Development of Strategies to Promote Circular Economy in the Management of Construction and Demolition Waste: A Case Study in Manaus, Brazil

Construction and Demolition Waste (CDW) cause environmental impacts in a worldwide scale. The existing international concern regarding the adequate management of CDW is justied by the large amount of this waste produced in a daily basis, together with its potential hazardous effects on ecosystems and human health. In countries with growing economies, like Brazil, it is of the utmost importance to promote sustainability-oriented practices that can co-exist with economic development. In this scope, the present research proposes strategies regarding the management of CDW based on the Circular Economy principles, focusing the case study of the municipality of Manaus, in the centre of the Amazon Forest. The characterization of the reference situation regarding CDW management in Manaus revealed several deciencies, namely the lack of reuse and recycling opportunities, the unsupervised disposal of CDW in illegal landlls, together with insucient surveillance procedures and inadequate policies from regional authorities like the Manaus City Hall and the Amazon’s Regional Council of Engineering and Agronomy (CREA-AM). The acknowledgement of these problems led to the identication of improvement opportunities and to the development and operationalization of Circular Economy promotion strategies: valorisation of CDW through the enhancement of reuse and recycling opportunities, operationalized through a mobile phone application; inclusion of sensibilization and surveillance practices regarding professional activities related to CDW management on the CREA-AM inspection plan; and the proposal of alterations in the municipal policies regarding CDW disposal in the public landll. These strategies have been implemented in the Manaus municipality, but are easily adaptable to other Brazilian municipalities and even to other countries’ realities.


Introduction
Inadequate management of construction and demolition waste (CDW) is a worldwide environmental problem that has been increasing over the years due to the growth of the construction industry in developed and developing countries. It is widely recognized that the generation of CDW is a consequence of economic and social development, since these wastes are a subproduct of urban lifestyle (Mesjasz- The amount of CDW generated and the correspondent management practices differ from country to country, depending on the existing policies, regulations, and waste disposal infrastructures (Blaisi 2019; As waste material produced in the process of construction, renovation or demolition of structures, CDW mainly consists of concrete, bricks, asphalt, excavated soil, metals, wood, ceramics, plastics, glass and cardboard (Yeheyis et  Hazardous substances may be found in CDW, like oil, paints, solvents and wood preservatives, as well as toxic materials resulting from demolition works, like for example asbestos and polychlorinated biphenyls (PCB) (Esa et al. 2017). Therefore, the inadequate handling and disposal of CDW can cause several negative environmental impacts, such as soil and water contamination, proliferation of plagues and diseases' transmission vectors (like insects and rats), landscape degradation, and obstruction of rivers and other drainage channels (Yeheyis et  The focus of the present study is the municipality of Manaus (Amazonas-Brazil), located in the centre of the Amazon Forest, with more than 2 million inhabitants and a rising construction industry. Clandestine illegal land lls are common in the outskirts of Manaus, and are considered a low-cost solution for the disposal of CDW as an alternative to the disposal in the city's o cial land ll complex. These clandestine land lls lack environmental professionals to supervise the mitigation of the negative environmental impacts caused, and in addition, no inspection from competent government sectors occurs in these sites. Therefore, the current situation regarding CDW management and disposal in Manaus is harmful for the environment, negatively affects the ecosystem of the Amazon region, and has direct negative impacts on public health.
In this context, the present research aims to develop and operationalize new strategies to improve the management of CDW in the municipality of Manaus, involving different stakeholders in the public and private sectors. To achieve the research goal, literature has been reviewed in order to understand the state of the art regarding circular economy principles applied to the management of CDW. A detailed analysis of the current practices for CDW management in the municipality of Manaus has been performed, enabling the identi cation of improvement opportunities. New strategies have been de ned and operationalized to reduce the environmental burden caused by CDW, bene ting the residents of Manaus and contributing to the preservation of the Amazon.

