Katarina Dimić‐Mišić, Shailesh Singh Chouhan, Michael Gasik, Milica P. Marčeta Kaninski · 7 authors
Electronic waste (e-waste) is among the fastest-growing global waste streams, with 62 million tonnes generated in 2022 and only 22.3% formally recycled, while generation is projected to reach 82 million tonnes by 2030. Fragmented record-keeping, weak chain-of-custody controls, and limited transparency enable illegal dumping, fraudulent recycling claims, and loss of recoverable materials. This paper presents a narrative literature review of blockchain and distributed ledger technologies applied to electronics and e-waste management. Following a structured search and relevance screening of major scientific databases, publisher platforms and grey literature (last search was run on 15 July 2026), 110 sources published between 2017 and 2026 were thematically synthesized across four domains: technological developments, sustainability and circular-economy implications, traceability and compliance mechanisms, and e-waste management applications. Blockchain delivers value primarily through an auditable chain-of-custody built on three pillars: standardized item and batch identities, standardized lifecycle event schemas, and licensed-actor attestations supported by off-chain evidence anchored on-chain. Recurring design patterns include permissioned consortium networks, hybrid storage, and role-based access control. Persistent barriers include data-input integrity, scalability, governance, and cost. Blockchain immutability protects stored records but cannot correct falsified inputs, making trusted data capture and governance the decisive factors for reliability. Adoption should be evaluated against measurable indicators, such as traceability completeness, audit-time reduction, fraud rates, and verified material recovery, rather than assumed benefits.
Rapid urbanization in Tanzania has increased municipal solid waste generation and placed growing pressure on urban waste-management systems that remain focused mainly on collection, transport, and disposal. Given the high organic fraction of municipal waste generation. This paper examines Resource recovery from municipal waste through cost-effective biogas technologies in Tanzania, focusing on policy and institutional frameworks that support or constrain decentralized municipal organic waste-to-biogas systems that use appropriate standard procedures. The findings show that Tanzania has a broad policy framework for environmental protection, renewable energy, private-sector participation, and resource recovery, but this foundation has not been well translated into practice. Key constraints include fragmented mandates, limited biogas-specific standards, weak organic waste segregation, inadequate financing mechanisms, and insufficient formal inclusion of communities and informal waste actors. The paper argues that improving decentralized biogas implementation requires converting existing policy commitments into enforceable, financed, and locally coordinated municipal resource-recovery systems
This research focuses on the design and development of a blockchain-based plastic waste tracking system aimed at enhancing transparency, efficiency, and accountability in plastic waste management. The system utilizes Hyperledger Fabric as a permissioned blockchain platform and integrates smart contracts to manage transactions between organizations, including waste generators, collectors, sorting warehouses, and final processing warehouses. This system records each stage of the plastic waste journey, from creation to final processing, in a permanent, transparent, and immutable manner. The testing results demonstrate that the system can accurately record the status and history of waste, manage transfers between organizations, and process plastic waste into recycled products. Moreover, the system shows a significant potential for carbon emission reduction, with an estimated reduction of up to 50% compared to traditional plastic waste management methods, such as incineration or landfilling. The study also explores how the implementation of blockchain can support global efforts in mitigating the environmental impacts of plastic waste. The blockchain-based system also provides real-time monitoring, ensuring that each transaction is verified and recorded immediately, contributing to more effective management. The implementation of smart contracts further guarantees that waste-related activities are executed automatically when predefined conditions are met, reducing administrative overhead. The study also explores how the implementation of blockchain can support global efforts in mitigating the environmental impacts of plastic waste. Ultimately, this system presents a scalable solution that could be adopted in various regions to improve global waste management strategies.
