Sustainable Wet Processing Technologies for the Textile Industry: A Comprehensive Review

Abstract

The textile industry ranks among the highest water-consuming sectors globally, with annual usage reaching billions of cubic meters. In manufacturing, wet processing, including dyeing, printing, and finishing, accounts for 72% of this water demand. These stages not only require vast water volumes but also produce wastewater containing hazardous chemicals, polluting ecosystems and reducing soil fertility. Furthermore, the energy-intensive nature of these processes, combined with a heavy reliance on fossil fuels, contributes significantly to greenhouse gas emissions. In response to these environmental challenges, innovative technologies have emerged, such as waterless dyeing using supercritical carbon dioxide, digital printing, ultrasonic-assisted processing, foam dyeing, laser-based denim finishing, and dope dyeing for man-made fibers. These methods drastically reduce water consumption, lower energy use, and minimize emissions while maintaining textile quality. However, the widespread adoption of these alternatives faces challenges, including high implementation costs, process scalability, and compatibility with existing infrastructure. This review critically explores current advancements in sustainable textile wet processing, analyzing their effectiveness, limitations, and industrial viability. By addressing these challenges, the textile industry can transition toward environmentally friendly and resource-efficient manufacturing processes.

1. Introduction

The textile sector is a significant contributor to the global economy; however, it also presents major environmental challenges due to its high consumption of water, energy and chemicals. In 2015, the textile industry was estimated to have consumed 79 billion cubic meters of water, emitted 1715 million tons of CO₂, a greenhouse gas, and generated 92 million tons of waste [1]. By 2030, these values are expected to increase by 63% [1].

Among the various stages of textile production, wet processing is responsible for a substantial share of water consumption, greenhouse gas emissions, and chemical waste generation. It is estimated that textile wet processing accounts for 72% of the industry’s total water use and up to 52% of its total greenhouse gas emissions [2,3,4,5]. Conventional textile wet processing relies heavily on immersion-based techniques, where large volumes of water act as a medium for chemical interactions, leading to substantial wastewater production. The improper disposal of wastewater results in severe soil and water contamination, posing risks to both the environment and human health [2]. Additionally, most conventional processes operate at high temperatures, requiring substantial energy input. Reliance on fossil fuels for heat and electricity results in atmospheric emissions and contributes to climate change and greenhouse gas emissions, with the textile sector accounting for 10% of global emissions [3,6].

In response to growing sustainability concerns, numerous research projects, initiatives, and programs have been developed to mitigate the environmental impact of wet processes. These efforts mainly focus on the reduction of energy consumption, elimination of process water and wastewater discharge, and decrease of chemicals consumption [7]. Innovations include low-liquor ratio dyeing, waterless or near-waterless technologies, and advanced chemical application techniques that improve process efficiency. While some of these technologies have already been adopted at an industrial scale, others remain under development, requiring further research to optimize performance, cost-effectiveness, and scalability.

This review provides a comprehensive overview of both widely implemented and emerging technologies in textile wet processing, emphasizing their role in reducing water, energy, and chemicals consumption. It explores advancements that enhance process efficiency and sustainability while maintaining or enhancing textile quality. By examining the latest advancements and industrial applications, this review aims to highlight the transformative potential of new technologies in driving the textile industry toward greater environmental responsibility.

2. Research Methodology

This review was conducted through a comprehensive literature search using reputable, multidisciplinary databases, including Wiley Online Library, SpringerLink, ScienceDirect, and Google Scholar. A significant portion of the references was sourced from high-impact, peer-reviewed journals recognized in the textile and sustainability fields, such as Cellulose, Fibres and Polymers, Journal of Cleaner Production, Textile Research Journal and The Journal of The Textile Institute.

The search focused on publications from 2015 to 2024 to capture recent advancements in sustainable wet processing technologies. However, earlier studies from 2000 were also included for foundational insights. Of the 171 references cited, the majority (86) were published between 2020 and 2024, showing rapid development in the field. An additional 64 references were from 2015 to 2019, supporting recent progress. A smaller set (21 references) was included from 2000 to 2014 to highlight key technological developments.

Only English-language articles were included to ensure accessibility and consistency in terminology.

Initial search terms and keywords included “sustainable wet processing,” “textile dyeing,” “waterless dyeing,” as well as specific fibers (e.g., “cotton”, “polyester”, “wool”) and processes relevant to wet processing stages (e.g., “pre-treatment,” “dyeing,” “finishing”).

To provide clarity and facilitate understanding of the current state of these innovations, the reviewed literature was categorized into three groups:

• Established and Widely Studied Innovative Systems: Commercially available technologies with broad industrial applications or expanding across sectors.
• Developing and Specialized Technologies: Solutions at early industrial stages or commercially available but with limited adoption.
• Other Emerging Technologies: Innovations still being tested, scaled up, or undergoing regulatory assessments.

The review follows a clear structure based on the logical sequence of textile wet processing operations—starting with pre-treatment, moving through dyeing and printing, and concluding with finishing processes. This framework allows for a clear understanding of how sustainable innovations can be integrated throughout the textile production cycle.

Potential bias was considered due to the specific choice of databases and high-impact journals. While these sources provide reputable and peer-reviewed information, their tendency to publish studies with significant findings may introduce selection bias. Where relevant, potential biases in the research articles and results were pointed out to ensure transparency and help the reader assess the validity of the conclusions drawn.

The final section of each technology overview includes information on its industrial positioning, including details on products, processes, equipment, and resource consumption (e.g., water, auxiliaries, and energy use). This data was sourced primarily from official company websites, which may present information in a way that emphasizes favorable outcomes.

3. Textile Wet Processing

Within the diverse stages involved in textile production, wet processing is possibly the strongest contributor to the improved value of textiles [8]. It is during wet processing that textiles acquire desirable properties such as color, softness, and the incorporation of interesting functionalities, such as anti-bacterial, anti-UV, dirt-repellent and non-flammability [9]. The conventional wet processes used to obtain such properties are known for requiring the use of a large amount of water, harsh chemicals, high salt concentrations and high temperatures, all of which are critiqued due to their environmental cost [10].

Textile wet processing can be divided into pre-treatment (which includes processes like desizing, scouring, bleaching, and mercerizing), dyeing and printing, washing, and finishing [2,3,7,11,12]. This section describes the importance of each wet processing step and the environmental impact of the products used. A brief description of each process and the composition of generated wastewaters are summarized in

Table 1. Description of the main textile wet processes and typical composition of generated wastewaters (Adapted from [3,8,9,13]).

Process	Description	Wastewater Composition
Desizing	Remove starch or wax-like sizes applied to improve tensile strength during weaving or knitting	Sizes Enzymes Starch	Waxes Suspended solids TOC
Scouring	Remove natural non-cellulosic impurities such as pectin, wax, protein, dirt, oil, seed husk fragments and mineral matter	NaOH Surfactants Detergents Fats	Pectin Oils Sizes Waxes
Bleaching	Remove yellow shades and brighten the fabric	H2O2 Sodium silicate Organic stabilizer	Alkalis Suspended solids
Mercerizing	Improve shine and dye uptake	NaOH	High pH
Dyeing and Printing	Provide color	Dyes Color pigments Heavy metals Salts Surfactants	Alkalis Urea Formaldehyde Solvents BOD
Finishing	Grant desirable qualities or functionalities	Softeners Solvents Resins Waxes	BOD COD VOC Suspended solids

BOD—Biochemical oxygen demand; COD—Chemical oxygen demand; VOC—Volatile organic compounds; TOC—Total organic carbon.

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3.1. Pre-Treatment

Optimal dyeing and finishing of textiles can be prevented by: (1) the hydrophobic nature of sizing materials, such as starch and waxes, applied on fibers’ surface to facilitate weaving or knitting; (2) the presence of impurities, including pectin, wax, protein, dirt, and oil; and (3) the fibers’ innate slight coloration [13]. Therefore, preparing the fabrics before further treatment is essential to ensure optimal results in subsequent processes.

Conventional textile wet processing typically involves desizing, scouring with sodium hydroxide (NaOH), bleaching with hydrogen peroxide (H₂O₂) and mercerizing. The application of these processes guarantees the removal of impurities, the improvement of fiber wettability, and, consequently, dyeing, printing, and finishing efficiency and uniformity. However, traditional pre-treatments require high temperatures and substantial water consumption to remove residual alkali and other auxiliaries from the textiles. This leads to the production of wastewaters with high values of biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total organic carbon (TOC) [8]. Additionally, the harsh conditions involved in textile pre-treatment can often weaken the fibers and reduce their tensile strength, compromising the overall quality and durability of the fabric [13,14].

3.2. Dyeing and Printing

Dyeing and printing both involve applying color to the fabrics, but they differ in their application methods and outcomes. Dyeing typically results in a uniform color applied on both sides of the fabric, using dye in the form of a solution. In contrast, printing involves applying one or more colors onto one side of the fabric in defined patterns, using a thick paste for conventional methods such as screen and rotary screen printing [3,8,9]. Even though the application methods are different, both processes use products and generate wastewaters that are very similar.

