Design of Indicators of Circular Economy as Instruments for the Evaluation of Sustainability and Efficiency in Wastewater from Pig Farming Industry

Nutrient recovery and valorisation from pig slurry liquid fraction with membrane technologies

Livestock slurry has been reported to be a potential secondary raw material as it contains macronutrients ‑nitrogen, phosphorus and potassium-, which could be valorised as high-quality fertilizers if proper separation and concentration of valuable compounds is performed. In this work, pig slurry liquid fraction was assessed for nutrient recovery and valorisation as fertilizer. Some indicators were used to evaluate the performance of proposed train of technologies within the framework of circular economy. As ammonium and potassium species are highly soluble at the whole pH range, a study based on phosphate speciation at pH from 4 to 8 was assessed to improve the macronutrients recovery from the slurry, resulting in two different treatment trains at acidic and alkaline conditions. The acidic treatment system based on centrifugation, microfiltration and forward osmosis was applied to obtain a nutrient-rich liquid organic fertilizer containing 1.3 % N, 1.3 % P₂O₅ and 1.5 % K₂O. The alkaline path of valorisation was composed by centrifugation and stripping by using membrane contactors to produce an organic solid fertilizer -7.7 % N, 8,0 % P₂O₅ and 2.3 % K₂O-, ammonium sulphate solution -1.4 % N- and irrigation water. In terms of circularity indicators, 45.8 % of the initial water content and <50 % of contained nutrients were recovered - 28.3 % N, 43.5 % P₂O₅ and 46.6 % K₂O - in the acidic treatment resulting in 68.68 g fertilizer per kg of treated slurry. 75.1 % of water was recovered as irrigation water and 80.6 % N, 99.9 % P₂O₅, 83.4 % K₂O was valorised in the alkaline treatment, as 219.60 g fertilizer per kg of treated slurry. Treatment paths at acidic and alkaline conditions yield promising results for nutrients recovery and valorisation as the obtained products (nutrient rich organic fertilizer, solid soil amendment and ammonium sulphate solution) fulfil the European Regulation for fertilizers to be potentially used in crop fields.

Toward a Socio-Political Approach to Promote the Development of Circular Agriculture: A Critical Review

Under the dual pressure of ensuring global food security and coping with the effects of climate change, many countries have proposed projects of circular agriculture to mitigate the vulnerability of agricultural systems. However, due to the different utilizations of agricultural resources in different countries, there are still some important limitations and obstacles to the promotion of agricultural recycling technologies. This review discusses global circular agriculture projects from a social science perspective. We found that (1) current research on circular agriculture is concentrated in the field of natural sciences with a focus on technological upgrading, neglecting social, political and economic research; (2) top-down circular agriculture projects rely on infrastructure and technical inputs for management, which undermines the focus on public participation and is limited by the timing and intensity of state intervention; (3) the development model led by enterprises or associations relies on cooperation and benefit games with farmers, and its sustainability depends largely on changes in the regulation of the agricultural waste utilization system. Based on this, this review argues that circular agriculture projects are not only technical issues in the field of natural sciences, but also strongly influenced by social development. For future research, we strongly recommend cross-disciplinary cooperation, not limited to technology development.

Advancements in laundry wastewater treatment for reuse: a review

Laundry related activities produce huge quantity of wastewater that is very rich in lint, dyes, surfactants, and detergents. The large amount of laundry wastewater (LWW) is generated by extensive human activities. LWW needs to be treated in order to tackle the challenging problem of water pollution and to accomplish water sustainability. To achieve this success, LWW can be reused for several purposes such as irrigation, construction activities, vehicle washing etc. However, there are several challenges in the reclamation of LWW like effective handling of the wastewater and meeting the regulatory criteria. Based on the literature review it seems that a single treatment process is not sufficient to treat LWW up to acceptable reuse standards. To that end, different treatment chains have been proposed: i) hybrid processes combining membrane filtration with adsorption; ii) advanced oxidation process using ultraviolet (UV) and hydrogen peroxide (H₂O₂); iii) coagulation-flocculation combined with sand filtration; iv) combination of ozonation process, adsorption, and ultrafiltration (UF). This review paper discusses the selection of suitable treatment technology depends on several factors: i) a well-designed equipment, ii) cost-effectiveness of treatment method and iii) desired characteristics of the treated water. The review paper also presents solutions for treatment and reclamation of LWW.