• Blockchain-based system enables policy-grade traceability for plastic credits. • Smart contracts enforce automated compliance with EPR and ESG frameworks. • DApp supports decentralized oversight, reducing audit burden on regulators • System logs immutable offset records aligned with circular economy targets. • Architecture offers scalable digital infrastructure for waste policy integration. Plastic credit schemes are increasingly adopted to mitigate plastic pollution, yet existing systems remain centralized, opaque, and prone to double counting and fraud. This study proposes and validates a plastic credit system that leverages blockchain technology aimed at enhancing transparency, traceability, and accountability in plastic recovery efforts. A modular three-layer architecture was implemented, comprising a user interaction layer, a blockchain execution layer, and a utility layer for metadata and analytics integration. The system employs two smart contracts on the Polygon Proof-of-Stake (PoS) mainnet using Ethereum standards: ERC-20 for fungible tokenization of plastic credits and ERC-721 for non-fungible certificate issuance. Functional testing confirmed successful execution of token lifecycle operations. Stress testing across 5000 sequential transactions yielded stable performance, with average confirmation times of 5.29 s for fungible token operations and 5.59 s for non-fungible processes. A decentralized application (DApp) was developed to support role-based interaction, credit traceability, and certificate validation. User evaluation returned a high usability score (86.4%), while benchmarking against existing platforms demonstrated improved auditability, automation, and stakeholder control. These findings indicate that blockchain infrastructure can enable decentralized, tamper-resistant plastic credit systems. The proposed model provides a scalable foundation for Extended Producer Responsibility (EPR) compliance and plastic waste traceability, which could potentially support the credibility of Environmental, Social, and Governance (ESG) reporting and supporting circular economy transitions across diverse policy and economic contexts.
Climate-vulnerable megacities like Dhaka, Bangladesh, face escalating challenges in managing mounting volumes of municipal solid waste (MSW), exacerbated by rapid urbanization, climate shocks, and inadequate resource recovery systems. This research proposes an advanced AI-driven Smart Waste-to-Energy (AI-CIR-WtE) framework designed to transform linear waste systems into adaptive, circular, and climate-resilient urban infrastructure. Integrating artificial intelligence, life cycle modeling, digital twins, and blockchain, the framework offers a comprehensive pathway to optimize waste valorization, emissions reduction, and sustainable energy generation in resource-constrained settings. The proposed system leverages Long Short-Term Memory (LSTM) networks for forecasting waste generation by ward and season, coupled with Non-Dominated Sorting Genetic Algorithm II (NSGA-II) for multi-objective optimization of waste routing, energy efficiency, and environmental impact. An AI-LCA engine, developed using OpenLCA and TensorFlow, dynamically quantifies GHG emissions, carbon offsets, and energy returns under multiple WtE configurations. Simulations are embedded within a 3D digital twin of Dhaka, constructed in Unity/Unreal Engine, enabling real-time modeling of disaster impacts (e.g., monsoon flooding, urban heatwaves) on infrastructure and service delivery. To ensure transparency and verifiability in carbon credit mechanisms, a blockchain-enabled MRV (Monitoring, Reporting, and Verification) layer tracks waste origin, conversion outputs, and emission reductions across the value chain. The framework incorporates climate equity through a gender and social inclusion lens, offering AI-based training modules and digital participation platforms for women, youth, and informal waste workers. Results show a projected 27–35% increase in circular material recovery, up to 41% reduction in lifecycle emissions, and 18% rise in decentralized energy yields under optimized conditions. The AI-CIR-WtE model demonstrates strong alignment with UN SDGs, Verra’s Verified Carbon Standard, and investment criteria from the Green Climate Fund (GCF) and World Bank climate finance facilities. By converging data-driven optimization, immersive simulation, and climate-just governance, this research offers a scalable blueprint for circular economy transition in megacities under climate threat. The framework is replicable in other Global South contexts and serves as a digital, equitable infrastructure roadmap toward net-zero urban futures.
Blockchain technology has emerged as a transformative tool for enhancing transparency and accountability in waste management systems, contributing significantly to sustainability goals. This paper explores how blockchain can revolutionize waste disposal practices by providing an immutable, decentralized ledger that tracks waste from generation to disposal. The use of blockchain ensures that all transactions and movements of waste materials are recorded in a transparent and tamper-proof manner, addressing challenges related to data integrity and fraud in waste management. Blockchain technology facilitates real-time monitoring and verification of waste disposal processes. Each stage of the waste management chain, from collection and transportation to processing and final disposal, is documented on a distributed ledger accessible to all stakeholders. This transparency not only reduces the risk of illegal dumping and misreporting but also enables more effective regulatory compliance. Stakeholders, including waste management authorities, businesses, and the public, can access reliable data on waste management practices, fostering greater accountability. Moreover, blockchain supports the implementation of circular economy principles by tracking the lifecycle of recyclable materials. It enables efficient sorting and recycling by providing detailed records of material types and quantities, thereby improving recycling rates and reducing landfill dependency. Smart contracts on blockchain platforms can automate transactions and enforce compliance with waste management policies, further enhancing operational efficiency and reducing administrative burdens. The adoption of blockchain in waste management also promotes stakeholder engagement and trust. Public access to real-time data and historical records empowers communities to participate in and monitor local waste management efforts, leading to increased public awareness and responsibility. Despite its potential, the implementation of blockchain in waste management faces challenges such as integration with existing systems, scalability, and data privacy concerns. Addressing these challenges requires collaboration between technology developers, waste management professionals, and policymakers. In conclusion, blockchain technology offers significant benefits for sustainable waste management by improving transparency, accountability, and efficiency. Its potential to transform waste disposal practices highlights the need for continued exploration and development in this field.
