Sustainable Treatments in Denim Fabric: A Systematic Review of Environmental Impact

Abstract

The denim production is among the most polluting processes in textiles due to its high consumption of water, energy, and chemicals. This study presents a Systematic Literature Review (PRISMA 2020) on sustainable treatments applied to denim, with emphasis on their environmental impacts, evaluation methodologies, and main implementation challenges. A total of 26 open-access articles published between 2020 and 2024 in Scopus and Web of Science, in English and Spanish, were analyzed. The most relevant treatments include enzymes, ozone, laser, nebulization, and recycled materials, which report reductions of up to 60% in water consumption, decreased use of chemicals, lower CO₂ emissions, and reduced solid waste generation, consolidating them as viable alternatives to conventional methods. Life Cycle Assessment (LCA) emerges as the main evaluation tool, although its application remains partial and inconsistent. The findings highlight the need to standardize methodologies and integrate economic, social, and regulatory dimensions in order to foster a sustainable transition aligned with the Sustainable Development Goals.

1. Introduction

Denim, a durable and versatile fabric, has retained its relevance since the 17th century. Originally conceived as workwear, it has now become an icon of contemporary fashion [1]. The growing demand for denim garments has intensified finishing processes, particularly washing, making it one of the most polluting stages in the textile value chain. It is estimated that producing a single pair of jeans may require up to 3781 litres of water, generate 33.4 kg of CO₂, and use approximately 12 m² of land [2,3].

The use of synthetic indigo, along with reactive dyes and dyeing auxiliaries, produces effluents loaded with toxic substances and microfibres that contaminate water bodies and soils [4]. These practices, common in wet textile processing, exacerbate the environmental impact, with water consumption representing between 18% and 42% of the total used throughout the production chain [5,6]. Furthermore, prolonged exposure to harsh chemical agents poses significant risks to human health and biodiversity [7,8,9].

In this context, sustainability emerges as a strategic axis for the denim industry and is directly linked to the Sustainable Development Goals (SDGs)particularly SDG 6 (Clean Water and Sanitation), SDG 9 (Industry, Innovation and Infrastructure), SDG 12 (Responsible Consumption and Production), and SDG 13 (Climate Action). The adoption of clean technologies in denim finishing processes has led to measurable improvements environmental performance response and a commitment to global targets for reducing water and carbon footprints, promoting the transition towards a circular economy, and mitigating the effects of climate change.

The circular economy refers to a production model aimed at minimizing waste and maximizing resource efficiency by extending product lifecycles through recycling, reuse, and sustainable design [10]. Similarly, Life Cycle Assessment (LCA) is a standardized methodological framework (ISO 14040/14044) that quantifies the environmental impacts associated with a product or process throughout its entire lifecycle, from raw material extraction to disposal [11].

Emerging technologies such as ozone washing, laser fading, enzymatic treatments, and wastewater reuse are positioned as alternatives with a lower ecological footprint [8,12,13]. These innovations aim to significantly reduce the consumption of water, chemicals, and energy, as well as the generation of solid waste, aligning with the principles of circular economy. At the same time, the growing consumer interest in environmental impact has driven greater demand for sustainable denim garments, positioning sustainability as a key element in the transformation of denim finishing processes. As highlighted by Lou and Xu [14], this trend reflects increased environmental awareness and represents a strategic opportunity for producers and retailers by aligning technological innovation with market expectations.

The effective implementation of sustainable treatments still faces significant challenges. Previous studies have highlighted the lack of comprehensive LCA, limitations in scalability and industrial replicability, and gaps in the measurement of economic and social indicators specific to the textile sector [15,16]. Although several reviews have addressed sustainability in textiles, these have typically focused on general processes or isolated technologies, without systematically integrating recent evidence related to denim. This research gap underscores the relevance of conducting an updated and comprehensive analysis that synthesizes the advances, barriers, and opportunities within the sector.

This systematic review addresses a significant research gap by integrating evidence on sustainable denim finishing technologies published between 2020 and 2024, a period of accelerated innovation toward carbon and water footprint reduction. Unlike earlier fragmented studies focused on single processes, this review consolidates findings across environmental, technological, and methodological dimensions.

Given this scenario, the present Systematic Literature Review (SLR) aims to critically analyze sustainable treatments applied to denim, their environmental impacts, the methodologies used for their assessment, and the challenges and opportunities identified in the recent literature. To achieve this, studies published in the Scopus (Elsevier B.V., Amsterdam, Netherlands) and Web of Science Core Collection (Clarivate Analytics, Philadelphia, PA, USA) were compiled and examined, with the purpose of providing consolidated evidence that promotes the adoption of cleaner practices in the denim processing and contributes to mitigating its global environmental impact.

2. Materials and Methods

This study was conducted through a SLR, following the guidelines proposed by Petersen et al. [17], complemented by the criteria of the PRISMA 2020 statement [18] and the recommendations of Mengist et al. [19]. These frameworks enabled the establishment of a rigorous, transparent, and reproducible protocol, designed to address specific research questions with minimal bias.

