Life Cycle Thinking for a Circular Bioeconomy: Current Development, Challenges, and Future Perspectives

Abstract

The circular bioeconomy (CBE) is an increasingly popular method used to add value to bio-based products. However, these products entail impacts on sustainability that can be assessed by life cycle thinking (LCT). Therefore, this manuscript aims to describe the current development of using LCT for a CBE and to identify challenges and future perspectives with regard to this topic. A systematic literature review was conducted using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA), analyzing a final portfolio of 57 documents. The results indicated that the use of LCT for a CBE is very recent and has been increasing over the years, is concentrated in Europe, and mainly assesses the conversion of biowastes in biofuels through biorefinery processes, considering mostly environmental concerns, by applying life cycle assessment; thus neglecting economic and social issues. The use of system boundaries, software, databases, and impact assessment methods was reviewed. Five challenges were revealed (the expansion of system boundaries, the consideration of more endpoints, the development and use of regional databases, the development of policies to encourage CBE, and the addition of economic and social issues. Future perspectives will be aimed at considering microalgae, wastewater, and animal biomass in CBE processes, developing more value-added bioproducts and biofuels, and adding cost assessment and more circularity to CBE processes.

1. Introduction

Accelerated global population growth has increased the demand for products and energy, generating a scarcity of non-renewable natural resources [1]. In that sense, the bioeconomy is one of the most popular solutions to replace non-renewable resources with renewable natural ones [2] for producing bio-based products and bioenergy. The bioeconomy attracts the attention of academics and policymakers [3] because it is claimed to lead the transition toward a sustainable economy [4], significantly influencing all of the dimensions of sustainability (environmental, economic and social) [2].

The transition from a linear to a circular economy stimulates the inclusion of bio-based products in the so-called circular bioeconomy (CBE). The CBE is an increasingly popular method used to create high added value products from bioresources [5] using conversion biotechnologies [1]. Although CBE has inherent sustainability at its core, CBE should reduce the environmental and social pressures along the life cycle of bio-based products [6].

Thus, life cycle thinking (LCT) is an approach to assess the impacts of products throughout their life cycles by using different tools, namely: (environmental) life cycle assessment (LCA), life cycle costing (LCC), social life cycle assessment (SLCA) and life cycle sustainability assessment (LCSA), which is a combination of the three and aims to assess the impacts of all of the three dimensions of sustainability [7].

Recent studies reviewed the use of LCT tools in the bioeconomy of some specific sectors, such as forest-based products [8], biorefinery systems [9], and specific processes, e.g., anaerobic digestion (AD) [10]. Other studies have focused on the analysis of LCA for a circular economy [11,12], particularly by converting biowastes (food wastes) into bioenergy [11,13]; however, they do not use the term CBE.

A recent review [14] reported the use of LCA to inform the development of a CBE. This study focused on the challenges of LCA to be implemented on CBE, arguing that a critical challenge for the bioeconomy is to improve the efficiency of conversion processes maintaining the compatibility across several sustainability indicators, and public acceptance [15], confirming the importance of the inclusion of social sustainability into the bioeconomy and, thus, the assessment of all the dimensions of sustainability in CBE activities.

An issue still neglected in the literature is the analysis of whether CBE is really contributing to the sustainability of the bioeconomy, representing a research gap that should be fulfilled. This issue is deemed important because sustainability is the biggest challenge for a bioeconomy and also for a CBE [16] due to the increasing demands of food and energy, which generates higher prices for these products [1]. In this sense, CBE must consider techniques for better life cycle management, with a special focus on the end-of-life of bio-based products and the consideration of stakeholders [16]. Considering this context, it is important to address whether CBE is contributing to the sustainability of a bioeconomy.

Despite the vast literature about LCT in a bioeconomy and a circular economy, to the best of our knowledge, there is not any study that systematically reviewed the literature about LCT for a CBE, analyzing the current developments on LCT tools in all of the three sustainability dimensions (environmental, economic and social), or the main challenges and future perspectives of this topic in order to analyze the contribution of CBE to the sustainability of a bioeconomy.

Therefore, the purpose of this manuscript is to describe the current development of the use of LCT for a CBE, and to identify challenges and future perspectives on this topic, by analyzing the literature about LCT and its tools (LCA, LCC, SLCA and LCSA) for a CBE. The novelty of this manuscript is focused on it being the first study to describe the state-of-the-art of a recent and rising method, i.e., CBE, in combination with the most popular approach to assess sustainability, i.e., LCT, aiming to offer research drivers and policy implications to develop a sustainable CBE and bioeconomy. Furthermore, this review gathers the main literature on LCT for a CBE to be aware of what is deemed important on this theme, providing an analysis of the main methodological and strategic challenges to trace these tactics in order to surpass them.

The next sections of the article are structured as follows: the Section 2 describes the methods used for the systematic literature review, the Section 3 involves the analysis of the current development of LCT for a CBE, the Section 4 lists and discusses the main challenges to apply LCT for a CBE, the Section 5 considers the future perspectives on this topic, the Section 6 presents the implications for stakeholders; and, finally, the Section 7 includes the conclusions reached and the final remarks of this review.

2. Materials and Methods

The systematic literature review was conducted in four steps considering the PRISMA 2020 [17], but in its variation for systematic environmental reviews and maps, it followed ROSES [18]. During each search step, the ROSES checklist was followed to enhance the quality of the final portfolio. These steps were: (1) database selection and search strategy, (2) document screening and inclusion criteria, (3) a systematic review of the final portfolio, and (4) data synthesis and presentation.

2.1. Database Selection and Search Strategy

The searches were conducted in three databases (Scopus, Web of Science, and Science Direct). The choice of the databases is justified because they present the most high-impact sources in the sustainability theme [19]. Moreover, recent related reviews used these three databases for document collection [20,21].

Table 1. Search protocol and document collection details.

Feature	Description
Search string	(“Circular bioeconomy” OR “Circular bio-economy”) AND (“Life cycle thinking” OR “Life cycle perspective” OR “Life cycle approach” OR “Life cycle management” OR “Life cycle engineering” OR “Life cycle sustainability assessment” OR “Life cycle sustainability analysis” OR “LCSA” OR “Life cycle assessment” OR “Life cycle analysis” OR “LCA” OR “Life cycle cost*” OR “LCC” OR “Social LCA” OR “SLCA” OR “S-LCA”)
Databases	Scopus, Web-of-Science, ScienceDirect 1
Search options	Topic or title, abstract and keywords
Search date	1 January 2023
Temporal range	Up to 2022
Inclusion filters	Articles or reviews from peer-reviewed journals in English

¹ Due to the limitation of eight keywords per search on ScienceDirect, three searches were conducted in this database, and results were combined in a single Mendeley file, excluding duplicates and grey literature. The keyword “Life cycle cost*” was replaced by the string “Life cycle costing” OR “Life cycle cost”.

shows the search protocol, specifying the search string used, the temporal range, the search date, and inclusion filters.

2.2. Document Screening and Inclusion Criteria

Mendeley desktop v.1.19.8 software was used for a better management of the documents collected from the searches. Hence, in a first instance, duplicates were removed using Mendeley features and, in a second instance, a fast reading of documents’ titles were conducted to check for duplicates.

The screening strategy was to read the remaining documents’ titles, abstracts, and keywords. The articles not aligned with this manuscript’s theme were then excluded considering the following inclusion criteria: (1) only documents whose object of study is LCT (LCA, LCC, SLCA, or LCSA) and (2) documents focusing on CBE or recovering organic/agricultural/biomass wastes. Figure 1 shows the flow of documents in the first three steps of the systematic review.

The authors undertook a mutual review of each criterion to exclude the papers, making the exclusion a mutual decision of the authors. With regard to the papers in the final portfolio, the authors reviewed the process and highlighted the contribution of the papers to the review. In establishing this method, the authors managed the risk of some papers that had a biased study in the final portfolio or some papers that were excluded for the wrong reasons.