To provide color, dyeing and printing processes currently rely on synthetic dyes in the interest of a wide range of colors, improved quality of the textiles, higher reproducibility, and desirable fastness properties [15]. However, several dyes are toxic and potentially carcinogenic. Therefore, the production and use of such dyes create worker safety concerns and generate hazardous waste. Even non-toxic synthetic dyes can become toxic during natural decomposition in the environment. Furthermore, during the subsequent washing of the dyed and/or printed fabrics, a high concentration of unfixed dyes is removed. Accordingly, wastewater resulting from these processes can have up to 50% of the dye initially introduced, which further highlights the improvements needed in dyeing and printing processes [3,8].

Besides synthetic dyes, traditional dyeing processes often use salts, such as sodium chloride or sodium sulfate, as electrolytes to improve the interaction between dyes and fibers [16,17]. While the exhaustion rate is favored, as more dye molecules interact with fibers, high salt concentrations in wastewater can have harmful environmental effects such as soil degradation and disruption of aquatic life. Furthermore, process water needs additional treatment to remove salt before it can be recycled, resulting in higher energy requirements [18].

In conventional printing, since it is a fast process and does not involve fabric immersion, the diffusion of dye from the paste onto the fabric can be less efficient. Urea present in the printing paste improves dye solubility and controls the evaporation of water during the fixation process, retaining humidity [19,20]. However, washing fabrics treated with urea generates wastewater with a high pollution load due to the easy decomposition of urea in nitrogenous compounds, which can lead to water eutrophication [20,21].

3.3. Finishing

The finishing process is a very important stage of wet processing, where the highest added value of textiles is achieved by improving their handle, performance, and functional properties [9,22]. This step ensures that textiles meet consumer expectations and industry standards. Without proper finishing, fabrics may exhibit rough texture, shrinkage or inadequate durability, which would limit their suitability for high-quality applications such as apparel, home textiles and technical applications.

To obtain precise characteristics in the refined fabric, finishing processes are applied by chemical or mechanical methods [9]. Unlike mechanical methods that use techniques such as pressing and sanding on the textiles, chemical methods rely on water-intensive treatments and functionalization agents to obtain the desired properties. For instance, softening treatments can release volatile organic compounds (VOCs), contributing to air pollution [11]. Water and oil-repellent finishes contain perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), which despite their effectiveness, are very persistent, bioaccumulative and toxic, having been linked to carcinogenic diseases [23,24]. Flame retardants, often applied to protective clothing and home textiles, historically relied on halogenated compounds, which, while effective, can release toxic gases during combustion [25]. Additionally, most of these processes require high-temperature curing or padding techniques, consuming significant amounts of water and energy.

The environmental impact of finishing processes is substantial due to the release of wastewaters with chemical products. These pollutants can contribute to long-term environmental damage, bioaccumulation, and potential health hazards.

4. Innovation in Textile Processing Systems

Conventional dyeing, printing, and finishing require vast amounts of water for processing baths, rinsing, and fixation, generating significant volumes of wastewater polluted with dyes, salts, and auxiliaries. With increasing pressure to reduce freshwater consumption, the textile industry has prioritized the development of innovative processing systems that significantly reduce water use while maintaining or enhancing textile quality and performance.

Emerging technologies are addressing this challenge through diverse approaches, including low-liquor application techniques, targeted chemical delivery systems, and alternative processing media that minimize or eliminate water dependence. Some advancements focus on optimizing conventional wet processes by reducing water-to-fabric ratios, while others replace immersion-based techniques with more controlled application methods such as spraying, foaming, or atomization. Furthermore, novel waterless and near-waterless technologies are redefining industry standards by using alternative media such as air, carbon dioxide, or solvent-based systems, significantly decreasing wastewater generation and chemicals discharge. In addition to water conservation, these innovations enhance overall process efficiency, often reducing processing time, energy consumption, and auxiliary products needs.

This section explores a range of innovative textile processing technologies that are reshaping the future of textile production by offering more sustainable, efficient, and environmentally friendly alternatives to conventional methods. These innovations not only contribute to resource conservation but also align with global efforts to create a more sustainable textile industry. A summary presenting the advantages, challenges, sustainability impacts and industrial feasibility of each technology, including scalability concerns, is provided in

Table 2. Summary of the emerging technologies discussed, presenting advantages, challenges, sustainability impacts and industrial feasibility.

Technology	Advantages	Challenges	Sustainability Impacts	Industrial Feasibility
Established and Widely Studied Innovative Systems
Ultrasonic-assisted wet processing	- Enhances dye/chemical uptake - Reduces processing time	- Requires specialized equipment	- Lower water, auxiliaries and energy consumption	Industrial systems available (Geratex, Sonovia, Siansonic, Sono-Tek, Cheersonic and GRINP®); scale-up ongoing
Ozonation	- Dry process - Effective bleaching and denim finishing - Reduced processing time	- High initial equipment cost - Ozone handling safety - Fiber damage if overused	- Lower water and auxiliaries consumption	Commercially adopted in denim finishing (Absolute Ozone®, Ozcon Environmental, Ozon denim, Jeanologia and Tonello®)
Plasma	- Dry process - Enhances fiber surface properties - Enables functional finishes - Low-temperature process	- High initial equipment cost - Limited for bulk processing	- Lower water and auxiliaries consumption	Industrial systems available (Acxys, Ahlbrandt, GRINP®, Enercon, Plasma Etch, AGC Plasma Technology Solutions, Plasmatreat and Thierry Corporation); industrial uptake growing
Laser	- Dry process - Precision patterning - - Fast processing	- High initial equipment cost - Potential fiber damage	- Eliminates water and chemicals use in denim finishing - Lower energy consumption	Widely adopted in denim finishing (SEI Laser, Jeanologia, Portlaser and Zaitex); expanding into other areas
Digital Inkjet Printing	- Precision application - Waste reduction	- Pre/post-treatment may affect sustainability - Speed limitations in high-volume production	- Lower water, auxiliaries and energy consumption	Industrial systems widely available (Zimmer, EFI® Reggiani, Konica Minolta, MS Printing Solutions and Durst Group)
Atomization systems	- Precision application - Low liquor ratio - No need for fabric immersion	- Requires precise control of droplet size - Potential concentration of pollutants	- Lower water and auxiliaries consumption - Reduces energy for drying	Industrial systems available (Care Applications, Tonello®, AirDye®, Then-Airflow®, Imogo, Baldwin®); industry uptake increasing
Supercritical Carbon Dioxide	- Dry process - Dye and CO2 can be recovered and reused	- High initial equipment cost - Limited compatibility with natural fibers - Specialized dyes needed	- Eliminates water use - Reduced energy consumption - No wastewater generation	Industrially available for synthetics (DyeCoo®, Deven Supercriticals and Qarboon); natural fiber solutions under development
Developing and Specialized Technologies
Reverse Micelle Dyeing	- Enables dyeing in non-polar solvents - No salt required - Reusable solvents	- Use of volatile organic solvents - Limited industrial-scale validation	- Minimizes water use - Lower wastewater - generation	Lab-scale research promising; industrial application not yet confirmed
Foam technology	- Low liquor ratio - Fast drying	- Requires foam stability control - Less suitable for complex finishing	- Lower water and auxiliaries consumption - Reduces energy for drying	Early-stage industrial applications; more data on scaling needed
Microwave	- Reduces process time - Lowers processing temperature	- Equipment not widely available for textiles	- Lower auxiliaries and energy consumption	Early-stage industrial applications (Ferrite Microwave Technologies, ITA RWTH Aachen, Püschner, and DyStar); lab and pilot stages
Dope dyeing	- Excellent color fastness - Eliminates the need for post-extrusion dyeing - Cost-effective for mass production	- Limited compatibility with cellulosic fibers - Less flexibility in color changes - Limits to design diversity	- Eliminates water use in dyeing - Lower auxiliaries and energy consumption	Industrially available for synthetics (Recron®, Filatex India Limited, Diklatex, Far Eastern New Century, Thai Polyester Co., Ltd., GAC Acelon, We aRe SpinDye® and Birla cellulose); expanding into cellulosic fibers
Other Emerging Technologies
Ultraviolet Technology	- Enables surface modifications - Can cure coatings quickly	- Limited to surface treatments - Safety considerations for operators - Limited scalability and cost-effectiveness	- Lower water, auxiliaries and energy consumption	Pilot applications (RUDOLF GmbH and Trelleborg Engineered Coated Fabrics); scalability studies ongoing
Electrochemical dyeing	- Replaces chemical reducing agents - Reusable dye bath	- Scalability issues - Requires specialized equipment	- Lower water and auxiliaries consumption - Minimizes water pollution	Pilot projects (RedElec); currently in the research and validation phase
Nanotechnology	- Improves fastness properties - Adds functionalities	- Potential nanoparticle environmental risks - High material costs - Requires specialized equipment	- Lower auxiliaries and energy consumption - Enhances durability, extending textile life	Research-to-commercial pipeline growing (functional textiles); regulatory considerations ongoing
Low-temperature processing	- Minimizes thermal degradation of fibers - Compatible with sensitive substrates	- Some dyes/finishes may require reformulation - May result in longer processing times	- Lower energy consumption - Smaller carbon footprint	Commercial processes available (Bozzetto Group, CHT Group, Ever dye, MCTRON Technologies); industry adoption is growing

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4.1. Established and Widely Studied Innovative Systems

4.1.1. Ultrasonic Assisted Wet Processing

The physical phenomenon in ultrasound is cavitation. Cavitation is essentially the formation, growth, and collapse of vapor-filled micro-bubbles in a liquid due to pressure changes induced by the sound waves generated by the ultrasound process [26,27]. This phenomenon can be effectively utilized in the textile industry in pre-treatment, preparation of dye baths, washing and more, as an alternative to conventional high-temperature methods [7,28].

