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Blockchain for Waste Management in Smart Cities: A SurveyBlockchain for Waste Management in Smart Cities: A Survey
This paper was downloaded from TechRxiv (https://www.techrxiv.org).
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CC BY 4.0
SUBMISSION DATE / POSTED DATE
31-03-2021 / 13-04-2021
CITATION
Ahmad, Raja Wasim; Salah, Khaled; Jayaraman, Raja; Yaqoob, Ibrar; Omar, Mohammed (2021): Blockchain
for Waste Management in Smart Cities: A Survey. TechRxiv. Preprint.
https://doi.org/10.36227/techrxiv.14345534.v1
DOI
10.36227/techrxiv.14345534.v1
1
Blockchain for Waste Management in Smart Cities:
A Survey
Raja Wasim Ahmad, Khaled Salah, Raja Jayaraman, Ibrar Yaqoob, Mohammed Omar
Abstract—Smart cities have the potential to overcome en-
vironmental problems caused by improper waste disposal to
improve human health, protect the aquatic ecosystem, and
reduce air pollution. However, today’s systems, approaches, and
technologies leveraged for waste management are manual and
centralized that make 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 track-
ing 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 manage-
ment 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.
Index Terms—Blockchain; Waste management; Traceability;
Security; IoT; Smart Cities
I. INTRODUCTION
Since the past decade, worldwide cities have been continu-
ously generating an enormous amount of waste that is putting
a harmful effect on human health and the environment. It is
estimated that the world generates up to 1.3 billion tonnes of
solid waste each year and it is expected to increase to 2.2
billion tonnes per year by 2025. On average, every human
being generates around 0.11 to 4.54 kilograms of solid waste
per day. It is reported that 33% of the generated solid waste
in cities do not manage in an environmentally friendly and
safer way [1, 2]. The improper management of waste can
contaminate the oceans, cause diseases spreading, and harm
animals that eat waste (e.g., food waste or plastic bags) un-
knowingly. The proper management of waste in smart cities re-
quire close coordination and collaboration among the involved
R. W. Ahmad, K. Salah, and I. Yaqoob are associated with Department of
Electrical Engineering and Computer Science, Khalifa University of Science
and Technology, Abu Dhabi 127788, UAE.
R. Jayaraman and M. Omar are associated with Department of Industrial
& Systems Engineering, Khalifa University of Science and Technology, Abu
Dhabi 127788, UAE.
Corresponding author: Ibrar Yaqoob (ibraryaqoob@ieee.org)
stakeholders such as waste generators, collectors, shipper,
and waste treatment facilities. However, the existing systems
leveraged to manage waste are highly disintegrated and face
several challenges because of a lack of means to adequately
share waste-related data among involved stakeholders in waste
management processes [3–5]. Blockchain technology presents
a single and unified platform that can be used by the involved
stakeholders in waste management of cities to share data in
an effective, secure, transparent, and verifiable manner [6–8].
Since blockchain follows decentralized architecture, hence it
is a highly fault-tolerant, robust, and trusted technology.
Modern cities face manifold challenges related to air pollu-
tion, deteriorating and inappropriate water management, sus-
tainable and eco-friendly energy creation, and environmentally
friendly waste management. Smart cities aim to improve
citizens’ quality of life, protect the environment, minimize
traffic congestion, and increase the local economy by leverag-
ing state-of-the-art Information Communication Technologies
(ICT) [9, 10]. Effective and sustainable waste management
policies assist in improving air and water quality and lessening
carbon emissions to clean the environment. Many of the waste
management systems are highly Internet of Things (IoT)-based
and leverages centralized cloud-based resources to process
the waste-related data. IoT-based nodes sense, monitor, and
transmit the capacity and type of waste in bins, temperature,
and humidity level, and estimated arrival time and route
data about the waste carrying trucks to the cloud servers for
processing and decision making [3, 4, 11]. For instance, the
smart bins capacity data can be used to forecast the availability
of the vehicles near the waste bin site [12]. The centralized
data storage and processing often result in data inconsistency
among the involved waste handling participants, thereby of-
fering limited collaboration opportunities to the stakeholders.
Also, the data stored on a centralized-based system is less
trustworthy as it is highly vulnerable to modifications, fraud,
or deletion by intruders.
Blockchain is a decentralized technology that can assist in
securing data and transactions by storing and executing them
in a trustful manner. It follows a Peer-to-Peer (P2P) archi-
tecture to store and process data in a highly reliable, secure,
transparent, and trusted way [13, 14]. Blockchain technology
allows and provides incentives to the miners to participate in
the consensus process to validate the transactions and create
new blocks. Consensus algorithms secure the blockchain by
ensuring that unverified transactions cannot be executed and
stored on the blockchain [15]. Since blockchain platforms
follow a distributed architecture, the consensus algorithms
such as Proof-of-Work (PoW) [16], Proof-of-Stake (PoS) [17],
2
and Proof-of-Authority (PoA) [18] are obliged to ensure the
agreement to the current state of the blockchain among all
distributed nodes. Broadly, existing blockchain platforms are
categorized as permissionless and permissioned. Permission-
less blockchain platforms are public and allow users full
access to the transactions stored on the ledger. Permissioned
blockchain platforms are usually private and controlled by a
designated organization. It offers access to a limited number of
organizations to assure that data privacy and security are pre-
served [19]. Ethereum [20] is a decentralized and open-source
permissionless blockchain platform that allows digitizing and
tracking the assets through smart contracts. Nevertheless,
Quorum [21] that basis on the Ethereum platform is classified
as a permissioned platform. Similarly, Hyperledger Fabric [22]
falls under the permissioned platform category as it allows the
stakeholders to communicate in a private manner.
Smart contracts represent programs stored on the blockchain
with terms of the agreement between participants of waste
management processes. They automatically execute and trigger
events after meeting predetermined criteria in the agreement.