2.3. Systematic Review of the Final Portfolio

The systematic review was shaped through the entire reading of the papers in the final portfolio, collecting the following information: authors, year of publication, title, journal, country of application, type of biomass/waste, the process of biomass conversion, CBE sector, bio-based product, sustainability dimensions covered, type of life cycle tool, system boundaries, software, database, the methods for impact assessment, level of assessment (midpoint–endpoint), number of midpoints, number of endpoints, main results of the assessment, limitations, and future studies. The authors mutually considered the systematic review results and discussions. All of the outcomes in the portfolio were double checked.

2.4. Data Synthesis and Presentation

For better visualization and presentation of the results, graphs were constructed using Microsoft Power BI. Moreover, the VosViewer v.1.6.19 developed by the Centre for Science and Technology Studies, Leiden University, Leiden, The Netherlands) [22] was used to construct a visual map in an overlay visualization to note the occurrence of keywords using the settings specified in

Table 2. Settings for the co-occurrence visual map in VosViewer.

Setting	Value
Counting method	Full counting
Unit of analysis	Keywords
Minimum number of occurrences	3
Type of label	Frames
Thesaurus file 1	Yes
Show	All items

¹ A thesaurus file is a text file that allows for the combining of different variants of a keyword (e.g., life cycle assessment and LCA; bioeconomy and bio-economy).

.

This visual map in an overlay visualization has a temporal scale that allows for the recognition of the most used keywords over time; the most recent keywords are colored yellow, while the oldest ones are in purple.

After the application of the four-step methodology for systematic literature review and the analysis of the final portfolio, it is possible to describe, in the next sections, the current development of the LCT for a CBE, in addition to its challenges and future directions.

3. Current Development of Life Cycle Thinking for a Circular Bioeconomy

In this section, the following topics are reviewed: (1) temporal evolution, (2) the geographical distribution of studies, (3) the analysis of sources, (4) the type of biomass/biowaste, CBE sectors and processes assessed, and (5) the sustainability dimensions covered by studies.

3.1. Temporal Evolution of Studies

The use of LCT for a CBE is very recent. In fact, the first study to report the use of life cycle tools was published in 2017. Farzad et al. [23] applied LCA and LCC to assess the environmental and economic impacts of the diversification of sugarcane industry wastes due to the development of lignocellulosic biorefineries in South Africa.

From there, only one article per year was published in the next two years (2018–2019). In 2018, Bais-Moleman et al. [24] calculated the greenhouse gas (GHG) emissions of wood products, focusing on the European context. Meanwhile, in 2019, Chen et al. [25] applied a hybrid LCA approach to quantify the socio-economic impacts of introducing a circular economy in rice production in Greece.

The year 2020 was a breaking point for publications on LCA for a CBE. Since that year, the production of articles on this topic has increased, achieving the maximum in 2022, with 28 articles. Even at the end of 2022, three articles were already scheduled to be published in 2023. Figure 2 shows the temporal evolution of publication on LCA for a CBE.

The COVID-19 pandemic might explain this increasing number of publications from 2020 onwards because it created an awareness in society about the importance of sustainability and the valorization of healthcare and the equilibrium between the planet and humans, making the emerging of new alternatives for more responsible management of wastes imperative [26], which is significantly aligned with the principles of a circular economy and CBE.

Moreover, several review articles were published from 2020 onwards. This fact can be explained by the comprehensive coverage of the bioeconomy. In this sense, some reviews focus on the assessment of environmental aspects of different sectors of the bioeconomy, such as forest-based products [8], wood-based products [20], algal-based biofuels [27], or products and energy obtained from agricultural [28] and organic wastes [13], and, furthermore, more specific processes that are commonly used in CBE, such as anaerobic digestion [10]. All of these review studies help to us understand and manage the transition to a CBE [21], which is also the objective of this review.

3.2. Geographical Distribution of Studies

It is possible to see that the publications on LCT for a CBE are more concentrated in Europe (Figure 3). The countries with the more significant number of applications of life cycle tools in CBE are Spain and Italy (with five publications each), followed by Germany (four publications) and Denmark (three publications).

Previously, D’Amato et al. [8] reported a concentration of studies on European countries, an idea that this study reaffirmed. In Europe, the circular economy and CBE are priorities for national policies [8]. Hence, the development of sustainability assessments in CBE is expected to be greater in Europe than in other continents.

The bioeconomy in Europe is seen as the correct way to use natural resources and is highly monitored, since it is part of the strategic plan of the European Commission [29]. The strong economy of European countries makes the implementation of bioeconomy and CBE projects possible despite the high costs associated with it. The market is solid for sustainable and locally bio-based products and services [9].

As a solution to encourage CBE in Europe, the use of a biorefinery is a widely applied method of recovering biofuels and bioenergy from biowastes [9]. Specifically, in Nordic countries, the biorefinery is seen as the way to achieve a CBE; e.g., in Denmark, the strategy to replace fossil fuels (natural gas and coal) is to increase the consumption of biomass by 10% per year until 2030 [30]. Thus, several alternatives were developed for the production of biofuels, such as biodiesel [31] or biogas [32] to replace natural gas, and wood pellets and chips to replace coal [31,33].

In western Europe, where most publications are concentrated, a variety of bio-based products has been environmentally assessed in the recent literature, such as biopolymers [34,35,36], bio-based pigments [37,38], biochemicals [39], and bio-based proteins [40,41], as well as biorefinery systems to produce biodiesel [42], biogas [41,43,44] and bioelectricity [24]. In these countries, CBE is a new method of achieving sustainable development.

Outside of Europe, a few countries from Asia (Iran, India, and China) and the Americas (Brazil and the USA) presented two publications on this issue. Finally, 15 other countries published one time on this topic. In Asia, the literature is almost exclusively focused on the environmental assessment of biorefinery processes to produce biodiesel [45,46,47], biogas [47,48], and natural antioxidants for biodiesel production [46,49]. Only two articles from Asian countries assessed other bio-based products, such as propionic acid [50] and xylitol from sugarcane bagasse [51].

In America, studies have also focused on biorefinery systems to produce biogas [52,53,54] and biodiesel [53,55]. Moreover, other studies assessed other products rather than biofuels, such as bio-based proteins [56], biopolymers [57], and bio-based construction materials [58].

Finally, in Africa, only three articles were found in sub-Saharan Africa; they aimed exclusively at the assessment of the environmental aspects of biorefinery process biogas [59,60] and biodiesel [23]. The administration of municipal wastes is still a challenge for African governments, so they usually take the biomass for biorefining from the organic fraction of urban wastes [60] to produce bioenergy, and cleaner cooking biofuel to enhance the quality of life of a part of the African population.

Thus, in every continent, the LCT for a CBE has begun to gain importance in recent years, mainly due to the environmental assessment and application of LCA in biorefinery systems to produce biofuels (especially biodiesel and biogas). Europe is the leading continent with regard to the application of life cycle tools for a CBE. On the contrary, the number of publications in other regions is limited. Hence, applying more life cycle tools in other world regions is essential to closing this gap and promote CBE’s encouragement in public policies because it is the correct way forward in terms of sustainable development.

3.3. Source Analysis

Analyzing the journals where documents are published helps map the main sources interested in the LCT for a CBE. Figure 4 shows the journals that published the documents considered in this review. The primary source that published on this theme is the Journal of Cleaner Production. The most recurrent types of study published in this source are case studies and methodological proposals with case studies, so a practical application of life cycle tools for a CBE may be considered a key factor to publishing in that journal. The only review published in this journal focused on analyses of using LCA as a guide for fabricating wood-based panels [20].

The Journal of Cleaner Production published articles on LCT for a CBE from 2018 onward, reaching a peak in 2022, when seven articles about this theme were published. Research articles from this source focus mainly on the production of bio-based proteins [25,56,61,62] and biogas and biofertilizer products of anaerobic digestion [44,48,60].

