Recent Advances in Microbial Enzyme Applications for Sustainable Textile Processing and Waste Management

Abstract

Microbial enzymes have revolutionised the textile industry by replacing harmful chemicals with eco-friendly alternatives, enhancing processes such as desizing, scouring, dyeing, finishing, and promoting water conservation while reducing pollution. This review explores the role of enzymes like amylases, pectinases, cellulases, catalases, laccases, and peroxidases in sustainable textile processing, focusing on their ability to mitigate environmental pollution from textile effluents. The review also examines the types and characteristics of hazardous textile waste and evaluates traditional waste treatment methods, highlighting sustainable alternatives such as microbial enzyme treatments for effluent treatment. Recent advancements in recombinant enzyme technology, including enzyme engineering and immobilisation techniques to enhance stability, reusability, and catalytic performance, are also explored. Additionally, the potential of extremozymes in textile processing and effluent treatment is explored, emphasising their stability under harsh industrial conditions. Strategies for reducing textile waste through enzyme-based processes are presented, focusing on principles of the circular economy. The review also addresses challenges such as scalability, cost, and process optimisation, while proposing potential solutions and outlining future directions for the widespread adoption of microbial enzymes in sustainable textile production and waste management. This review underscores the transformative potential of microbial enzymes in achieving greener textile manufacturing practices.

1. Introduction

Enzymes are biological macromolecules that catalyse reactions with high specificity and efficiency, making them essential in numerous industrial applications. Microbial enzymes are recognised as superior biocatalysts due to their scalability, cost-effectiveness, and alignment with sustainability goals [1]. These enzymes are widely utilised in fields such as pharmaceuticals, nutraceuticals, diagnostics, detergents, cosmetics, and textile processing [2].

In the textile industry, enzyme-based biotechnology has revolutionised traditional processes by replacing hazardous chemicals with eco-friendly solutions. Enzymes play an integral role in textile manufacturing, facilitating processes such as desizing, scouring, bleaching, biopolishing, and dyeing, while offering advantages including reduced environmental impact, water conservation, and compatibility with mild processing conditions [3,4]. Key microbial sources, such as Aspergillus, Trichoderma, Streptomyces, and Bacillus, serve as platforms for enzyme production. Enzymes like amylase, cellulase, catalase, protease, pectinase, laccase, and lipase are widely employed due to their biodegradability, specificity, and efficacy in enhancing textile quality [5]. These biocatalysts significantly lower energy, water, and time requirements, establishing enzymatic strategies as a scientifically robust and sustainable alternative to conventional chemical treatments in the textile industry [3]. Despite these benefits, widespread adoption is limited by high production costs and the complexity of enzyme isolation and purification [6].

The textile industry remains a significant source of environmental pollution, with effluents containing hazardous chemicals such as volatile organic compounds, heavy metals, dyes, and ionic liquids posing severe risks to human health and ecosystems [7]. Enzymatic treatment of these effluents has emerged as a green technology, with enzymes like laccases and peroxidases effectively degrading toxic pollutants and reducing environmental impact [8]. Bernal et al. explored filamentous fungi from textile wastewater for enzyme production and dye discolouration. They identified Aspergillus sydowii (ITF 30) as the most effective producer of cellulase, amylase, lipase, and laccase. This strain also exhibited significant discolouration of Remazol Brilliant Blue R (RBBR). Another strain, A. sydowii (ITF 27), demonstrated notable dye discolouration capacity [9]. These findings highlight the potential of these enzymes for bioremediation in textile industrial effluents.

While enzymatic textile processing and waste treatment have been extensively studied, this review provides a distinct perspective by focusing on advancements in enzyme technology, including enzyme engineering and immobilisation, to enhance stability, reusability, and catalytic performance. The discussion emphasises their robustness under harsh industrial conditions and explores strategies to overcome scalability and cost barriers. Furthermore, this review highlights enzyme-based processes aimed at reducing textile waste and emphasises the transformative potential of microbial enzymes in achieving greener and more sustainable textile manufacturing practices. By integrating recent innovations and addressing critical challenges, this review highlights pathways for successful enzyme application in eco-friendly textile production.

2. Textile Industrial Processes

Textile processing converts raw materials like cotton, silk, wool, jute, polyester, and nylon into finished products. Natural fibres are sourced from plants and animals, while synthetic fibres are made from petrochemicals [10]. Natural fibres are biodegradable and eco-friendly, whereas synthetic fibres are durable and versatile but contribute to pollution and health risks due to their chemical components.

The textile production process includes five main stages: yarn formation, fabric formation, wet processing, fabrication, and final product development, as depicted in Figure 1. Wet processing is a critical stage that generates most of the wastewater, involving the use of water, dyes, and chemicals, leading to significant environmental concerns [4].

2.1. Yarn Formation

Yarn is a continuous strand of fibres, either natural or synthetic, used to create fabric through knitting or weaving. Fibre preparation removes impurities to improve absorption for dyeing, printing, and finishing. Synthetic fibres generally lack these natural impurities. The main techniques in yarn formation include texturising and spinning. Texturising, mainly for synthetic fibres, adds bulk and elasticity through processes like crimping and heat-setting. Spinning, which twists fibres together, forms strong yarns using methods such as ring, rotor, and air-jet spinning, depending on the desired yarn quality and production speed.

2.2. Fabric Formation

Fabric formation includes processes like warping, slashing, weaving, knitting, and sizing. Warping aligns yarns for uniform tension, while slashing applies a coating to strengthen yarns for weaving. Weaving interlaces yarns to create different fabric types, and knitting loops yarns to form flexible, elastic fabrics. Sizing coats yarns to improve strength and smoothness, enhancing weaving efficiency and reducing yarn breakage. These processes together improve fabric strength, texture, and performance [11].