How Can Biodigesters Help Drive the Circular Economy? An Analysis Based on the SWOT Matrix and Case Studies

The use of biodigesters and the circular economy (CE) has been gaining attention in recent years. Both biodigesters and CE have the potential to minimize negative impacts—not only environmental, but also economic and social. However, little attention has been paid to the relationship between biodigesters and CE. Therefore, the objective of this paper is to identify and analyze the implications of the use of biodigesters in the light of a CE concept. To do this, a SWOT matrix was developed based on the opinion of experts and two case studies were conducted in companies operating in different sectors in Brazil. The results showed that the use of biodigesters can drive CE through biogas, which is a renewable energy source, closing the cycle of organic materials, increasing the economic power of companies and small producers, improving basic sanitation in remote areas, and stimulating industrial symbiosis. However, this study identified barriers in the use of biodigesters in the context of CE, such as lack of government incentives and composting being shown to be more cost-effective than the use of biodigesters for the treatment of solid waste.

A review of circularity and sustainability in anaerobic digestion processes

The debate on the relationship between the long-established concept of sustainability, and the relatively novel one of circularity in constantly increasing biogas production remains. In this study, additional discussion elements to such an open debate are provided. With its role in the bioeconomy and ongoing ambiguity, a bibliographic review of anaerobic digestion is provided. In particular, this study aims to i) verify whether sustainability assessments and circularity measurements are performed in different ways in anaerobic digestion projects and ii) understand which indicators have been utilized for each pillar of sustainability. Initially, 152 scientific documents from the Scopus and Web of Science scholarly journal databases were selected. Specific eligibility criteria that were any type of measurement of circularity and/or assessment of sustainability, were used for screening. Fifty-eight articles met these criteria and were analyzed in depth. The results show that the terms circularity and sustainability are not always univocal concepts in the reviewed scientific contributions. Consequently, the relative criteria or measurements for their analysis are not the same. As a result, a different interpretation of the two concepts is suggested. Circularity should be considered as one of the ways to achieve the broadest objective of sustainability.

Implications for Sustainability of the Joint Application of Bioeconomy and Circular Economy: A Worldwide Trend Study

The joint application of bioeconomy (BE) and circular economy (CE) promotes the sustainable use of natural resources, since by applying a systemic approach, it improves the efficiency of these resources and reduces the impact on the environment. Both strategies, which belong to the area of green economy, provide a global and integrated approach towards environmental sustainability, as regards the extraction of biological materials, the protection of biodiversity and even the primary function of food production in agriculture. The objective was to analyze the implications for sustainability of BE and CE joint application. A systematic and bibliometric review has been applied to a sample of 1961 articles, selected from the period 2004–May 2021. A quantitative and qualitative advance is observed in this field of study. The expansion of scientific production is due to its multidisciplinary nature, since it implies technical, environmental and economic knowledge. The main contribution of this study is to understand the state of research on the implications for sustainability that BE and CE have when combined, in relation to their evolution, the scientific collaboration between the main driving agents, and the identification of the main lines of research developed.