Also, they assist the stakeholders in performing business
operations in a faster, cheaper, and secure way compared to
traditional systems that require intermediaries to commit the
business operations. Based on characteristics and lifetime of
smart contracts, they are of several types such as dormant,
active, prolific, self-destructed, and active. The existing studies
that have employed smart contracts to automate the smart cities
services have mainly considered smart grids, smart healthcare,
smart homes, smart transportation, supply chain management,
smart industries, and agriculture [23–27].
To the best of our knowledge, none of the existing stud-
ies have explored or reviewed the opportunities offered by
blockchain in terms of waste management of smart cities.
We conduct this study to explore the role of blockchain in
waste management, present several blockchain-based research
projects and case studies, and discuss the challenges that need
further research to improve waste management services in
smart cities. The key contributions of this paper are as follows:
•We review the key opportunities brought about by
blockchain technology for waste management of smart
cities to improve operational transparency, traceability,
security, and accountability in waste management pro-
cesses.
•We present a blockchain-based framework for waste
management services and compare existing state-of-the-
art blockchain-based waste management solutions based
on important parameters.
•We report several blockchain-based research projects and
case studies to demonstrate the practicality of blockchain
technology in waste management of smart cities.
•We identify and discuss several open research challenges
hindering the successful implementation of blockchain
technology in terms of waste management within smart
cities.
The rest of the paper is organized as follows. Section II
presents the opportunities offered by blockchain technology
in terms of waste management in smart cities. Additionally,
it presents a tabular comparison of existing blockchain-based
studies related to waste management. Section III discusses
recent blockchain-based projects and case studies related to
waste management in smart cities. Section IV presents a
discussion on research challenges in the waste management
field. Section V provides concluding remarks.
II. OPPORTUNITIES FOR BLOCKCHAIN IN WASTE
MA NAG EM E NT O F SMART CITIES
The rapid worldwide expansion of cities causes several
environmental and social challenges. The increased rate of ur-
banization, economic development, world population growth,
and the rise in the standard of living in developing counties
are major causes of the amount, rate, and variety of generated
waste [28, 29]. Figure 1 highlights the key opportunities
offered by blockchain technology to enforce trust among
participating organizations involved in the waste management
of smart cities. Further discussion is provided in the following
subsections.
A. Tracing and Tracking of Waste of Smart Cities
Smart cities generate domestic, commercial, medical, agri-
cultural, and industrial waste. Such waste is often sent to
landfills, waste recycling facilities, composters, and waste to
energy generation plants. Tracing and tracking features can be
useful to verify the authenticity of data and ethical practices
involved in the collection, processing, and shipment of smart
cities waste [30–33]. These features assist in monitoring the
current location and state of the waste during their collection,
segregation, shipment, treatment, and disposal or recycling.
The traceability feature is valuable since it assists in identi-
fying, storing, and managing detailed data about the activities
and outcomes during waste management processes. The most
important data which is recorded during waste management
includes waste type, volume, shipping location and route,
transit time status, and details about the waste handler and their
actions in each waste management stage. Examples of smart
cities’ waste include liquid or solid household waste, medical
waste, hazardous waste, recyclable waste, green waste, and
electrical waste (E-waste). Today’s centralized systems that are
often employed to manage waste-related data are vulnerable
to modification and alteration by the planned or accidental
damages [34].
The traceability feature assures that the waste generated by
smart cities is handled in compliance with the waste handling
guidelines to protect the environment from pollution. It also
enables users to efficiently track the end of life of the smart
cities waste [35]. For instance, blockchain can be used to
identify the type of healthcare waste that is processed at a
waste recycling facility and is used in manufacturing medical
equipment and devices. The industries can employ blockchain
technology to identify which and from where leftovers and
food waste are shipped to a waste recycling plant to make
fertilizer. Based on such data, a new fertilizer production
line can be established near the waste source to reduce the
waste transportation cost. The tracking feature of blockchain
technology enables users to record the current location of
3
Fig. 1. An overview of the key opportunities offered by blockchain in terms of waste management in smart cities.
trucks shipping smart cities waste along with other data such
as shortest route and waste weight. Such data related to the
waste shipping location can be used to verify that the waste-
carrying truck has traveled through certain stations before
reaching the final destination. Waste is usually transported
from different locations and communities, the blockchain can
assist assuring using sensors attached to waste bags that
hazardous waste does not get mixed with nonhazardous waste
during its transportation for human safety assurance. Lastly,
due to transparency and immutability features, blockchain can
be used to track the amount of waste shipped, received, and
recycled at the recycling plant, credentials of the waste handler
and their actions, and storage location of waste when it is
segregated, sorted, and recycled or disposed of. 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. Figure 2 highlights a
blockchain-based system in which the smart city users store
and retrieve waste management-related data using deployed
smart contracts. The presented system allows citizens to view
the current location and route trajectory of their generated
waste.
B. Reliable Channelization of Waste
The life period and reliability of many electronic devices
are different, and it truly depends on electronic devices’
composition, working environment, temperature, and required
voltage supply level to operate it. After the expiry of such
electronic devices, they should be recycled or disposed of
responsibly at authorized E-waste recycling plants. For in-
stance, many smartphone devices contain expensive lithium
and cobalt materials that could be reused after smartphone
expiry to manufacture new products [30]. Therefore, reliably
channelizing the E-waste can lead to a pollution-free smart
city. The producers of the electronic devices (e.g., smart
TVs, refrigerators, and smartphones) are usually required to
monitor such electronic devices after their expiry [36, 37].
They can assure that E-waste of all sold electronic devices is
collected at the waste treatment centers. Through the lifetime
of each electronic device and total supply in the market,
blockchain technology can assist to assure that E-waste of all
sold-out electronic devices is collected at the waste treatment
centers. The producers can collect the E-waste using registered
retailers, designated collection centers, or authorized disman-
tlers/recyclers. Through reward and penalty smart contracts, it
can be assured that the retailers and collection centers should
ship the E-waste to the producer within a threshold period to
keep the city clean and safe.