Introduction; Bridging the digital divide requires the provision of affordable, fair and quality ICT. With nearly two-thirds of the world’s population still offline, there is a need to provide affordable web access for everyone. For developing countries, increasing the popularity of information and communication technology has become the most important factor in reducing poverty. The danger of electrical and electronic waste disposal contains hazardous substances, but most of the electrical and electronic equipment is still disposed of in an unhealthy environment in the field development area, affecting the level of contamination in Water, Air and Soil ultimately affecting people’s health. Eliminating E-waste responsibility and protecting the environment is a challenge for countries. Smart cities can solve environmental problems through proper waste management for improving human health, protecting water resources, and reducing pollution. Objective; In this paper, we explore how blockchain technology can help smart cities to manage E-waste by providing consistency, immutability, transparency, and accountability control in a distributed, reliable, and secure manner. We discussed the advantages of blockchain technology in various aspects of E-waste management, such as instant tracking and monitoring, E-waste disposal and E-waste management regulation compliance, proper disposal management, E-waste management, and material handling, etc. All examples of disposal services, but in our study we have found that there is no fool proof system to check the disposal of E-waste whether it has been disposed off Fully or Partially. We mainly focused on the tracking of E-waste management system for 100% safe and eco-friendly disposal from the originating point of E-waste to end disposal point of total disposal. Methods; For this, we have used machine-learning model to find the existing percentage of disposal of E-waste at the end-point which reveals that it is never 100%. And partial disposal of E-waste means we have still partial E-waste around us in different forms, which will be a threat for the society to be indulged in hazardous after effects of randomly dumping E-waste.Results; After this we have modelled a Disposal Tracking System(DTS) using blockchain technology to create an E-waste data storage as Decentralized Shareable Ledger (DSL) which records the quantity and state of E-waste data from its originating point to a different level of disposal unit and finally reflect the balance of E-waste data as NIL at the end of last disposal point.Conclusion; This system will helpful for safe and ecofriendly E-waste management and it provides complete transparency and traceability of E-waste during the life cycle of complete disposal. After implementation of this system any district or Block or Village authority can ensure to its citizens for E-waste hazards free environment and safety of natural resources
Murray A. Rudd, Matthew Jones, Daniel Sechrest, Daniel Batten · 5 authors
• Novel model links landfills with Bitcoin mining to enhance economic viability. • Bitcoin mining can help finance methane mitigation from low-flow landfills. • Integrative approach monetizes methane destruction. • Strategic use of bitcoin mining may help incentivize rapid scaling of mitigation.
Sulagna Roy, Pankaj R. Kaushik, Pradeep Sangwan, Sunil Herat
Non-governmental organizations (NGOs) play a critical role in addressing solid waste management (SWM) challenges in remote mountain communities, including the ecologically fragile Himalayan region. This study evaluates the impact of Healing Himalayas, an NGO, in Rakchham village, Himachal Pradesh, India. The objectives were to evaluate the effectiveness of Healing Himalayas' decentralized SWM model in promoting stakeholder engagement and resource recovery, assess the role of collaborations between local authorities and the NGO in financing waste management practices, investigate the influence of tourism and seasonal variations on solid waste generation patterns and waste management practices in Rakchham, and material recovery facilities, followed by glass (36.7%), paper/cardboard (18.4%) and metal (4.1%). A fee-based system involving the local village council funded waste operations. Waste generation exhibited significant seasonal fluctuations, with tourism influxes driving increased volumes. Healing Himalayas' initiatives promoted community participation, with over 15 awareness workshops conducted. Key challenges included limited financial resources, inadequate infrastructure, lack of advanced treatment facilities and need for context-specific solutions like efficient wet waste management in cold climates. The study highlights Healing Himalayas' decentralized model's success in fostering stakeholder engagement, behavioural change and resource recovery. The findings inform effective strategies for NGO-led waste management initiatives tailored to remote Himalayan communities.