Conventional textile processing methods usually rely on the use of chemicals and/or temperature as a means of accelerating, assisting, or retarding the rate of reaction. Ultrasound technology can be a sustainable method of activation due to the mechanical agitation produced in processing baths, which can accelerate the rate of diffusion of components inside the fibers [18,26]. This action can reduce processing time while causing little damage to the fibers and reducing water pollution load with the possibility of using smaller concentrations of chemicals due to the improved efficiency of diffusion [18,29,30]. Additionally, the ultrasound effect alone can remove impurities purely by mechanical action during pre-treatment [27].

Ultrasound can aid in the diffusion of enzymes inside the textile substrate during pre-treatment and finishing processes, surpassing enzymes’ mobility limitations and increasing process efficiency [26,31,32]. The even dispersion of enzymes produces textiles with increased wettability and little fiber degradation. A combination of ultrasound and pectinase on a laboratory scale was studied for the bio-scouring of greige cotton, with the resulting fabrics presenting wettability comparable to that of the conventional 90-min alkali process after a 45-min treatment for lightweight and heavyweight cotton [27]. In another study, the application of ultrasound during pre-treatment with enzymes was deemed the most important parameter for obtaining better wettability of cotton fabrics while obtaining a good whiteness index (WI) with reduced tensile strength loss [32].

Likewise, the introduction of ultrasounds in dyeing can help with dye dispersion and increase solubility and dye uptake [26,28]. As dye uptake is increased, the use of smaller concentrations of dye during the process is a possibility, as well as a potential reduction of salt concentration [16,17,29]. Ultrasound technology proved to contribute to higher color yields with natural dyes [16,32,33], reactive dyes [17,34,35], acid dyes [30,36,37,38] and disperse dyes [39] than those obtained without ultrasound. The ultrasound technology was also used to dye at lower temperatures. In the study performed by Tissera et al. [17], dyeing a cotton fabric with reactive dyes at 40 °C for 60 min employing sonication resulted in a color yield of 5.7, while conventional dyeing at 60 °C for 60 min resulted in a color yield of 4.9. Other studies focused on the dyeing of wool substrates concluded that fibers dyed in the presence of ultrasounds at 60 °C, 70 °C and 80 °C were comparable to fibers dyed with the conventional process at 95 °C [36,37]. The near-boiling temperature needed for wool dyeing has a negative effect on the fibers, contributing to their tensile strength loss. Ultrasound technology could be an alternative for reducing process temperature. Additionally, sonication has proved to increase the deagglomeration of dye molecules in low liquor ratio dyeing [33] when compared to the effect of agglomeration-preventing agents alone [30]. Accordingly, dyeing processes that require less water can become more attractive to the textile industry by employing ultrasound technology, which can increase dye uniformity without the addition of auxiliary products.

Other than pre-treatment and dyeing of textiles, ultrasound can also be used in finishing processes, assisting in the even dispersion of finishing solutions on the surface of fabrics and improving particle adhesion [28,31,40]. For instance, sonication was effectively used to coat cotton fabrics with flame-retardant solutions, where ultrasonic vibrations facilitated uniform heat distribution in the solution, resulting in a consistent coating on the fabric surface [25]. Ultrasound technology has been demonstrated to enhance the adhesion of antibacterial coatings on cotton fibers by promoting the attachment of titanium dioxide (TiO₂) nanoparticles, leading to significant antibacterial properties. Samples without ultrasound treatment did not show visible particles on the fiber surface, highlighting the key role of ultrasound [40]. Similarly, ultrasound improved the distribution of silicon dioxide (SiO₂) nanoparticles on wool fabrics, resulting in a more homogeneous coating and a slight increase in tensile strength compared to conventional methods [38]. Additionally, an ultrasonic-assisted method promoted the efficient mixing of solutions, accelerating the migration of newly formed SiO₂ nanoparticles to the cotton surface. This process resulted in highly efficient fabrics for oil/water separation, maintaining efficiency even after 50 separation cycles, making them suitable for situations such as oil spill accidents [41].

Currently, several companies are investing in the development of industry-oriented ultrasonic devices, such as Geratex (Karjan, India) with SonicWash™ and Eco-Scour, which are modular machines designed to integrate into an existing textile plant. Other companies, including Sonovia (Ramar Gan, Israel), Siansonic (Beijing, China), Sono-Tek (Milton, MA, USA), Cheersonic (Hangzhou, China) and GRINP^®(Settimo Torinese, Italy), are also pioneering solutions in this field. However, studies need to be conducted at an industrial scale, and water, energy, and chemical products consumption in ultrasound technology should be determined so that manufacturers are aware of cost benefits and accept initial high implementation costs.

4.1.2. Ozonation

Ozone is a gas composed of three oxygen atoms (O₃). This gas is not very stable and spontaneously decomposes into oxygen (O₂), producing a free oxygen atom (O⁻) that is highly reactive and readily oxidizes other substances present in its environment [9,42,43]. Ozone is very reactive, which impedes its storage and transportation [42,44]. Consequently, an ozone generator is necessary to employ this technology.

The oxidizing reaction in the ozonation process can be exploited in favor of textile pre-treatment processes as a cleaner method with lower water and chemical products consumption and no waste generation [42,44]. Bleaching of terry cotton fabrics with an ozonation dose of 500 mL·min⁻¹ for 30 min resulted in WI values comparable to the conventional bleaching process. However, wettability values were far from acceptable [45]. In another study, application of ozonation with a 5 L·min⁻¹ dose for 1 h in combination with 5 min of sonication resulted in wettability values comparable to those of the conventional process [46]. Despite the advantages of ozonation, this technology must be applied in moderate concentrations and short periods of time to preserve fibers’ tensile strength and prevent weight loss [46,47,48].

Denim garments are often washed and bleached to reach a certain aesthetic finish to the final clothing article. Conventional processes, such as bleaching and enzyme and stone washing, are water and energy-consuming [42,44]. Additionally, wastewater produced has harmful effects on the environment and human health, containing bleaching agents such as sodium chlorite, sodium hypochlorite and peroxides [49]. Ozone oxidizing power can break down indigo dye, which is the most common dye used in denim, successfully bleaching garments while minimizing water consumption by 72% and chemicals consumption by 91% [47,50]. Ozonation was reported to have comparable results with conventional processes in just 15 min using an ozone dose of 500 g·h⁻¹ [50] and in 20 min using 130 mg·L⁻¹·min⁻¹ in acidic conditions [48].

Ozonation can also be used in wastewater treatment for color removal, reduction of acute ecotoxicity and COD values [9,42,43]. Wastewater treated with this technology can possibly be reused in the textile process, for example, in the washing steps following dyeing. Considering that wastewater treatment is not the focus of the present review, no further information will be provided on this topic, even though it is an emerging technique that can reduce the environmental impact of the wastewaters generated during textile wet processes.

Most reports on ozonation in the textile industry are focused on removing impurities, fading denim, or wastewater treatment. However, a study conducted by Anam et al. [51] shows that using ozone technology after dyeing cotton with direct and reactive dyes can improve color strength by 50% while maintaining fastness properties. These findings suggest that lower dye concentrations can be used to obtain the desired color strengths, reducing wastewater contamination. Additionally, the ozonation dose used in the previous study was very low (0.5 to 1 g·h⁻¹) compared to doses used in ozone-assisted bleaching processes, not posing a threat to fiber integrity.

Ozonation systems are increasingly being adopted in denim production facilities as sustainable alternatives to conventional mechanical and chemical finishing processes. Several companies have already provided industrial solutions for sustainable ozone systems, such as Absolute Ozone^®(Edmonton, Canada), Ozcon Environmental (Birmingham, UK), Ozon Denim (Istanbul, Turkey), and Jeanologia (Paterna, Spain). Both Ozon Denim and Jeanologia offer ozone washing machines tailored specifically to answer textile industry concerns. Additionally, Tonello^® (Sarcedo, Italy) has introduced OBleach, a process that uses ozone combined with Core technology to achieve bleaching without other chemical additives. Despite the environmental and operational benefits, widespread adoption of ozonation technology requires substantial initial capital investment. Manufacturers must also comply with strict safety regulations, as ozone inhalation can cause significant respiratory irritation [43]. Proper safety protocols and well-maintained ozone discharge systems are essential to prevent toxic exposure and ensure the safe and effective use of ozone in industrial applications [43,50].