Smart cities’ users can use blockchain to channelize their
domestic, medical, agricultural, and electronic waste, and in-
centives are issued to them on selling this waste. The auditable,
immutable, and transparent features of blockchain technology
can increase the trust of smart city users in monetizing their
waste to channelize it. Smart contracts can be developed and
deployed on blockchain to enforce customers to transfer an
escrow amount into a smart contract wallet on purchasing a
product. This escrow amount will be automatically released
to the wallet of the consumer on returning the waste of pur-
chased product after their usage [10, 38, 39]. Hence, through
blockchain-based data, it can be ensured that the waste of
all products has been collected successfully. Usually, citizens
are charged a flat service fee to ship their waste to sell it at a
retailer or waste treatment facility. A smart contract calculating
and automatically transferring cryptocurrency in a consumer’s
wallet based on the weight of the waste can motivate citizens
to produce less waste. Blockchain in such a scenario can be
used to settle payment-related issues, and it can identify the
waste-related frauds [40]. Also, in another case study related to
smart agriculture, the farmers can sell crop straws and animal
residue to a company generating electricity from the waste.
As a reward, users/farmers are provided with coupons against
the provided waste in compliance with the rules stated in a
smart contract [41, 42]. These coupons can be used to pay
their monthly electricity bills. Also, through smart contracts,
blockchain technology can automatically calculate the wages
to be paid to the participants involved in waste segregation.
C. Protection of Waste Management Documentation
Today’s centralized systems leveraged for managing waste
management within smart cities are less trustworthy as they
4
Fig. 2. An overview of waste-related data storing and retrieving using the blockchain-based system.
offer limited transparency features. As a result, it is diffi-
cult to verify that waste management practices adopted by
an industry such as healthcare are complying with rules
proposed by regularities for the safety of humans and the
environment. The waste management-related certificates and
documents state the rules, methods, and procedures to be
followed during the collection, transportation, segregation, and
recycling of waste. The key documents and certificates that are
maintained by the waste handling organizations during waste
management include waste disposal recycling form, waste
declaration form, dangerous goods shipping document (e.g.,
asbestos or flammable liquids), waste management inspection
plan document, and waste manifest form, to name a few [43–
45]. The certificates of an individual or organization such as
license documents are issued by the authorities to assure safe
and environmentally friendly waste management. All waste
management-related documents and forms are duly signed by
the authorized and relevant organizations before processing the
waste, and they can be used as proof to resolve the conflicts
among organizations. Since these documents and certificates
are managed manually or using centralized systems, hence
they are subject to any accidental loss, damage, manipulation,
and modification performed by hackers.
Blockchain technology can be used to minimize frauds
related to documents (e.g., scraps metal dealers licenses)
maintained during waste handling within a city. It employs
self-executing smart contracts and irreversible hash functions
to speed up the waste management process, protect the
documents from manipulation, and data inconsistency. The
documents related to waste management should be encrypted
and stored on InterPlanetary File System (IPFS) [46, 47] to
efficiently utilized blockchain storage capacity. The hashes
of such documents should be securely shared among the
participating organizations through a blockchain platform. Any
alteration to the waste management documents stored on the
IPFS can be identified using the stored on-chain IPFS hash
of the document. Hence, the participating organizations can
quickly verify the authenticity of documents related to waste
management and the licenses of the participants involved in the
waste management activities. The consensus protocols that are
proposed to commit the waste management transactions and
immutable data provenance make forging of license or waste
management documents forging theoretically impossible.
D. Efficient Waste Resources Management
The IoT-based systems enable remote monitoring and assist
in controlling smart cities through a network of deployed
sensors to collect real-time data and getting insights from such
5
Fig. 3. Blockchain-based framework for waste management services in smart cities.
data. Based on such data, plans and actions can be made to re-
duce congestion and traffic interruption, disease transmission,
carbon dioxide emission, and make the environment cleaner
and safer by timely collecting and processing smart cities
waste [48, 49]. Through the analysis of smart city data, the idle
resources in a city can be identified and optimally used. The
key resources used in waste management of the smart cities
include waste bins, transportation trucks, Waste management
workers, waste segregation or dumping location, waste-to-
energy facility, disposal sites, and residential waste places.
These resources are required to be efficiently handled to
minimize the waste management cost and improve well being
of citizens. The lack of transparency to the waste management
resources and activities in existing centralized-based systems
can lead to less trustworthy, inefficient, non-fault tolerant, and
insecure systems. Thus, the resource management decisions
on the basis of potentially untrusted and modifiable data can
be inefficient and costly.
Data immutability and fault tolerance features make
blockchain a favorite technology for authorities to efficiently
and quickly manage resources in smart cities. Blockchain
can register all the entities along with their role, and smart
cities resources using a registration smart contract. Authorities
can use the deployed audit smart contract to identify that
how many waste management resources are underutilized in a
particular area of a smart city since last month. Usually, RFID
sensors are attached to the waste management resources such
as smart bins to periodically monitor and store data about
their available storage capacity on the blockchain. Through
the analysis of blockchain-based waste management-related
data, it can be estimated that how frequently the waste bins
request the transporters to move the collected waste to the
waste treatment/disposal facility. Authorities can estimate the
volume of waste being transported from a particular area of
6
the smart city using analysis of such data. Based on this waste
data, authorities can shift the underutilized waste management
resources to the needed areas for efficient utilization of existing
resources. Also, the trusted waste data acts as a business
opportunity to establish the waste treatment plants near the
waste source. On identifying the type of waste in the collected
food waste, the food industry can be strengthened by opening
new restaurants in smart cities based on the food requirement
of the citizens. Figure 3 presents a blockchain-based system
that can be used to digitize the services of waste management
in smart cities. The presented system has shown a set of
services that can be implemented through smart contracts. For
instance, based on the location data and capacity of the waste
bins, the drivers can be notified about the shortest and fuel-
friendly path to collect the waste in a smart city. A system
presented in figure 4 highlights the interaction between waste
collectors and waste recycling centers. It assures that waste
collectors have received their funds on selling their collected
waste to the waste recycling center.