The information search was performed in the Scopus database (Elsevier B.V., Amsterdam, Netherlands) and Web of Science Core Collection (Clarivate Analytics, Philadelphia, PA, USA), using predefined Boolean operators and key terms related to denim, sustainable treatments, and the circular economy. Inclusion and exclusion criteria were applied to ensure the quality, timeliness, and relevance of the selected studies, considering only scientific articles published between 2020 and 2024, available in full text, and written in English or Spanish.

Figure 1 illustrates the methodological flow followed throughout the review process.

2.1. Activity Planning

This section outlines the activities carried out within the framework of the SLR.

2.1.1. Importance of the Study

The textile industry ranks among the most polluting sectors globally, particularly in denim manufacturing, due to its high consumption of water and energy resources, intensive use of chemical agents, and generation of toxic waste during stages such as pretreatment, indigo dyeing, and final washing, as reported by Fidan et al. [20]. In light of the increasing pressure to adopt environmentally responsible processes, it is crucial to explore innovative solutions that mitigate these impacts without compromising the quality of the final product.

Within this framework, the present study conducts a systematic review focused on sustainable treatments applied to denim, assessing their technical efficiency, industrial applicability, and effects on the ecological footprint. Through a critical analysis of recent literature, the study seeks to identify the most relevant strategies aimed at reducing water, chemical, and energy consumption, as well as optimizing processing times through the use of clean technologies. This review provides a valuable scientific foundation to advance towards more efficient textile production aligned with the principles of the circular economy, as highlighted by Aykaç Özen et al. [21].

2.1.2. Research Questions

Given the growing demand for sustainable practices in the textile industry, it is essential to assess the treatments applied to denim production that can effectively reduce its environmental impact. In this context, the objective of the present study is to conduct a SLR on sustainable treatments applied to denim, with the purpose of identifying practices that significantly contribute to reducing the consumption of water, chemicals, and dyes.

Based on this objective, the SLR seeks to answer the following research questions:

• RQ1. What are the emerging sustainable treatments in the denim finishing processes and what evidence exists regarding their effectiveness in reducing specific environmental impacts (e.g., water consumption, carbon emissions, use of chemical products)?
• RQ2. How does the environmental performance of sustainable treatments compare with conventional denim finishing methods, and which studies have addressed this comparison using metrics such as LCA and carbon footprint?
• RQ3. What are the challenges and limitations reported in the implementation and adoption of sustainable treatments in the denim industry, and how have these been addressed in the scientific literature?
• RQ4. What methodologies are used to evaluate the environmental impacts of sustainable denim treatments, and to what extent are these methodologies adequate and consistent for comparison across studies?
• RQ5. What are the main recommendations and priority areas for future research on sustainable denim treatments, based on the trends and gaps identified in the current literature?

Based on these research questions, exploratory searches were carried out to assess the relevance of the selected keywords and determine their relationship to the research area (

Table 1. Keywords used for the information search.

Term	Synonyms or Related Terms in the Literature
Denim Industry	Denim manufacturing, Textile industry, Sustainable denim production.
Clean Technologies	Green technologies, Sustainable textile processing.
Sustainable Treatments	Biodegradable textile treatments.
Circular Economy	LCA in textiles.

).

2.1.3. Guidelines for the Systematic Review

The SLR was structured into three phases, as shown in Figure 1: (a) definition of inclusion and exclusion criteria, (b) design of search strategies, and (c) formulation of search strings using Boolean operators.

These phases enabled a clear and replicable organization of the study selection process. Their application ensured the methodological consistency of the analysis.

2.1.4. Definition of Inclusion and Exclusion Criteria

To fulfil the objective of this study, only scientific articles related to sustainable treatments in denim production were selected. To ensure the quality and relevance of the studies, specific inclusion and exclusion criteria were established, as presented in

Table 2. Inclusion and exclusion criteria.

Criterion	Inclusion	Exclusion
Publication Year	2020–2024	Before 2020
Accessibility	Open access	Not open access
Document Type	Scientific articles	Theses, doctoral dissertations, book chapters
Article Type	Peer-reviewed original research articles and systematic reviews related to sustainable denim treatments	Original research articles without peer review and systematic reviews unrelated to sustainable denim treatments
Language	English and Spanish	Languages other than English or Spanish

.

The inclusion period (2020–2024) was defined to focus on recent advances and technologies aligned with the Sustainable Development Goals (SDGs) and current environmental standards. Earlier studies were excluded to ensure that the analysis reflected the latest scientific evidence and industrial practices.

Theses, doctoral dissertations, and book chapters were excluded because they are not peer-reviewed publications. This criterion ensured methodological rigour and comparability among the selected studies, consistent with PRISMA 2020 guidelines.

2.1.5. Search Strategies

For the data collection process, two academic databases available through the Technical University of the North’s library were selected: Scopus (Elsevier B.V., Amsterdam, Netherlands) and Web of Science Core Collection (Clarivate Analytics, Philadelphia, PA, USA). Both platforms were chosen due to their high scientific reputation and extensive coverage of high-impact literature. In addition, they allow the use of structured search strings, which facilitates a precise and systematic retrieval of relevant studies.

2.1.6. Search Strings

Once the keywords, research questions, and inclusion and exclusion criteria were defined, structured search strings were designed and applied to the selected databases. The keywords were combined using the Boolean operators AND and OR, which optimized the retrieval of relevant information and enabled more accurate and diversified searches.

