Citrus Waste Valorisation Processes from an Environmental Sustainability Perspective: A Scoping Literature Review of Life Cycle Assessment Studies

Abstract

Citrus fruits and related processed products represent a major agricultural sector worldwide, contributing to food supply chains and to regional economies, particularly in Mediterranean and subtropical areas. Citrus processing generates significant amounts of post-processing waste, and their sustainable management is a critical challenge, driving growing scientific interest in exploring environmentally sustainable and profitable valorisation strategies. This study aimed at mapping the sustainability of post-processing citrus valorisation strategies documented in the scientific literature, through a scoping literature review based on the PRISMA-ScR model. Only peer-reviewed studies in English were selected from Scopus and Web of Science; in detail, 29 life cycle assessment studies (LCAs) focusing on the valorisation of citrus by-products have been analysed. Most of the studies were focused on essential oil extraction and energy production. Most of the biorefinery systems and valorisation aims proposed were found to be better than the business-as-usual solution. However, results are strongly influenced by the functional unit and allocation method. Economic allocation to the main product resulted in better environmental performances. The major environmental hotspot is the agrochemicals required for crop management. The analysis of LCAs facilitated the identification of valorisation strategies that deserve greater interest from the scientific community to propose sustainable bio-circular solutions in the agro-industrial and agricultural sectors.

1. Introduction

The global agri-food sector faces significant challenges related to waste management, with the increasing consumption of food products leading to substantial amounts of organic residues [1]. Among these, post-processing citrus waste (CW), primarily consisting of peels and pressed pulp, represents approximately 50% of the fruit’s weight [2]. The composition of post-processing citrus waste can vary significantly from different species and cultivars as represented in Figure 1 [3]. Regions with prominent citrus-processing industries, such as southern Italy, face the economic and environmental challenges of managing these residues [4]. The chosen management strategy for these flows directly impacts the environmental sustainability of the sector.

Conventional disposal methods like landfilling (LAND) are often economically unattractive and discouraged by modern environmental policies due to their negative impacts, including greenhouse gas emissions, resource depletion, and water and soil pollution [5].

The scientific literature is increasingly rich in innovative processes for producing bio-based products and energy from citrus residues, in line with the principles of the circular economy. A transition towards more sustainable supply chains can be achieved through the valorisation of CW into valuable resources, moving beyond traditional disposal practices. This aligns with the growing need to adopt more sustainable waste management paradigms based on circular economy principles [6]. These principles propose production models for reducing waste, with the objective of a more efficient use of raw materials, and valorise the secondary raw materials from production waste. To evaluate the environmental performance of those models, a tool recognised worldwide is the life cycle assessment (LCA) method, derived from ISO 14001 standard [7]. LCA makes it possible to analyse each production phase and waste valorisation path, comparing different scenarios, and highlighting environmental hotspots. Therefore, the LCA and LCA-derived methods perfectly integrate with circular economy principles [8,9].

Numerous reviews have explored citrus waste valorisation from technological, biochemical, and sustainability perspectives. As summarised in

Table 1. Brief summary of previous reviews on citrus waste valorisation.

Review	Objectives	Main Results
[10]	To assess citrus by-products in the context of net-zero emissions and explore innovative low-carbon processing technologies.	Highlighted the potential of citrus by-products for carbon footprint reduction in food systems, energy production, and sustainable materials through green processing and renewable energy use.
[11]	To evaluate GHG reduction potentials in citrus and sugarcane by-product valorisation pathways using bioconversion and biorefinery approaches.	Bioconversion methods like fermentation and anaerobic digestion have lower emissions than chemical methods; biorefineries show great sustainability potential.
[12]	To assess the sustainability of orange peel waste valorisation via mass flow and LCA analysis.	Innovative technologies outperformed conventional ones in energy efficiency, yield, and environmental impact; complex biorefineries show environmental benefits but higher costs.
[13]	To systematically review LCA studies on citrus processing, focusing on the drying phase.	Drying is the most energy-intensive phase; gasification and biodiesel production are less sustainable valorisation practices; animal feed and anaerobic co-digestion are more favourable practices, particularly with optimised drying.
[5]	To analyse citrus peel waste characteristics and valorisation methods across different uses.	Direct uses (e.g., animal feed and compost) are widespread; high-value compound extraction is promising but often not economically viable due to processing costs and storage challenges.
[14]	To review methods for extracting value-added products from citrus waste and their applications.	Citrus waste contains bioactive compounds suitable for food, pharma, and energy; enzymatic and chemical extraction methods are discussed along with the need for D-limonene removal in bioethanol production.
[15]	To evaluate limonene recovery from citrus waste and its implications for energy valorisation.	Limonene extraction is crucial before anaerobic digestion or fermentation; greener methods are needed to avoid solvent pollution and energy loss.
[16]	To assess the potential of deep eutectic solvents in green extraction of bioactive compounds from citrus by-products.	Deep eutectic solvents offer a sustainable alternative to conventional solvents, improving extraction efficiency and environmental safety while reducing process costs and toxicity.