E. Penalties for Non-compliance
According to the waste management act 2016, the waste
generators within a community are responsible to segregate
and store the waste in appropriate bins, and handover it to
the waste handling workers to dispose of it at the regis-
tered waste treatment facilities. In the design of IoT-enabled
smart cities, all types of waste such as biodegradable and
non-biodegradable, domestic hazardous, and industrial wastes
should be stored in separate waste bins classified by different
colors. The volume of the waste generated by smart cities in-
dustries depends on their size, type of services, and production
level. Hence, based on the volume and type of waste generated
by industries in smart cities, they are required to be registered
under hazardous waste producers on producing more than 500
kilogram of hazardous waste in a year [36, 50]. Also, waste
treatment processes of the waste treatment plants should be
covered under certain environmental permits to protect the
environment from the effects of harmful carbon emissions.
Individuals, organizations, and industries are imposed heavy
fines or penalties such as license cancellation on any non-
compliance with the approved waste management practices.
The architectural decentralization, traceability through the
timestamped transactions, and use of consensus protocols
make blockchain a fault tolerance technology that drives the
authorities to use it for assurance of compliance of actions
with approved waste management rules. Further, it assists in
automating the imposing of fines and issuing penalties on
identifying any non-compliance with the approved rules in
a transparent and audit-able way. For instance, during the
pandemic caused by the COVID-19 outbreak, it was declared
by the World Health Organization (WHO) that the users in
COVID-19 hospitals or testing centers should carefully collect
and store COVID-19 related waste to minimize the virus from
spreading. Also, the bags carrying the COVID-19 related waste
should be sealed properly to assure that they are not exposed
by the handlers during their shipment. Blockchain, in this case,
can assist in monitoring the shipment and issue penalties to the
waste handlers on identifying any non-compliance with waste
transportation rules [34, 51]. It is desired that the COVID-
19 waste should be transported by licensed users. Blockchain
can assist the authorities to verify the license of a shipper
through the immutable record of transactions and data, and
issue heavy fines on identifying any non-compliance with the
rules. Minimizing the food waste in smart cities is another
challenge for the authorities to protect the citizens from disease
and infection. Blockchain can play a role in identifying and
issuing penalties to an individual/industry involved in food
waste. For this purpose, a smart contract can verify the type
of waste generated by a community, and it issues fines on
encountering a non-compliance with the food waste-related
rules. For instance, it can impose penalties on citizens on
identifying that the average food waste per day is above a
pre-defined threshold limit.
F. Transparency in Waste Collection and Trucks Route Opti-
mization
In smart cities, the IoT-enabled smart waste bins that are
capable of monitoring the waste state inside the bins and trans-
mitting real-time data to the central storage servers through
wireless links are deployed [52]. The sensors attached to the
smart bins can measure waste level, humidity, temperature,
weight, and type of waste inside the bins. Data collected by
such sensors about the waste can assist to predict the bins
fill level, identify potential diseases in a community based
on the type of collected waste, and forecast the volume of
waste that will be collected in near future based on the current
waste generation rate by a community. The waste collection
involves several stakeholders such as municipality workers,
waste shipment trucks, waste sources, and environment pro-
tecting agencies. Waste collection in smart cities is a daily
activity that involves truck route planning and optimization
while considering environmental and socioeconomic factors.
The routes planning for collecting smart cities waste is affected
by several parameters such as traffic jams, fuel costs, amount
of waste collected per route, and the number of trucks available
along with their capacity [39, 53, 54]. The route planning
on the basis of a centralized-based system can be ineffective
or costly since data can be compromised or tampered with.
Also, the existing systems offer limited transparency to the
waste management data, which can affect the truck’s route
optimizations.
Blockchain technology can assist in tracking the amount of
waste collected, the details about who collected it, the location
from where this waste is collected, and the current and final lo-
cation of the waste. Through the data stored on the blockchain
by the sensors, a route and schedule to pick up the waste can
be formulated to minimize the fuel consumption rate of the
trucks and maximize the amount of waste collection per route.
The high visibility and transparency to the waste collection
activities and sensor data can enable the authorities to assure
that the filled waste bins are picked up timely by legitimate
users. The smart contracts can trigger a notification to the truck
drivers on identifying that the storage capacity of the waste
bin has reached an unsafe threshold value. Also, other than
7
the sensors located inside the bins, external sensors attached
to the bins can continuously monitor their surroundings. Thus,
through such sensors and rotatable cameras attached to the
bins, any illegal dumping near the waste bin is identified and
recorded on the blockchain along with the identifier of the
individual who caused it. On encountering any such incident,
the smart contracts can notify the authorities about such users
for any legal actions. Further, an analysis of trusted healthcare
waste data and food waste collected through trucks can enable
authorities to identify common community diseases. Figure 5
discusses the activities of stakeholders involved in waste to
energy transformation processes. As highlighted in figure 5,
the farmers are rewarded with tokens for disposing of their
waste properly. Such tokens can be used to purchase food,
pay utility bills, and exchange them into cash money.
G. Robots-Assisted and Reliable Waste Segregation
Industrial and smart home waste such as paper and glass is
recyclable. Therefore, recycling of such materials can increase
their circular economy. The industrial and smart home waste
in smart cities can be classified as hazardous waste, liquid
waste, solid non-hazardous waste, and bio-degradable wastes.
Among all aforementioned waste types, liquid waste includes
wash water, organic liquid, waste detergents, and dirty water
[55, 56]. The segregation process aims at identifying the
recyclable materials from the waste to protect the ecosystem,
save energy, reduce carbon emissions, and conserve natural
resources. The older systems involved humans segregating
the waste in the hazardous environment that, as a result,
can affect their health. Modern waste management methods
have started practicing robots to segregate the waste, thus
minimizing the human interaction with hazardous waste [57–
59]. The automated robots-based waste segregation system
highly depends on image processing techniques for object
recognition and Artificial algorithms (AI) algorithms to ac-
curately classify the waste based on their type, color, or shape
[60]. However, the existing robots-based waste segregation
systems are less trustworthy because of the following of the
centralized architectures.