Literature Review Circular Economy
The concept of Circular Economy (CE), introduced by Boulding (1966) and complemented by Pearce and Turner (1990), defends the need for the establishment of closed-loop resource systems (Boulding 1966;Pearce and Turner 1990). Counteracting on traditional linear production and consumption practices, CE defends industrial models that are restorative by design, where materials are recovered and reused instead of being discarded as waste (Smol et al. 2017;Fiksel et al. 2020).
CE is based on the following principles (Adams et al. 2017;Smol et al. 2017): -To preserve natural resources by increasing materials' productivity.
-To increase or maintain the value of materials and to circulate them at the highest utility, thus eliminating (or at least minimising) waste.
-To re-design production systems to enhance closed-loop processes regarding material and energy ows.
Pursuing these goals, CE models are supported by concepts like Industrial Ecology, reverse logistics, cradle-to-cradle design, eco-e ciency, and the 3R hierarchy for waste management -reduce, reuse, recycle (Fiksel et al. 2020;Ogunmakinde et al. 2021).
Considering that there is a relevant number of waste streams that are presently underutilized (Fiksel et al. 2020), the promotion of CE-based business models could result in considerable economic and environmental bene ts: conservation of natural resources, economic valorisation of waste, opportunities for new economic activities with job creation, reduction in energy consumption and consequentially in greenhouse gas emissions, besides the avoidance of costs and environmental burdens associated with waste treatment (Smol et al. 2017;Ogunmakinde et al. 2021). Also, by reducing dependence on scarce resources and long-distance supply chains, CE enhances business and community resilience (Fiksel et al. 2020).
Many countries have introduced CE principles in their policies and legislations -e.g. China, Japan, United Kingdom and all the countries belonging to the European Union (Smol et al. 2017). However, the implementation of CE in different industrial sectors has followed diverse approaches, and the lack of common strategies and instruments has limited the desired widespread of CE (Singh et al. 2021).
Modern technological tools have a fundamental role in the support of CE strategies: digital networks and intelligent robotics are frequently used in waste management processes, like for example sensor-based infrastructures for waste collection, digital image analysis and robotics for waste separation, geographic information systems and global positioning system to assist waste disposal, and data sharing technologies to support product lifecycle analysis (Paz et  With signi cant impacts on the consumption of raw materials and on waste production, CE is crucial for the promotion of Sustainable Development strategies (Lin 2020). In fact, CE enables economic growth without increasing resources' consumption, and is a concept that implies the redesign of industrial systems, and deep transformations on production chains and consumption habits. Thus, CE strategies are clearly aligned with the United Nations Sustainable Development Goals (United Nations 2015), specially with Goal 8 -Promote sustained, inclusive and sustainable economic growth, full and productive employment and decent work for all , Goal 9 -Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation and Goal 12 -Ensure sustainable consumption and production patterns.
Circular Economy applied to CDW management An industry with high material intensity like construction can achieve considerable economic and environmental bene ts by increasing material e ciency through the adoption of CE strategies. In what concerns CDW management, CE relies upon the 3Rs principles: promote waste reduction opportunities, and enhance reuse and recycle to close material loops.
CDW reduction is the waste management option having the least negative environmental impacts, therefore it should be the highest priority in waste management plans. CDW reduction is highly dependent on strategies developed in the design stage to enhance resource e ciency. For example, the use of Reuse of CDW consists in using building materials more than once, either in their original function or considering a different purpose. This implies effective CDW collection and sorting practices, which may be di cult to operationalize due to lack of knowledge and technical equipment regarding waste sorting at the source, and lack of space to store separated waste. Also, the lack of formal criteria to assure the quality of reused building materials affects consumers' quality perceptions, and are therefore major drawbacks for CDW reusing practices (Huang et  Several authors have studied best practices and improvement opportunities regarding CDW management strategies in the different phases of the construction and demolition process. Table 1 presents a summary of the main results obtained from these studies. Nevertheless, the results of the implementation of these strategies are beyond expectations, mainly due to the inadequate understanding of the following key factors: regulatory framework (obligation), stakeholders' attitudes (who), CDW life-cycle design (when) and CDW management tools (how) (Kabirifar et al. 2020 -To adequately plan on-site waste management: identify all potential waste and de ne speci c actions for every type of waste produced, including re-use and recycling opportunities; -To assure the existence of all the required technical equipment for effective waste management; -To train and educate the construction workforce regarding effective ways to minimize waste generation; -To adequately plan supply chain management in order to control material stocks. Ajayi and Oyedele (2017) defend that adequate legislation and scal policies are crucial for CDW minimisation, namely the inclusion of tax bene ts and incentives to good performers, and the requirement to use proven waste e cient design, procurement and construction methods. These authors also highlight the importance of the following enablers and facilitators to corroborate policy requirements -adequate information regarding the quality, availability and bene ts of secondary materials; and adequate markets to provide access to recycled materials (Ajayi and Oyedele 2017). In what concerns CDW, Brazilian legislation stipulates that the responsibility for its adequate disposal belongs to the waste producers. In the municipality of Manaus, the only available legal solution for CDW disposal is the municipal land ll. However, high deposition costs are applied, and therefore construction companies tend to outsource the transport and disposal of their CDW to private companies operating in The inadequate disposal of CDW in unprepared places currently occurring in Manaus has substantial negative impacts, described in Table 2. corresponding to over 90 000 m 2 of constructed area. Wood, paper/cardboard and debris (concrete, bricks and ceramics) represent the majority of the CDW produced in the construction works under analysis. These construction companies refer very high costs with CDW management -only metal waste is sold for recycling purposes, and the transport and disposal of other produced waste is outsourced to private companies. Wood and paper/cardboard waste, produced in high quantities in these industries and having high reuse and recycling potential, are not being valorised due to the lack of an organized system for waste commercialization (Oliveira et al. 2019a).
The role of regional administration authorities in the CDW management process in Manaus has also been studied through the analysis of the actions promoted and the results obtained by the Regional Council of Engineering and Agronomy of the state of Amazonas (CREA-AM) (Oliveira et al. 2021b). This regional administration body is responsible for the supervision of technical professions to prevent inadequate practices and has, since 2017, an Inspection and Surveillance Plan for the Civil Engineering Chamber focusing professionals and companies in the construction industry area. The analysis of the records of inadequate practices regarding the construction industry and CDW management companies during 2017 and 2018 led to the conclusion that the major irregularities detected were related with the lack of adequate company's licencing procedures and with the development of activities without the supervision of technicians duly registered in CREA-AM. In what concerns the records existing in CREA-AM regarding the activities of environmental professionals in CDW management, a signi cant decrease was veri ed from 2017 to 2018 (Fig. 2). These results demonstrate that construction activities in Manaus are being performed without the adequate support of skilled professionals to mitigate the negative environmental impacts associated with CDW, highlighting the need to increase educational and surveillance actions directed both to technicians and construction industries (Oliveira et al. 2021b).