, these studies highlight a broad range of applications, from bioactive compound recovery to energy production and emissions reduction. However, they often lack a focus on environmental performance based on standardised LCA methodologies. The novelty of this review lies in the scoping approach adopted: all studies in the literature applying LCA to the valorisation of citrus waste were collected and analysed, considering the entire spectrum of methodologies applied and valorisation strategies considered. This method offers a comprehensive evaluation of citrus waste valorisation systems through a robust environmental sustainability lens. The methodology is divided into four main phases. Firstly, in the definition of goals and scope, system boundaries and functional unit (FU) are defined. The most commonly used system boundaries for analysing agro-industrial activities and waste valorisation strategies are “cradle-to-grave”, which includes the agricultural and transformation phases, and “gate-to gate”, which encompasses only agro-industrial and waste transformation phases. Moreover, when more co-products result from a process, the allocation method is defined. Allocation methods, which are based on mass, economic value or energy, are essential for attributing a part of the environmental impacts to the different co-products of the system. The zero-burden assumption is commonly applied to waste and excludes upstream impacts of the primary product, thereby simplifying the system but potentially underestimating the environmental trade-offs of valorisation pathways. Secondly, in the inventory analysis, all input and output data are collected. Then the characterisation is carried out, followed by the calculation of environmental impacts, i.e., the life cycle impact assessment. Environmental impacts can be at midpoint, or endpoint levels. In particular, the midpoint method characterises impacts at an intermediate level of the cause–effect chain and the advantage is that provides granular and less uncertain environmental results. Conversely, the endpoint method aggregates impacts further down the chain into damages on areas of protection such as human health, ecosystems, and resource availability. The endpoint results are easier to communicate to policymakers and non-experts, but they come with higher uncertainty due to a greater number of modelling assumptions. Finally, the interpretation of results completes the assessment.

This scoping literature review is aimed at synthesising and critically evaluating the various valorisation strategies for citrus waste by examining research studies applying the LCA methodology. The research questions are as follows:

RQ1: What valorisation strategies for citrus waste have been assessed through LCA?

RQ2: What critical factors influence the environmental sustainability of valorisation strategies across different implementation scales?

This review consolidates the current knowledge on the environmental impact of converting citrus waste into a range of valuable products, from biofuels and bio-hydrogen to soluble dietary fibres and other bio-based chemicals, and highlights the critical factors influencing their sustainable implementation across various scales.

2. Materials and Methods

2.1. Research Strategies and Inclusion–Exclusion Criteria

Following the PRISMA statement, the authors of this scoping literature review screened all the articles deriving from the following search:

• In the title, abstract and keywords are as follows: (citrus OR orange OR lemon OR grapefruit) AND (LCA OR (“life cycle assessment”) OR (“carbon footprint”)) AND (peel OR waste OR by-product OR residues OR juice OR pulp);
• Reviews, book chapters, conference proceedings, and conference reviews were excluded;
• Only manuscripts written in English were considered;
• The articles were published between 2013 and 2025.

The databases selected for this review were Scopus and Web of Science since they are widely recognised as the most important data sources for the field under investigation.

To ensure consistency and comparability in the review, the selection of studies followed a set of clearly defined inclusion and exclusion criteria.

Inclusion Criteria:

• Peer-reviewed LCA studies;
• Studies focusing on the valorisation of citrus post-processing biomass, including orange, lemon, and grapefruit residues;
• Articles presenting quantitative environmental impact results (e.g., expressed in standardised units such as kg CO₂ eq, kg SO₂ eq, MJ, etc.).

Exclusion Criteria:

• Conference papers and non-peer-reviewed literature;
• Review articles or meta-studies;
• Studies reporting environmental impacts only in normalised or aggregated form, without raw values;
• LCA studies with unconsistent functional units (FU);
• Studies assessing multi-biomass or multi-feedstock valorisation, unless specific data for citrus waste were clearly distinguishable.

The information needed for a critical analysis of the environmental impacts of citrus waste valorisation strategies was obtained by reading each article and looking for comprehensive environmental impacts reported in tables and graphs. These items allowed for the identification of environmental hotspots and best practices within the analysed strategies. Regarding bias risk, it should be highlighted that inclusion of only peer-reviewed studies is a strength, as it prioritises quality and validated research. However, it might exclude relevant findings from non-peer-reviewed sources (e.g., technical reports, and grey literature) that, while not peer-reviewed, could still contain valuable data, especially for emerging technologies or niche applications. Another limitation concerns the choice of environmental impact categories used to report LCA results. Studies relying on single-issue assessments (such as the carbon footprint only) or endpoint analyses often reduce the level of granularity of results, which complicates consistent and transparent comparisons across scenarios. Moreover, restricting the analysis to LCA studies may introduce a publication bias, as studies reporting ‘negative’ or less favourable environmental outcomes are less likely to be published or pass the peer-review process, thereby contributing to a potential overrepresentation of positive results in the literature. Therefore, a special emphasis was given to those LCA studies in which the baseline scenario (i.e., the business-as-usual option, such as landfilling or conventional waste management practices) performed better than the alternative scenarios (i.e., valorisation strategies such as energy recovery, composting, or bioproduct extraction), to ensure that such results were adequately represented in the synthesis.

The collected data from each selected study were then presented in a comprehensive table showing the characteristics of the LCAs (i.e., FU, systems boundaries, life cycle impact assessment methods, and scenarios), species investigated, year of publication, valorisation aim, and the scale of the study (i.e., laboratory or industrial scale).

2.2. Bibliometric Analysis

To complement the quantitative findings of the review, a bibliometric keyword co-occurrence analysis was performed by using the VOSviewer software (version 1.6.20). This approach aimed at identifying thematic clusters and research trends across the LCA studies related to citrus waste valorisation.