Another source that publishes on the theme is the journal Science of the Total Environment, which mainly publishes case studies that environmentally assess the production of a set of bio-based products such as biodiesel from safflower seeds and straw [63], essential oils and citric acid from orange peel [64], biogas from the anaerobic digestion of seagrass wrack [43], and wastewater from the food industry [38]. On the other hand, the journal Renewable and Sustainable Energy Reviews publishes mainly reviews because it is the primary purpose of this source, which focuses on the production of biogas and biofertilizer [31,32] and includes reviews about biorefinery systems [9,45] and, more specifically, anaerobic digestion [10].

Four journals (“Bioresource Technology,” “Bioresource Technology Reports,” “Energies,” and “Sustainability”) published three articles on the theme. The main themes of LCT for a CBE published on these sources are biorefineries for the production of biogas [47,52,53,59], biodiesel [47,53,55], and biochar [47,59], and the production of biopolymers [34,57]. Finally, 20 other journals published two articles or less on this topic (see Figure 4).

3.4. Type of Biomass/Biowaste, CBE Sectors and Processes Assessed

From the review of studies that applied life cycle tools for a CBE, 68.42% (26 out of 38) use wastes to recover bio-based products, biofuels, or bioenergy (

Table 3. Characterization of biomass/wastes, processes, sector, and products.

Type	Origin	Ref.	Description	Process	CBE Sector	Final Products
Biomass	Algal	[47]	Several types of microalgae	AD, TE, pyrolysis	Aquaculture, biorefinery	Biogas (for EHP), biodiesel, biochar
		[56]	Several types of microalgae	Cultivation, harvesting	Aquaculture	Bio-based protein, algal carbohydrate
		[61]	Chlorella	Ultrafiltration, HT liquefaction	Aquaculture, biorefinery	Bio-based protein, biocrude oil
	Vegetal	[33]	Willow wood	Drying, pyrolysis	Forestry	Biochar, wood chips
		[43]	Seagrass wrack	AD, composting	Aquaculture	Biogas (for EHP), BF
		[44]	Seagrass wrack	AD	Aquaculture	Biogas (for EHP), BF
		[65]	Giant miscanthus	Cultivation, harvesting	Agroindustry	Biomass feedstock
Biomass/ Waste	Vegetal, industrial	[24]	Wood and paper wastes	Reuse in process, incineration	Forestry, paper industry	Paper, bioelectricity
	Vegetal	[35]	Sugar beet, pineapple leaves	Polymerization	Agroindustry, textile industry	Bio-based leather
	Vegetal, urban	[36]	Maize, sugarcane and OFMSW	Polymerization	Agroindustry, plastic industry	Bioplastic
	Algal, WW	[38]	Spirulina, urban and industry WW	AD, pigment extraction	Aquaculture, biorefinery	Biogas (for EHP), BF, bio-pigment
	Algal, urban	[40]	Galdieria sulphuaria, OFMSW	Hydrolysis, fermentation	Aquaculture, municipal	Algal-based protein
Waste	Animal	[55]	Salmon wastes	Transesterification	Fishing	Biodiesel
		[66]	Swine manure	AD	Livestock	Biogas (for EHP), BF
	Industrial	[34]	Lignin from paper pulp	HT treatment	Paper industry	Bio-based filler (for polymer blends)
	Urban	[32]	OFMSW	AD	Municipal	Biogas (for EHP), BF
		[59]	OFMSW	AD, pyrolysis	Municipal	Biogas (for BM), biochar
		[60]	OFMSW	AD, composting, incineration	Municipal	Biogas (for EHP), BF, bioelectricity
	Vegetal	[23]	Sugarcane bagasse	Transesterification	Agroindustry, biorefinery	Bioethanol, bioelectricity
		[25]	Rice husk and bran	Incineration, composting	Agroindustry	Steam, BF
		[37]	Pomegranate bagasse	Pigment extraction	Agroindustry	Bio-pigment
		[39]	Tomato pomace	Polymerization	Agroindustry	Bio-based lacquer
		[42]	Date seeds	Transesterification	Agroindustry	Biodiesel
		[46]	Olive bagasse and leaves	Transesterification	Agroindustry	Bio-based antioxidant, biodiesel
		[49]	Walnut husk	Phenolic extraction	Agroindustry	Bio-based antioxidant
		[51]	Sugarcane bagasse	Fermentation, crystallization	Agroindustry	Xylitol (sweetener)
		[52]	Sugarcane bagasse and vinasse	AD	Agroindustry, biorefinery	Biogas (for EHP), BF
		[53]	Castor-oil seeds	AD, Transesterification	Agroindustry, biorefinery	Biogas (for EHP), biodiesel
		[57]	Rice husk	Polymerization	Agroindustry	Bioplastic
		[58]	Açai seeds	Incineration	Agroindustry	Mortar for construction
		[62]	Potato bagasse	Drying, heating	Agroindustry	Potato fiber, protein and BF
		[63]	Safflower seeds and straw	Transesterification	Agroindustry, biorefinery	Bioethanol, biodiesel
		[64]	Orange bagasse	Fermentation, crystallization	Agroindustry	Essential oil, citric acid, animal feed
	WW	[31]	Urban WW	AD, fermentation	WW Treatment	Biogas (for BM), SCP
		[41]	Food industry WW	AD, fermentation	Agroindustry	Biogas (for EHP), SCP
		[48]	Urban WW	AD	WW Treatment	Biogas (for EHP), BF
		[50]	Urban WW	Fermentation	WW Treatment	Propionic acid
		[54]	Duckweed WW	AD	Aquaculture, biorefinery	Biogas (for EHP), BF

AD: Anaerobic digestion, BM: Biomethane, BF: Biofertilizer, EHP: Electricity and heat purposes, HT: Hydrothermal, OFMSW: Organic fraction of municipal solid wastes, SCP: Single-cell proteins, WW: Wastewater.

). Vegetal wastes are the most used for CBE, followed by wastewater and urban wastes (organic fraction of municipal wastes). Only 18.42% of the studies (seven out of 39) worked with pure biomass of algal or vegetal origin. Finally, 13.16% of the articles (five out of 39) combined biomass and waste.

CBE incentivizes the conversion of bioresources and wastes to create high-added-value products [5]. It is reflected in the results of this review because life cycle tools are predominantly applied to biowastes instead of to pure biomass. In this regard, the products found in the biowastes depend on their origin (animal, urban, industrial, vegetal, or wastewater).

For example, animal wastes are more related to biorefinery processes to produce biofuels (such as biodiesel [55] and biogas [66]). Meanwhile, urban wastes and wastewater are almost exclusively related to being treated by anaerobic digestion to produce biogas (as the main product) and biofertilizer [32,60], or other by-products, e.g., biochar after pyrolysis of the digestate [48,54,59]. Nevertheless, sometimes biogas is passed to be the by-product, e.g., when producing single-cell proteins (the main product), a fermentation process (the main process) is precedes the anaerobic digestion of its effluents [31,41].

Furthermore, an interesting point is the combination of both pure biomass and biowastes to produce high-added value bio-based products, e.g., bio-based proteins [40], bio-based pigments [38], biopolymers [36], and bio-based leather [35]. These bio-based products stand out as alternatives to produce products of high value rather than a straightforward energetic recuperation.

Meanwhile, vegetal wastes are more related to the production of bio-based products than biofuels. In this review, only six (out of 16) studies that processed vegetal wastes used biorefinery processes to produce biodiesel [42,45,46,53], bioethanol [23,63], or biogas [52,53]. The other ten documents assessed the production of other bio-based products, such as biopolymers [34,57], bio-based pigments [37], lacquer [38], antioxidants [49], fiber and protein [62], xylitol [51], mortar (for construction) [58], and animal feed [25,64].

On the contrary, the results demonstrate that the use of pure biomass is almost exclusively associated with biofuel production, such as biodiesel [47], biochar [33], and biogas for electricity and heat purposes [43,44,47], or the cultivation of biomass to serve as feedstock [65]. Only two recent studies used biomass to develop other high-added-value products (bio-based proteins [56,61]).