Additionally, supplementary criteria were established to ensure the relevance and currency of the studies: publications between 2020 and 2024, articles written in English or Spanish, and open-access or full-text availability within the database. The final search string used is presented in

Table 3. Search string results.

Database		Search String
Scopus (Elsevier B.V., Amsterdam, Netherlands)	104	(“denim finishing” OR “denim treatment”OR “denim washing” OR “denim processing” OR “denim bleaching”) AND (“sustainability” OR “environmental impact” OR “water consumption” OR “chemical reduction” OR “energy efficiency”) AND (“innovation” OR “technology” OR “advancements” OR “new techniques” OR “process improvement”)
Web of Science Core Collection (Clarivate Analytics, Philadelphia, PA, USA) (WoS)	15
Total	119

.

2.1.7. Evaluation of the Review Protocol

The present SLR was conducted in accordance with the methodological guidelines of the PRISMA 2020 protocol (Preferred Reporting Items for Systematic Reviews and Meta-Analyses), which provides a structured framework to ensure transparency, completeness, and reproducibility in the synthesis of scientific evidence, as outlined by Page et al. [22]. The PRISMA flow diagram was created using Microsoft Word 2016 (Microsoft Corporation, Redmond, WA, USA) employed to document the phases of identification, screening, eligibility, and inclusion of the studies analyzed (see Figure 2).

The methodological design was further supported by the recommendations of Petersen et al. [17] for systematic mapping studies, and the guidelines proposed by Mengist et al. [19] for environmental science reviews. These references made it possible to construct a review protocol that integrates scientific rigour with sectoral relevance.

2.2. Phase: Development

The SLR was conducted in three essential stages: (1) Selection of relevant primary studies, (2) Critical assessment of their methodological quality, and (3) Extraction and synthesis of the information contained in the scientific articles.

2.2.1. Selection of Relevant Primary Studies

The identified documents were downloaded from the Scopus database (Elsevier B.V., Amsterdam, Netherlands) and Web of Science Core Collection (Clarivate Analytics, Philadelphia, PA, USA) in CSV (comma-separated values) format and organized in a Microsoft Excel 2016 spreadsheet (Microsoft Corporation, Redmond, WA, USA), which facilitated their classification and subsequent analysis.

The data were processed using Microsoft Excel 2016 and the tables and figures, including the evaluation matrix presented in Appendix A, were prepared using Microsoft Word 2016 (Microsoft Corporation, Redmond, WA, USA).

As shown in Figure 2, during the initial identification phase, a total of 119 articles were collected: 104 from the Scopus (Elsevier B.V., Amsterdam, Netherlands) database and 15 from Web of Science Core Collection (Clarivate Analytics, Philadelphia, PA, USA). In the selection phase, 14 duplicate records were removed using filters in Microsoft Excel 2016 (Microsoft Corporation, Redmond, WA, USA), with the title serving as the primary matching criterion. Subsequently, during the eligibility phase, the titles, abstracts, and keywords of each study were carefully reviewed, applying the exclusion criteria and verifying their alignment with the defined search string. This process resulted in a pre-selection of 47 articles, which were then subjected to full-text reading and in-depth analysis.

2.2.2. Quality Assessment of the Studies

The methodological quality of the selected studies was evaluated through a rigorous quantitative analysis, using a structured checklist presented in

Table 4. Quantitative checklist for study quality assessment.

No.	Question	Criterion
1	Does the study clearly state an objective or research question related to the environmental impact of sustainable treatments in denim?	Yes/No/Partial
2	Is the study design appropriate to address the research question?	Yes/No/Partial
3	Does the study use a transparent and reproducible methodology to assess environmental impacts?	Yes/No/Partial
4	Are the environmental indicators used to measure the impact (e.g., water use, energy consumption, carbon emissions, chemical products) adequate and widely recognized?	Yes/No/Partial
5	Does the study comparatively evaluate sustainable treatments against conventional or alternative denim finishing processes?	Yes/No/Partial
6	Are the limitations of the study adequately reported, and are potential biases or uncertainties in the results mentioned?	Yes/No/Partial
7	Does the study consider the entire life cycle of denim fabric, from raw material production to product disposal or recycling?	Yes/No/Partial
8	Is the literature review comprehensive and does it include current and relevant sources to contextualize sustainable treatments in denim?	Yes/No/Partial
9	Has the study undergone peer review or been published in a high-impact or well-recognized journal in the field of sustainability or textiles?	Yes/No/Partial
10	Are the results and conclusions of the study supported by robust statistical analyses appropriate to the sample and study design?	Yes/No/Partial

.

Each item was rated using a three-level Likert scale: Yes (1 point), Partially (0.5 points), and No (0 points). The maximum score per study was 10 points. Based on methodological literature on systematic reviews in applied sciences [23,24], a cut-off score of ≥7 points was established as the inclusion criterion for studies considered in the final analysis. This threshold was selected for two main reasons:

First, to avoid methodological bias studies scoring below 7 exhibited notable deficiencies in terms of clarity of design, replicability, or data quality, which could compromise the validity of the findings.