Urban Water Inclusive Sustainability: Evidence from 38 Cities in the Yangtze River Economic Belt in China

The ecological environment of urban water resources in the Yangtze River Economic Belt (YREB) is in a huge challenge; yet, while myriad studies have investigated the carrying capacity or sustainable utilization of Chinese water resources, few to none have looked at the inclusive sustainable development of water resources. In this article, a new concept of urban water inclusive sustainability (UWIS) is firstly proposed, and the conceptual framework of ASFII and a five-dimensional indicator system are developed, integrating availability, sustainability, friendliness, inclusiveness and innovation. The panel data of 38 cities in the YREB are adopted from 2008 to 2018 to measure UWIS and five development indexes by the TOPSIS (technique for order preference by similarity to ideal solution) and entropy method. Moreover, the characteristics of the temporal–spatial evolution of the overall system and subsystems coupling coordination are described using the coupling coordination degree model. Key factors that hinder UWIS are identified through the obstacle degree model. The results indicate that the overall UWIS showed a gradual upward trend at a lower to medium level from 2008 to 2018 and a friendliness > sustainability > inclusiveness > innovation > availability index. The UWIS from high to low is YRDUA (Yangtze River Delta urban agglomeration), MRYRUA (middle reaches of the Yangtze River urban agglomeration) and CCUA (Chengdu–Chongqing urban agglomeration). The 38 cities are in low-level coordination, and their temporal characteristics show a trend of economy > science and technology > water resources > environment > societal system, YRDUA > MRYRUA > CCUA. The spatial differentiation is manifested as high in the east and low in the west. The main obstacles come from 12 factors, such as the water resources utilization rate, etc. The findings of our study will be a scientific reference for the Chinese government to track UWIS and ensure urban water resources security in the YREB.

Correlations between the Composition of Liquid Fraction of Full-Scale Digestates and Process Conditions

Fast development of centralized agricultural biogas plants leads to high amounts of digestate production. The treatment and disposal of liquid fractions after on-site digestate solid–liquid separation remains problematic due to their high organic, nutrient and aromatic contents. This work aims to study the variability of the remaining compounds in the digestate liquid fractions in relation to substrate origin, process parameters and solid–liquid separation techniques. Twenty-nine digestates from full-scale codigestion biogas plants and one waste activated sludge (WAS) digestate were collected and characterized. This study highlighted the combined effect of the solid–liquid separation process and the anaerobic digestion feedstock on the characteristics of liquid fractions of digestates. Two major clusters were found: (1) liquid fractions from high efficiency separation process equipment (e.g., centrifuge and others with addition of coagulant, flocculent or polymer) and (2) liquid fractions from low efficiency separation processes (e.g., screw press, vibrating screen and rotary drum), in this latter case, the concentration of chemical oxygen demand (COD) was associated with the proportion of cow manure and energy crops at biogas plant input. Finally, SUVA254, an indicator for aromatic molecule content and the stabilization of organic matter, was associated with the hydraulic retention time (HRT).

From Circular Economy to Circular Ecology: A Review on the Solution of Environmental Problems through Circular Waste Management Approaches

(1) Background: The application of concepts linked to the circular economy (CE) has led to a sudden development of studies in numerous fields. However, the level of environmental sustainability of CE strategies could be improved and this topic deserves more attention by the scientific community. This research addresses this gap and aims at presenting a new concept, named circular ecology (CEL), and its application to the field of waste management. (2) Methods: The paper presents a literature review on the criticalities of CE and on examples of studies that implement the CEL principles. (3) Results: The review highlights that CEL principles are widely applied to several fields of waste management, showing promising opportunities to export the results to other geographical contexts. (4) Conclusions: If supported by governments, CEL approaches may allow solving multiple environmental problems at once, with clear economic, time, resources, and emission savings.

Water-Energy-Nutrients Synergies in the Agrifood Sector: A Circular Economy Framework

Circular economy is emerging as a regenerative concept that minimizes emissions, relies on renewable energy, and eliminates waste based on the design of closed-loop systems and the reuse of materials and resources. The implementation of circular economy practices in resource-consuming agricultural systems is essential for reducing the environmental ramifications of the currently linear systems. As the renewable segment of circular economy, bioeconomy facilitates the production of renewable biological resources (i.e., biomass) that transform into nutrients, bio-based products, and bioenergy. The use of recycled agro-industrial wastewater in agricultural activities (e.g., irrigation) can further foster the circularity of the bio-based systems. In this context, this paper aims to provide a literature review in the field of circular economy for the agrifood sector to enhance resource efficiency by: (i) minimizing the use of natural resources (e.g., water, energy), (ii) decreasing the use of chemical fertilizers, (iii) utilizing bio-based materials (e.g., agricultural/livestock residues), and (iv) reusing wastewater from agrifood operations. The final objective is to investigate any direct or indirect interactions within the water-energy-nutrients nexus. The derived framework of synergetic circular economy interventions in agriculture can act as a basis for developing circular bio-based business models and creating value-added agrifood products.