The VOSviewer network was generated from author keywords and index terms extracted from the selected publications. Terms with at least 4 occurrences were included to ensure relevance and reduce noise. Keywords were cleaned and normalised (e.g., “bio-energy” in “bioenergy”) to merge synonyms and spelling variations. VOSviewer’s clustering algorithm grouped terms based on the strength of their co-occurrence in the same documents, revealing clusters that represent major thematic areas in the literature.

Each node represents a keyword, with its size being proportional to its frequency. Connections between nodes indicate co-occurrence relationships, and colours denote clusters identified by the software. The analysis thus offers a visual representation of how research themes interconnect, supporting qualitative interpretation of the LCA findings. A map was developed based on the keywords extracted from the corpus of LCA studies analysed in this review, and therefore, all the words “ life cycle”, “life cycle assessment” and “lca” were removed from the analysis as it was assumed that every article in the panel would have at least one of these terms and so it would be meaningless for the co-occurrence keyword analysis.

3. Results

3.1. Bibliographic Research and Article Classification

Following the PRISMA statement, Figure 2 shows the flowchart of the identification–screening–inclusion framework. The identification phase was supported by automatic tools offered by the databases, which were useful to disregard in the review paper, conference papers, and book chapters. Firstly, the screening phase required reading of all the titles and abstracts, resulting in the removal of nine articles belonging to other fields of research. Secondly, a more in-depth reading of the manuscripts was required to eliminate articles where the methods and results appeared to align with the exclusion criteria.

The co-occurrence network from VOSviewer revealed three dominant thematic clusters reflecting the structure and evolution of research in citrus waste valorisation from an environmental perspective (Figure 3). The purple group is the most densely connected and central in the network. It includes keywords such as citrus fruits, biomass, biorefinery, biogas, circular economy, environmental sustainability, essential oils, pectin, extraction, climate change, and waste valorisations. The emphasis is on valorising citrus by-products within biorefinery systems and closed-loop production models that support circular economy goals. High-value product recovery (e.g., limonene, and cellulose) is also a focus, especially in conjunction with environmental indicators like climate change. The keywords in green include sustainable development, carbon footprint, economic analysis, carbon dioxide, food waste, and techno–economic analysis, representing studies grounded in LCA-based environmental accounting and economic feasibility assessments.

The co-occurrence of environmental and economic terms highlights the growing demand for integrated sustainability evaluation frameworks that support informed decision-making. The blue group of words includes bioenergy, global warming, orange peels, and waste incineration, indicating studies addressing the potential of thermal valorisation (e.g., incineration, and combustion) of citrus residues and their implications in terms of greenhouse gas emissions. The connection to global warming and carbon dioxide suggests that these pathways are frequently evaluated for their climate-related trade-offs. The keywords in yellow centre on terms such as anaerobic digestion, biofuel, cellulose, citrus, and refining. This group of connected words captures the interest in biochemical conversion processes (e.g., fermentation, and enzymatic hydrolysis) and the recovery of energy or materials from citrus waste. The presence of cellulose and biofuel indicates the exploration of citrus residues as second-generation bioenergy sources. These results emphasise the importance of energy-efficient technologies, territorial LCA approaches, and interdisciplinary research in future studies aimed at sustainable bio-circular transitions in agro-industrial systems. The term “citrus fruits” acts as the central node, connecting all clusters and underlining the multidisciplinary nature of this research domain, which spans agricultural systems, industrial biotechnology, and environmental science. Thematic convergence in the network also suggests that the majority of studies focus on citrus waste, in general, or orange peel waste (OPW) and less on lemons and grapefruits.

Overall, this thematic analysis confirms that while a wide range of valorisation pathways for citrus waste is being explored, not all strategies perform equally from an environmental standpoint. It highlights the importance of integrating scoping LCA approaches with territorial and technological considerations to advance sustainable solutions for citrus by-product management.

3.2. Objectives and Findings from Selected Articles

All the selected articles described LCA studies on the valorisation of citrus post-processing waste. Table 2 shows the main methodological features of each article selected in this review. Columns 5 to 9 refer to LCA methodological aspects, which are useful for analysing the results of the studies. As shown in Figure 4, most of the studies and experiments have been developed in Italy, Latin America, and India. In Italy, a wide range of topics has been developed, including energy purposes, bio-based products, animal feed, and fertilisers. In Figure 5 the total count is more than 29 because each study usually explores and proposes more than one scenario and valorisation aim, the topics of the studies are briefly summarised as well as the areas where they were developed; the considered valorisation strategies are summarised in Figure 6. The total count in the table is more than the 29 papers because each study usually explores and proposes more than one scenario and valorisation aim.

In Table 2, particular attention should be paid to the “best scenario” column as it highlights the best scenario among those reported in the scenario column which emerged for each study, and represents a significant indicator of CW management best practices. Finally, the last column indicates if the study was conducted at industrial (IND) or laboratory (LAB) scale. Most of the LAB scale studies present technical methods to convert CW into value-added products such as essential oils (EO), limonene, pectin, biofuels, and biogas. From the selected studies, the co-digestion of CW with other agro-industrial and agricultural waste, and anaerobic digestion (AD) in combination with the extraction of EOs, also referred to “complex biorefineries” in Table 2, emerge as best environmental practices. These two practices, above all, showed lower environmental impacts in terms of Global Warming Potential (GWP), acidification (AC), and human toxicity (HT) [15,17,18,19]. Complex biorefinery such as those proposed by Machine–Ferrero et al. and Mariana et al. [17,18] resulted in better environmental results when analysed by using economic allocation. Ortiz-Sanchez et al. [19] also assessed that scenarios involving biogas production showed higher levels of the social sustainability index. Nevertheless, this practice seems to represents a risk for water eutrophication [15,20] and water depletion [18].