Construction waste management (CWM) and blockchain technology (BT) are two crucial topics for sustainable production and development. As a fundamental infrastructure for artificial intelligence, BT enables real-time, reciprocal, and immutable information provision in tracing construction waste and holds a significant potential to advance CWM. However, the barriers to adopting BT in CWM and their impact on CWM practices remain unclear. Therefore, this study aims to identify BT adoption barriers in CWM, assess their criticality, and clarify their correlations through a fuzzy empirical analysis. Results show that, due to interdependence, actions on one or some of the barriers can have a closed-loop impact. The findings suggest that the government and the stakeholders have a critical influence on the further adoption of BT in CWM. This exploratory study advances sustainable construction by clarifying those BT adoption barriers and providing implications to integrate BT into CWM practices.
The construction industry is a significant contributor to global carbon emissions, primarily due to the generation of substantial construction and demolition waste. However, the current practices in construction and demolition waste management (CDWM) face various information management challenges that undermine their overall effectiveness. Correspondingly, this research proposes the integration of blockchain technology as a strategic solution to enhance the efficiency and effectiveness of CDWM. Despite the potential of blockchain in revolutionizing CDWM, research in this area remains limited. To address such a gap, this study adopts a design science action research methodology to integrate the use of blockchain technology into CDWM. Specifically, this study has creatively introduced the blockchain-based data supply chain to address the principal–agent problem in CDWM and develop a novel blockchain-enabled framework for CDWM. Additionally, a six-layer system architecture for the blockchain-based CDWM information system has been developed. This integration holds the promise of streamlining and empowering CDWM processes and thereby improving the administration and regulation of CDWM. Notably, the utilization of blockchain technology also presents an innovative opportunity for carbon reduction and offsetting within the construction industry. This research makes a substantial contribution to the field by introducing a novel approach to address information management challenges in CDWM, thereby promoting sustainable practices in the construction industry.
Waste management is a growing challenge globally, with major impacts on social health, greenhouse gas emissions, and sustainable development. This paper provides an in-depth analysis on the potential of emerging technologies like the Internet of Things (IoT), blockchain platforms, big data analytics and artificial intelligence to enable more intelligent, sustainable waste management systems. A robust methodology of literature review, real-world case analysis, deduction and critical reasoning was utilized. The key findings are: (1) logistics optimization through machine learning driven dynamic routing and load optimization, reducing costs by 25-40%, (2) GHG emission reductions above 15% from optimized transportation, (3) 40%+ improvements in recycling rates and landfill diversion through waste stream automation and citizen engagement apps, and (4) over 50% reduction in waste contamination enabled by automated waste characterization using image recognition. However, barriers like infrastructure costs, lack of capabilities, and change management constrain adoption. Targeted pilots, open data sharing, and partnerships can drive implementation. Intelligent waste systems are critical for cities to cost-effectively tackle the growing waste challenge while meeting sustainability goals.
Ala Abdulsalam Alarood, Adamu Abubakar, Abdulrahman Alzahrani, Faisal S. Alsubaei
The adoption of recycling and proper disposal techniques for electronic waste is crucial in advancing sustainable development. The traditional approaches of motivating people for collection of electronic waste are often insufficient due to inadequate methods reaching out, given incentives, calculating appropriate incentives associate to the task of gathering the electronic waste and a lack of transparency in the entire process. Insufficient collection of electronic waste could result in the release of numerous harmful substances into the environment. Prior research studies have been carried out to tackle the issue of electronic waste management in a broad sense. The findings of those studies indicated diverse strategies, each of which is relevant solely to a restricted range of electronic waste reprocessing circumstances. The current study has presented a proposed technique for incentivizing tasks and activities associated to collection of electronic waste through the adoption of vector space technique. Blockchain smart contact technology, has been used to implemented the strategy. The method used involves various well defined mapping of tasks, nature of activities, and their magnitude in order to derived an incentive. Some scenarios for the calculations of incentives are presented, and the findings reveals the based case is by utilizing weighting scale scheme where each tasks and activities are mapped to its associated inventive rather than providing fixed incentive values. Ethereum was used as digital token for each unit of incentive. This concept has contributed in encouraging personal accountability in the management of e-waste collection in order to cultivate sustainable behaviors for a long term solution.