Second, to ensure thematic consistency and scientific rigour the objective was to prioritize research that met a minimum standard of methodological quality without being overly restrictive, thus allowing for a representative and diverse sample in terms of approach, yet robust in credibility.

Out of a total of 47 eligible studies, 26 articles met this criterion and were included in the final analysis. The results of this evaluation are presented in Appendix A.

2.2.3. Data Extraction and Synthesis

The data extraction process was carried out in two distinct stages. In the first stage, the general metadata of each study were compiled, including: authors, article title, year of publication, DOI identifier, document type, language, keywords, and abstract.

In the second stage, specific analysis categories were defined, encompassing: the objective and design of the study, country of origin, strategies, tools, and methods employed, as well as the reported benefits derived from the implementation of sustainable processes in denim laundries, with particular emphasis on the reduction in natural resource consumption.

2.3. Phase 3: Reporting of Results

The presentation of the study results is developed in the following section, where the main findings obtained from the analysis of the selected articles are presented.

3. Results

This section provides the answers to the research questions formulated within the framework of the SLR, based on the analysis of data extracted from the selected studies.

Regarding the first research question (RQ1) What are the emerging sustainable treatments in the denim finishing processes and what evidence exists regarding their effectiveness in reducing specific environmental impacts (e.g., water consumption, carbon emissions, use of chemical products)? the results reveal a clear adoption of clean technologies by denim manufacturers and research institutions seeking to reduce water and chemical consumption

Of the 26 studies analyzed, 10 highlight the use of enzymes as the most frequently reported sustainable treatment, followed by 5 studies that describe the application of laser technology and ozone-based treatments, as well as others that mention alternatives such as pumice stone substitutes. These results are summarized in

Table 5. Sustainable treatments in the denim finishing processes.

Treatment	Sustainable Description	Reference Studies	Percentage
Ozone Treatments	Dyeing and finishing procedures based on ozone, effective in reducing dyes and chemicals while shortening processing times.	[25,26,27]	11.54%
Laser Technology	Laser-based fading strategy that reduces water and chemical consumption, providing a high-quality sustainable finish.	[26,27,28,29]	19.23%
Bottle Cap Washing	Replacement of pumice stones with recycled plastic bottle caps, reducing sludge and industrial waste without affecting garment properties.	[30]	3.85%
Use of Enzymes	Application of enzymes (e.g., laccases and cellulases) for bioscouring, bleaching, and decolourisation, resulting in reduced CO2 emissions and fewer harsh chemicals.	[31,32,33,34,35,36,37,38,39,40]	38.46%
Advanced Methods such as Membrane Processes (Reverse Osmosis and Nanofiltration)	Closed-loop water reuse processes.	[41,42,43]	11.54%
Adjusted Powder Bleaching Wash	Bleaching with powder agents on 100% cotton denim dyed with sulphur, leading to zero effluent discharge.	[44]	3.85%
Nebulisation Technique (Core 2.0)	Saves water and energy with lower waste generation.	[28]	3.85%
Natural/Synthetic Materials	Substitutes such as peach kernel or synthetic stones that reduce chemical use and CO2 emissions.	[45]	3.85%
Heterogeneous Solar Fenton Process (HSF)	Achieves a 91.2% reduction in Chemical Oxygen Demand (COD).	[46]	3.85%
Cathodic Reduction of Indigo	Technology that replaces non-regenerable reducing agents in dyeing processes.	[47]	3.85%
Electrocoagulation (EC) for Denim Dye Effluents	Optimization of process parameters such as pH, flow rate, number, and material of electrodes, decreasing COD and effluent colour before discharge.	[48]	3.85%
Upflow Anaerobic Sludge Blanket (UASB) Reactor	Treatment in an upflow anaerobic reactor reduces toxicity and COD in wastewater by 50%.	[49]	3.85%

.

It is important to note that the sum of the percentages presented in Table 5 exceeds 100%. This occurs because a single study may report two or more sustainable treatments, either as complementary (inclusive) strategies or as comparative (exclusive) alternatives. Consequently, the percentages reflect the relative frequency of each treatment mentioned across the total number of articles analyzed, rather than the proportion of unique studies. This approach allows for a more accurate representation of the diversity of strategies documented in the literature.

In terms of environmental effectiveness, 14 studies provide evidence of a significant reduction in water and chemical consumption, directly contributing to the mitigation of the environmental impact associated with the denim finishing process:

Anam et al. [25] report that ozone-based dyeing methods allow for a substantial reduction in the use of dyes and chemical auxiliaries, thereby contributing to cleaner and more sustainable processes.

Bidart et al. [33] highlight the use of enzymes and biotechnology in indigo treatment as a more environmentally friendly alternative, reducing CO₂ emissions and minimizing worker exposure to hazardous substances.

Costa et al. [34] demonstrate that the addition of montmorillonite in the biostoning process enabled the reuse of effluent across different stages, representing an effective strategy for reducing water consumption in the denim industry.

Hasan et al. [28] base their study on the application of the nebulisation technique, which proved efficient in both energy and water consumption, while also generating less waste and pollution.