Regarding the processes, anaerobic digestion was applied in 37% of the application cases; hence, it stands out as a popular bioprocess and an excellent ally for a CBE, as previously observed by Tsapekos et al. [10]. Anaerobic digestion is normally used for electricity and heat purposes [38,43,44,47,48,52,53,54,60,66] and, in a few cases, a concentration of methane is further applied to produce biomethane [31,59], or a combined system for both purposes (bioelectricity and biomethane) [32]. Moreover, anaerobic digestion is a versatile process that can be combined with others, either previous to (to treat the effluents, e.g., pigment extraction [38] and fermentation to produce bio-based proteins [31,41]) or after anaerobic digestion (to treat the digestate, e.g., pyrolysis to produce biochar [47,59].

Two other processes stand out in the literature: transesterification for producing biodiesel [42,45,46,53,55], and polymerization for producing bioplastics [35,36,39,57]. Although the valorization of wastes requires a high level of technology [1], the rule that the more specialized the conversion technique, the greater the value added to bio-based products is only sometimes fulfilled. Some simple initiatives, such as the reinsertion of wastes into the production process, can add greater circularity, rather than firing the same wastes [24].

Considering the CBE sectors, agroindustry has a notorious predominance, and 50% of the studies (19 out of 38) applied life cycle tools to assess the sustainability of agricultural and agroindustry wastes. Agroindustry includes the cultivation of crops for manufacturing purposes, e.g., the production of fruit pulp and juices [37,42,58,64], olive oil [46], sugar [51] and rice [25,57], as well as for biorefinery purposes, e.g., sugarcane [23,51,52], Ricinus [53], or safflower [63] to produce biofuels (i.e., biodiesel or bioethanol). Other studies applied LCT to a combination of agroindustry with the textile [35] or plastic industries [36].

Other CBE sectors assessed by life cycle tools are aquaculture (the cultivation of algae [38,47,56,61], seagrass [43,44] and duckweed [54]), forestry [33], fishing [55], livestock [66], and paper production [34]. Other sectors often assessed in CBE are the treatment of the organic fraction of urban solid wastes [32,40,59,60] and urban wastewater and sewage [31,48,50]; these two activities are usually undertaken by municipalities or other government entities; hence, municipal wastes represent a great feedstock source for CBE.

3.5. Sustainability Dimensions Covered

Figure 5 shows the number of application cases (excluding review articles) sorted by the sustainability dimensions they covered (economic, environmental, or social). In this regard, 67% of the application cases (26 out of 39) assessed the environmental dimension exclusively; hence, LCA is the most used tool of LCT for a CBE; independent of the time, LCA is of significant interest to sustainability academics and practitioners and is confirmed as a popular tool to assess the environmental dimension of sustainability. Some 97% of the case studies (38 out of 39) considered the environmental dimension in their scope.

The use of life cycle tools for a CBE repeated the tendency of using LCA in other sectors where the environmental dimension of sustainability is always the most explored, followed by the economic dimension and, in last place, the social dimension [67,68]; this trend is even repeated in the bioeconomy [15] despite the recognized necessity of assessing social topics and applying SLCA in a bioeconomy and CBE [69].

Therefore, to achieve real sustainable development in a CBE, it is imperative to close the gap between the number of studies related to assessing the environmental dimension and the other two dimensions (economic and social), especially for the social dimension of sustainability, because it is the least developed. Thus, it is necessary to review the main characteristics of life cycle tools applied to bio-based products in each sustainability dimension to know the current development of LCT for a CBE.

3.5.1. Environmental Dimension

As specified in Section 3.5, environmental assessments (by LCA) are the most frequent in the current literature on LCT for a CBE. In this sense, more than 97% of the case studies (38 out of 39) applied an LCA.

Table 4. Characteristics of the LCA applications reviewed.

Syst. Bound.	Ref.	Software	Database	Method for IA	M/E	N° of Midpoints	N° of Endpoints
Gate-to-gate	[4]	SimaPro 8.0	Ecoinvent 3	ReCiPe 2016	M/E	18	3
	[32]	SimaPro 8.5	Ecoinvent 3.3	Impact 2002+	E	-	4
	[55]	SimaPro 9.3	Ecoinvent 3	Impact world+	M/E	18	2
	[57]	OpenLCA 1.10	Ecoinvent 3.7	ReCiPe 2016	M/E	18	3
Cradle-to-gate	[23]	SimaPro 8.0	U.I.	CML-IA, Eco-indicator 99	M	20	-
	[31]	SimaPro 9.1	Ecoinvent 3	ReCiPe 2016	M/E	11	3
	[33]	GaBi 9.2	GaBi Thinkstep	CML-2001	M	1	-
	[34]	Umberto LCA+ 10.0.3	Ecoinvent 3.6	IPCC 2013	M	1	-
	[35]	GaBi 6.0	GaBi Thinkstep, Ecoinvent 3.5	EF 2.0	M	16	-
	[37]	SimaPro 8.5	Ecoinvent 3.5	IPCC 2013, ReCiPe 2016	M	19	-
	[39]	GaBi 9.2	GaBi Thinkstep, Ecoinvent 3.5	EF 3.0	M	16	-
	[40]	SimaPro 8.0	Ecoinvent v.3.4	Impact 2002+	M	15	-
	[42]	U.I.	U.I.	CML-IA, ReCiPe 2016	M/E	11	3
	[44]	SimaPro 8	Ecoinvent v.3	CML-IA, ReCiPe 2016	M	9	-
	[46]	SimaPro 8.2	Ecoinvent 3.2	Impact 2002+	E	-	4
	[48]	U.I.	U.I.	Impact 2002+	E	-	4
	[50]	SimaPro 8.5	Ecoinvent 3.5	CML-IA, Impact 2002+, IPCC 2013	M/E	12	4
	[51]	OpenLCA 1.10	Ecoinvent 3.3	ReCiPe 2016	M	7	-
	[53]	OpenLCA 1.10	Agribalyse 3.0.1	CML-2001	M	12	-
	[54]	Brightway 2	Ecoinvent 3.3	IPCC 2013/ReCiPe 2016	M/E	4	1
	[56]	OpenLCA 1.11	Ecoinvent 3.6	IPCC 2021	M	1	-
	[58]	U.I.	Ecoinvent 3.6	EN 15804 + A2	M	1	-
	[60]	SimaPro 9.1	U.I.	ReCiPe 2016	M	10	-
	[61]	TELCA	ICE 2.0	IPCC 2013	M	1	-
	[62]	SimaPro 9.3	Ecoinvent 3.8	ReCiPe 2016	M/E	18	1
	[63]	SimaPro 8.0	Ecoinvent 3	Impact 2002+	E	-	4
	[64]	SimaPro 9.0	Ecoinvent 3.6	EF 3.0	M	6	-
	[65]	U.I.	U.I.	ReCiPe 2016	M	8	-
	[66]	SimaPro 9.2	Ecoinvent 3	CML-IA	M	11	-
Cradle-to-use	[59]	SimaPro 8.5	Ecoinvent 3.1, Agrifootprint	ReCiPe 2016	M	8	-
Cradle-to-grave	[24]	U.I.	U.I.	IPCC 2006	M	1	-
	[36]	U.I.	Ecoinvent 3.6	IPCC 2006	M	1	-
	[38]	SimaPro 9.0	Ecoinvent 3.7	ReCiPe 2016	M	10	-
	[47]	SimaPro 8.0	U.I.	ReCiPe 2016	M/E	14	2
	[49]	SimaPro 8.2	Ecoinvent 3.0	Impact 2002+	M/E	13	4
	[52]	SimaPro 8.0	Ecoinvent 3	ReCiPe 2008	M	9	-
	[70]	GaBi 6.0	GaBi Thinkstep	CML-2001	M	1	-
Hybrid LCA	[41]	U.I.	Exiobase, Agrifootprint	IPCC 2013	M	1	-

E: Endpoints, EF: Environmental footprint, IA: Impact assessment, ICE: Inventory of carbon and energy, LCA: Life cycle assessment, M: Midpoints, M/E: Midpoints and endpoints, U.I.: Unknown information.

specifies the features of LCA application cases analyzed in this review.