A swarm consists of a network of heterogeneous robots
that work together to perform the required task or actions.
In the waste segregation process, a swarm of robots can
automatically identify the recyclable materials from the waste
by communicating with each other and sharing their opinion
about the type of waste under consideration. Each robot is
AI-enabled, thus it is capable of interacting with others by
following a predefined set of rules. Blockchain technology
enables robots to securely communicate with each other in a
trusted way. Through this technology, swarm operations are
autonomous, flexible, and even profitable. The information
shared by the robots in a swarm is trustworthy for others since
the sender uses its digital signature to sign it. Also, through a
blockchain-assisted voting-based system [47, 61], the swarm
can decide about a particular item in the waste based on a set of
parameters such as shape, color, and texture. The rules defined
in the smart contracts can calculate the sum of the opinions of
the robots and declares the opinion of the majority as the final
decision. Blockchain can minimize the waste segregation time,
improves waste handling efficiency, and present an audit-able
way to issue incentives to the owners of the robots involved
in the waste segregation process.
H. Accountability of Waste Management Operations
The waste in smart cities produced by the hospitals, smart
industries, homes, and smart grid systems is often collected
and managed by private companies, community owners, or
designated representatives of the state. The waste manage-
ment strategies such as recycling, recovery, prevention, and
reuse involve diverse stakeholders effectively and sustainably
utilizing waste management-related resources such as waste
landfill [56, 62]. The involved stakeholders in the waste
management process identify waste material to be recycled
using their RFID tags [63]. The actions of the stakeholders
involved in managing waste in smart cities should comply
with the waste management laws to govern the storage, treat-
ment, shipment, recycling, and disposal of all types of waste.
The existing systems responsible to manage waste in smart
cities are inefficient in holding individuals or organizations
accountable for their services that have caused a delay or loss
of waste at any stage. Through blockchain technology, the
involved stakeholders such as producer, shipper, consumer,
and waste handler can be placed into a single network of
connected nodes, thus, making data and transactions visible
and transparent to the authorized parties.
There are many use case scenarios that require account-
ability of the user’s actions involved in waste management
to assure compliance with rules for a cleaner and safer city.
Through blockchain, the authorities can verify that the haz-
ardous industrial waste is unloaded at the designated recycling
location. It can further assist in verifying the lost waste by
comparing the volume of shipped and received waste at the
disposal center, establish provenance data about the household
waste, calculate and present the percentage of incinerated and
disposed of waste, and verify the recycling capability of a
plant and the actual waste recycled for plannings, based on
the analysis of the waste-related data stored on blockchain
[64]. Through transaction transparency and data traceability
features, it can identify the impossible fast transportation
and unnecessary fuel consumption during waste shipment. It
can also assist the authorities to trace the waste shipped to
illegal dumping sites to avoid waste landfill taxes. Finally, the
blockchain can identify that the industrial water in a particular
industry has been given Wastewater treatment or not [65].
Table I compares the existing blockchain-based solutions
related to waste management. The solutions mainly focus on
waste shipment tracking, waste-related fraud identification,
transparent waste sorting, and accountability of stakeholder’s
actions. They are based on highly proficient models to motivate
the citizens to channelize their waste by issuing rewards
and penalties. Also, some of the existing studies focus on
electronic, general, solid, agricultural, and industrial waste to
provide incentives to citizens to channelize their waste.
8
Fig. 4. Interaction between waste collectors and the waste recycling center using a blockchain-based smart contract.
Fig. 5. Highlighting the actions of stakeholders using a blockchain-based system to generate energy from the agricultural waste.
III. RESEARCH PROJECTS AND CASE ST UDI ES
This section presents insightful discussions on the recent
blockchain-based projects and case studies that mainly focus
on digitizing waste management operations within smart cities.
A. Recerreum
Recently, many countries have formulated legislation about
domestic waste management in urban areas. Many govern-
ments have proposed monetary incentives or punishments to
motivate citizens to channelize their domestic waste, thereby
increasing the waste recycling rate. The main barriers to
the success of existing centralized-based waste management
include waste-related information modification, technological
externalities, high search and transaction costs due to highly
disintegrated waste channelization centers, and consumer per-
ceptions about the waste management responsibilities. Recer-
reum (RCM) is an Ethereum based framework that gives mon-
etary benefits to the citizens as a reward to sort the domestic
waste at waste source [68]. It aims that the citizens should be
able to make money from every recycled bottle, battery, bottle,
or piece of electronic equipment in a transparent and effective
manner. The RCM coins can be deposited in the wallet of
the citizens on depositing waste at a designated center such
as bottles vending machine, stations collecting recyclables,
and waste collections centers. These coins can be used by
the citizens for making payments against their electricity bills
or any other services. The blockchain in RCM has many
applications such as smart contracts based verification of the
waste deposited, fast and automated payment settlement, and
9
TABLE I
COMPARISON OF THE EXISTING BLOCKCHAIN-BASED S OL UT IO NS P ROP OS ED F OR WAS TE M AN AGE ME NT I N SM ART C IT IE S.