Madhu et al. [35] investigated the application of immobilized cellulase enzymes for the biofinishing of denim fabrics, achieving efficient removal of surface impurities and enhanced colour fading performance. Their findings indicate that this enzymatic process allows denim garments to be reused for up to three finishing cycles while significantly reducing chemical consumption compared to conventional treatments. These results confirm that immobilized enzyme systems offer a practical and environmentally sustainable alternative for denim processing.

Shinde et al. [44] analyze bleaching of denim fabrics using powder bleach, proposing an environmentally responsible alternative aligned with the concept of Zero Liquid Discharge (ZLD).

Unuofin [36] explores the implementation of microbial technologies, applying bacterial strains Hb16c and Berl11b2 for the synthesis of fine biochemicals, thereby reducing waste and pollutants derived from bio-based processes.

Zhang et al. [38] develop an optimized and controlled denim decolourisation process based on horseradish peroxidase with H₂O₂, achieving indigo degradation into low-molecular-weight compounds. The method reduces both chemical use and processing time, establishing itself as a sustainable alternative.

Ivedi and Cay [45] demonstrate that the use of natural and synthetic materials under low liquor ratio conditions reduces chemical use, energy demand, and CO₂ emissions, highlighting peach kernel and synthetic stones as sustainable substitutes.

Nayak et al. [27] emphasize the potential of waterless technologies such as laser and ozone treatments, noting that they can achieve up to a 97% reduction in water usage, while also minimizing chemical consumption and contributing to circular fashion.

Rathinamoorthy and Karthik [43] analyze various stages of denim production, focusing on alternative wastewater treatment practices and demonstrating their effectiveness in reducing environmental pollution.

Samanta et al. [29] conclude that water-free technologies, such as CO₂ laser fading, provide visual results comparable to conventional methods, while enabling more environmentally friendly production.

Unuofin [39,40] assessed the valorization of wheat bran through the production of a laccase enzyme (Jb1b) applied to denim dye decolourisation. Furthermore, effective bleaching using mandarin peel extract produced treated wastewater suitable for agricultural reuse, thereby closing a positive ecological cycle.

Regarding Research Question 2 (RQ2) How does the environmental performance of sustainable treatments compare with conventional denim finishing methods, and which studies have addressed this comparison using metrics such as LCA and carbon footprint? the results indicate that the vast majority of the studies included in the review explicitly address this issue. Of the 26 studies analyzed, 22 conducted a direct comparison between the environmental performance of sustainable and conventional treatments, confirming the growing of comparative environmental assessment in the textile finishing field.

The findings consistently demonstrate, based on comparative analyses, that sustainable treatments outperform conventional processes in key environmental indicators, including water, chemical, and energy use. In most cases, these technologies achieved reductions exceeding 50% in resource consumption and pollutant generation. Among the methods analyzed, enzymatic, ozone-based, and laser treatments were the most extensively validated alternatives, showing measurable improvements in water reuse, energy efficiency, and reduced effluent toxicity.

Table 6. Comparison of environmental performance between sustainable and conventional denim treatments.

Type of Sustainable Treatment	Conventional Reference Method	Environmental Metric Evaluated	LCA Application	Carbon Footprint Assessment	Studies	Percentage
Ozone and Laser	Conventional dyeing with reactive dyes	Reduction in water and chemical consumption	No	Partial	[25,27,29]	13.64%
Use of Enzymes	Dyeing with synthetic dyes	Reduction in water and chemical consumption, and CO2 emissions	No	Partial	[31,32,33,34,35,36,39,40]	36.36%
Heterogeneous Solar Fenton Process (HSF)	Dyeing with pollutant effluents	Reduction in COD, TOC, turbidity, and colour; PET reuse	No	No	[46]	4.55%
optimization of Industrial Washes	Conventional denim washing	Reduction in microfibre (MF) emissions	No	No	[41]	4.55%
Nebulisation Technique (Core 2.0)	Conventional dyeing	Reduction in water, energy, and chemical consumption	No	No	[28]	4.55%
Upflow Anaerobic Sludge Blanket (UASB) Reactor and Electrocoagulation.	Conventional dyeing with pollutant effluents	Reduction in wastewater toxicity and COD	No	Partial	[42,43,48,49]	18.18%
Plastic Bottle Caps and Peach kernel	Pumice stone washing	Lower liquor-to-garment ratio and reduction in solid waste	No	Yes	[30,45]	9.09%
Powder Bleach Washing	Conventional washing	Reduction in water consumption, effluent generation, and solid waste	No	No	[44]	4.55%
Horseradish Peroxidase/H2O2 (HRP/H2O2) System	Stone and bleach washing	Reduction in water and chemical use; prevention of toxic effluents	No	No	[38]	4.55%

summarizes these comparisons, organizing sustainable treatments according to their reference methods, evaluated metrics, and the implementation of analytical tools such as LCA and carbon footprint assessment. Although most studies evaluate specific parameters (e.g., water use, chemical load, CO₂ emissions), only a limited subset applies a complete life cycle perspective. This methodological gap underscores the need for greater standardization in sustainability assessments to enable comparability and scalability across studies.