Ideally, an LCA study should assess the environmental impacts of products from cradle-to-grave (full assessment). Nevertheless, in this review, the most observed configuration of system boundaries is from cradle-to-gate. It was an expected fact that corroborated the results of previous reviews of LCA in specific bioeconomy sectors, such as wood-based products [20] and biorefinery systems [9], where the system boundaries from cradle-to-gate are also the most common.

Regarding the use of software and databases in LCA studies, there is a predominance of SimaPro and Ecoinvent, respectively. SimaPro was used in approximately 53% of the studies (20 out of 38), followed by GaBi and OpenLCA software, with four occurrences each. Other software used, such as Umberto LCA+ and Brightway 2, appear only one time.

An interesting aspect is the recent use of open-source software packages for LCA, such as OpenLCA and Brightway 2, which encourages the application of LCA with more transparency and fewer costs [71]. The occurrences of the use of OpenLCA software are all from 2022; thus, the use of OpenLCA has been increasing in recent years. Meanwhile, Brightway 2 is a software package written in Python whose target audience is users of Jupyter notebooks [72]. Moreover, in one case, the use of a regional platform was found. Karan et al. [61] utilized the TELCA platform v.2.1, which was specifically developed to assess products in an Australian context.

The use of databases is even more centralized. Ecoinvent has a notorious predominance when compared with other databases, appearing in 71% of the studies (27 out of 38), and it is followed by the GaBi Thinkstep database, which was used in only the four studies that used GaBi software [33,35,39,70]; even the GaBi Thinkstep database may be combined with Ecoinvent [35,39]. Furthermore, since CBE is closely related to agriculture and agroindustry, the use of specific databases for assessing agricultural products is expected; in this sense, some studies used Agrifootprint [41,59] and Agribalyse [53] in the LCA of products from biorefinery processes.

Considering the life cycle impact assessment (LCIA) of the reviewed studies, approximately 63% of the studies (24 out of 38) only assessed the midpoints, 11% (4 out of 38) only assessed the endpoints, and 26% (10 out of 38) assessed both midpoints and endpoints. Hence, there is an evident lack of the assessment of the endpoints.

Concerning the methods used for LCIA, Figure 6 shows the most popular methods for impact assessment in the literature reviewed; they are presented at least in five application cases. ReCiPe 2016 stands out as the most prevalent method for LCIA, appearing in 14 studies. The popularity of ReCiPe 2016 can be explained by two factors: (1) it has an extended set of impact categories that allow for the assessing of midpoints and endpoints, and (2) its characterization factors are representative of a global scale rather than a European scale (as a significant part of LCIA methods) [73].

Ideally, an LCA study should assess the environmental impacts of products from cradle-to-grave (full assessment). Nevertheless, in this review, the most observed configuration of system boundaries is from cradle-to-gate. It was an expected fact that corroborated the results of previous reviews of LCA in specific bioeconomy sectors, such as wood-based products [20] and biorefinery systems [9], where the system boundaries from cradle-to-gate are also the most common.

For its part, Impact 2002+ was used in seven studies (out of 38). This method was almost exclusively applied to assess endpoints. Impact 2002+ groups 15 midpoints to assess four endpoints in the last instance (climate change, human health, ecosystem quality, and resources) [74]. IPCC 2013 (six occurrences) and the CML-IA baseline (five occurrences) are also frequently used methods.

IPCC 2013 is a single-issue approach used to calculate the carbon footprint, expressed in the quantity of GHG emissions (climate change); hence, in this review, some studies [34,41,61] are only intended to conduct the assessment of GHG emissions considering a particular impact category (climate change 100 years). On the contrary, the CML-IA baseline is a broader approach for LCIA, that is exclusively used to assess several midpoints, and was developed for European contexts. However, some studies from Europe used the CML-IA baseline but always combined it with other methods such as IPCC 2013, Impact 2002+ [50], or Eco-Indicator 99 [23].

Regarding the impact subcategories, all of the reviewed studies assessed climate change. This category is present in all of the LCIA methods used in the studies, even in the single-issue approaches, e.g., IPCC 2013. This demonstrates that the main preoccupation of sustainability researchers in applying life cycle tools for a CBE is the quantity of GHG emissions, a standard indicator to assess the environmental sustainability in an LCT [24]. Other popular impact categories presented in the studies are fine particulate matter formation (12 occurrences), fossil resource scarcity (11 occurrences), and freshwater eutrophication (11 occurrences), demonstrating the relevance not only of the emissions to the air but also of the effluents discarded into the water and the depletion of fossil fuels generated by the bio-based products.

Another interesting point are the findings of hybrid LCA studies. Hybrid LCA combines input-output models to assess a complete system boundary and, thus, provides more accurate results than process-based LCA [75]. Hybrid LCA can assess not only environmental impacts but also economic and social ones [25]. However, its use is limited to assessing GHG emissions (in the environmental dimension), gross value added (in the economic dimension), and the generation of employment hours (in the social dimension).

3.5.2. Economic and Social Dimensions

As explained in Section 3.4, the economic and social dimensions of sustainability have gained a small number of life cycle tool applications in the CBE literature compared to the environmental one. In this sense, there is a notable gap in the related literature, so it is imperative to further assess the economic and social issues of CBE. Only 30% of the studies (12 out of 39) considered the economic dimension in the scope of their assessments, and only 5% of the studies (2 out of 39) contemplated a few social issues.

Regarding the economic dimension, the use of LCC (with this name) is present in a few cases [43,44]; several authors prefer using it over other names such as economic assessment [23,40,53], financial assessment [33] or techno-economic assessment [51,54,56].

Table 5. Characteristics of studies in economic and social dimensions.

Dim.	Ref.	Type of Assessment	Data Source	Database	Indicators
Economic	[23]	Economic assessment	Secondary	Aspen Plus EE	Direct costs (CAPEX, OPEX), IRR
	[25]	Hybrid LCA	Secondary	Exiobase	Gross value added
	[33]	Financial assessment	Primary	-	Direct costs (CAPEX, OPEX), CFA, NPV, IRR
	[40]	Economic assessment	Primary	-	Direct costs (CAPEX, OPEX), Necessary break-even price
	[41]	Hybrid LCA	Secondary	Exiobase	Gross value added
	[43]	LCC	Primary	-	Direct costs (CAPEX, OPEX), Indirect costs (environmental costs and benefits), NPV
	[44]	LCC	Primary	-	Direct costs (CAPEX, OPEX), Indirect costs (consequence of actions), external costs (environmental costs), NPV
	[51]	TEA	Secondary	Aspen Plus EE	Direct costs (CAPEX, OPEX), IRR
	[53]	Economic assessment	Primary	-	Total revenues from potential sales of bioproducts
	[54]	TEA	Secondary	NREL report	Direct costs (CAPEX, OPEX), IRR
	[56]	TEA	Secondary	IEA bioenergy	Direct costs (CAPEX, OPEX)
	[57]	Environmental costs assessment	Secondary	Ecovalue 14	Environmental Costs associated to impact categories
	[61]	TELCA	Primary	-	Direct costs (CAPEX, OPEX), IRR, NPV
Social	[25]	Hybrid LCA	Primary	Exiobase	Number of hours of employment
	[41]	Hybrid LCA	Primary	Exiobase	Number of hours of employment
	[61]	TELCA	Primary	-	Energy returned on energy invested (ERoEI)

CAPEX: Capital expenditures, CFA: Cash flow analyses, EE: Economic evaluator, FE: Freshwater eutrophication, IRR: Internal rate of return, LCA: Life cycle assessment, LCC: Life cycle costing, NPV: Net present value, OPEX: Operational expenditures, TEA: Techno-economic assessment, TELCA: Techno-economic and life cycle assessment.

shows the main features of the studies that consider economic and social topics.