4.1.3. Plasma

When energy is applied to a solid, it melts into liquid form, and when energy is applied to a liquid, it evaporates into gaseous form. Similarly, when energy is applied to a gas, electrons become free of atoms and/or molecules, and an ionized gas is produced. This is called the plasma phase, which is an energy-rich state that is highly reactive [9,52,53]. This reactivity can be used to create surface modifications onto fibers, assisting in textiles pre-treatment or finishing processes [54]. Plasma technology is a dry process applied at low temperatures that is beneficial to textile processing as it reduces the need for water and chemicals. Since textiles are heat-sensitive, non-thermal plasma is used for fabric processing. In this category, low-pressure plasma, which operates in a vacuum and generates more precise treatments, and atmospheric-pressure plasma, which operates at normal atmospheric pressure, are included, making them more suitable for continuous processing in industrial settings. In

Table 3. Non-thermal plasma technologies used for textile processing.

Low-Pressure Plasma	Atmospheric-Pressure Plasma
Microwave plasma Inductively coupled plasma Capacitive coupled plasma	Dielectric barrier discharge (DBD) plasma Corona plasma/discharges Plasma jet Gliding arc plasma Glow discharge

, different plasma technologies currently being used in textile processing are presented.

Plasma technology as a pre-treatment has been continuously linked to increased wettability of fibers, which can reduce processing time and the use of chemical products. Dielectric barrier discharge (DBD) plasma was applied to raw cotton for 2 min, substantially increasing its wettability when compared to conventional chemical processing and affecting only the fiber surface and not the inner structure [55]. The application of plasma jet technology followed by conventional scouring resulted in shorter scouring times while improving fabrics’ wettability [56]. Plasma technology was also tested in a pilot facility for continuous production for 27 weeks [57]. In this study, two different baths were tested: pulse discharge followed by an enzymatic bath for bleaching and polishing and a second enzymatic bath for H₂O₂ degradation. Resulting fabrics presented comparable wettability, WI and tensile strength values to those of the conventional H₂O₂ bleaching process while contributing to a 66% reduction in water consumption and a 60% reduction in COD, total nitrogen, ammonia nitrogen and total phosphorus loads in wastewater. These studies evidence that plasma technology, in combination with enzymes, can be an interesting alternative to reduce water and auxiliary products usage.

Other studies have focused on the effects of plasma technology on the dyeing process. By applying low-pressure plasma for natural wool dyeing with pomegranate dye, the color strength of the fabrics, as well as fastness properties and tensile strength, were improved [58]. Silk fabrics were also tested with glow discharge as a pre-treatment to natural dyeing, effectively increasing color strength and maintaining fastness properties [59]. These results suggest that plasma technology could be an alternative to metal salts and traditional mordanting in the natural dyeing process. Plasma technology was also used in the printing process. In the study performed by Ahmed et al. [60], the application of DBD for a maximum of 10 min resulted in improved printability and fastness properties with Cochineal natural dye. Similarly, DBD treatment has been demonstrated to improve color strength and promote clearer edge definition in ink-jet printing of polyester fabrics [61].

In addition to surface treatment for improvement in dyeing and printing, plasma technology is also an alternative to conventional finishing processes, optimizing the interaction between finishing/functional agents and the fiber surface. Polypropylene materials for medical products were effectively imparted with antibacterial properties using low-pressure plasma to stabilize the deposition and fixation of silver nanoparticles [62]. Similarly, super-hydrophobic cotton was produced using low-pressure plasma to etch the fabric surface and deposit lauryl methacrylate as a functional monomer with low surface energy, obtaining excellent washing durability with little effect on permeability [63]. Flame retardancy was also successfully applied to polyester and cotton fabrics using plasma technology [64,65].

Atmospheric pressure plasma is more convenient for textile processing because, unlike low-pressure plasmas, expensive vacuum equipment is not needed, allowing the continuous processing of fibers on a large scale [52]. However, low-pressure plasma offers a high-precision process. Several companies have commercially available industrial-level atmospheric plasma products, such as Acxys (Saint Martin le Vinoux, France), Ahlbrandt (St. Louis, USA), GRINP^® (Settimo Torinese, Italy) and Enercon (Aurich, Germany), while others, such as Plasma Etch (Carson City, USA) and AGC Plasma Technology Solutions (Charleroi, Belgium), focus on low-pressure plasma. There are also companies commercializing both technologies. Plasmatreat (Alcorcón, Spain), for example, offers solutions of both technologies for improved wettability before dyeing and functional finishes, such as antibacterial, hydrophobicity, and dirt repellency. Thierry Corporation (Royal Oak, USA) also commercializes both solutions, focusing on waterproof and water-permeable finishes and textile reinforcement of fibers.

4.1.4. Laser

Laser stands for “Light Amplification by Stimulated Emission of Radiation” and is essentially a tool that can successfully turn light into a precise and powerful beam. When in contact with fabrics, a localized reaction caused by heat is produced. This reaction often results in surface alterations such as marking and etching of textile materials or even cutting for garment production, depending on the intensity of the application [66]. Laser is a dry technology that allows for precision details and design flexibility, reproducing repeatable patterns easily.

This technology is widely used by the textile industry for precision cutwork, enhancing accuracy while minimizing fabric waste. Mind Technology (Espargo, Portugal) provides industry-oriented solutions in this field, such as MindCUT, an automatic cutting system designed for optimal material use, precise cutting, and piece selection.

As an alternative to wet processing, one of the most prominent applications of laser in textiles is denim finishing, where it serves as a sustainable alternative to traditional processes such as stone washing, enzymatic washing, and chemical bleaching [66,67]. As mentioned in Section 4.1.2, conventional denim finishing requires large volumes of water and auxiliaries, often leading to environmental pollution and fabric damage. Laser finishing allows for controlled fading and distressing effects while eliminating or drastically reducing water and chemical products usage. Different studies demonstrated that laser technology can promote a better color-fading effect than enzymatic treatments, with fewer rinsing steps and significant savings in time, water, and energy [67,68]. A practical example showed that laser-based denim treatment was completed in just 3 min at room temperature, compared to 45 min at 55 °C for enzyme-based stone washing [67]. Additionally, laser bleaching was found to be the most effective method for denim in comparison to four conventional methods (cellulase enzyme, sodium hypochlorite, potassium permanganate, and H₂O₂) while maintaining comparable fastness properties [49].

Although cutwork and denim finishing are the leading applications of laser technology in textiles, research has expanded into other textile processing areas. Peri-dyeing was tested as a technique to apply standard dyestuffs and auxiliaries to textile samples, followed immediately by laser irradiation. This method allowed dye diffusion and reaction to occur precisely at the point where the laser interacts with the fabric, enabling highly controlled coloration without direct contact [69]. However, laser technology was associated with increased fiber yellowness and decreased mechanical properties in both cotton and polyester [70]. To mitigate these effects, some studies demonstrated that chemical pre-treatment before laser exposure can eliminate the need for enzymatic washing and enhance mechanical properties while reducing discoloration [71]. Another research study demonstrated that pigment printing on laser-treated fabrics can improve certain mechanical properties, such as the ability to recover after tensile stress [72]. Laser pre-treatment improved dye absorption and breaking elongation on wool. Additionally, results for felting shrinkage were comparable to those of the conventional chlorination process, offering a more sustainable alternative for wool processing [73].

Several companies are at the forefront of laser technology innovation in textile processing, offering sustainable and efficient alternatives to conventional methods. SEI Laser (Curno, Italy) states that Flexi Denim, a laser system designed for denim finishing and cutting, reduces water consumption by up to 80% while eliminating the need for hazardous chemicals. Jeanologia (Paterna, Spain) offers advanced solutions such as Handman, an automated laser robot that combines robotic precision with human oversight, enabling a clean, efficient, and scalable production environment. Portlaser (Barcelos, Portugal) specializes in both horizontal and vertical laser processing for denim and other textiles, further demonstrating the versatility of this technology. These advancements reflect the increasing adoption of laser systems as scalable, eco-friendly solutions for modern textile manufacturing. Zaitex (Dueville, Italy) developed Garment Flash Printing, a process in which pigments are added by laser. Additionally, the ZETAKIN LST product can be added to garments to enhance the natural look of lasered denim, replicating the result of manual scraping.

4.1.5. Digital Inkjet Printing

The printing process usually requires a pre-treatment for improved dye absorption, a printing step for the addition of color and a post-treatment for fixation, usually steaming and curing at high temperatures. In conventional textile printing, specific patterns are created by pressing thick printing pastes consisting of dyes and auxiliaries on the surface of textiles using mesh screens and printing plates. In contrast, digital inkjet printers apply tiny droplets of dye only directly onto fabrics, accurately replicating digital images and enabling the production of intricate designs with exceptional versatility. This technology requires considerably less water consumption as only dyes are applied straight onto fabrics. Digital inkjet printing minimizes waste and lowers water consumption and chemicals discharge, making it an appealing alternative to conventional printing. While the digital printing process itself is inherently more sustainable and undeniably a better alternative to conventional printing, the overall environmental impact is influenced by the chosen pre-treatments, dyes and post-treatments that can compromise its sustainability.