EVAS - a practical tool to assess the sustainability of small wastewater treatment systems in low and lower-middle-income countries

Small wastewater treatment systems (WWTSs) in low and lower-middle income countries still face challenges to achieve optimal performance and acceptable levels of sustainability. Thus, a practical tool, easy to apply by locals, to diagnose the actual status of WWTSs is required in order to identify weak areas for further improvement. This study presents a sustainability assessment tool, EVAS (EVAluación de Sostenibilidad: EVAluation of Sustainability), for small WWTSs in low and lower-middle income countries. The EVAS tool is developed based on a set of contextualized sustainability indicators and sub-indicators in five dimensions (technical, environmental, social, economic, institutional). Each indicator or sub-indicator is broken down into factors, each associated with specific targets to fulfil, and scored using a traffic light scale (0 to 4) indicating unsustainable-low-medium to high levels of sustainability. The tool was developed taking into consideration that local data may sometimes be incomplete and encourages the collection and monitoring of relevant data. The assessment results support local managers or other stakeholders responsible for wastewater management with the identification of weaknesses that need to be addressed. The tool was tested using two case studies involving WWTSs in Bolivia. One WWTS received a medium sustainability rating, whereas the other system received a low sustainability rating, which indicates that several improvements are required in all sustainability dimensions. Stakeholders in the case studies found the tool useful, and suggested ways in which it could be further improved. It is expected that the application of this tool can contribute to raising the sustainability level of small WWTSs in low and lower-middle-income countries.

A New Mindset for Circular Economy Strategies: Case Studies of Circularity in the Use of Water

In a circular economy (CE) environment, it is important to make good and efficient use of resources and consider that the waste generated in production processes can be a valuable resource. However, the tools and methodologies conventionally used to analyze and evaluate production systems are based on techniques focused on linear production management models, where the primary purpose is to reduce the treatment and management of waste as much as possible and where productive and environmental efficiency are not evaluated simultaneously. Changing the paradigm from a linear to a circular economy requires that a new strategy for production systems be defined, one that makes production processes simultaneously circular and efficient (in terms of quality and productivity). In this context, a holistic vision is needed when implementing CE strategies. Therefore, the main aim of this paper is to provide evidence, through two real case studies in the use of water, that the management of this resource without considering systemic thinking may not be the most circular solution. Main results showed that improvements based on the traditional approach of reducing resource use cannot provide the best results if they are supported only by current process consumption without considering the circularity of resources.

Community-Based Cooperatives: A New Business Model for the Development of Italian Inner Areas

Italian municipalities distant from main service supply hubs are defined by the Development Ministry as “inner areas”. A new business model, called community-based cooperatives, has recently developed in these areas. The name itself highlights the strong link between these firms and the local population. Their essential features are the pursuit of general interest and the creation of partnerships. This research explores the potential contribution of these enterprises to the growth of Italian inner areas. The data come from a direct survey, and the methodology includes text analysis techniques and correspondence analysis to create useful concept maps that define the paths that community-based cooperatives can take to regenerate their territories. The results highlight the critical issues of inner areas and the needs of their communities, together with the potential fields of business for the establishment of a community-based cooperative. In conclusion, these new firms may lead to real and enduring benefits to local communities. They could also contribute to demographic decline inversion by introducing new practices that reduce inequalities, enhance social, natural, and artificial capital, and boost the sustainable development process.