Article Waste Type Objectives Services Rewards/Penalties
[10] Electronic Waste To efficiently manage electronic waste using an Ethereum blockchain
platform in 5G- enabled environment Asset Tracking Rewards
[38] Electronic Waste To investigate the role of blockchain for waste handling in compliance
with rules stated in waste management act
Waste Shipment Tracking,
Auditability Both
[64] General Waste To track and monitor the flow of waste across the borders in a way that
is transparent
Waste Shipment Tracking,
Auditability N/A
[66] General Waste To connect all participants and track the waste by assuring waste data
reporting on a single platform
Waste Tracking,
Auditability N/A
[34] Medical Waste To assure that medical waste is handled in compliance with safety rules
Waste Shipment Tracking,
Auditability,
Transparency
Penalties
[67] Solid Waste Employing a blockchain-based system for life cycle assessment of solid
materials
Waste Tracking,
Policy Implications N/A
[41] Agricultural Waste To transparently provide incentives to the farmers against agricultural
waste in waste-to-energy project
Waste to Energy,
Auditability Rewards
[40] Domestic Waste To efficiently manage and monitor smart garbage through a blockchain-
based system
Waste Frauds,
Smart Bins Monitoring Penalties
[42] Solid Waste To develop an Ethereum-based system to securely transfer tokens
to users as a reward for participating in waste management activities
Waste Sorting,
Transparency Rewards
[37] Electronic Waste To implement a blockchain-based system that can trace the assets
throughout their life cycle Smartphone Tracking Rewards
[45] General Waste To highlight the processes/participants involved in waste management
activities using a blockchain based system
Waste Documentation,
Waste Shipment Tracking N/A
[65] Industrial Waste To present a conceptual architecture of a system employing blockchain
technology for the industrial wastewater management
Water Waste Monitoring,
Automation N/A
supply chain operations [68–70]. The supply chain feature
enables users to verify and trace the waste submitted by them.
It can further assist in discovering the products manufactured
by the waste submitted by the citizens.
B. Swachcoin
Swachcoin has leveraged multiple cutting-edge technolo-
gies to effectively manage residuals and industrial waste for
converting it into useful products. Like Recerreum, it has
implemented Ethereum-based smart contracts to calculate and
transfer incentives to citizens for channelizing their waste.
The key modules of the Swachcoin system include Swachh
Adaptive Intelligence (SwATEL), Swachh Internet of Things
(SwIOT), Swachh Bins (SwBIN), Swachh Big Data (SwATA),
and Swachh Decentralised Application (SwAPP) [71, 72].
Among others, SwATEL is responsible for making the waste
management equipment intelligent to increase their operational
efficiency, thereby increasing the system productivity. The
SwBIN module is capable of automatically segregate the waste
based on its type, color, and dimension. The SwIOT enables
to remotely control and manage the waste bins. The SwATA
module is responsible for analyzing the waste management
data to optimize routes of trucks to minimize fuel consumption
rates. The SwAPP refers to an interface that offers unique
features to the users such as user wallet, token credit system,
truck location tracking, SwBIN waste level status, and unique
user identification. Swachcoin offers both token-based and flat-
based means to present incentives to the users for channelizing
their waste properly. The blockchain part of Swachcoin records
the transaction data on the public Ethereum platform. It
also stores other data such as machine logs and prescriptive
analytic reports on the blockchain for easy auditing and high
transparency [71, 73].
C. Plastic Bank
Plastic Bank is a multi-technology-based project run by
a Canada-based company. It has recently established several
waste collection centers in the Philippines, Haiti, and Indone-
sia. It aims to enable waste collectors to sell the collected waste
at a locally designated center at a competent rate [74, 75].
It offers incentives to the waste collectors as a reward for
cleaning the ocean based on the type and weight of the
waste collected. Subsequently, it sells the recycled waste to
the manufacturers to manufacture new products. The role of
blockchain technology in Plastic Bank is to register entities
and immutability record each recycling activity for making the
waste recycling process highly secure, trusted, auditable, and
transparent. The plastic bank has considered IBM’s blockchain
platform, known as Hyperledger Fabric, that is hosted on a
private network which is managed by the cognition foundry
[76–78]. Blockchain technology assists automate the transfer
of the cryptocurrency tokens to the wallet of the recyclers
following successful recycling. The payments to the recyclers
can be tracked, hence blockchain can eliminate the risk of
data loss or theft. It also allows exchanging cryptocurrency
tokens against the local currency. The registered organizations
on this network can use the earned cryptocurrency tokens to
pay tuition fees, get medical insurance, and pay basic utilities.
It has provided a smartphone-based application that is linked
to the blockchain-based wallet, and it assists the recyclers or
waste collectors in managing their cryptocurrencies [74–77].
D. RecycleGo and Empower
RecycleGO has collaborated with DeepDive technologies
group to bring about trust in the supply chain business of
recycling materials. It has employed a Hyperledger Fabric
platform to verify, track, trace, and report activities in recycling
10
supply chain businesses. It connects the participants such
as buyers, suppliers, shippers, recyclers, and other supply
chain actors to the recycling services using smart contracts
deployed on blockchain to increase the visibility for better
decision making. It can assist to track the plastic bottles
throughout their lifetime; from its manufacturing to collection
and conversion back to the raw material for manufacturing new
products. Apart from the supply chain operations, it also assists
the haulers of recyclables to follow the optimal route as they
are integrated with fleet management and route optimization
system. The key hauling services offered by RecyleGo include
routing efficiency, dispatch messaging service, containers’
location tracking, and instant pickup confirmation service [79–
81]. Empower is a Plastic Bank-type blockchain-based startup
that allows citizens to sell plastic waste in exchange for tokens
(1kg plastic waste = 1 EMP); the earned tokens are securely
awarded and can be exchanged against the money or used to
pay for waste clean up in other locations. Empower aims to
develop a global waste deposit and tracking System that should
allow the users to trace and track waste in a transparent way.
It aims to use the Zafeplace blockchain platform to trace and
track the end-of-life of the plastics [78, 82–84].
E. Troventum and Agora Tech Lab (ATL) Project
Troventum is a sustainable development digital project that
aims to interconnect every participant of the waste supply
chain through a trusted and decentralized platform. It facil-
itates the waste management participants such as producers,
procurers, recyclers, product manufacturers, shippers, and re-
tailers to perform their business activities in a secure, trusted,
and auditable way. Troventum consists of several modules and
has been implemented on the Ethereum blockchain platform.
The users are offered cryptocurrency tokens as a reward
for engaging in waste collection, sorting, and channelization.