Table 2. Summary of main characteristics of the selected articles.

Ref	Year	Location	Species	Scenarios	Valorisation Aim	Functional Unit	System Boundaries	Best Scenario	LCIA 1 Method	Scale
[21]	2013	Florida	Citrus	Biomethane, limonene, digestate production (small refinery); small refinery + ethanol (large refinery)	Integrated biorefinery, biofuel and energy production	1 ton CW for comparison	Cradle-to-gate (Credits for replacing fossil fuels)	Large biorefinery	ISO 14040:2006 [7]	IND
[22]	2016	Turkey	Orange	Pectin jelly film vs. LDPE 2	Packaging replacement	1 m2 film polymer for packaging	Cradle-to-gate + simulated biodegradation	LDPE2	CML-IA baseline	LAB
[15]	2017	Italy	Orange	Incineration; limonene extraction; AD; Co-digestion; compost; FEED; LAND	Waste treatment and energy	1 t OPW wet weight	Zero burden approach	Co-digestion and FEED	IPCC 2007, ReCiPe (2008), CML 2002	IND
[23]	2018	United Kingdom	Citrus	PLC from citrus vs. algae	Biopolymer production	21,600 t PLC/year	Cradle-to-gate	Citrus-based PLC	ReCiPe Midpoint (SimaPro)	IND
[24]	2019	Italy	Citrus	Natural gas vs. gasification + CHP 3	Energy recovery	35,000 t citrus peels/year	Partial cradle-to-gate	Integrated system	Carbon footprint	IND
[25]	2019	Mexico	Orange	Fuel oil vs. orange peel as solid biofuel	Energy and biofuel production	1 MJ steam	Gate-to-gate	Orange peel biofuel	ISO 14040:2006	IND
[26]	2020	India	Orange	EO or pectin extraction to ethanol, limonene, methane	Biorefinery	2500 kg citrus waste	Gate-to-gate	Microwave-based	ISO 14040:2006	IND
[20]	2020	Colombia	Orange	Landfill vs. AD vs. INC	Energy production	1 L juice	Cradle-to-gate	INC or AD spreading digestate	ILCD	IND
[27]	2020	Spain	Citrus	Hydro-distillation; cold pressing; ethanol or hexane as solvent extractive agents	D-limonene extraction	100 kg/h citrus waste	Cradle-to-gate	Cold pressing	CML 2001 v2.05	IND
[28]	2021	Italy	Orange	Innovative metal-adsorbent polymer vs. activated carbon	Eos and polymer	1 kg organic residue	Gate-to-gate	Activated carbon	Midpoint EF 3.0	LAB
[29]	2021	Italy	Lemon, orange, olive pomace	Pyrolysis at 400–650 °C of different agro-industrial waste.	Energy	1 MJ thermal energy	Cradle-to-gate	Orange peel pyrolysed at 500 °C	ILCD 2011 midpoint	LAB
[18]	2020	Colombia	Orange	LAND vs. complex or high-complex biorefinery + AD (EO, esperidind, pectine, acetone, ethanol, buthanol, biogas, and fertiliser production)	Integrated biorefinery and energy production	1 L of orange juice	Cradle-to-gate	High-complex biorefinery	ReCiPe midpoint	IND
[30]	2021	Italy	Citrus	Gasification including and excluding CW drying	Electricity generation	1 MWh	Cradle-to-gate	Excluding drying	CO2-eq comparison	IND
[31]	2022	Italy	Orange	Essential oil and pectin production	EOs extraction	15 kg processed orange	Cradle-to-gate	Steam distillation	ReCiPe 2016 midpoint (H)	IND
[32].	2022	Mexico	Orange	LAND vs. wax recovery	Fungicide production	1 m2 fungicide	Cradle-to-gate	Wax recovery	CML-IA 2016	LAB
[17]	2022	Argentina	Lemon	Syngas, biogas, co-digestion	Energy	1 kg lemon	Cradle-to-gate	Co-digestion	ReCiPe 2016 midpoint (H)	IND
[33]	2022	Mexico	Orange and sugarcane straw	Heavy fuel oil vs. orange peels + sugarcane straw heat production	Biomass-based heat	44,150 MWh/year heat	Cradle-to-gate	Orange peels + straw heat recovery	CML-IA baseline	IND
[34]	2022	Italy	Citrus	Bio-hydrogen from gasification	CHP and hydrogen production	1 kg H2	Gate-to-gate	Alternative process	Not specified	IND
[35]	2022	India	Orange	Biochar-catalysed biodiesel	Biofuel production	1 kg biodiesel	Well-to-wheel	FW-based biodiesel	ReCiPe 2016 midpoint	LAB
[36]	2022	Denmark	Orange	Biorefinery, animal feed, incineration	Integrated biorefinery, energy production, and animal feed	1 t OPW	Cradle-to-gate	Wind + biogas (attributional)	EF method (EU)	LAB
[37]	2023	India	Orange	Extrusion vs. ultrasonication	SDF from orange peel	0.1 kg fresh orange peel	Gate-to-gate	Extrusion	CML 2001	LAB
[38]	2023	India	Orange	Micronisation, autoclave, hybrid	SDF from orange peel	0.1 kg fresh orange peel	Gate-to-gate	Hybrid method	CML 2001	LAB
[39]	2023	India	Mixed	SDF concentration methods: micronisation, autoclave, extrusion, and ultrasonication	Energy production	Not specified	Cradle-to-gate	Extrusion	Carbon footprint	IND
[40]	2023	Spain–Germany	Orange	Limonene vs. petrochemical TMB	Eos extraction	1 t expander molecule	Cradle-to-gate	Limonene-based	Not specified	IND
[41]	2024	Argentina	Lemon	Conventional, biogas, biomass, compost	Energy, compost	1 t product	Cradle-to-gate	Biogas, biomass and compost	ISO 14040:2006	IND
[42]	2024	Italy	Orange	Pectin + limonene extraction	Biobased chemical production	300 g OPW	Post-transformation	One-pot extraction	Impact 2002+	LAB
[19]	2024	Colombia	Orange	AD, Steam distillation, enzymatic hydrolysis, integrated biorefinery	Integrated biorefinery and energy production	1 kg orange peel	Gate-to-gate	EO extraction+ AD	ISO 14040:2006	IND
[43]	2025	Spain	Orange (and tomato)	Solvent, ultrasound, microwave, subcritical water extraction	Phenolic compound production	100 t phenolic powder/year	Cradle-to-gate	Microwave	ReCiPe midpoint and endpoint	IND
[44]	2025	Italy	Grapefruit	Pectin extraction: conventional heating vs. bacteria encapsulation	Bacteria encapsulation	1 kg encapsulated bacteria	Gate-to-gate	Conventional heating	ILCD 2011	LAB