Identi cation and operationalization of improvement strategies
The analysis of the current practices of CDW management in Manaus described in the previous section highlights the following existing problems: There are very little reuse and recycling opportunities regarding CDW; Construction industries are not hiring environmental technicians to support the management of the produced CDW; Construction industries and CDW management companies are using illegal land lls to dispose waste; Most companies operating in the CDW management, transport and disposal areas do not have the required technical skills to prevent environmental burdens; The public land ll does not have the necessary infrastructures to promote the reuse and recycling of CDW; The surveillance of regional administration bodies is not effective in the prevention of inadequate practices from construction industries and CDW management companies.
In Under this premise, the operationalization of an organized market for CDW reuse and recycling in Manaus was enhanced through the development of a mobile app (Oliveira et al. 2019b). Focusing the disclosure of reuse and recycling opportunities for the most common CDW produced in Manaus, this tool can be used by construction professionals and even common citizens who need to dispose construction waste from private construction works (Fig. 4). Waste disposal companies can also be an important user of this mobile app tool, since it can be used to advertise their services regarding the different disposal options.
Since it is aimed to promote good practices in CDW management, the mobile app includes the possibility of tracking and inspecting the disposal of CDW by citizens, companies and public sectors responsible for inspection in the environmental area. Therefore, only companies dully registered and legalized can access the mobile app for advertisement purposes, and all information regarding the destination of the waste transacted through the mobile app must be communicated.
The adequate use of this mobile app tool requires its potential users to have high awareness levels regarding CDW management options, including the environmental and social impacts of inadequate practices. This can be achieved through education and training programs. A few pilot tests have already been performed, and the interest and acceptability levels associated with the mobile app tool were very high among construction professionals and common citizens (Oliveira et al. 2019b).
Revision of the policies regarding the public land ll of Manaus The presently occurring overload of the capacity of Manaus' public land ll is unsustainable, and measures should be promoted to effectively reduce the amount of waste disposed in this land ll, specially focusing waste with reuse and recycling potential.
On the other hand, the promotion of CDW disposal in the public land ll is important to assure that all necessary precautions are being taken regarding the prevention of environmental hazards -which do not occur when CDW disposal is performed in illegal dumps. The promotion of the public land ll as a legal and safe disposal option for CDW could be made through the de nition of adequate disposal fees. The de nition of the fees applied to CDW disposal in the public land ll must consider the balance between low-cost options, which would be ine cient in the promotion of reduction opportunities, and high-cost options that would enhance the use of illegal dumps (Huang et al. 2018;Cristiano et al. 2021).
In this context, the following measures have been proposed to the Manaus City Hall, the entity responsible for the management of the public land ll: 1. to install equipment for adequately sorting the CDW received in the public land ll, therefore enabling materials reuse and recycling; 2. to install equipment for crushing CDW, reducing its volume and promoting its safe and costly transport to recycling facilities; 3. to promote the donation, sale or exchange of the material with reuse and recycling potential using the mobile app tool developed on the scope of the present study; and 4. to implement tax favouring policies for companies that promote reduce, reuse and recycling practices regarding CDW. In this scope, alterations were proposed to the existing Inspection and Surveillance Plan for the Civil Engineering Chamber of CREA-AM, and are expected to be operationalized in the biennium 2021-2022.