Despite some studies not using LCC as the terminology for their economic assessments, some indicators help to better understand the assessment of the economic dimension in the LCT for a CBE study. In this sense, LCC has some levels to be applied [7]: (1) conventional LCC, which only considers internal costs and benefits; (2) LCC, including internal and relevant external costs; and (3) societal LCC, including every internal and external cost.

Following this classification, 54% of the economic assessments (seven out of 13) may be sorted as conventional LCC [21,33,40,51,54,61] because they are limited to the consideration of the direct costs of production from Capital Expenditures (CAPEX) and Operational Expenditures (OPEX), and the use of the internal rate of return (IRR) and net present value (NPV) as indicators for decision-making.

Moreover, 23% of the economic assessments (three out of 12) included (in addition to direct costs, such asCAPEX and OPEX), the indirect values associated with the monetization of the leading environmental impacts related to the results of LCA (environmental costs and benefits) [43,44,57]. The other three studies only considered some single indicators for economic assessment, such as the gross value added to products (in hybrid LCA applications) [25,41] or the total revenues from the potential sale of bio-based products [53]. Concerning societal LCC, there are no studies considering all of the internal and external (environmental and social) costs, which is most likely due to the lack of consideration of the social impacts in almost all of the studies.

Regarding the social dimension in the literature of LCT for a CBE, only three case studies considered social issues in their scope, using some single indicators such as the number of hours of employment (in hybrid LCA studies) [25,41] or the energy returned on energy invested, arguing that energy assurance is crucial for the social acceptance of biorefinery projects [61].

Hence, the social issues considered in these studies are limited, and a complete SLCA was never conducted. The current literature only covers a social topic or impact subcategory (local employment) and a stakeholder (local community). Thus, the addition of more social topics, or even the application of SLCA for a CBE, is imperative in order to attend to all of the sustainability dimensions, as well as the consideration of all the stakeholders involved in the life cycle of CBE products (workers, consumers, the local community, society, and other value chain actors).

4. Challenges of Life Cycle Thinking for a Circular Bioeconomy

The portfolio review revealed several challenges to be faced by sustainability academics and practitioners in LCT for a CBE. There are three methodological/technical challenges when applying life cycle tools for a CBE: (1) the expansion of system boundaries in LCA studies; (2) the consideration of more endpoints in LCA studies, and (3) the development and use of regional databases; and two strategic challenges to achieve sustainable development in a CBE: (4) the development of policies to encourage a CBE; and (5) the addition of economic and social issues.

4.1. Expansion of System Boundaries in LCA Studies

The definition of processes and system boundaries is a critical factor that leads to reliable results in LCA studies [64]. In this review, as seen in Section 3.5.1, 66% of LCA studies (25 out of 38) used the configuration of system boundaries from cradle-to-gate. Meanwhile, only 18% of studies (seven out of 38) used them from cradle-to-grave. This demonstrates the need to expand the coverage of life cycle stages in LCA studies. The expansion of system boundaries is usually found to be a limitation of LCA studies [9] or a suggestion for further research [34].

A highlighting point is the low number of gate-to-gate studies (four out of 38), representing an effort by sustainability researchers to expand system boundaries, especially with regard to upstream processes (cradle-to-gate). However, the literature still lacks complete LCA studies that consider downstream processes in their system boundary configurations (cradle-to-grave or cradle-to-cradle).

A limitation for expanding system boundaries in LCA studies is the limited availability of data about the downstream processes of CBE products [34]. In this sense, bio-based products, at their end of life, have many options to be reutilized, or, in the worst case, discarded. However, a few studies have considered these recirculation alternatives in their scope [24,47], mainly resulting from the difficulty of finding related data, which often leads to excluding some life cycle stages, such as the distribution, use, and the end of life of bio-based products [54].

The results of LCAs in a cradle-to-grave configuration seem more reliable than those using other configurations of system boundaries [52]. In this sense, the inclusion of all of the life cycle stages, especially at the end-of-life, is important because, since CBE products are named as circular, they should promote the reuse of their wastes, and this represents substantially less environmental impacts when compared to disposal in a landfill, for example [36]. Thus, assessing more CBE products from cradle-to-grave is highly suggested, because cradle-to-gate assessments need clarification about how wastes are recirculating. In contrast, cradle-to-grave assessments provide greater clarity about how products affect the environment throughout their life cycles.

4.2. The Consideration of More Endpoints in LCA Studies

In the literature reviewed, most LCA studies conducted midpoint assessments (34 out of 38), and only some studies assessed the endpoint (14 out of 38). Endpoint assessments are crucial for LCA because they use indicators that consider the areas of protection [76] where emissions are aggregated in indexes whose units are closely related to societal concerns [77]. This is different from midpoint assessments, whose indicators are ubicated in any place between the emission and the area of [76], and the use equivalences to be expressed, such as the acidification potential in terms of SO₂-eq [77].

The assessment of endpoints depends on the use of specific LCIA methods; the most used for this purpose are ReCiPe 2016 (endpoint categories) and Impact 2002+ (damage categories) (Figure 6). Both methods were created for assessing endpoints globally and not for specific contexts (European or North American) [73,74,78], as are other popular LCIA methods of midpoint assessment. Moreover, both methods consider three common areas of protection:

• Human health: Expressed in disability-adjusted life years (DALY), this is a single measure that “combines the mortality and morbidity […] to estimate global disease burden and the effectiveness of health interventions” [79] (p. 10);
• Ecosystem quality: Expressed in potentially disappeared fraction (PDF) by m2/year (Impact 2002+) or simply species by year (ReCiPe 2016), it is the condition of an ecosystem compared to a reference state which can be from the past, present, or future (in a potential situation/condition) [80];
• Resource scarcity: Also known as resources (in Impact 2002+), it is expressed in megajoules (MJ), and refers to the consumption of non-renewable energy and minerals [78].

It is worthy of note that Impact 2002+ considers the use of climate change; however, its use is not precise because it is “the same category as the midpoint category Global Warming […] and is still expressed in kg CO2-eq” [78], so it is not aggregated with other midpoint categories, as with the other endpoints.

Furthermore, in any case, the number of endpoint indicators is smaller than midpoint indicators [76], and the complexity of calculating them is higher [77]. However, the assessment of endpoints is necessary for implementing the LCT in a CBE because bio-based products (as every product) and wastes directly impact human health [26], mainly due to the emissions and particulate matter they generate from potentially toxic substances along CBE processes of a biorefinery, for example [39].

Moreover, due to its close relation to agriculture, CBE has great potential to impact land use changes, so it can compromise ecosystems and jeopardize biodiversity. In this sense, Bartek et al. [62] argue that CBE can reduce damage to ecosystems and maintain flora and fauna, but only if sustainable agriculture is promoted and supervised in the first instance.

4.3. The Creation and Use of Regional Databases

Since its publication in 2003, Ecoinvent has become the most widely used database for background LCI data [81] in CBE and other sectors. In this study, 66% of LCA studies (25 out of 38) used the Ecoinvent database to extract data for the LCI construction, demonstrating the predominance of the use of this database. It is likely explained by the significant number of datasets. Ecoinvent contains datasets to assess more than 18,000 activities on industrial and agricultural processes, considering the natural resources, emissions, effluents, products, and wastes produced [82].

Nevertheless, some studies reported a limitation regarding using the Ecoinvent database because of the generic character of the data [34,70] or the lack of datasets for specific products they were assessing [37]. The problem is that LCA results may be either overrated or underrated, reflecting, for example, the results of GHG emissions or overestimated savings [24]. These limitations occasionally led the authors to use data from literature sources or personal communications [60], because they find them better for context-specific LCA assessments.

As a solution to this problem, the development and use of national/regional databases stands out. This has been encouraged since the early 2000s [83]; from that time, some countries, namely Europe, the United States, Australia and Japan, have pioneered the creation of databases for LCA, but the difference in technological levels and production processes between these countries and the rest of the world have led to the creation of national databases incorporating the vision of the stakeholders [84].