¹ Life cycle impact assessment. ² Low-density polyethylene. ³ Combined heat and power.

Table 2. Summary of main characteristics of the selected articles.

Ref	Year	Location	Species	Scenarios	Valorisation Aim	Functional Unit	System Boundaries	Best Scenario	LCIA 1 Method	Scale
[21]	2013	Florida	Citrus	Biomethane, limonene, digestate production (small refinery); small refinery + ethanol (large refinery)	Integrated biorefinery, biofuel and energy production	1 ton CW for comparison	Cradle-to-gate (Credits for replacing fossil fuels)	Large biorefinery	ISO 14040:2006 [7]	IND
[22]	2016	Turkey	Orange	Pectin jelly film vs. LDPE 2	Packaging replacement	1 m2 film polymer for packaging	Cradle-to-gate + simulated biodegradation	LDPE2	CML-IA baseline	LAB
[15]	2017	Italy	Orange	Incineration; limonene extraction; AD; Co-digestion; compost; FEED; LAND	Waste treatment and energy	1 t OPW wet weight	Zero burden approach	Co-digestion and FEED	IPCC 2007, ReCiPe (2008), CML 2002	IND
[23]	2018	United Kingdom	Citrus	PLC from citrus vs. algae	Biopolymer production	21,600 t PLC/year	Cradle-to-gate	Citrus-based PLC	ReCiPe Midpoint (SimaPro)	IND
[24]	2019	Italy	Citrus	Natural gas vs. gasification + CHP 3	Energy recovery	35,000 t citrus peels/year	Partial cradle-to-gate	Integrated system	Carbon footprint	IND
[25]	2019	Mexico	Orange	Fuel oil vs. orange peel as solid biofuel	Energy and biofuel production	1 MJ steam	Gate-to-gate	Orange peel biofuel	ISO 14040:2006	IND
[26]	2020	India	Orange	EO or pectin extraction to ethanol, limonene, methane	Biorefinery	2500 kg citrus waste	Gate-to-gate	Microwave-based	ISO 14040:2006	IND
[20]	2020	Colombia	Orange	Landfill vs. AD vs. INC	Energy production	1 L juice	Cradle-to-gate	INC or AD spreading digestate	ILCD	IND
[27]	2020	Spain	Citrus	Hydro-distillation; cold pressing; ethanol or hexane as solvent extractive agents	D-limonene extraction	100 kg/h citrus waste	Cradle-to-gate	Cold pressing	CML 2001 v2.05	IND
[28]	2021	Italy	Orange	Innovative metal-adsorbent polymer vs. activated carbon	Eos and polymer	1 kg organic residue	Gate-to-gate	Activated carbon	Midpoint EF 3.0	LAB
[29]	2021	Italy	Lemon, orange, olive pomace	Pyrolysis at 400–650 °C of different agro-industrial waste.	Energy	1 MJ thermal energy	Cradle-to-gate	Orange peel pyrolysed at 500 °C	ILCD 2011 midpoint	LAB
[18]	2020	Colombia	Orange	LAND vs. complex or high-complex biorefinery + AD (EO, esperidind, pectine, acetone, ethanol, buthanol, biogas, and fertiliser production)	Integrated biorefinery and energy production	1 L of orange juice	Cradle-to-gate	High-complex biorefinery	ReCiPe midpoint	IND
[30]	2021	Italy	Citrus	Gasification including and excluding CW drying	Electricity generation	1 MWh	Cradle-to-gate	Excluding drying	CO2-eq comparison	IND
[31]	2022	Italy	Orange	Essential oil and pectin production	EOs extraction	15 kg processed orange	Cradle-to-gate	Steam distillation	ReCiPe 2016 midpoint (H)	IND
[32].	2022	Mexico	Orange	LAND vs. wax recovery	Fungicide production	1 m2 fungicide	Cradle-to-gate	Wax recovery	CML-IA 2016	LAB
[17]	2022	Argentina	Lemon	Syngas, biogas, co-digestion	Energy	1 kg lemon	Cradle-to-gate	Co-digestion	ReCiPe 2016 midpoint (H)	IND
[33]	2022	Mexico	Orange and sugarcane straw	Heavy fuel oil vs. orange peels + sugarcane straw heat production	Biomass-based heat	44,150 MWh/year heat	Cradle-to-gate	Orange peels + straw heat recovery	CML-IA baseline	IND
[34]	2022	Italy	Citrus	Bio-hydrogen from gasification	CHP and hydrogen production	1 kg H2	Gate-to-gate	Alternative process	Not specified	IND
[35]	2022	India	Orange	Biochar-catalysed biodiesel	Biofuel production	1 kg biodiesel	Well-to-wheel	FW-based biodiesel	ReCiPe 2016 midpoint	LAB
[36]	2022	Denmark	Orange	Biorefinery, animal feed, incineration	Integrated biorefinery, energy production, and animal feed	1 t OPW	Cradle-to-gate	Wind + biogas (attributional)	EF method (EU)	LAB
[37]	2023	India	Orange	Extrusion vs. ultrasonication	SDF from orange peel	0.1 kg fresh orange peel	Gate-to-gate	Extrusion	CML 2001	LAB
[38]	2023	India	Orange	Micronisation, autoclave, hybrid	SDF from orange peel	0.1 kg fresh orange peel	Gate-to-gate	Hybrid method	CML 2001	LAB
[39]	2023	India	Mixed	SDF concentration methods: micronisation, autoclave, extrusion, and ultrasonication	Energy production	Not specified	Cradle-to-gate	Extrusion	Carbon footprint	IND
[40]	2023	Spain–Germany	Orange	Limonene vs. petrochemical TMB	Eos extraction	1 t expander molecule	Cradle-to-gate	Limonene-based	Not specified	IND
[41]	2024	Argentina	Lemon	Conventional, biogas, biomass, compost	Energy, compost	1 t product	Cradle-to-gate	Biogas, biomass and compost	ISO 14040:2006	IND
[42]	2024	Italy	Orange	Pectin + limonene extraction	Biobased chemical production	300 g OPW	Post-transformation	One-pot extraction	Impact 2002+	LAB
[19]	2024	Colombia	Orange	AD, Steam distillation, enzymatic hydrolysis, integrated biorefinery	Integrated biorefinery and energy production	1 kg orange peel	Gate-to-gate	EO extraction+ AD	ISO 14040:2006	IND
[43]	2025	Spain	Orange (and tomato)	Solvent, ultrasound, microwave, subcritical water extraction	Phenolic compound production	100 t phenolic powder/year	Cradle-to-gate	Microwave	ReCiPe midpoint and endpoint	IND
[44]	2025	Italy	Grapefruit	Pectin extraction: conventional heating vs. bacteria encapsulation	Bacteria encapsulation	1 kg encapsulated bacteria	Gate-to-gate	Conventional heating	ILCD 2011	LAB