Moving bed biofilm reactor as an alternative wastewater treatment process for nutrient removal and recovery in the circular economy model

Over the last years, an increasing concern has emerged regarding the eco-friendly management of wastewater. Apart from the role of wastewater treatment plants (WWTPs) for wastewater and sewage sludge treatment, the increasing need of the recovery of the resources contained in wastewater, such as nutrients and water, should be highlighted. This would allow for transforming a wastewater treatment plant (WWTP) into a sustainable technological system. The objective of this review is to propose a moving bed biofilm reactor (MBBR) as a novel technology that contributes to the circularity of the wastewater treatment sector according to the principles of circular economy. In this regard, this paper aims to consider the MBBR process as the initial step for water reuse, and nutrient removal and recovery, within the circular economy model.

Industry 4.0 to Accelerate the Circular Economy: A Case Study of Electric Scooter Sharing

To achieve sustainability, the circular economy (CE) concept is challenging traditional linear enterprise models due to the need to manage geographically distributed product life cycle and value chains. Concurrently, Industry 4.0 is being used to bring productivity to higher levels by reducing waste and improving the efficiency of production processes via more precise real-time planning. There is significant potential to combine these two frameworks to enhance the sustainability of manufacturing sectors. This paper discusses the fundamental concepts of Industry 4.0 and explores the influential factors of Industry 4.0 that accelerate the sharing economy in the CE context via a case of electric scooters in Taiwan. The result shows Industry 4.0 can provide an enabling framework for the sharing economy in CE implementation.

Sustainability Indicators Concerning Waste Management for Implementation of the Circular Economy Model on the University of Lome (Togo) Campus

The circular economy aims to reduce the volume of waste generated in the world, transforming it into resources. The concept of indicator of circular economy was introduced to evaluate the improvement obtained regarding efficiency in terms of reduction, reuse and recycling of waste generated on the campus of the University of Lome (Togo). These indicators showed that 59.5% of the waste generated on the campus in 2018 could be introduced into the circular economy paradigm through composting, and 27.0% of the energy consumed could be replaced by clean energy obtained from biogas. The entire plastic fraction can be introduced into the circular economy paradigm by reusing plastic bottles and selling the rest in the port of the city. Thus, the income obtained could range from €15.5/day in 2018 to €34.5/day in 2027. Concerning old tires, 1.5% of the rubber needed to pave the entire roadway of the campus could be replaced by the waste generated by the tires currently existing there. Consequently, waste management on the campus could be controlled thanks to these indicators, and this could serve as a model for the rest of the country.

Setting the Common Ground: A Generic Framework for Material Flow Analysis of Complex Systems

Circular economy is currently characterized by various definitions, measurement approaches, and critical analyses thereof coexisting alongside each other. Whether the concept eventually prevails or collapses will depend to some extent on our success in harmonizing assessment methods among public, scientific, and private institutions, as well as across different materials and scales. Therefore, in this article, we present a generic material flow analysis framework that might serve as a common basis for circularity assessment, and test it by means of three case studies. It proved impossible to eliminate all subjective assumptions when transforming a real complex system into the generic framework, especially regarding the definition of by-products. However, by introducing subsystems it is at least possible to make such assumptions transparent. Therefore, adequate comparability across regions, materials, and scales is provided. Moreover, the generic system allows for coupled analysis of multiple materials simultaneously so that interactions between them can be studied, as well and a deeper insight into overall sustainability of the system can be gained.