Enzymatic treatments exhibit superior performance in reducing chemical oxygen demand (COD) and CO₂ emissions compared to traditional bleaching, primarily due to their lower energy requirements and biodegradability of enzymatic catalysts. Likewise, ozone-based processes achieve notable reductions in water and chemical consumption, up to 60% according to Atav et al. [50], while maintaining the colour quality of denim fabrics. Laser fading, meanwhile, stands out for its capacity to minimize wastewater discharge and chemical use, making it one of the most promising alternatives for large-scale adoption.

Despite these advances, the limited implementation of full LCA or carbon footprint evaluations suggests that the environmental benefits of these innovations may still be underreported. Comprehensive studies integrating multiple impact categories (e.g., eutrophication, toxicity, and energy footprint) are required to validate these improvements under real industrial conditions. Furthermore, the results highlight that sustainability gains are not only dependent on technological innovation but also on process integration, operator training, and the use of renewable energy sources within production systems.

The sustainable denim finishing technologies consistently demonstrate superior environmental performance relative to conventional treatments. However, the absence of unified methodological frameworks and the predominance of laboratory-scale analyses highlight the need for broader, multi-impact evaluations that can substantiate their long-term environmental benefits and industrial feasibility.

Findings related to research question 3 (RQ3): What are the challenges and limitations reported in the implementation and adoption of sustainable treatments in the denim industry, and how have these been addressed in the scientific literature? (See Figure 3).

Among the studies analyzed, economic limitations were identified as the main barrier to the adoption of sustainable treatments in the denim industry, representing 22% of all mentions [25,26,28,29,31,32,33,34,37,38,39,41,43,44,45,46,47,48,51]. This difficulty, referring to the economic barriers hindering the adoption of sustainable technologies, is linked to high investment costs in technology and infrastructure, as well as the limited availability of long-term financing, particularly affecting small- and medium-sized enterprises (SMEs).

Scalability ranked second (21%) [25,26,28,29,31,32,33,34,37,38,39,41,43,44,45,46,47,48,51], since many sustainable treatments demonstrate positive results at the pilot stage but face significant obstacles when transferred to real industrial environments. These difficulties arise mainly from increased operational costs and the lack of large-scale technical validation.

Other, less frequent barriers with an incidence between 3% and 5% include technological challenges, cultural resistance to innovation, and the absence of clear regulatory frameworks supporting sustainable implementation [25,28,32,34,40,41,43,49,51].

In parallel, the reviewed literature proposes several strategies to overcome these limitations. Among them, technological improvements driven by leading companies stand out (14%) [25,26,28,29,31,32,33,34,37,38,41,44,47,48,49,51,52], along with public–private collaboration, process optimization, and the implementation of training programmes (8%) [25,26,29,35,43,45,48,51], which strengthen knowledge transfer to the industrial sector. Additionally, 3% of the studies [23,33,41] highlight the importance of clear regulatory policies and government incentives, which are regarded as key instruments to facilitate the transition towards a more sustainable and efficient production model in the denim sector.

With regard to Research Question 4 (RQ4) What methodologies are used to evaluate the environmental impacts of sustainable treatments in denim, and to what extent are these methodologies adequate and consistent for comparison across studies? a notable methodological diversity was observed among the 26 articles analyzed.

Approximately 11.53% of the studies, including those by Bidart et al. [33], Nergis [51], and Rathinamoorthy & Karthik [43], applied LCA as an evaluation tool. However, the remaining 88.45% presented partial or qualitative assessments, and in many cases, the functional unit used was not specified, which limits the comparability of results across studies.

In relation to the adequacy of the methodologies applied to sustainable treatments, it was identified that 16 studies directly implemented specific techniques. Two investigations analyzed ozone-based technologies [25,26], while Nayak et al. [27], Nergis [51], and Samanta et al. [29] focused on the application of laser technology. Enzymatic treatments constitute the most widely represented category, with significant contributions found in the works of Atav et al. [31], Ben Fraj & Jaouachi [32], Bidart et al. 33], Costa et al. [34], Madhu [35], as well as in several studies by Unuofin [36,39,40], Ivedi and Cay [45], Shinde et al. [44], and Zhang et al. [38]. In addition, practices aimed at water recycling were also documented, demonstrating thematic consistency with the sustainability principles that guide these innovations.

However, several limitations were identified in the literature. Among them, the most notable are the scarcity of direct comparisons between sustainable and conventional processes, and the lack of specific primary data related to the denim washing process. The most frequently used indicators include water and energy consumption, effluent pollutant load, and CO₂ emissions, which were already addressed in the results of the first research question (RQ1).

Table 7. Recommendations for Future Research on Sustainable Denim Treatments.

Studies	Priority Areas	Specific Recommendation
[29,32,37,41,43,44,47,49]	Development and Validation of New Sustainable Technologies	Promote pilot studies in real production contexts to verify the technical, economic, and environmental efficiency of innovative treatments.
[33,43,51]	Comprehensive LCA and Development of Specific Databases	Standardize the use of LCA and encourage the creation of databases tailored to denim washing and finishing processes.
[28,32]	Evaluation of Circularity and Closure of Production Loops	Develop specific metrics and indicators to assess the degree of circularity of each treatment, including water, material, and energy reuse.
[27,28,30,33,34,35,39,42,45,47,48]	Assessment of Economic Feasibility and Industrial Acceptance	Include economic feasibility studies, investment and return analyses, and evaluate technological acceptance within denim manufacturing companies.
[30,45]	Social Impact and Consumer Perception	Integrate qualitative and quantitative methodologies to assess social, cultural, and consumer behaviour aspects related to sustainable denim.

responds to Research Question 5 (RQ5) What are the main recommendations and priority areas for future research on sustainable denim treatments, based on the trends and gaps identified in the current literature?