Troventum OS module of Troventum refers to a suite of
software that offers bonuses to the people collecting and
selling the domestic waste. The Recycler OS module enables
waste recyclers to keep an immutable record of transactions
related to receiving and recycling various types of waste. The
Troventum. Coin module allows the product manufacturer to
buy raw materials generated from the recycled waste from
the suppliers/recyclers. Troventum. Trad streamlines the raw
material shipment process between the raw material suppliers
and product manufacturer [78, 85, 86]. Agora Tech Lab (ATL)
aims to leverage a customized blockchain platform to securely
transfer tokens as a reward to encourage the citizens to keep
the environment pollution-free by channelizing their waste.
ATL is a Rotterdam-based organization that integrates waste
management systems to the blockchain platform to immutably
store the waste management-related transactions on it. The
tokens received by the waste collectors can be used for
personal government services [78].
IV. OPE N RESEARCH CHALLENGES
In this section, we discuss several open research challenges
that hinder the successful adoption of blockchain technology
into smart cities for waste management.
A. Smart Contracts Security
The blockchain-based systems leveraged to manage waste
in smart cities employ smart contracts to execute events and
functions. Examples of such smart contracts include IoT-based
waste bins monitoring, real-time waste shipment tracking,
waste fraud detection, and stopping the illegal waste land-
fills. Solidity language is used to develop Ethereum smart
contracts for waste management in smart cities. Being just
another version of the software that runs on a distributed
and permissionless network, the Ethereum smart contracts
are prone to several security issues. Smart contracts are
immutably stored on the blockchain that presents various
pros and cons. For instance, smart contracts are safe against
any modification by hackers; but, they cannot be modified
by the developers to meet the new business requirements
after their deployment. The hackers attempt to manipulate the
execution of the smart contracts using loopholes present in
smart contracts to execute it in favor of their activities (e.g.,
stealing the virtual currencies) [65, 87, 88]. The common
vulnerabilities in smart contacts that are often exploited by
hackers include reentrance attack, integer overflow, denial
of service attacks, and remote code execution. Hence, it is
very important to rigorously test the smart contracts before
their deployment using highly proficient security analysis tools
such as Smartcheck, ReGuard, OYENTE, Mythril, Securify,
GASPER, to name a few [65, 87].
B. Storage
The business processes involved in waste monitoring, col-
lection, segregation, transportation, and disposal generate the
large amount of data. Such data could be in various forms
such as videos, images, or documents that assure the waste
management activities complies with local and global envi-
ronmental protection and human safety laws. The examples
of gathered data include the type of waste collected, real-
time location of the shipped waste, recycling/landfill sites,
and transportation route followed by waste transporting trucks
[64]. Such data comes from several hundred thousand sensors
deployed in smart cities to monitor the waste continuously,
and storing it on the blockchain. Every node in the blockchain
network stores a copy of this data, thus it leads to a shortage
of blockchain storage capacity. The performance of blockchain
technology is high when it stores and processes data of small-
scale businesses. However, the performance of blockchain is
severely affected by large-scale business applications. The
decentralized storage systems such as IPFS, Filecoin, and
Storj.Io store large-sized waste-related data in an efficient way
[87, 89]. The integration of blockchain with such systems
can overcome the limitations of blockchain technology. A
decentralized storage system (e.g., IPFS) generates an irre-
versible hash of the stored data. Such hashes can be immutably
recorded on the blockchain to assure that data stored on the
decentralized storage system has not been modified [47]. Also,
blockchain-based systems can limit the size of data stored on
blockchain by leveraging off-chain communication channels.
11
C. Scalability
The stakeholders involved in the waste management process
in smart cities require high quality of services (QoS) while
using blockchain-based platforms. Among many other met-
rics, transaction throughput, the latency of the transaction’s
execution, and transactions cost highly impact the QoS of a
blockchain platform. Considering the decentralized and self-
governing blockchain technology, it is difficult to improve such
parameters while ensuring high transaction execution trans-
parency, security, and privacy. Bitcoin platform’s throughput
is up to seven transactions per second. It has been reported in
various studies that the throughput of the Ethereum 1.0 plat-
form is 16 to 20 transactions per second; whereas, Ethereum
2.0 promises a throughput of 100,000 transactions per sec-
ond [34, 47, 90]. The existing solutions proposed to handle
blockchain scalability issues are mainly classified into two
layers. The layer 1 solutions concentrate on improving the on-
chain blockchain features such as consensus algorithm, block
size, and structure of the ledger. However, each solution has its
associated problems. For instance, the approach extending a
block size can maximize the system throughput; but, it extends
block propagation time. The extended blockchain propagation
time can cause multiple blockchain forks. On the other hand,
the layer 2 solutions have focused on shifting the complex
operations to off-chain, thereby minimizing the burden on on-
chain blockchain resources to improve its throughput [91].
Among many solutions, Bitcoin-cashing, block compressing,
lightweight and fast consensus algorithms, and sharding have
focused on maximizing the throughput of the blockchain-based
systems. Side-chain and cross-chain approaches are some
examples of the layer-2 solutions that can assist in maximizing
the throughput of the existing platforms [23, 34, 90, 91].
D. Platform Interoperability Support
Generally, the stakeholders (i.e., waste generators, collec-
tors, shippers, and recyclers) involved in the waste man-
agement of smart cities have competing interests among
themselves, and they belong to different organizations. Fur-
ther, such organizations could have deployed heterogeneous
blockchain platforms to perform their business activities. The
high coordination and communication among the participating
stakeholders require a smooth, timely, and fast execution
of transactions related to waste management. The interoper-
ability feature enables organizations that use heterogeneous
blockchain platforms to interact and share data among them-
selves uninterruptedly, seamlessly, securely, and efficiently
without any intervention by the end-users. Hence, despite
the diversity in the supported language, interfaces, consensus
protocols, and hashing algorithms, blockchain platforms im-
plement technical and semantic interoperability to allow the
participating stakeholders to perform cross-chain transactions
[47, 92]. For instance, atomic swaps allow trustful cryp-
tocurrency exchange by enabling the waste-handling players
to transfer certain tokens from the Bitcoin platform to the
Ethereum platform. Komodo’s BarterDex tool has used atomic
swaps to exchange cryptocurrencies in a decentralized network
[93]. The approach mentioned in PolkaDot has implemented
a designated blockchain platform that can work as a relay
node to provide blockchain interoperability support [92]. One
of the key requirements of the stakeholders involved in waste
management activities is the security and privacy of data and
transactions when interacting with another platform’s user.
