each transaction.This ensures that stakeholders do not engage in inappropriate or unauthorized activities, such as illegal dumping or export of e-waste.(3) Lifecycle tracking of electronic devices: Blockchain technology can be leveraged to track the lifecycle of electronic devices from production to disposal.Each stage of the lifecycle can be recorded on the blockchain, providing a transparent and immutable record that helps manage the end-of-life process for electronics, facilitating reuse, recycling, and proper disposal. [69] Textile waste (1) Decentralized transaction confirmation: Blockchain allows for the confirmation of transactions without the need for authentication by a central authority.This decentralization can streamline the process of textile waste transactions, such as the exchange of recycled materials, by allowing parties to directly interact and verify transactions on the blockchain.(2) Immutable ledger: The blockchain ledger is immutable, meaning once data are recorded, it cannot be altered.This feature is crucial for the traceability of textile waste, ensuring that the history of a textile product, from production through to its recycling or disposal, is permanently recorded and easily verifiable, enhancing accountability in the supply chain.(3) Transparent transactions: Blockchain's transparency ensures that all transactions are visible to authorized parties, which can build trust among stakeholders in the textile recycling ecosystem.This can encourage responsible sourcing and disposal practices, as the movement of textile waste can be tracked and audited to prevent illegal dumping and encourage recycling. [70] Medical waste (1) Real-time recording and sharing: Blockchain facilitates the real-time recording and sharing of information regarding waste treatment systems.Hospitals and waste treatment facilities can instantly update and access waste processing data, ensuring timely and efficient medical waste management.(2) Transparency of stakeholder information: All parties involved in handling medical waste can have their information transparently recorded on the blockchain.This visibility includes waste generators (like hospitals), transporters, and treatment facilities, making it easier to hold each entity accountable for their role in the waste management process.(3) Easy tracking back to waste sources: Using metadata on the blockchain allows for the easy tracking of medical waste back to its source.This feature is particularly useful for regulatory compliance, ensuring that waste is handled appropriately at each stage of its lifecycle.(4) Forgery and tamper prevention: The security features of blockchain prevent forgery and tampering of information.Once recorded, the data cannot be altered retroactively, which is crucial for maintaining accurate records in the highly regulated medical waste management sector.(5) Support for transactions: Blockchain can support and streamline transactions between medical centers and waste centers, recycling plants, and sorting factories.Smart contracts can automate the financial and operational aspects of these transactions, reducing bureaucracy and errors, and ensuring compliance with legal and environmental standards.This system can facilitate the entire lifecycle of medical waste, from collection and transportation to treatment and final disposal or recycling. [71] Table 1.Cont.

Type of Waste Applications of Blockchain Technology in Waste Management
Ref.

Hazardous waste
(1) Differentiated information sharing: Blockchain allows for controlled information sharing among various participants, such as production, transportation, and treatment companies.This differentiation ensures that each entity only accesses the data necessary for its role, enhancing security and confidentiality while still maintaining the integrity of the waste management process.(2) Tracing information: All relevant information, such as the time of business transactions, participating companies, personnel involved, and business details, can be automatically stored as hash values on the blockchain.This hashed information, which serves as a digital fingerprint, ensures that the data cannot be altered and can always be traced back to their source for verification and audit purposes.(3) Real-time supervision: Blockchain enables the real-time supervision of the hazardous waste transfer process.Smart contracts can manage the entire process including application, review, transportation, receipt, payment, and invoicing.This real-time capability ensures that all steps in the hazardous waste lifecycle are monitored and recorded, which is essential for regulatory compliance and environmental protection.With blockchain, regulatory bodies can also monitor the compliance of these processes in real time, allowing for prompt intervention when necessary. [72] Consequently, we can significantly reduce the volume of plastic waste subjected to incineration or land disposal.The plastics' circular economy serves to safeguard the environment and bolster the energy transition in three key ways: it lessens our reliance on fresh plastics sourced from fossil fuels, diminishes carbon emissions originating from incineration processes, and prevents pollution stemming from landfill sites [74].