Unlike dyeing, printing is a fast and precise process. However, its rapid nature presents certain challenges, such as insufficient time and water for the proper dissolution and diffusion of dyes into natural fabrics, which can result in reduced design precision and increased dye discharge during washing [74,75]. To address this issue, urea is commonly used on conventional printing pastes and during the pre-treatment of digital printing to attract and retain moisture inside the fibers, effectively slowing the drying process and ensuring proper dye fixation [76]. However, as mentioned in Section 3, urea has significant environmental drawbacks, contributing to water pollution. Advanced water treatment systems can remove urea and its by-products from wastewater; however, these systems can be slow, expensive and energy-intensive, making them less suitable for widespread use in the textile industry [77]. To counter these issues, innovative solutions using eco-friendly alternatives to urea are being developed, such as sustainable urea substitutes with a good ability to swell fibers, cationic agents that improve dye fixation by adding positive charges to fabrics’ surface without requiring moisture and dye modifications to increase dye fixation. In

Table 4. Effect of eco-friendly alternatives to urea and their color performance for different fabrics.

	Alternative agent	Substrate	Effects on Color Strength, Fastness, and Dyeing Properties	References
Urea substitutes	Polyethylene glycol 400 (PEG-400)	Cotton	Urea reductions above 70% result in color performance similar to urea conventional treatment.	[78]
			Resulted in superior dye penetration and improved sharpness of the edges.	[79]
	Glycerol and 1,4-butanediol formulation	Viscose, cotton, linen and silk	Resulted in similar color strength and improved dye penetration, maintaining fastness properties.	[80,81]
		Silk	Resulted in increased color strength and similar fastness properties.	[82]
	Guar gum	Wool and cotton	Resulted in increased color strength on wool and similar color strength on cotton fabrics.	[83]
	Carboxymethyl guar gum (CMG)	Hemp fibers	Resulted in color strength increases above 26% for all primary colors and black and similar color fastness.	[84]
	Co-polymer (NS)	Cotton	Resulted in increased color strength and fastness properties with 1 wt% NS-02 treatment.	[74]
Cationic agents	3-Chloro-2-hydroxypropyl trimethylammonium chloride (CHPTAC)	Cotton	Resulted in an increase of 38% in color strength and 37% in dye fixation.	[21]
			Resulted in excellent color fastness and significant environmental advantages with nearly colorless wastewater.	[85]
			One-step printing technology applying cationic agents and dyes simultaneously resulted in sharper edges, improved color strength, and nearly colorless wastewater compared to the two-step process. However, urea was used in pre-treatment.	[86]
	N-(2-hydroxy)propyl-3-trimethylammonium chitosan chloride (HTCC)	Cotton	Resulted in increased color strength values and better fastness properties.	[87]
Dye modifications	Reactive dye containing CHPTAC	Cotton	Resulted in an increase in color strength by 35% when compared to normal reactive dye. However, urea was used in pre-treatment.	[75]
	Reactive dyes with multifunctional groups	Cotton	Multifunctional groups had low dependence on urea, which resulted in 98% dye fixation and good fastness properties	[88]

, some of these alternatives and their color performance are explored.

The exploration of urea alternatives has gained significant attention in recent research, aiming for its full substitution. However, many of these alternatives still involve urea. Despite the promising results observed with novel alternatives, the successful transition to industrial-scale implementation remains a critical challenge.

Unlike alternative solutions presented above, an innovative ecosteam method for digital printing on cotton, eliminating the need for urea, was developed. This approach proposes bypassing the drying steps before and after printing, using fabric still damp from the pre-treatment step to directly print and steam, resulting in an increase in dye fixation by 15% and higher color fastness values [76]. However, the study conducted did not address the sharpness of the design, raising the question of whether this technique is suitable only for overall printing rather than detailed pattern printing.

Digital inkjet printing is already established in the textile industry due to its versatility, sustainability and cost-effectiveness. Several companies have already commercialized industrial and laboratory-scale systems, such as Zimmer (Zug, Switzerland), with the COLARIS line for fabric and carpet substrates. EFI^® Reggiani (Londonderry, USA) states that its ecoTERRA solution, which uses water-based inks, eliminates pre-treatment while still producing high-quality prints and reduces water and energy consumption by 90% and 60%, respectively. Most inkjet-printing systems require scanning of the print head over the same portion of the fabrics to achieve the desired color strength and quality, significantly increasing production time. Konica Minolta (Prior Velho, Portugal), MS Printing Solutions (Guanzate, Italy) and EFI^® Reggiani (Londonderry, USA) commercialize single-pass digital machine solutions that have an in-line pre-treatment unit and, unlike typical digital printing machines, have immobile printing heads covering fabrics’ whole width and enabling faster production rates. Durst Group’s (Brixen, Italy) Alpha Series uses Greentex and Water Technology innovations, offering significant water and energy savings.

4.1.6. Atomization Systems

The atomization, or nebulization, process reduces liquor particles to a micro- or nano-size version, creating a mist that is controllably diffused onto fabrics. Accordingly, the smaller liquor particles exhibit a great diffusion rate onto fibers, adhering effectively. Figure 1 presents a schematic representation of the atomization process.

Nebulization was tested as a washing step during denim finishing, enabling a reduction of 90% in water consumption when compared to the conventional finishing process [89]. This process complied with the industry’s standards for fastness properties; however, this study only used nebulization in 1 out of the 28 steps of the denim finishing process. Additionally, no investigation was carried out into the influence this technology would have on chemical impacts in wastewater, which is highly relevant since wastewaters will be more concentrated. Another study successfully applied 11 reactive dyes onto a cotton fabric using nebulization technology with a liquor ratio of 1:1, obtaining comparable results to conventional exhaust methods with no water discharge during the main dyeing cycle [90].

Care Applications^® (Alcoy, Spain) claims that its ECOFinish nebulizer, designed for both sample and industrial purposes, reduces liquor ratios to as low as 1:0.2 and enables dyeing without the addition of salt. Similarly, Tonello^® (Sarcedo, Italy) has Core 2.0 technology for sampling and production application of garment washing and dyeing. These systems are already being implemented in the textile industry as an ecological solution. AirDye^® (Osaka, Japan) technology atomizes liquor particles’ size, similarly to nebulization; however, liquor particles are mixed with high-pressure airflow and sprayed onto the fabrics. By using air instead of water as a medium for dye diffusion, the manufacturer states that this novel method reduces up to 95% in water consumption. This dyeing solution is available for polyester and polyester blends; however, pigment printing technology for pre-dyed fabrics and 3D effects are available for all fabric compositions and blends. Another promising innovation, Then-Airflow^® (Schwäbisch Hall, Germany) technology, is comparable to a dyeing jet; however, it uses air instead of water to circulate fabrics. Similar to the AirDye^® system, dye liquor is atomized and sprayed into the jet’s chamber, effectively dyeing fabrics. The manufacturer states that this system reduces energy consumption by approximately 40% when compared to conventional jet-dyeing machines, and liquor ratios can be as low as 1:2, substantially reducing water consumption. Imogo (Limhamn, Sweden), focusing on spray systems for bleaching, dyeing, and finishing, offers a solution for both laboratory and industrial production needs, stating that a reduction of water consumption by up to 90% can be achieved through a liquid ratio of less than 1:1. The system is capable of spraying on one or both sides of the fabric, contributing to its efficiency. Baldwin^®’s (St. Louis, USA) TexCoat™ precision spray application system is another notable example of innovative technology in the textile industry. The system applies water or chemicals uniformly across one or both sides of a moving web roll of fabric, using an application system with evenly spaced spray nozzles that span the width of the web. These developments highlight the growing trend toward more sustainable and water-efficient technologies in textile dyeing and finishing processes.

4.1.7. Supercritical Carbon Dioxide

Supercritical carbon dioxide (SC-CO₂) consists of CO₂ subjected to temperature and pressure beyond its critical point, entering the fluid supercritical phase. In this state, CO₂ exhibits both liquid and gas properties, infiltrating materials like a gas and dissolving substances like a liquid [18]. This technology has gained attention in the textile industry because it is a dry process, and CO₂ is inexpensive, non-toxic, and readily available [4,91]. Additionally, CO₂ exists as a supercritical fluid at about 31 °C, which is near ambient temperature, and pressures above 72 bar, which are relatively low.

These characteristics make SC-CO₂ an excellent alternative processing medium, removing entirely the need for water and revolutionizing the traditional textile dyeing process [92,93]. Additionally, reduced energy needs are expected for this technology when compared to the energetic demand of conventional textile finishing processes. In its supercritical state, CO₂ functions as a non-polar solvent that is highly compatible with hydrophobic dyes and fibers, allowing dyes to dissolve and be transported efficiently into fibers. Due to the excellent diffusion of dye particles, dispersing agents that were once indispensable for dispersing dye application are completely removed from the process, effectively reducing pollutant load in wastewater [94]. SC-CO₂ application as a medium proved to successfully dye polyester [94,95], polypropylene [96,97] and polyamide [98,99] fibers at relatively low temperatures and with no water consumption. At the end of the dyeing process, CO₂ and residual dyes can be recovered and reused, making this technology not only environmentally safer but economically attractive.