From the analysis of the reviewed studies, five key areas were identified that require priority attention in future research. These recommendations emerge from the conceptual, methodological, and applied gaps detected in the literature and aim to guide the development of more effective, scalable, and environmentally sustainable solutions in denim treatment.

4. Discussion

The objective of this SLR was to identify and critically analyze the main sustainable technologies applied to denim finishing, their environmental impacts, implementation barriers, and the gaps in scientific literature. The findings provide a comprehensive overview of the recent advances and the persistent challenges within the sector.

Firstly, it was observed that enzymes constitute the most frequently reported sustainable treatment in the literature, followed by laser- and ozone-based technologies. This trend aligns with the findings of Periyasamy et al. [53], who highlight biological and oxidative methods as the most promising innovations for sustainable denim finishing. Similarly, Hasan et al. [28] report that ozone and laser technologies, applied individually or in complementary stages, significantly reduce water and chemical consumption while improving the aesthetic quality of denim fabrics compared with conventional washing methods.

However, some discrepancies were also identified. While most studies emphasize the efficacy of enzymatic treatments, research by Khan and Mondal [54] warns that inadequate application may negatively affect the mechanical strength of garments. Likewise, although laser technology is considered one of the cleanest and most scalable solutions, some studies report undesirable thermal effects when high power levels are applied [55]. These results suggest that, although the effectiveness of emerging technologies is evident, further optimization processes are still required to ensure consistent and reproducible large-scale results.

Enzymatic treatments demonstrate notable operational and environmental advantages, particularly in the desizing and decolourisation stages of denim processing [53,56,57]. Beyond their effectiveness, their low energy demand reinforces their viability as an eco-friendly alternative to conventional methods. Similarly, ozone technology has been shown to reduce chemical use and effluent pollutant load by up to 60%, consistent with the findings of Atav et al. [50] and Powar et al. [58]. These benefits are further enhanced by shorter processing times and lower water consumption.

In turn, laser fading stands out as one of the cleanest and most scalable technologies, as it maintains the aesthetic and quality characteristics of the final product while significantly reducing CO₂ emissions [27,29], findings consistent with those reported by Hung et al. [59].

Although technological innovations in denim finishing have yielded measurable environmental improvements, several studies continue to report the use of potentially hazardous substances such as potassium permanganate (KMnO₄) [13,28]. These compounds, despite being integral to certain bleaching or fading processes, pose ongoing ecological and occupational health risks, reinforcing the need for continued substitution with safer alternatives.

Emerging innovations have also been reported, such as the use of recycled materials (e.g., peach kernel and plastic bottle caps) as sustainable substitutes for pumice stones, thereby promoting the valorization of agro-industrial waste [30,45]. Overall, the reviewed studies show reductions exceeding 50% in water and chemical consumption, as well as lower sludge generation, toxic waste, and pollutant emissions, consistent with the findings of Rahaman et al. [60].

While the use of recycled materials such as plastic bottle caps offers waste-reduction benefits, it may paradoxically contribute to microplastic release during mechanical abrasion. Moreover, the continued reliance on synthetic dyes and high-impact auxiliaries poses challenges to achieving full process circularity, underscoring the need for stricter chemical management and substitution with bio-based alternatives.

Regarding evaluation methodologies, the results indicate that only a minority of studies apply comprehensive approaches such as LCA, while most are limited to isolated parameters such as water use, chemical consumption, or CO₂ emissions. Although a considerable number of studies include direct comparisons between sustainable and conventional treatments, most of these analyses are limited to isolated parameters rather than comprehensive evaluations. The scarcity lies not in the quantity of comparative research, but in the methodological depth and consistency across studies, as few employ full life cycle approaches or integrate multiple environmental indicators.

This trend aligns with Watson and Wiedemann [61], who point out that the textile industry faces methodological constraints in its environmental assessments, as many LCAs omit key impact categories such as eutrophication, acidification, or toxicity due to data inventory gaps and the limited coverage of existing methods. The lack of standardization in system boundaries (cradle-to-gate vs. cradle-to-grave), functional units, and indicators employed hinders comparability between studies, confirming the observations of Sari et al. [62]. Although the carbon footprint has become a useful comparative indicator, particularly for clean technologies such as laser finishing [63], there remains a methodological inconsistency that limits the generalization of results.

In terms of implementation challenges, the main barriers identified were economic (22%) and technological scalability (21%). These limitations are consistent with those reported by Periyasamy and Periyasami [53] and Catarino et al. [64], who acknowledge that high investment costs, lack of incentives, and difficulties in transferring pilot results to industrial contexts constitute significant obstacles. Cultural and organizational barriers were also detected, including resistance to change and poorly integrated supply chains within the denim finishing sector [27,32,40,43,51], as well as fragmented regulations that restrict international investment and process comparability [25,41,45,49]. These findings are in line with Thatta and Polisetty [65], who identify persistent structural challenges even within established sustainability frameworks.