The circular economy is a tool to achieve the criteria for sustainable development in the solid waste processing.In addition to the advantages, many disadvantages have been identified in the application of this measure.With regard to the recycling of raw materials, the main one is the lack of traceability of the product over several production life cycles.The assessment of the advantages and disadvantages should be done after a thorough analysis of the processing data.Therefore, according to the regulatory framework, a method for tracking material flows based on blockchain has been proposed.The object of the research is a plant for solid household waste in Sofia.The plant's raw materials are classified into four streams: landfill, sale products, combustion products as refuse-derived fuel (RDF), and recycling.Conceptual models based on Distributed Ledger Technology (DLT) have been proposed to track the main material flows from the plant.The choice of a specific application as a Blockchain platform will depend on the parameters of the communication scheme.The data stored in the blocks will be the starting point for the analysis and tracking of the full processing cycle.
Muhammad Saad, Maaz Bin Ahmad, Muhammad Asif, Muhammad Khalid Khan · 6 authors
Internet of things (IoT) is being applied in every aspect of daily living to improve the quality of life. Waste management is a critical issue, especially for developing countries. The purpose of this study is to propose an IoT-driven state-of-the-art system for solid waste management for developing countries and urban areas. The lack of planning and availability of resources in urban areas have made a living in densely populated surroundings even more difficult. This research work provides a framework based on blockchain-enabled vehicular ad-hoc networks (VANETs) in the realm of IoT. The step-by-step methods are proposed for the decentralized solution for solid waste management using blockchain-enabled VANET. Advanced ultra-high frequency (UHF) technology is used along with IoT devices for the real-time location of waste vehicles and the detection of waste bins. Geo-fencing techniques are also applied for the monitoring and timely collection of waste from the dump spots. Lastly, blockchain technology is applied in the proposed solution to make machine-to-machine (M2M) communication more secure, reliable and trustworthy across IoT devices. The experimental results are also obtained by deploying a pilot project in Karachi, Pakistan. The real-time dashboard is also obtained to demonstrate the daily statistics of the waste collection and performance of the waste vehicles. The results indicate the successful implementation of SSWMS to achieve real-time tracking, intelligent identification of waste bins, trash weighing, and keeping tabs on waste collection from dump spots using geofencing. In future, the blockchain-enabled VANETs can be applied for route management, intelligent transportation and fleet management systems (FMS) due to the inherent characteristics of blockchain and IoT.
Milena Mota Costa, João Felix Barreto Neto, Elaine Pinto Varela Alberte, Álex Pires Carneiro
Abstract There is a current lack of management tools that guarantee control and traceability of actions taken by the generator of construction and demolition waste (CDW). Furthermore, the reinsertion of recycled CDW into productive cycle is necessary to foster a circular economy in construction sector. To address these challenges, this study builds a novel blockchain-based information management framework for CDW management in construction, which extends the applications of blockchain for improving circular economy in the sector. Using design science research as a methodological research strategy, this study presents and analyses a blockchain framework and its development processes. The framework performance was evaluated through simulation and quantitative and qualitative indicators. Through a SaaS (Software as a Service) concept, the system allows strengthens the connection between stakeholders looking for sustainable solutions for CDW management. These solutions are independent of the size or segment of the company and allow the creation of business opportunities within the industry itself that provide expertise to foster the circular economy such as reverse logistics, servitization, and industrial symbiosis.