¹ Life cycle impact assessment. ² Low-density polyethylene. ³ Combined heat and power.

Most of the studies emphasised sustainability and the circular economy concept, aiming at improving environmental profiles by substituting traditional waste disposal methods (i.e., landfilling, and incineration) with valorisation techniques. However, some studies declared that the valorisation solution proposed was not environmentally sustainable. This is the case of Günkaya et al. [22] and Amato et al. [28] who compared a complex valorisation process aiming at producing a value-added product from CW with the traditional products it had to substitute. In particular, Günkaya et al. [22] revealed that creating 1 m² of the suggested biodegradable bio-composite film, made from pectin jelly derived from orange peels and corn starch, resulted in greater environmental impacts than LDPE across nearly all evaluated categories, such as global warming, abiotic resource consumption, toxicity, and eutrophication. The only exception was acidification, primarily caused by electricity consumption during the extrusion process and the use of modified starch. This finding highlights the environmental limitations of producing sustainable bioplastics for packaging within a circular economy context.

Findings from the most common valorisation strategies revealed that composting could be considered a simple and sustainable solution. It enables nutrient recovery and humus formation, and it lowers the environmental impacts of CW management when compared to the landfill scenario [15]. On the other hand, it has a low economic value, and it causes acidification due to ammonia emission, and the presence of EO or other value-added chemicals compounds makes the composting process more difficult to be obtained when compared to other biomasses such as olive pomace [45]. Therefore, the best practice to be considered should be initially extracting EO and implementing other biorefinery valorisation and then valorising the remaining CW through composting. Other solutions, environmentally suitable after the EO and pectin extraction, are anaerobic digestion and the co-digestion of CW with other biomass, which generate renewable energy. Moreover, the remaining digestate can be used as fertiliser. This practice can reduce climate change impacts by 72% and it also has a positive effect on many other impacts: terrestrial acidification, human toxicity, freshwater ecotoxicity, marine ecotoxicity, ionising radiation, agricultural land occupation, urban land occupation, water depletion, metal depletion, and fossil depletion.

Some of the LCA studies [13,20,25,30,34,38] regard EOs and value-added chemicals as the main co-products of citrus processing, instead of a waste, demonstrating how it might be economically attractive from some industrial contexts. In practical terms, this means that the cradle-to-gate study proposes an agro-industrial system integrated with the biorefinery plant for extracting value-added products, emphasising the importance of transportation distances in valorisation strategies and industrial symbiosis. Da Costa et al. [31] used an economic allocation model and, in particular, pectin was assigned 84.79% of the impact (main product), essential oil was assigned 13.24% of the impact, and juice was assigned 1.97% of the impact. This choice is justified by the higher market value and yield of pectin, making it the dominant economic product. Machin–Ferrero et al. [17] allocated about 21% to EOs, 69% to concentrated juice, and 9% to dehydrated peel. This choice underlined the common practice in Latin America, particularly in Argentina, to consider dehydrated citrus peel as a marketable product [41].