Optimisation of bioscrubber systems to simultaneously remove methane and purify wastewater from intensive pig farms

The use of bioscrubber is attracting increasing attention for exhaust gas treatment in intensive pig farming. However, the challenge is to improve the methane (CH₄) removal efficiency as well as the possibility of pig house wastewater treatment. Three laboratory-scale bioscrubbers, each equipped with different recirculation water types, livestock wastewater (10-times-diluted pig house wastewater supernatant), a methanotroph growth medium (10-times-diluted), and tap water, were established to evaluate the performance of CH₄ removal and wastewater treatment. The results showed that enhanced CH₄ removal efficiency (25%) can be rapidly achieved with improved methanotrophic activity due to extra nutrient support from the wastewater. The majority of the CH₄ was removed in the middle to end part of the bioscrubbers, which indicated that CH₄ removal could be potentially optimised by extending the length of the reactor. Moreover, 52-86% of the ammonium (NH₄⁺-N), total organic carbon (TOC), and phosphate (PO₄^3--P) removal were simultaneously achieved with CH₄ removal in the present study. Based on these results, this study introduces a low-cost and simple-to-operate method to improve CH₄ removal and simultaneously treat pig farm wastewater in bioscrubbers.

Worldwide Research on Circular Economy and Environment: A Bibliometric Analysis

The relevance of circular economy to environmental science has led to a notable increase of research works during the last few years. It is very important to know the evolution of the publications that relate these two concepts, as well as the main areas of knowledge in which these investigations are framed. The purpose is to understand and highlight the state of art of circular economy and the role and relationship of the environment. Bibliometric analysis allows to evaluate developments in knowledge on a specific subject and assesses the scientific influence of researches and sources. This paper analyses the worldwide research dynamics on circular economy in the period from 2006 to 2017. A bibliometric analysis of 743 articles was completed. The most productive journals in this field were Journal of Cleaner Production. The five most productive countries were China, United Kingdom, Italy, the Netherlands, and Germany. Works on the circular economy and environment has considerable potential and it is open to research fields as sustainability or industrial production. The findings of this study could prove useful for studies into environmental circular economy, as they show a global sight of this line of study. Thus, the article represents a contribution to identify the main trends in circular economy research and environment and, from there, propose future research initiatives.

A Systematic Literature Review of Bio, Green and Circular Economy Trends in Publications in the Field of Economics and Business Management

The concepts of bioeconomy, green economy and circular economy share the common objective of developing a sustainable economy, and they attract enormous political, academic, social and business interest. However, an analysis of these concepts in the fields of economics and business management is lacking. The objective of this article is to classify the publications on these topics by subject of study, to analyse trends in publications and to guide researchers interested in selecting articles. The review was performed using Scopus for the period 1960 to 2017. Four hundred and forty-nine publications were obtained and classified into 17 categories. The results show that the existing literature is rich in analysing implemented policies and issues related to the strategies and organizational models of companies looking for a more sustainable path, and research in China and the European Union is highlighted. However, there is still a long way to go in researching implemented case studies and evaluating the economic impact of these concepts. For this to happen, the need to promote, encourage and support companies to implement cleaner production and approach a more sustainable path must be prioritised. Possible gaps in current research that allow future lines of work are also identified.

Prediction of Life Cycle Carbon Emissions of Sponge City Projects: A Case Study in Shanghai, China

In recent years, China has been vigorously carrying out the planning and implementation of Sponge City. Since the implementation of Sponge City projects involves substantial materials and energy consumption, it is significant to account corresponding carbon emissions and sinks. The existed studies about carbon emission of stormwater management measures, however, are not able to take the whole life cycle and different facilities into consideration. Therefore, this study develops a comprehensive accounting model based on Intergovernmental Panel on Climate Change (IPCC) guidelines and life cycle assessment (LCA) method to predict carbon emissions and carbon sinks of Sponge City projects more comprehensively and accurately. The model is applied to an actual residential community in Shanghai as a case study. Results show that the total indirect carbon emission is estimated to be 774,277 kg CO2 eq during a 30-year lifespan, among which carbon emissions from operation and maintenance phases are 2570 kg CO2 eq/year and 7309 kg CO2 eq/year, respectively, both directly proportional to the service life of the facilities. Three kinds of achievable carbon sinks are carbon sequestration in green space (5450 kg CO2 eq/year), carbon sink from rainwater utilization (15,379 kg CO2 eq/year) and carbon sink from runoff pollutant removal (19,552 kg CO2 eq/year). Carbon neutrality is expected to be reached after approximately 19 years. The established carbon emission accounting model can contribute to better planning and construction of Sponge City in China and enhance further energy conservation and carbon emission reduction.