Conclusions
This paper has underscored the importance of implementing the European Commission's Green Deal policy for advancing industrial development and environmental protection, especially via establishing closed-loop systems to reuse products and minimize waste.In this context, the emergent technologies associated with Industry 4.0, such as the blockchain, have been identified as potentially transformative in revolutionizing waste management practices.Our exploration into the integration of the blockchain within the circular economy has revealed that automated systems, powered by the blockchain and connected through the Internet-of-Things, can significantly enhance the efficiency and transparency of waste management systems.
The studies referenced throughout our discussion provide empirical backing for this conclusion, demonstrating how blockchain technology fosters transparent transactions for all stakeholders and accurately tracks the lifecycle of products.For instance, research highlighting the blockchain's role in improving the traceability of waste streams has shown that such transparency is not just conceptually appealing but also practically beneficial.The introduction of digital product passports, as part of a blockchain ecosystem, offers comprehensive data on proper disposal methods, laying the groundwork for an integrated supply chain that meticulously monitors a product's journey from production to reuse or recycling.
However, the blockchain not only has the ability to enhance technological capabilities; its policy implications are vast.Used in alignment with the Green Deal's ambitious goals, blockchain technology can address critical challenges such as waste mismanagement, environmental harm, and system inefficiencies.Studies have shown that the blockchain can not only enhance transparency, traceability, and accountability, but also make waste management processes more sustainable, eco-friendly, and economically viable.
The current literature further describes the differentiated sharing of information among various stakeholders in the waste management process, facilitated by the blockchain's immutable and transparent ledger.These capabilities ensure that all aspects of hazardous and medical waste management, including transportation and treatment, are supervised in real time, which is integral to the environmental integrity and safety protocols mandated by the Green Deal.
Recognition of the limitations of the present studies indicates a need for future research to delve deeper into the scalability of blockchain solutions and their long-term sustainability impacts.It is imperative to continuously evaluate the effectiveness of blockchain applications in real-world scenarios and to adapt policy frameworks accordingly.
In conclusion, blockchain technology could indeed be a solution for waste management, helping to address some of the most pressing environmental challenges of our time.As we increase our understanding of the blockchain's capabilities and limitations through ongoing research, we move closer to realizing the full potential of this technology in creating a sustainable, efficient, and transparent waste management system in alignment with the Green Deal's objectives.
The most important findings of this review are: (1) The significance of the European Commission's Green Deal: The study emphasizes the critical importance of implementing the Green Deal policy, which supports industrial development and environmental protection.The policy is particularly focused on creating closed-loop systems for reusing products and reducing waste.(2) The role of Industry 4.0 technologies: As an Industry 4.0 technology, the blockchain is highlighted as having significant potential to transform waste management practices.
The study suggests that the blockchain could be integral in the development of more efficient and sustainable waste management systems.(3) The integration of the blockchain in a circular economy: The paper discusses how blockchain technology can be integrated into the circular economy to automate systems and connect various Internet-of-things (IoT) solutions and service systems.(4) The importance of using the blockchain for waste management: It is noted that blockchain technology is vital for ensuring transparent transactions among all stakeholders and for accurate tracking of a product's lifecycle.(5) The role of digital product passports: The introduction of a digital product passport is suggested as a means to provide comprehensive information on proper disposal methods, supporting an integrated supply chain.(6) The potential impact of the blockchain: The study concludes that blockchain technology could be a game-changer in waste management by addressing issues of mismanagement, environmental harm, and inefficiencies.It is proposed that the blockchain can contribute to making waste management more sustainable, eco-friendly, and economically efficient.

Figure 1 .
Figure 1.Scheme of a sequence of data blocks in blockchain technology.

Figure 1 .
Figure 1.Scheme of a sequence of data blocks in blockchain technology.

Figure 2 .
Figure 2. The environment of blockchain technology.

Figure 2 .
Figure 2. The environment of blockchain technology.

Figure 3 .
Figure 3.The use of blockchain in different sectors.Adapted from Pandey and Sen [29].

•Figure 3 .
Figure 3.The use of blockchain in different sectors.Adapted from Pandey and Sen [29].

Table 1 .
Applications of blockchain technology in waste management.