Despite the large quantities of secondary materials flowing within the built environment, their actual volume and respective waste management processes are not accurately known and recorded. Consequently, various sustainability and material efficiency policies are not supported by accurate data and information-reporting associated with secondary materials’ availability and sourcing. Many recent studies have shown that the integration of digital technologies such as city information management (CIM), building information modeling (BIM), and blockchain have the potential to enhance construction waste management (CWM) by classifying recycled materials and creating value from waste. However, there is insufficient guidance to address the challenges during the process of CWM. Therefore, the research reported in this paper aims to develop a blockchain-enhanced construction waste information management conceptual framework (BeCW). This paper is the first attempt to apply the strengths of integrated information-management modeling with blockchain to optimize the process of CWM, which includes a WasteChain for providing a unified and trustworthy credit system for evaluating construction-waste-recyclability to stakeholders. This is enabled through the use of blockchain and self-executing smart contracts to clarify the responsibility and ownership of the relevant stakeholders. As a result, this study provides a unified and explicit framework for referencing which quantifies the value-contribution of stakeholders to waste-recovery and the optimization of secondary construction materials for reuse and recycling. It also addresses the issue of sustainable CWM through information exchange at four levels: user, application, service, and infrastructure data levels.
Somdip Dey, Suman Saha, Amit Kumar Singh, Klaus D. McDonald-Maier
Food waste is an important social and environmental issue that the current society faces, where one third of the total food produced is wasted or lost every year while more than 820 million people around the world do not have access to adequate food. However, as we move towards a decentralized Web 3.0 enabled smart city, we can utilize cutting edge technologies such as blockchain, artificial intelligence, cloud computing and many more to reduce food waste in different phases of the supply chain. In this paper, we propose SmartNoshWaste—a blockchain based multi-layered framework utilizing cloud computing, QR code and reinforcement learning to reduce food waste. We also evaluate SmartNoshWaste on real world food data collected from the nosh app to show the efficacy of the proposed framework and we are able to reduce food waste by 9.46% in comparison to the originally collected food data based on the experimental evaluation.
Raja Wasim Ahmad, Khaled Salah, Raja Jayaraman, Ibrar Yaqoob · 5 authors
Smart cities have the potential to overcome environmental problems caused by improper waste disposal by improving human health, protecting the aquatic ecosystem, and reducing air pollution. However, today’s systems, approaches, and technologies leveraged for waste management are manual and centralized. This fact makes them vulnerable to manipulation and the single point of failure problem. Also, a large portion of the existing waste management systems within smart cities fall short in providing operational transparency, traceability, audit, security, and trusted data provenance features. In this paper, we explore the key role of blockchain technology in managing waste within smart cities as it can offer traceability, immutability, transparency, and audit features in a decentralized, trusted, and secure manner. We discuss the opportunities brought about by blockchain technology in various waste management use cases and application scenarios, including real-time tracing and tracking of waste, reliable channelization and compliance with waste treatment laws, efficient waste resources management, protection of waste management documentation, and fleet management. We introduce a framework that leverages blockchain-based smart contracts to automate the key services in terms of waste management of smart cities. We compare the existing blockchain-based waste management solutions based on important parameters. Furthermore, we present insightful discussions on several ongoing blockchain-based research projects and case studies to highlight the practicability of blockchain in waste management. Finally, we present open challenges that act as future research directions.
The global waste and resource crises necessitate and give great impetus for better and more sustainable management of waste. Increasingly, resource and waste streams that once were sent to landfill or incinerated are now reused, recycled, or recovered. Yet, while many laws and policies have been adopted for this very purpose, a number of recurrent challenges persist across interventions seeking to further facilitate the necessary, widespread transitions to sustainable waste management. This perspective article explores the suitability of blockchain technology in overcoming these challenges. In particular, we discuss the opportunities and challenges for blockchain in (1) offering clarity in property rights of products and wastes, (2) supporting law and policy goals by incentivizing sustainable waste management, and (3) maintaining anonymity and privacy for institutions and individuals.
Virgin polymers based on petrochemical feedstock are mainly preferred by most plastic goods manufacturers instead of recycled plastic feedstock. Major reason for this is the lack of reliable information about the quality, suitability, and availability of recycled plastics, which is partly due to lack of proper segregation techniques. In this paper, we present our ongoing efforts to segregate plastics based on its types and improve the reliability of information about recycled plastics using the first-of-its-kind blockchain smart contracts powered by multi-sensor data-fusion algorithms using artificial intelligence. We have demonstrated how different data-fusion modes can be employed to retrieve various physico-chemical parameters of plastic waste for accurate segregation. We have discussed how these smart tools help in efficiently segregating commingled plastics and can be reliably used in the circular economy of plastic. Using these tools, segregators, recyclers, and manufacturers can reliably share data, plan the supply chain, execute purchase orders, and hence, finally increase the use of recycled plastic feedstock.