To address these limitations, the literature proposes a range of strategies, including the improvement of production processes, the development of technical capacities, and multisectoral collaboration among academia, industry, and government bodies [25,29,35,43,45,48,51]. Fiscal and regulatory policies aimed at promoting textile circularity are also recommended [66]. Convergently, recent studies [46,67] emphasize the need to close technological and methodological gaps, prioritizing the development of innovations that integrate sustainability from their design phase, such as optimized enzymes, biosurfactants, waterless processes, and digitalisation tools.

Furthermore, the improvement of LCA implementation is highlighted as a critical step, particularly through the use of real data on energy consumption, emissions, and textile-specific inputs, alongside the creation of standardized databases that enable rigorous cross-study comparisons. In line with Ermini et al. [68], ecodesign, effluent recycling, and waste valorisation emerge as key pathways for achieving a structural transformation of the textile production model.

The findings expand existing literature by providing a consolidated framework that compares the environmental efficiency of sustainable denim treatments and identifies methodological trends in the application of LCA in textile finishing studies.

Finally, from a socio-economic perspective, there remains a strong need to evaluate the economic feasibility of these technologies across different production scales, encompassing both large industries and small and medium-sized enterprises (SMEs) [69,70,71]. Similarly, consumer acceptance remains a largely unexplored area, despite its direct influence on the adoption of sustainable innovations.

5. Conclusions

This SLR provides a critical and up-to-date synthesis of sustainable treatments applied to denim finishing, highlighting both technical advances and persistent limitations in the recent scientific literature.

First, technologies such as enzymes (laccases and celluloses), ozone, laser, nebulization, and the use of recycled materials demonstrate superior environmental performance compared with conventional methods. These innovations achieve reductions of up to 60% in water and chemical consumption, along with significant decreases in CO₂ emissions and solid waste generation, positioning themselves as viable alternatives for cleaner production.

Nevertheless, relevant methodological limitations were identified: only 11.53% of the studies employed comprehensive LCA approaches, and the lack of standardization in system boundaries, functional units, and indicators limits comparability among studies. This methodological heterogeneity underscores the urgency of adopting internationally standardized protocols (ISO 14040/14044) and strengthening sector-specific databases with representative primary data.

In terms of industrial implementation, the main barriers identified are economic and technological—notably, high initial investment costs, scalability challenges, and the absence of consistent regulatory frameworks. Added to these are organizational and cultural resistances that slow down large-scale adoption. Overcoming these obstacles requires combined strategies, including regulatory incentives, technical training programmers, multisectoral collaboration, and the development of emerging technologies designed under sustainability principles.

Finally, the findings reveal that the transition towards sustainable denim demands the integration of not only the environmental dimension, but also the economic and social ones. In this regard, future research should focus on assessing the economic feasibility of these technologies at different production scales, as well as analyzing industrial and consumer acceptance dimensions that remain underexplored yet are crucial for the adoption of sustainable innovations.

The structural transformation of the denim finishing sector will depend on the convergence of technological innovation, methodological standardization, and coherent regulatory frameworks, in synergy with active collaboration between academia, industry, and government. Only through this integrated approach will it be possible to consolidate a sustainable, resilient, and SDG-aligned textile production model.

6. Limitations and Future Research Directions

Although this SLR provides broad coverage of sustainable treatments applied to denim, several relevant limitations remain that affect the external validity and replicability of the results. Although some studies addressed bio-based dyes and auxiliary agents, these were excluded from the synthesis when they were not directly linked to denim finishing treatments. The limited representation of sustainable material alternatives observed in the reviewed literature reveals a current research gap, particularly concerning bio-based innovations with potential to reduce chemical toxicity and microplastic emissions. Furthermore, although earlier studies (2000–2019) were reviewed during the screening phase to provide historical context, they were excluded from the final synthesis. This decision ensured methodological consistency with the study’s focus on post-2020 technological and environmental innovations. One of the main constraints is the methodological heterogeneity among the analyzed studies, particularly in the application of LCA, which complicates the comparison and synthesis of findings. Likewise, there is a scarcity of primary data obtained under real production conditions, limiting the practical applicability of the collected evidence. Most investigations focus on laboratory- or pilot-scale experiments, without including subsequent stages of industrial validation or longitudinal analyses to assess the sustained impact of these technologies.

From an economic and social perspective, significant gaps persist in the evaluation of the economic feasibility of these treatments within denim production and finishing processes among small and medium-sized enterprises (SMEs), as well as in understanding the degree of acceptance among consumers and industrial stakeholders.

Based on these limitations, the following future research lines are proposed: methodological standardization in environmental assessment studies; development of public and up-to-date databases containing representative data from real textile processes; comprehensive evaluation of circularity, encompassing recycling, reuse, and ecodesign strategies; promotion of participatory research that integrates industrial and community stakeholders; exploration and validation of emerging technologies under sustainability criteria, from their design stage through to industrial-scale implementation.