Improvement of surveillance practices
The alterations proposed aim to intensify the surveillance on CDW management, transport, disposal and treatment practices, speci cally focusing: the registration and GPS tracking of all CDW collection boxes that are stored in construction sites; the veri cation of compliance regarding the existence of legal permits / legal registration for all companies operating with CDW management, transport and disposal; the surveillance of clandestine land lls used to dispose CDW; and the supervision of technical activity registration processes to ensure that the necessary technical environmental support is being provided.
It must be highlighted that CREA-AM surveillance activities should be complemented with environmental education actions to promote adequate waste management procedures in construction sites, enhancing the existing options regarding construction waste materials reuse and recycling.

Conclusion
The analysis of the current practices of CDW production, management and disposal in the municipality of Manaus revealed several de ciencies that are affecting the Amazonian ecosystem and the health of the population: due to the lack of recycling and reuse opportunities for CDW, these wastes are being disposed in illegal and clandestine land lls, and the surveillance of local administration bodies is not enough to assure the minimization of the corresponding negative environmental impacts.
The acknowledgement of these problems and the understanding of their causes led to the identi cation of important improvement opportunities, considering the Circular Economy principles applied to the construction industry analysed in the literature review. The following strategic measures were identi ed and operationalized: i. Promotion of CDW reuse and recycling practices, operationalized through the elaboration of a mobile phone application promoting good practices for exchanging, donating, selling and disposing of CDW; ii. Promotion of awareness, education and training sessions for technical professionals and construction industries regarding adequate CDW management practices to prevent environmental impacts; iii. Improvement of the role of local administration bodies regarding the prevention of inadequate practices among technical professionals and companies operating in the construction area, operationalized through the updating of the CREA-AM Inspection and Surveillance Plan, to enhance the adequate environmental surveillance of land lls used for CDW disposal, including GPS tracking of CDW collection boxes; and iv. Adaptation of the regional public policies to promote the adequate management of CDW, proposed to the Manaus City Hall in the scope of the management of the Manaus Land ll Complex.
The operationalization of the strategies developed within this research are expected to result in the reduction of the amount of CDW produced -due to the reuse and recycling opportunities identi ed and operationalized -and in the promotion of adequate CDW disposal practices -due to the improvement of policies and surveillance practices from regional authorities. These are the main contributions of the present research, which are expected to lead to an important reduction of the negative environmental impacts caused by the inadequate disposal of CDW presently occurring in Manaus.
The new CDW management strategies developed within the scope of this research were based on the case study of the municipality of Manaus, but are extendable to any other municipality in Brazil or in other developing countries. Thus, it is hoped to contribute to foster the principles of the Circular Economy in Brazil, which are currently taking their rst steps, but are essential for the promotion of Sustainability that brings co-existence between economic, social and environmental growth.

Declarations Funding
No funding was received for conducting this study.

Con icts of interest/Competing interests
The authors have no con icts of interest to declare that are relevant to the content of this article.
Availability of data and material (data transparency) Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

Authors' contributions
All authors contributed to the study conception and design. Material preparation, data collection and

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