3.3. Technical Differences in the Analysed Citrus Waste Valorisation Processes

Techniques for valorising citrus waste vary significantly, including steam distillation, cold pressing, hydro-distillation, solvent extraction, ultrasonication, extrusion, micronisation, pyrolysis, anaerobic digestion, and combined extraction methods for limonene and pectin.

Industrial-scale assessments dominate the field (66%), suggesting increasing interest in commercialisation. Nevertheless, laboratory-scale studies (34%) are essential for testing emerging techniques like microwave-assisted extraction, thermo-sonication, or hybrid digestion systems.

Some of the technical details and engineering choices that hinder the efficiency of pyrolysis in the process of valorising citrus waste are high operating temperatures, prolonged process times and sub-optimal valorisation of by-products (gas, bio-oil, biochar and heat), which could instead be used as alternative energy sources. The aforementioned factors result in high energy consumption, especially when the energy used comes from the conventional electricity grid powered by fossil fuels. A number of studies have demonstrated that pilot or small-scale plants exhibit considerably diminished thermal and energy yields in comparison to optimised industrial plants. A recent study [29] demonstrated that the pyrolysis of orange waste at 500 °C results in a reduced environmental impact in comparison to other agro-industrial residues, such as olive pomace and lemon peel, with an average reduction of 16% compared to olive pruning residues, for example. The study under discussion draws attention to the fact that the principal contribution to environmental impacts is made by electricity consumption during the operational phase. It is therefore suggested that the use of renewable sources [46] to power the process or combustion systems, self-financed through the biochar produced, can significantly increase the sustainability of pyrolysis. In terms of impact categories, this translates into an increase mainly in GWP.

Studies selected also explored different technical practices to extract EO and pectin. The best practices from an environmental point of view are the following:

• Steam distillation [31]: It represents a traditional method and has low environmental impacts thanks to the simplicity of its application because it does not need organic solvents and it works with low temperatures (about 100 °C).
• Cold pressing: It is a technique that consumes less energy compared to steam distillation (lower temperatures about 60 °C) and does not require solvents [31,42].
• Microwave-assisted extraction: It is effective due to the reduced extraction time and the possibility of avoiding solvents. Amato et al. [28] found >90% of ethanol recovery, while Da Costa et al. [31] found higher essential oil yield with ~30–50% of energy savings compared to conventional distillation, and reduced water usage.
• Ultrasonication: It is a practice suitable for its high efficiency and high-quality product production. It was found that the CC impact is about 22.9 g CO₂-eq/MJ for limonene while the acetone substitution was >90 g CO₂-eq/MJ. Moreover, this technique can increase pectin or EO yield by 10–40% compared to conventional methods, improving mass efficiency [31,42].
• One-pot extraction: It makes it possible to extract multiple chemicals compounds in one line of production [42].

3.4. Summary of Key Findings of Scoping Review

Key findings from selected studies included the following:

• Biorefinery alternatives are environmentally superior to OPW landfilling.
• Greater complexity in biorefinery configurations may increase the environmental burden attributed to the main citrus product (e.g., juice or marmalade) when using mass allocation. This trend is not observed under economic allocation, which distributes the impacts more favourably due to the inclusion of high-value co-products. Mass allocation is more appropriate when the functional unit is associated with biorefinery-derived products, since these typically represent a small proportion of the total product mass, and allocating impacts by mass better reflects their relative contribution to the system.
• A shift from attributional to consequential analysis is deemed not possible because products like pectin, essential oil, ethanol, butanol, acetone, and orange do not act as inputs to each other’s production processes, making system expansion or substitution approaches methodologically inappropriate. This approach is indeed more suitable for sustainability studies of energy recovery systems.

4. Discussion

The scientific literature is rich in studies proposing biomass valorisation strategies for citrus post-processing waste. Environmental and economic sustainability assessments of well-established circular economy approaches—such as essential oil extraction—often model citrus biomass as a by-product and apply economic allocation in LCA. However, the choice of allocation method has a significant influence on the results of environmental impact assessments, highlighting the importance of methodological consistency and transparency in LCA studies. Indeed, using economic allocation for citrus waste valorisation generally led to a reduction in environmental impacts of the valorisation process. Economic allocation distributes the environmental burdens of a multi-output process based on the economic value of each product. This can lead to lower impacts assigned to the main product (e.g., orange juice) when high-value co-products (e.g., essential oil, pectin, hesperidin) are produced alongside it. Consequently, when the number and value of co-products increase, the main product or the functional unit receives less environmental burden under economic allocation. This explains why in some studies, more complex biorefineries, with more high-value products, show decreasing CO₂, PM, and N emissions under economic allocation [18,21,36].

Given the significance attributed to EOs and the environmental implications of pomace dehydration [5,13], future research initiatives may concentrate on cultivar selection and development, with the objective of cultivating varieties with reduced water content, while concurrently enhancing EO yield [47] and energy savings associated with CW processing.