However, the dyeing of natural fibers such as cotton, linen and silk has not achieved the same ground-breaking results. SC-CO₂ exhibits low permittivity, which is why it is effective for hydrophobic substances and fibers, but for hydrophilic dyes and fibers, it is a poor solvent [4]. Previous reports on natural fiber dyeing typically involve the use of dye molecule adaptation [92,100,101] and the addition of auxiliary and phase transfer catalytic agents [93] to facilitate the dissolution of the dye.

Although SC-CO₂ has proved to be an exceptional alternative for dyeing, pre-treatment and finishing of textiles were also studied using this technology. For instance, cotton was successfully bleached using 15% H₂O₂ at 80 °C for 20 min with no added auxiliaries, resulting in a similar WI to the conventional process and leading to higher color strength after dyeing [102]. SC-CO₂ technology was also used to remove olive oil, beeswax, and rabbit skin glue from cotton and silk fabrics, showing efficiencies of 74%, 55% and 87%, respectively [103]. Therefore, it can be argued that scouring with SC-CO₂ might be effective in removing impurities. Antibacterial finishes with silver nanoparticles and functional dyestuffs were successfully applied to wool and polyester fabrics, respectively, exhibiting excellent properties [104,105].

SC-CO₂ technology is already being used by the textile industry, especially as an alternative to synthetic fiber dyeing. At an industrial level, DyeCoo^® Textile Systems (Hoofddorp, Netherlands) developed a patented SC-CO₂ dyeing technology to dye polyester [92]. An experimental SC-CO₂ jigger dyeing apparatus was developed, and polyester fabrics were successfully dyed, making it a promising solution for industrial applications [106]. Additionally, Deven Supercriticals (Mumbai, India) and Qarboon (Clermont-Ferrand, France) enabled the use of SC-CO₂ technology to dye natural fibers, such as cotton, linen and silk. However, more effort is needed so that this technology becomes more attractive to manufacturers due to high initial investment, equipment costs, and limited options for natural fiber dyeing.

4.2. Developing and Specialized Technologies

4.2.1. Reverse Micelle Dyeing

Micelles are nanoscale spherical aggregates composed of surfactant molecules. These molecules consist of a hydrophilic head and a hydrophobic tail, and in polar solvents like water, they self-assemble into micelles with the hydrophilic heads facing outward toward the water while the hydrophobic tails are inside. Micelles are widely used across industries due to their ability to encapsulate and transport substances. In contrast, reverse micelles form in non-polar solvents, where the hydrophilic heads face inward, creating a water-containing core, while the hydrophobic tails point outward into the solvent. This structure allows reverse micelles to carry water and other polar substances, including water-soluble dyes, enabling the dyeing of fibers in non-aqueous media [107]. This novel method can minimize water consumption by using non-polar solvents and improve wastewater quality with a solvent recovery percentage above 90% and no added salt during the dyeing process [107,108]. In Figure 2, a schematic representation of a surfactant molecule, micelle and reverse micelle is presented.

Non-ionic poly(ethylene glycol)-based (PEG-based) surfactants have been extensively tested for cotton and wool salt-free reactive dyeing with reverse micelles. In a heptane medium, PEG-based surfactants, along with co-surfactants like n-octanol, enabled efficient dyeing of cotton fabrics, providing color strength, uniformity, and fastness properties comparable to conventional water-based methods [108,109]. Furthermore, 95.5% of the solvent was recovered for reuse, offering a sustainable approach to the process [108]. In a similar setup, the use of PEG-based surfactants with octane and nonane solvents resulted in improved color strength and better fastness compared to traditional methods when applied to cotton [107] and wool [110,111] fabrics. Additionally, wool dyeing tests were conducted under reduced temperatures and shorter processing time compared to the conventional process, requiring 50 min at 88 °C instead of 60 min at 98 °C. Nonane is particularly notable for being less harmful than heptane and octane. VOC leakage detection was performed during reverse micelle dyeing, resulting in levels in the 2–3 ppm range, which is acceptable [107]. This makes nonane a potentially safer option in reverse micelle dyeing, although it still requires careful handling due to its volatility.

Petroleum-based solvents like octane, heptane, and nonane are not the most environmentally friendly options for reverse micelle dyeing due to their volatility, fossil fuel origin, and associated toxicity concerns. Similarly, petroleum-derived surfactants pose sustainability challenges, highlighting the need for greener alternatives to reduce environmental impact. To address this, a biodegradable secondary alcohol ethoxylate (SAE)-based surfactant combined with nonane as a solvent demonstrated excellent color strength and uniformity in cotton dyeing, yielding results comparable to water-dyed samples [112]. Additionally, studies on microbial biosurfactant rhamnolipid (RL) explored its application with non-toxic solvents such as paraffin liquid (PL). While PL-based dyeing generally resulted in enhanced color strength, except for blue, uniformity issues were observed [113]. Alkane solvents demonstrated potential in achieving exceptional color strength and uniformity; however, modification of the dye recipe may be required for improved results with PL. Meanwhile, limonene with different chemical structures was tested as a bio solvent for RL reverse micelle dyeing, resulting in higher color strength and comparable uniformity to water-based dyeing methods [114].

Beyond reverse micelle dyeing, other solvent-based dyeing techniques have been explored. Research on ethanol, propanol and isopropanol as dyeing media for cotton resulted in improved color strength and significantly clearer dye baths compared to conventional aqueous dyeing [115]. Additionally, a study using decamethyl cyclopentasiloxane (D5)—a solvent safe for both humans and the environment—showed that cotton dyed with 2% reactive dyes in a D5 suspension achieved equal color strength as a 9% dye concentration in conventional water-based dyeing, with comparable color fastness [116].

Apart from the information herein presented, which is mainly sourced from the same research group, there is currently limited publicly available data on specific companies and organizations actively working on reverse micelle dyeing and solvent-based technologies for the textile industry. However, potential contributors to this field include textile chemical suppliers, equipment manufacturers and research partnerships. These systems, which eliminate the need for salt, reduce water consumption, and minimize chemicals discharge, hold significant promise for advancing more sustainable dyeing practices. However, to justify the shift from water to solvents, a closed-loop system for solvent recovery and reuse should be developed.

4.2.2. Foam Technology

The processing liquor can be incorporated with air by mechanical agitation or air injection in the presence of a foaming agent to create a foam, expanding the volume of the solution 5–25 times [117]. Foam is continuously generated during processing, and as it forms and collapses, the processing liquor is uniformly transferred to fibers. Foam technology enables application with 10–15% wet pickup as compared to 60–80% in conventional padding [118]. This alternative technique allows the reduction of the liquor-to-fabric ratio and drying time, contributing to significant savings in water and energy consumption [7].

In digital printing, material saturation during pre-treatment can lead to uneven prints. Foam technology was tested as a pre-treatment application due to its low liquor ratio, resulting in consistent print quality and reduced chemicals and energy use [119]. A system using foam as a medium for the delivery of bleaching agents, enzymes, finishing agents, and softeners was also developed [120].

Foam dyeing was compared with pad dyeing, which excelled in performance, sustainability, and cost. Dyeing of an intermediate color with reactive and direct dyes was successfully applied to cotton fabrics using a coating system [121]. The application of a dark color was also tested using foam technology, successfully dyeing cotton with indigo dye and saving up to 53% of water and energy used for drying [122].

Likewise, finishing agents can also be applied with foaming methods. In a study performed by Mohsin and Sardar [123], 11 different non-toxic finishing agents were successfully applied to cotton using foam as a medium. This method had more than 80% savings in water and chemicals compared to conventional padding. Another study successfully imparted cotton fabrics with antimicrobial and wrinkle-free finishing using foam technology [118].

Foam processing has numerous advantages; however, for this technology to be applied in industrial processes, precise control over foam generation and stability is needed. Foaming agents and stabilizers used during application need to be compatible with the processing liquors for a successful uniform application.

4.2.3. Microwave

Microwaves are a form of electromagnetic irradiation that primarily interacts with polar molecules, such as water, certain dyes, and even natural fibers like cotton and wool. In the presence of an electromagnetic field, molecules continuously reorient, generating internal heat through friction. This interaction can enhance textile processing by improving dye penetration, reaction efficiency, and overall process sustainability [124]. This technology can be particularly attractive due to its fast-heating speed, low energy consumption, and use of simple and safe equipment [125].

Microwave technology has been tested to improve natural fiber wettability in reactive dyeing. Studies on microwave-assisted dyeing of cotton and wool reported significant improvements in color strength, with similar color fastness properties, while reducing chemicals consumption [126,127]. Dyeing was successfully achieved with 700 W of irradiation in no more than 5 min, a significant time-saving advantage over conventional processes. Additionally, microwaves were explored for natural dyeing using extracted dyes from Cochineal [128], lac [129], Arjun bark [130,131], Neen bark [132], safflower [133] and coconut coir [134]. Irradiated extracts generally produced higher color strength compared to non-irradiated extracts, enhancing the feasibility of natural dyes for industrial applications. Furthermore, the irradiation of cotton, wool, and silk as a pre-treatment to improve dyeability was studied; however, the results remain inconclusive. Some studies report improved dye uptake with irradiation, while others suggest better results without it.