Hence, future interoperability-supported blockchain platforms
should be highly secure, fast, and privacy-preserving to meet
the requirements of involved stakeholders.
E. Privacy and Anonymity
Guaranteeing data privacy and entity anonymity by the un-
derlying blockchain-based platforms are the key requirements
of stakeholders managing waste in smart cities. By design,
blockchain is a distributed database that manages the data
and transactions related to waste management in smart cities
into a hierarchical chain of blocks. The security of waste
management-related data and transactions is assured through
cryptography hash functions and decentralized consensus pro-
tocols. The key features of existing blockchain platforms pre-
serving the security and privacy of data include integrity, con-
fidentiality, and anonymity of users’ identity through digital
signatures, system, data, and transactions availability through
decentralization, and unlinkability of transactions to calculate
the true identity of a user [14, 34, 94]. Ethereum provides the
pseudonymous identity of the users as it presents a disguised
identity for the user to preserve data privacy. The blockchain
platforms leverage the hash of the user’s public key to enable
users to interact with the system. The use of such identifiers
hides the identities of the users. However, successful inference
attacks on the blockchain can create the linkage among a user’s
transactions to reveal the identities of users. More specifically,
the public blockchain platforms are vulnerable to inference
attacks as transactions, pseudonymous addresses, and other
user data are publicly available. Private blockchain platforms
run in a controlled environment, thus they are more secure
than public blockchain platforms. Private blockchain platforms
such as Hyperledger Fabric and Hyperledger Besu [22, 88] can
preserve the privacy of waste management data through private
channels and Orion private transactions manager, respectively.
F. Slow Adoption
The sensing and data transmission capabilities of IoT-based
sensors have enabled officials to closely monitor the waste
bins’ status. Such data is useful to optimize routes of trucks
shipping the waste to recycling centers. Blockchain technology
has shown a great role to bring trust, security, fairness,
operational transparency, and audit features to existing affairs
of waste management handling in smart cities. It can assist
the authorities to verify that the hazardous waste is properly
disinfected before it is disposed of at a recycling center to
minimize the chances of disease spreading[30, 38, 56]. The
disposed of material at the recycling center can be sold to the
manufacturers to manufacture new products. Thus, the increase
in the rate of waste recycling can effectively strengthen the
circular economy of waste material. Despite the many advan-
tages of blockchain technology and the availability of several
open-source projects for waste management as highlighted in
12
Section III, blockchain adoption into the waste management
industry is in its infancy. Several technological, institutional,
and organizational factors can influence the adoption of
blockchain in the waste management industry. The availability
of a specific blockchain tool that can fully digitize the services
of the waste management industry can influences its adoption
[7, 8]. Also, the infrastructural facility that details various
facilities such as waste transportation network, traffic control
and management, fine-grained and transparent incentives and
penalties models, and real-time waste monitoring are required
for the successful adoption of the blockchain platform into the
waste management industry. Currently, laws and regulations
for blockchain are not mature enough, thereby affecting its
adaptability in the waste management industry. Finally, orga-
nizational factors such as training facilities, top management
support, perceived cost of investment, and available human
resources greatly influence the adoption of blockchain into
waste management within smart cities [7, 51, 88].
V. CONCLUDING RE MA R KS A ND RECOMMENDATIONS
In this paper, we have discussed how blockchain technology
can be leveraged for managing waste within smart cities
in a manner that is decentralized, tamper-proof, transparent,
traceable and trackable, auditable, secure, and trustworthy. We
explored the key opportunities offered by blockchain tech-
nology for managing various activities and actions related to
the collection, shipment, segregation, disposal, and recycling
of the waste in smart cities. We presented a blockchain-
based framework for waste management to highlight system
components, participants along with their role definition, and
data flow among system components. We provided insightful
discussions on the recent blockchain-based research projects
and case studies to highlight the practicability of blockchain
in the waste management of smart cities. We identified and
discussed several challenges remaining to be addressed to
unlock the full potential of blockchain in terms of waste
management within smart cities. Our concluding remarks
along with key recommendations include:
•The transparency and immutability features of blockchain
can assist in tracing and tracking the amount and type of
waste collected in a community, the details about waste
collectors, the location from where it was collected, and
the current shipment location and final destination of the
collected waste.
•The fault tolerance and data tamper-proofing properties
enable blockchain to efficiently manage scarce waste
management resources, identify frauds related to illegal
waste disposal and landfilling, and issue penalties to an
individual/industry involved in hazardous waste spread-
ing.
•The parameters such as system throughput, transaction
execution latency, data volume, competing interests of the
concerned participants, bugs and vulnerabilities in smart
contracts, and available gas and size of the block can
significantly affect the performance of blockchain-based
solutions developed to manage waste.
•Segregating waste within smart cities through highly
autonomous robots can assist in minimizing human inter-
ference for health safety purposes. Blockchain technology
can enable such robots to make effective decisions based
on highly trusted, secure, transparent, and verifiable data.
•Employing a public blockchain platform for digitizing
waste management services in smart cities faces many
challenges related to preserving data and transaction pri-
vacy. Ensuring compliance with General data protection
regulation laws for data privacy can increase the adapt-
ability of public blockchain platforms in smart cities.
•In the future, we aim to propose and implement a
Hyperledger Fabric-based system that will calculate the
reputation of each registered waste recycling unit based
on its environmentally friendly waste disposal policies.
ACK NOWL ED G ME NT
This publication is based upon work supported by the
Khalifa University of Science and Technology under Awards
No. CIRA-2019-001 and RCII-2019-002, Center for Digital
Supply Chain and Operations Management.
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