It was observed that laboratory-scale articles explored and proposed alternative solutions and products for the valorisation of citrus post-processing waste. In general, biorefinery practices and waste management strategies, including biomass valorisation, need more complex analysis and consideration when accounting for environmental impacts. On one hand, adding process, solvents, chemicals, and energy for biorefinery and value-added chemical products makes environmental impacts grow compared to simpler valorisation strategies. On the other hand, it would be useful to compare the production of value-added and substitutive products to the production of traditional products and compare the sustainable source. For example, Garcia–Cruiz et al. [32] found that delivering insoluble orange wax to landfill is a more sustainable practice than transforming it into a solid fuel. Instead, it would be beneficial to compare the production of traditional solid fuel with the citrus valorisation strategy. In the case study analysed by Günkaya et al. [22], the traditional production of LDPE for packaging resulted in better environmental performance with respect to the orange peel-derived film. Thus, the correct methodology for evaluating the valorisation system of those products is to compare the alternative product with the traditional one, since comparing it with a simpler product that could be obtained from citrus waste might not be useful.

Talking about LCA methodological aspects, in the papers analysed in this review, variations exist in the choice of FU, ranging from mass-based units (e.g., 1 kg of extracted limonene or pectin), to energy units (MWh of electricity produced from citrus residues), or even to economic units (e.g., revenue-based FU).

While some studies used well-known methods such as ILCD 2018, Eco-Indicator 99, or CML2001, others applied alternative or hybrid approaches. Commonly assessed impacts included climate change (carbon footprint), eutrophication, human toxicity, freshwater ecotoxicity, and resource depletion.

Differences are notable in allocation procedures. Some studies applied economic allocation, while others prefer mass or energy allocation depending on the study’s goal, significantly influencing the results:

• Economic allocation generally results in worse environmental performance (higher impacts per unit) for economically valuable but mass-scarce products (such as essential oils, and limonene), as these are assigned a greater share of impacts based on economic value. This is particularly evident for those articles comparing the two allocation models. Conversely, lower-value products (such as compost or animal feed) receive lower impacts, improving their apparent environmental performance. Economic allocation is to be preferred when the overall circular economy benefits and integrated sustainability of the entire citrus waste valorisation system would be emphasised.
• Mass allocation tends to assign environmental burdens proportionally based on mass, typically distributing impacts more evenly across products, significantly lowering impacts per unit for high-value low-mass products. Usually, this methodological choice leads to better environmental performance (lower impacts per unit) for valuable products due to small mass proportions compared to total processed biomass. Mass allocation is more favourable when assessing or highlighting specific high-value products (such as essential oils or purified compounds like limonene), as this allocation significantly reduces the perceived environmental impacts per unit produced, making these products appear more sustainable individually.

When the FU is directly related to the citrus waste processed, economic allocation often provides a balanced or even favourable result, clearly showing sustainability benefits because impacts are shared among multiple economically valuable outputs.

Conversely, when the FU is directly related to a specific, high-value, low-yield valorised product, the choice of economic allocation typically yields higher reported environmental impacts. On the other hand, mass allocation typically yields significantly lower environmental impacts for these products.

Despite the progress outlined, several gaps remain that warrant further investigation. First, there is a need for harmonised and geographically contextualised LCA frameworks that account for regional differences in energy mixes, transportation infrastructure, and waste composition. Such frameworks would improve the comparability of results and support evidence-based policymaking. Secondly, future research should explore LCA methodologies integrated with process modelling tools to support decision-making during the design phase of valorisation systems. Indeed, many studies have been developed at the laboratory scale and cannot give any information about the scalability of the solution.

Additionally, greater emphasis should be placed on techno–economic assessment together with environmental evaluation to ensure the commercial feasibility of bio-based product systems. Exploring the synergies between emerging valorisation technologies, such as enzymatic hydrolysis, green solvent extraction, and microbial fermentation, could yield novel process configurations with enhanced environmental and economic performance.

5. Conclusions

The increasing quantities of organic waste, particularly from the agro-industrial sector, highlight an emerging need for sustainable management strategies. In order to achieve the sustainable utilisation of citrus waste, it is essential to select methodologies that combine high process efficiency, the use of renewable energy sources, and the complete utilisation of secondary products. Conversely, traditional or inefficient technologies have been shown to have a distinctly negative impact on the environment, making them less sustainable; thus, where possible, their use should be avoided. The results of the articles selected for this scoping literature review demonstrate that extraction of EOs from citrus waste is an increasingly widespread practice. This means that it requires significant efforts to reduce the environmental impact of extraction practices. Furthermore, extraction by means of ethyl acetate EOs is a fundamental practice that makes other strategies for the recovery of citrus waste, such as anaerobic digestion and composting, more sustainable.

In order to facilitate studies on the sustainability of industrial processes, it is necessary to promote a systemic energy transition that incorporates both enhanced resource efficiency and increased utilisation of alternative sources to fossil fuels.

Moreover, it is evident that the selection of appropriate allocation criteria can exert a substantial influence on the environmental impacts associated with diverse practices.

This review underscores significant implications for public policy, notably the necessity for regulatory frameworks that can facilitate the valorisation of citrus waste while ensuring environmental integrity and consumer safety. At the industrial level, the findings emphasise the significance of plant design choices, where technology selection, process integration, and logistics strongly influence environmental performance and economic viability. It is recommended that future research adopt a more interdisciplinary approach, moving beyond laboratory-scale assessments to include experimental testing at pilot and industrial scales. In addition, transport modelling and GIS-based analyses should be applied to evaluate supply chain distances and environmental trade-offs. Furthermore, studies on consumer acceptance should be conducted. Collectively, these efforts are pivotal in facilitating the sustainable and large-scale implementation of citrus waste valorisation initiatives within a circular economy framework.