When viewed in this light, using national/regional databases for LCI analysis may result in more realistic environmental impact assessments [54] because they are adapted to the reality of each country. This is unlike global databases that cover many processes using generic data [34], and thus add uncertainty to the results [70]. Nonetheless, the development of databases represents a cooperative endeavour of sustainability researchers, practitioners, and government agencies that claim to support these initiatives [84]. Public and private policies are closely related with regard to developing LCI databases and implementing an LCT for a CBE.

4.4. Development of Policies to Encourage a CBE

Currently, the literature on LCT for a CBE is concentrated in Europe (Figure 3), especially in western Europe, confirming the results of previous reviews [8,9]. This fact is explained by European policies, which have both bioeconomy and circular economy at their core [29]. Hence, it is possible to recognize the importance of having public policies to promote a CBE to encourage the development of CBE projects and the sustainability assessment of those projects. However, in addition to public policies, the LCT for a CBE depends primarily on the effort of private organizations; thus, they have to be aware of the importance of reporting the sustainability impacts of their products [14].

Moreover, the bioeconomy depends on factors such as the time/season of the year and the region/country [70], which must be considered when defining public and private policies, because they can define the success or failure of CBE projects. In this sense, a factor in the failure of CBE projects is the lack of consideration for the seasonality of agricultural production and, thus, agricultural wastes, which are biomass feedstock. For this reason, it is necessary to think of more versatile production systems for a CBE, which can treat various types of biomasses. For example, Khounani et al. [46] considered the seasonality of olive production (as the primary biomass for biodiesel production) and included municipal solid waste as a secondary biomass to surpass the limitations of the quantity of feedstock in out-of-season conditions and to ensure continuous production.

Furthermore, agriculture is one of the most widespread economic sectors worldwide [85]. Thus, each country has specific agricultural characteristics (crops and techniques). Therefore, when defining policies to encourage a CBE, these countries’ specific agricultural characteristics must be taken into account because they are a factor in the success of CBE projects. The intensive cultivation of traditional crops generates great quantities of agricultural waste that, in a CBE, must be exploited to develop high-value-added products [5].

Other factors are the economic development of the countries and their necessity to decrease resource use. In this sense, many years ago, western Europe recognized the reduction of resource use and environmental impacts [70]; these countries enjoy developed economies [9]. These two factors triggered the bioeconomy and the realization of CBE projects and private and public policies for a CBE.

In general, all countries should search for a reduction of sustainability impact. Thus, with the basis of European policies, countries from other world regions can implement or enhance their policies. In this light, countries from the Global South usually enjoy a significant quantity of natural resources, and their economies are based on primary activities (agriculture, mining, and others). However, exploiting resources and land needs to be revisited [70]. Thus, CBE, through the use of bio-based wastes in biorefinery processes for producing biofuels and value-added materials [28], may represent a solution to relevant problems, especially for developing countries, such as food and energy security, employment, and reducing emissions of pollutants and motivating a greener energy matrix [61].

The call for implementing a bioeconomy and CBE is even more urgent in the least developed countries. For example, in sub-Saharan Africa, where many of the least developed countries are grouped, satisfying the basic needs of communities is a great challenge for governments. These countries might be the group that benefits the most from (bio)economic growth [70]. Basic needs fulfillment includes food and energy security that a CBE can directly satisfy [58]. In this regard, it is imperative to develop and offer win-win CBE solutions for Africa in order to optimize economic growth [60], the reduction of environmental impacts, and improve the population’s quality of life. Thus, public policies are highly relevant to encourage CBE at all levels, from community-based projects, to the improving of sustainable livelihoods [59], to regional and continental collaboration in Africa [60].

4.5. Inclusion of Economic and Social Issues

In the literature reviewed, 33% of application studies (13 out of 39) considered economic issues. Thus, the low number of economic assessments reflects an urgent need to incorporate sustainability’s economic dimension in the LCT for a CBE. Meanwhile, the insertion of social issues is even more urgent because only 8% of studies (three out of 39) included social issues in their scope. In this regard, despite the already recognized need for adding socio-economic aspects in bioeconomy LCT studies [68], several studies revealed the difficulty of incorporating economic and social issues in LCT studies for a CBE [14,35,44,53,57,59].

To think of a wholly sustainable CBE, in addition to the environmental dimension, including the economic and social dimensions is imperative. Economically, the development of complete LCC assessments of CBE products is advised. In addition to initial capital (CAPEX) and operational costs (OPEX), these LCCs must consider environmental and social costs/revenues from the main hotspots (impact categories) [43,57].

A correct and complete economic assessment (using LCC) helps to reduce the uncertainties about the feasibility of CBE projects. In a general sense, implementing CBE projects demands significant CAPEX and OPEX, which puts profitability into question [40]. However, when organizations prioritize profitability maximization over minimizing environmental (or social) impacts, they will tend to increase [47]. Thus, it is crucial to reach a point of balance between profitability and environmental and social impacts. For this reason, some strategic factors must be carefully considered when implementing a CBE project, such as the localization of production plants or the points of feedstock generation to reduce transport costs that may result in better economic feasibility [46].

Hence, it is important to monetarize all the impacts that CBE products entail throughout their life cycles, even the costs of degradation/benefit of areas of protection and other economic sectors. For example, Mainardis et al. [43] estimated the costs resulting from the reduction of tourism activities in a coastal town due to the implantation of a biorefinery of seagrass wrack; meanwhile, Vance et al. [44] recognized the necessity of the monetization of ecosystem degradation due to the extraction of seagrass wrack because it provides shelter and food to coastal species.

Regarding the social dimension, the realization of complete SLCA is highly recommended. The SLCA is a powerful tool to assess the social dimension of sustainability [69]. The application of SLCA is necessary for a better comprehension of the social hotspots of CBE projects and the engagement of stakeholders, which is another factor of success for CBE initiatives [44] because it determines their social acceptance [61].

In this sense, CBE has the potential to enhance the quality of life of communities [58] by offering decent work to their citizens [25], ensuring their food and energy security [61]. However, this also requires public policies to incentivize CBE and their social responsibility, which SLCA should assess.

Finally, the inclusion of environmental issues has been increased in LCT studies for a CBE in recent years; on the contrary, economic and social elements remain widely disregarded [15]. The inclusion of LCC and SLCA in LCT studies is necessary for providing a complete view of the entire impact of CBE [57] and offering consolidated suggestions to decision-makers [59]. Therefore, including economic and social issues is essential for a real contribution of CBE to the sustainability of a bioeconomy and better stakeholder management and engagement in CBE activities.

5. Future Perspectives of Life Cycle Thinking for a Circular Bioeconomy

In addition to the challenges of LCT for a CBE (Section 4), some topics in recent literature are relevant. A visual map (Figure 7) in an overlay visualization (using a temporal scale) was created using VosViewer v.1.6.19 [22] to visualize the most used keywords in LCT studies for a CBE. Following the scale in Figure 7, the labels on violet are the least recent, while those on yellow are the most recent.

Considering the above, the most recent relevant keywords used in LCT studies for a CBE are (1) microalgae, (2) wastewater, (3) animals, (4) bioproducts, (5) bioenergy, (6) circularity, (7) costs, and (8) sustainable development.