Outside the scope of dyeing, microwaves have been studied as an alternative to thermal drying and curing. When applied to finished wool at 700 W for 3 min, microwave dyeing resulted in a significant improvement in WI and adsorption capacity compared to 80 °C drying for 5 min and 130 °C curing for 5 min [135]. Microwave-assisted nanotechnology applications have also been explored. Fragrant nanocapsules applied to cotton via microwave irradiation prevented thermal degradation, which would occur in conventional processes [136]. Additionally, in-situ zinc oxide (ZnO) nanoparticle synthesis using microwaves enabled a single-step deposition of nanoparticles in cotton, supporting an efficient and scalable development of functional fabrics [125].

Microwave heating has been proposed as an alternative to conventional desizing, scouring, and bleaching. In experiments applying 800 W irradiation post-padding for each process, comparable results were achieved within 5 min versus 45–120 min in traditional methods [137]. A one-step microwave-based pre-treatment also showed acceptable results. However, conventional processes were not directly tested, and instead, values from other prior studies were used for comparison, raising questions about the effectiveness of this process. While no significant water or chemicals savings were observed, substantial energy savings could be achieved by applying microwave heating.

There is limited information on companies using microwave technology for textile wet processing. Some companies, such as Ferrite Microwave Technologies (Nashua, NH, USA), use this technology in systems specially developed for textile drying. Additionally, reports suggest that ITA RWTH Aachen (Aachen, Germany), Püschner (Schwanewede, Germany), and DyStar (Shanghai, China) are developing continuous microwave dyeing equipment, though public details on this innovation remain scarce.

4.2.4. Dope Dyeing

Dope dyeing is a dyeing technique in which pigments or dyes are added directly to the dope solution before it is extruded to form fibers. In this process, color is embedded throughout the fiber rather than being applied to the surface, resulting in textiles with excellent color fastness properties [138]. One of the major environmental benefits of dope dyeing is its significant reduction in water consumption and wastewater production, as it eliminates the need for conventional dyeing processes.

This technique is widely used in synthetic fibers like polyester, with companies such as Recron^® (Mumbai, India) (Duratarp), Filatex India Limited (New Delhi, India), Diklatex (Joinville, Brazil), Far Eastern New Century (Taiwan, China) (TOPGREEN^®), Thai Polyester Co., Ltd. (Bangkok, Thailand), GAC (New Taipei City, Taiwan) and Acelon (Changhua, Taiwan) (AceColor^®) commercializing dope dyed fibers. Notably, adding color to polyester melt to produce jet black fibers demonstrated to have a production cost of only 5% of traditional disperse dyeing processes, with mechanical properties comparable to virgin fibers [138]. A step further in sustainability is being taken by companies like We aRe SpinDye^® (Stockholm, Sweden), which uses recycled post-consumer water bottles and the dope-dyeing technique to create circular textiles with reduced environmental impact.

Dope dyeing has also been adapted for regenerated cellulose fibers like viscose, modal and lyocell. Regenerated cellulosic fibers present challenges due to the strong treatment of cellulose pulp, which may influence the stability of colorants. However, research demonstrated that dope dyeing can be successfully applied, achieving a reduction of 64% and 69% in water and energy consumption, respectively [139]. Vat dyes were incorporated into regenerated cellulosic fibers, resulting in higher wash fastness values without compromising fiber properties [140]. Additionally, pre- and post-consumer denim fabrics were successfully recycled to produce dark blue fibers through the addition of indigo to the spin dope [141]. Birla cellulose (Mumbai, India) developed Spunshades™, which corresponds to dope-dyed viscose fibers using their proprietary Color-Lock™ technology. However, there is still limited information on other companies utilizing dope dyeing for cellulosic fibers.

Bio-based synthetic fibers such as polylactic acid (PLA) were also successfully dope-dyed with bio-based dyes and pigments, offering similar performance to commercial dyes [142]. This further establishes dope dyeing as a sustainable alternative, particularly when paired with bio-based dyes.

Despite its advantages, traditional batch dyeing remains dominant, mainly due to dope dyeing’s requirement for early color decisions in fiber production, limiting flexibility to adapt to fast-changing fashion trends. However, as demand for sustainable textiles increases, advancements in polymer science and fiber engineering may expand the range of fibers and colors available through dope dyeing, making it an increasingly viable alternative to conventional dyeing processes.

4.3. Other Emerging Technologies

4.3.1. Ultraviolet Technology

Ultraviolet (UV) irradiation consists of high-energy electromagnetic waves that can break chemical bonds and induce photochemical reactions, allowing for surface modifications of textiles without altering their bulk properties [143]. Similar to other surface-modifying technologies, such as ozonation, SC-CO₂, plasma, and laser treatments, UV irradiation presents a promising alternative to conventional chemical-intensive processes.

In conventional bleaching, H₂O₂ produces perhydroxyl radicals (HOO⁻) under alkaline conditions, which react with fibers to promote bleaching. UV irradiation can enhance this process by generating the same reactive species with reduced chemicals consumption. Research has explored UV-assisted bleaching as an alternative to the pad-steam process (which uses padding followed by steaming to activate and accelerate the chemical reactions of bleaching agents, improving penetration into the fibers). One study demonstrated that using UV irradiation required half the NaOH concentration of conventional bleaching while achieving comparable WI, though with reduced tensile strength [144]. Further studies showed that fabrics bleached with H₂O₂ and UV irradiation, without additional auxiliary products, exhibited higher WI than fabrics treated with pad-steam process using H₂O₂ alone. When NaOH was added, WI increased for both treatments and in this setting, the UV-treated fabrics obtained results comparable to those of conventional methods [145]. Another comparison between UV and pad-steam bleaching found that, within the same processing time, UV-treated fabrics achieved similar WI while showing increased tensile strength, reduced water and energy consumption, and pilling resistance comparable to industrial enzyme-assisted bleaching with cellulase enzymes [146].

UV irradiation has also been explored as a pre-treatment for improving dyeability and color strength. In disperse dyeing of polyester, UV irradiation combined with H₂O₂ generates reactive carbons on the fiber surface via HOO⁻ radicals, facilitating dye uptake while reducing chemicals usage. This offers a potential alternative to conventional polyester dyeing, which requires high temperature and pressure conditions [147]. For cotton, UV pre-treatment was demonstrated to improve both color strength and fastness properties in reactive dyeing. One study demonstrated that irradiating both cotton fabric and reactive dyes before dyeing led to enhanced dye absorption [148]. Another study, which focused solely on UV irradiation of fabrics, found that 30 min of exposure already improved color strength, with a maximum improvement achieved at 90 min for both cotton and polyester fabrics [143]. However, these studies lack detailed comparisons with conventional processes, making industrial feasibility unclear.

UV curing has been widely explored in textile applications as a rapid and energy-efficient method for surface modification and finishing. This technique was used to create superhydrophobic cotton through rapid UV-curing processes, eliminating the need for prolonged heating [149]. Additionally, UV curing enabled the reduction of graphene oxide to graphene, imparting conductivity to cotton and wool fabrics [150]. It was also used to develop antibacterial cotton fabrics by modifying the fiber surface under UV irradiation, resulting in light-induced antimicrobial properties with excellent antibacterial performance [151]. Furthermore, UV curing emerged as a promising alternative for grafting low-toxicity flame retardants onto polyester/cotton fabrics, enhancing their fire resistance while maintaining a more sustainable approach [152]. In addition, a study demonstrated the fabrication of a UV-sensing textile by inkjet printing photochromic ink onto fabric, followed by UV curing to fix the ink. This process enabled the development of smart textiles capable of detecting and responding to UV irradiation through reversible color changes, offering potential applications in wearable sun protection monitoring and UV exposure detection [153].

The potential to improve fabric properties, such as bleaching and dyeing with fewer chemical products, as well as enhancing hydrophobicity, antimicrobial performance, and UV resistance, makes UV technology a promising solution for future developments. Companies such as RUDOLF GmbH (Geretsried, Germany) and Trelleborg Engineered Coated Fabrics (Trelleborg, Sweden) are at the forefront of this innovation, offering UV-curing solutions for coatings and durable UV printing for textiles, respectively. However, challenges such as scalability and cost-effectiveness still need to be addressed before widespread industrial adoption.

4.3.2. Electrochemical Dyeing

Vat dyes are a class of water-insoluble dyes valued for their high color fastness and durability. These properties make them a standard option for cotton fabrics such as beach and pool terry clothes, denim and other high-performance textiles. To enable fiber absorption, vat dyes must undergo a reduction process that converts them into a water-soluble form, followed by oxidation, which enables optimal fixation of the dye on the fibers [154]. In conventional vat dyeing, sodium hydrosulfite is predominantly used as a reducing agent under alkaline conditions due to its cost-effectiveness, while H₂O₂ serves as an oxidizing agent [155]. However, sodium hydrosulfite poses significant environmental risks, contributing to high COD values in wastewater, and its oxidized by-products are toxic [156]. To address this, eco-friendly reducing agents have been proposed to replace sodium hydrosulfite. However, issues such as strong-smelling products and slow reaction rates, which are unsuitable for large-scale textile processing, remain unsolved.