Enterprise Architecture for a Facilitated Transformation from a Linear to a Circular Economy

The circular economy is central to the agenda of responsible production and consumption with propositions for the conservation of natural resources and a broader understanding of the obligations of enterprises and product developers. The circular economy is challenging traditional operating models of enterprises due to the need to manage larger parts of the product life cycle and value chains. A linear economy will normally address a smaller part of the life cycle. The operating models of companies are supported with respect to information and technology with an enterprise architecture model. This article examines the necessary steps for analysing and designing the enterprise architecture model, aiming to facilitate the transformation of an enterprise from operating in a linear to operating in a circular economy model. The fundamentals and requirements of the circular economy enterprise are extracted to isolate the design requirements for the operating model, entailing cross-enterprise collaboration, traceability, and a broader value chain understanding. Furthermore, it conceptualizes enterprise architecture and its role and importance in connecting business strategies and operating technologies. This article develops an enterprise architecture framework, named the Circular Economy Enterprise Architecture Framework (CEEAF), which can form and support the effort of transitioning companies or be embedded into existing enterprise architecture frameworks. The CEEAF differs from traditional enterprise architecture frameworks by addressing the broader responsibility of the enterprise, the extended enterprise, the elimination of end-of-life perspectives and mind-sets, and the capabilities of the individual enterprise and its design activities.

A Review of Waste Management Decision Support Tools and Their Ability to Assess Circular Biowaste Management Systems

The circular economy concept offers a number of solutions to increasing amounts of biowaste and resource scarcity by valorising biowaste. However, it is necessary to consistently address the environmental benefits and impacts of circular biowaste management systems (CBWMS). Various decision support tools (DST) for environmental assessment of waste management systems (WMS) exist. This study provides a review of life cycle assessment based WMS-DSTs. Twenty-five WMS-DSTs were identified and analysed through a shortlisting procedure. Eight tools were shortlisted for the assessment of their applicability to deliver sustainability assessment of CBWMS. It was found that six tools model key properties that are necessary for assessing the environmental sustainability of CBWMSs, including waste-specific modelling of gaseous emissions, biogas generation or bioproduct composition. However, only two tools consider both waste-specific heavy metals content in bioproducts and the associated implications when applied on soil. Most of the shortlisted tools are flexible to simulate new technologies involved in CBWMS. Nevertheless, only two tools allow importing directly new background data, which is important when modelling substitution of new bioproducts developed in emerging biowaste refineries.

Proposal of Sustainability Indicators for the Waste Management from the Paper Industry within the Circular Economy Model

The optimization of water management in industrial processes is paramount in diminishing or mitigating, as far as possible, the negative externalities generated by its current use within the linear economy model. This research presents methods for the optimization of wastewater from paper mills which are associated with the new sustainability and circular economy model. In this way, the concept of circular economy was applied to the wastewater treatment from a paper mill, with the objective of recovering the resources contained in this type of effluent. The wastewater treatment plant is based on a biological reactor of activated sludge, and treats a flow of 4868 m3·day−1. This study proposes the development and evaluation of indicators of circular economy applied to wastewater from a paper mill, as well as the assessment of the removal performance of color, total suspended solids (TSS), biochemical oxygen demand on the fifth day (BOD5), and chemical oxygen demand (COD), which are higher than 96% in all cases. Per 1 m3 of wastewater from a paper mill, a volume of 0.9 m3 of potentially reusable water and a recovered sludge mass of 0.7 kg are generated; the latter is reused as a mineral filler during the process itself. In light of this, a multivariable statistical analysis was applied to determine the relationship of the operation variables and indicators of circular economy. In this way, wastewater from the paper mill can be regarded as a technological nutrient, which is partially reintroduced into the production process, enabling the recovery of the water and mineral fillers that it contains.