• Microalgae: The development of bio-based products from microalgae has been increasing in recent years [56]. Especially in developing and the least-developed countries, the biorefinery of microalgae to produce protein and energy can address hunger and energy demands [61]. Future works on CBE using algal biomass focus on achieving large-scale operations [56], ways for adding more value to algal-based products [39], as well as addressing the analysis to surpass the uncertainty of prices and demand for these products [27,47] and the inclusion of social and economic issues in related assessments [61];
• Wastewater: The treatment of wastewater represents an opportunity for CBE. Wastewater (from industries or domestic sewage) is a continuous feedstock whose treatment usually occurs through anaerobic digestion, allowing the recuperation of biogas and biofertilizers [11,43]. However, further studies are required in order to search for other alternatives for wastewater treatment [86], alternative feedstocks to be treated with wastewater [44], the management of risks [31], and the creation of more value-added products from wastewater, such as single-cell proteins [31,41];
• Animals: Using animal wastes in a CBE is strategic because it causes severe environmental damages; for example, dairy manure emits high quantities of methane [87]. For this reason, a trend in CBE is the use of animal manure and wastes for developing high added value products, especially biofuels such as biodiesel [55] or biogas [66], as well as the conversion of biomass in animal feed [25,64];
• Bioproducts: In a bioeconomy, a bioproduct encompasses every product made from biomass [88]. A CBE seeks the creation of high-value-added bioproducts [5], such as bio-chemicals [39,46,49,51], bio-based proteins [31,62], or biopolymers [35,36,57]. Trends in this topic are going toward ways of extracting more high-value products [40] that are technical, economical, and environmentally feasible [58];
• Bioenergy: Biowastes have a great potential to serve as a valuable source for bioenergy production [11]. Hence, some biorefinery processes are applied to recover bioenergy from biowastes (waste-to-energy), e.g., combustion for direct heating and electricity production [24,59,60], transesterification for producing biodiesel [42,45,46,55], and, especially, anaerobic digestion for producing biogas for heat and electricity purposes [10]. As for bioproducts, researchers are also seeking optimal ways to add more value to biofuels and more environmentally friendly processes [28];
• Circularity: A CBE inherently involves circularity at its core. CBE closed the loop between the bioeconomy and the circular economy [32]. In this sense, research trends are going towards new ways of reusing materials and energy in integrated models [33,89], the improvement of technology and processes for feedback loops [44], alternative recycling models in agriculture [25], the analysis of the difference in disposal impacts between recycled and market-substituted products [36], and the optimization of use efficiency in product cascading [24];
• Costs: As seen in Section 4.5, including economic aspects is crucial for the LCT for a CBE. In this regard, further studies must focus on the addition of economic features to ensure the feasibility of CBE projects [46], the reduction of economic uncertainties of producing bio-based products at a larger scale [37], the way to attract more capital investments in alternative value-chains [54], the inclusion of carbon trade schemes [32], and the monetization of the profit for all of the stakeholders of a CBE [44];
• Sustainable development: For thinking of a CBE that contributes to sustainable development, it is essential to consider (in addition to economic aspects) the social issues [41,53,89]. Hence, LCT for a CBE must consider the application of LCSA, which considers the three lifecycle tools (LCA, LCC, and SLCA) [7]. Research areas with regard to this topic focus on methods to consider more stakeholders in LCT studies and promote their engagement [44], the calculation of direct and indirect job positions, the quality of working life [23], and the creation and quantification of the social-economic value of bio-based products [41] that entails a contribution to the sustainability of a bioeconomy and a CBE.

6. Implications for the Stakeholders

The inclusion of economic and social aspects in CBE allows us to take into account the vision of the stakeholders of CBE. From the vision of the SLCA [90], there are five main stakeholders’ categories, namely workers, the local community, consumers, value chain actors (e.g., suppliers or competitors), and society (e.g., government agencies, ONGs); and from an economic vision, some stakeholders can be added, such as owners and shareholders.

The engagement of all of these stakeholders is crucial for achieving the sustainability of a CBE [43]. In this sense, this manuscript has some implications for them. Firstly, workers are at the core of every industrial activity; thus, they must be aware of the importance of the sustainability of CBE and its assessment; for instance, the application of an SLCA will entail the recognition of social hotspots affecting workers and initiatives to enhance working conditions (health and safety), and to ensure the respect of working rights (freedom of association, fair salary, reasonable working hours, social benefits) and human rights (child labor, forced labor, equal opportunities) [90].

The engagement of the local community is essential because it can determine the social acceptance of CBE projects and activities [61]; thus, CBE operations should not bother the community (e.g., putting the health, safety, or security of people at risk). On the contrary, they have to improve the quality-of-life of local citizens by designing initiatives to ensure the access to material and immaterial resources, or local employment, contributing to the development of sustainable communities. By applying LCA, CBE organizations can also measure their products’ levels of human toxicity, reducing this impact for more healthy living conditions for the communities.

Social sustainability assessment through SLCA may entail benefits for consumers to ensure the generation of innocuous products that do not jeopardize their health and safety and include an expanded responsibility over the waste management of bio-based products, promoting responsible consumption. In this sense, it is also imperative that CBE organizations trace reverse logistics strategies which ensure an expanded responsibility over the end life of their products [41]. Furthermore, other value chain actors such as competitors or suppliers can ensure ethical competition and fair agreements.

Moreover, organizations may contribute to a sustainable society by applying SLCA to ensure social issues such as the contribution to economic development, technological development, and combat corruption [90]. This manuscript also has implications for government agencies and policy developers because, as explained in Section 4.4, it is crucial to add a sustainable bioeconomy and CBE to reduce the impacts of products, especially in developing countries.

Finally, applying economic assessment (LCC) and, thus, calculating indicators, such as the net present value and the internal return on investment, offer a complete vision of the economic panorama to CBE business decision-makers (managers, owners, and shareholders). Similarly, applying a complete LCSA (LCA + LCC + SLCA) may help to make better decision-making, considering not only economic but also environmental and social issues that, from now on, must be considered for the development of a sustainable bioeconomy and CBE.

In this sense, CBE business decision-makers can use this manuscript to identify the trends in the assessment of sustainability through LCT of CBE activities. For instance, they can know the most used software, databases, and impact assessment methods to conduct an LCA in their organizations and gain more facility to find similar studies to compare their results, as well as to be aware of the inclusion of economic and social aspects to assess sustainability from a holistic vision, contributing in a tangible way to the sustainability of the bioeconomy and CBE, which is the ultimate objective of this manuscript.

7. Conclusions

This manuscript systematically reviewed the current literature with regard to LCT for a CBE to analyze the development of life cycle tools, the challenges in the application, and future perspectives on research in this topic.

The main issues of this manuscript showed that the related literature is very recent (from 2017 onwards) and is geographically focused on Europe. Most application studies conducted environmental assessments (through LCA) of bio-based products and biofuels that were mainly from agro-industrial wastes. A normally assessed biofuel is biogas (produced by anaerobic digestion), which is used for heat and energy purposes, and the most popular system boundary configuration is from cradle-to-gate.

Furthermore, five challenging topics for LCT for a CBE have been found: the expansion of system boundaries, the consideration of more endpoints, the development and use of regional databases, the development of policies to encourage a CBE, and the addition of economic and social issues. The first three challenges have practical implications for sustainability researchers and practitioners when applying LCA to a CBE. In comparison, the last two challenges have implications for policy developers and decision-makers because they addressed strategic points to endorse holistic sustainability in a CBE and public and private policies to promote CBE activities as a solution to adding value to biowastes and, thus, contributing to the sustainability of a bioeconomy and a CBE.

The areas of research aim to consider microalgal biomass, wastewater, and the animal-origin biomass for CBE and biorefinery processes. This includes the development of high value-added bio-based products and biofuels and ways to minimize their environmental impact. Similarly, the closing of loops in CBE production systems to become more circular, as well as the inclusion of cost assessments and social issues to think of a real contribution of CBE to the sustainability of a bioeconomy need to be considered. Implications for several stakeholders were found, particularly for workers, local communities, society (policy developers), value chain actors, consumers, and decision-makers (owners, managers, and shareholders).

Finally, this review tried to be as comprehensive as possible, using generic keywords, wide-ranging databases, and non-temporal limitations; however, some articles may have been excluded from the study due to not being indexed on these databases or covered by the search string, which is a limitation of this study. However, future studies are suggested to assess the sustainability of bio-based products, considering environmental issues (using LCA), and especially economic (by applying LCC) and social issues (by applying SLCA) for conducting a complete LCSA in CBE and being aware of all the impacts of bio-based products and the feasibility of CBE initiatives. For policy developers, the creation of public policies to encourage a CBE and the sustainability of a bioeconomy, especially in developing and least-developed countries considering policies from developed countries (e.g., European ones) as a benchmark, is recommended.