A promising solution to these issues is electrochemical dyeing, where an electric field is applied to the dye bath. In this process, electrons supplied by the electric current replace chemical-reducing agents, eliminating wastewater contaminants. Although this technology was extensively investigated in the 2000s, progress stagnated, likely due to scalability concerns. However, more recent studies have reinforced the potential of electrochemical dyeing for indigo dyeing in denim production, confirming findings from earlier research. These studies reported improvements in color strength and comparable fastness properties to conventional vat dyeing, alongside a reduction in COD values in wastewater. In a laboratory-scale study, the reduction medium could be reused for up to seven dyeing cycles, significantly reducing both water and chemicals consumption [157]. Another study employing a medium-scale padding system for room-temperature dyeing achieved color fastness comparable to conventional methods [158]. However, despite these promising developments, research on the broader industrial adoption of electrochemical dyeing remains limited. Several patents have been recently filed proposing electrochemical dyeing processes suitable for industrial applications [159,160]. A notable pilot-scale study from 2009 explored autoclave yarn dyeing with vat dyes, yielding uniformity and fastness properties similar to conventional processes. The dye bath was regenerated via ultrafiltration and reused, although the lowest liquor ratio used (1:55) was significantly higher than that used in traditional industrial dyeing, indicating a need for optimization [161].

While electrochemical dyeing presents significant advantages, commercial systems based on this technology have not yet been widely implemented. RedElec (Riddes, Switzerland), for instance, proposed a solution for the electrochemical reduction of dye baths, but the available information is limited to theoretical details, with little data on its practical implementation. Although electrochemical reduction has not prevailed in textile dyeing yet, extensive research continues to emerge, particularly in the field of wastewater decontamination. Electrochemical dyeing remains a promising and more sustainable alternative to traditional methods, offering notable potential for reducing water and chemicals consumption. However, overcoming challenges related to scalability and industrial adoption will require further research and optimization.

4.3.3. Nanotechnology

Nanotechnology involves the design, manipulation, and application of materials at the nanoscale (<1 µm). At this scale, materials exhibit unique physical, chemical, and biological properties that differ from their bulk counterparts due to their small size and high surface-to-volume ratio. Integrating nanotechnology into textile processing enhances efficiency, potentially leading to significant reductions in water and energy consumption.

Nanosized dyes can improve penetration into fibers, reducing the amount of dye and auxiliaries needed while achieving more vibrant shades. Nanosized vat dyes, prepared via ball milling and ultrasonication, which are more ecological fabrication methods, were reported to significantly increase the exhaustion rate and color strength during the dyeing and printing of cotton [162]. Similarly, disperse dyes processed through ultrasonication demonstrated superior color strength and improved fastness properties in both polyester and cotton [163]. As a more sustainable alternative, the application of nanosized natural dyes, such as curcumin, was investigated, resulting in significantly enhanced color strength and fastness on wool, silk and cotton fabrics. Furthermore, the use of nanosized mordants was explored, yielding improved color strength and fastness in comparison to the conventional dyeing and mordanting methods [164]. Silver nanoparticles were also applied to cotton, wool, and silk using direct dyes in padding, followed by curing. This treatment not only enhanced mechanical properties but also improved color strength, fastness, and antibacterial properties. The presence of these nanometal particles increases dye affinity towards the material, acting as mordants and further enhancing dyeing results [165].

Nanotechnology has the potential to play a pivotal role in textile finishing, enabling the development of high-performance textiles with advanced functionalities. Various nanoparticles, such as TiO₂ and silver nanoparticles (AgNPs), were incorporated into textiles to impart a range of functionalities, including antimicrobial, hydrophobic, oleophobic, and UV-resistant properties [136,165,166,167,168,169]. For instance, the insitu synthesis of ZnO nanoparticles using microwave irradiation proved to be an effective and scalable method for coating cotton fabrics, conferring self-cleaning, UV-blocking, and antibacterial properties [125]. Similarly, TiO₂ nanoparticles were successfully applied to textiles, enhancing the UV protection factor while preserving the intrinsic properties of the fabric [170]. Nanotechnology also holds promise in the development of superhydrophobic fabrics, which exhibit high resistance to harsh conditions, all while retaining excellent UV protection and antibacterial properties [169]. Furthermore, innovative applications, such as the nanoencapsulation of fragrant oils in cotton fabrics, were explored, providing a novel approach to embedding long-lasting fragrance into textiles while maintaining their functionality [136].

While these advancements in nanotechnology-driven textile finishing are driving the development of high-performance, multifunctional fabrics that enhance product quality, the long-term environmental safety of nanoparticles in textile applications remains uncertain. Further research is crucial to assess the potential environmental impacts of these materials, particularly concerning toxicity, bioaccumulation, and long-term safety. Additionally, challenges related to the high cost of certain nanomaterials, the requirement for specialized equipment, and scalability issues must be addressed for the widespread adoption of nanotechnology in textile processing.

4.3.4. Low Temperature Processing

Traditional wet processes often require high temperatures (typically 80–220 °C) to ensure proper substrate preparation and dye and finishing agents’ fixation [3]. However, advancements in dye chemistry, auxiliaries and innovative techniques now offer the potential to achieve comparable results to conventional processes at temperatures as low as 40–60 °C. Throughout this review, various technologies, including ultrasound [17,36,37], laser treatment [67], SC-CO₂ [94,97,98], and reverse micelle dyeing [110], have demonstrated the possibility of lowering processing temperatures while maintaining dye efficiency. Other technologies, such as enzymatic treatments and natural dyeing, can also be used as low-temperature processes while being biodegradable.

One of the key advantages of low-temperature dyeing is its reduced energy consumption, which leads to lower production costs and a smaller carbon footprint [4]. This approach is particularly beneficial for heat-sensitive fibers, as it prevents thermal degradation caused by high-temperature processes and helps preserve the mechanical properties of textiles. In a study performed by Ferrero and Periolatto [171], ultrasound and stirring were used in wool dyeing without auxiliary products, obtaining reduced degradation of fibers. The conventional 98 °C process resulted in a loss of 24% in tensile strength, while the novel 65 °C using ultrasound resulted in only 11% loss.

As sustainability becomes a priority in the textile industry, low-temperature processing is expected to play an increasingly critical role in sustainable manufacturing, offering an eco-friendly alternative without compromising color quality or fabric durability. For instance, Bozzetto Group (Filago, Italy) states that its low-temperature bleaching processes operate at 70 °C, while CHT Group (Tübingen, Germany) reports its dyeing process for polyester and polyester/elastane blends operates at 120 °C. Ever dye (Paris, France) developed a dyeing process that operates at ambient temperatures, further reducing energy consumption. Additionally, MCTRON Technologies (Greenville, USA) provides an emulsion that facilitates low cure temperatures while maintaining excellent fastness properties. Other companies, including those previously mentioned, are also exploring innovative solutions for lower-temperature processing, such as ultrasound-assisted laser treatment, SC-CO₂, and reverse micelle dyeing. These advancements collectively contribute to the ongoing efforts to enhance sustainability within textile manufacturing.

5. Final Considerations and Prospects

Innovations in textile wet processing have demonstrated significant potential in addressing the industry’s pressing environmental challenges, particularly in reducing water, energy, and chemicals consumption. Techniques such as ultrasonic dyeing, foam dyeing, plasma treatment, and SC-CO₂ technology have proven effective in optimizing resource efficiency while maintaining high-quality textile properties. However, despite the promising benefits of these technologies, widespread industrial adoption remains limited due to high initial investment costs, process scalability concerns, and the need for further optimization under industry-relevant manufacturing conditions.

Future research should prioritize large-scale studies that reflect actual industrial conditions, as many laboratory-scale experiments use unrealistically high liquor ratios or fail to consider factors such as energy demand, processing speed, and compatibility with existing machinery. Additionally, one of the key challenges in evaluating emerging technologies is the variability in conventional textile processing methods. Differences in processing temperatures, times, and chemical concentrations across the industry make it difficult to directly compare new technologies and assess their true industrial relevance. Addressing these inconsistencies will be essential for accurately measuring the benefits of emerging techniques and facilitating their broader adoption. Furthermore, regulations and industry standards must be updated and improved to ensure that new technologies can be safely and effectively implemented on a large scale, particularly concerning chemical sustainability, nanoparticle safety, and solvent recovery systems. The integration of wastewater recycling technologies and circular economy principles will also be essential in further improving the sustainability of textile wet processing. While this review focuses on alternative wet processing techniques, it is worth noting that some of the technologies discussed also hold potential for wastewater treatment applications, a crucial aspect of sustainable textile production that, although relevant, falls outside the scope of this article.

Moreover, sustainability in textiles should not only focus on production efficiency but also on the development of textiles that require less intensive treatment throughout their life cycle. Innovations that reduce the need for frequent washing, ironing, or chemical treatments in consumer use can significantly contribute to minimizing environmental impact.

While traditional water-intensive processes continue to dominate, the growing demand for sustainable fashion and stricter environmental regulations are driving the industry toward more responsible practices. Collaborative efforts between researchers, manufacturers, and policymakers will be crucial in scaling up sustainable solutions, ultimately reducing the environmental footprint of textile production and paving the way for a cleaner, more efficient future.