2.3. Wet Processing

Wet processing involves chemical treatments to improve textile quality [12,13]. Key steps include:

• ▪ Desizing: Removes sizing from fabric to improve absorption for dyeing and printing, often using eco-friendly enzymatic methods;
• ▪ Scouring: Removes impurities like oils and waxes, making fabric more absorbent;
• ▪ Bleaching: Whitens fabric by removing natural colours with chemicals like hydrogen peroxide (H₂O₂), sodium chlorite (NaClO₂), or sodium hypochlorite (NaOCl), but excessive bleaching can weaken fibres;
• ▪ Mercerisation: Treats fabric with sodium hydroxide (NaOH) to improve strength, lustre, and dye uptake;
• ▪ Dyeing and Printing: Colour fabrics, with dyeing applying colour evenly and printing for specific designs. Dyeing uses more water than printing.

  Table 1. Application of various dye types for synthetic and natural fabrics.

  Fabric Type	Example	Dye type Used for Dyeing *
  Synthetic fibres
  Polyester	Dacron, Terylene	Disperse, pigment
  Polyamide	Nylon, Perlon, Rilsan	Acid, reactive, disperse, mordant, pigment
  Polyacrylonitrile	Acrilan, Courtelle, Orlon	Basic, disperse, pigment
  Polyolefines	Meraklon, Prolene	Disperse
  Polyvinyl chloride	Envilon, Thermovyl	Basic, disperse
  Elastomers	Glospan, Lycra	Acid, disperse, reactive (wool), vat
  Natural fibres
  Silk	-	Azoic, basic, direct, oxidation, reactive, mordant, sulphur, vat
  Wool and wool blends	Wool–cotton, wool–viscose, etc.	Acid, basic, reactive, mordant, solubilised vat
  Cotton	-	Azoic, basic, direct, oxidation, reactive, mordant, sulphur, vat
  Modified cellulose fibres	Viscose, secondary acetate, triacetate	Disperse, direct, pigment, reactive, mordant, sulphur, vat, solubilised vat
  Bast	Linen, flax, ramie, hemp, jute	Acid, direct, reactive, disperse, vat, solubilised vat

  * Textile dye types are classified by their chemical properties and fibre interactions. Acid dyes bond with cationic sites in protein fibres, while basic dyes bind to anionic sites in synthetic fibres, both offering vivid hues. Azoic dyes form directly in fibres for brilliant cellulose colours. Disperse dyes penetrate synthetic fibres through hydrophobic interactions, and direct dyes attach to cellulose via hydrogen bonding. Mordant dyes use metal salts for colour fastness, and pigments adhere with binders for surface applications. Reactive dyes form covalent bonds, sulphur dyes offer dark shades, vat dyes ensure durability, and solubilised vat dyes simplify application with enhanced fastness.

  lists the dyes used for various synthetic and natural fabrics;
• ▪ Stone Washing: Fades colour in denim and canvas, often replaced by eco-friendly enzymatic biostoning;
• ▪ Polishing: Enhances fabric texture and brightness, often using cellulase enzymes for biopolishing.

2.4. Fabrication

Garment fabrication involves stages like designing, measuring, cutting fabrics, sewing, and final packing. Advanced technologies such as automated cutting machines and computer-aided design (CAD) are used to improve efficiency and precision in these processes.

2.5. Final Product

The final textile products serve various purposes, including clothing, household items, and technical textiles. Effective marketing strategies help connect manufacturers, retailers, and consumers, ensuring that the products meet fashion trends and consumer needs.

3. Textile Effluents

The textile industry is a major source of water pollution, primarily due to the heavy use of synthetic dyes and chemicals in its manufacturing processes [3,4,5]. The discharge of textile effluents containing toxic dyes and chemicals damages ecosystems and poses significant health risks to humans, aquatic life, and environmental impacts (

Table 2. Hazardous chemicals used in textile processes cause significant risks to both human health and the environment.

Textile Process	Toxic Chemicals	CAS Number	Hazardous Causes
Yarn sizing	Polyvinyl alcohol	9002-89-5	Eye irritation; discomfort in inhalation
Size preservative	Pentachlorophenol	87-86-5	Eye irritation; adverse neurological, blood, and liver effects
	Formaldehyde	50-00-0	Skin and eye irritation; coughing; wheezing; nausea; burning sensations in the nose and throat
Coating and degreasing	Synthetic non-biodegradable surfactants + solvents	-	Dermatological compatibility, toxicity, and biodegradability
Anti-caking agent in salt	Cyanide	57-12-5	Eyes, nose, and throat irritation; headache; prolonged exposure can cause coma and even death
Biocide on hosiery and fabrics	Tributyltin oxide	56-35-9	Extremely hazardous to aquatic lives
Bleaching	Calcium hypochlorite	7778-54-3	Coughing and breath shortness
	Sodium hypochlorite	7681-52-9	Skin irritation; coughing; stomach and abdominal pain
Peroxide stabiliser	Sodium silicate	1344-09-8	Skin and eye irritation
	Phosphorous-based compounds (Tris(2,4-di-tert-butylphenyl)phosphite)	31570-04-4	Causing explosion hazards
Detergents and emulsifiers	Non-ionic surfactants (octylphenol ethoxylate)	9036-19-5	Skin irritation; environmental risks
	Nonylphenol–ethylene oxide adducts (APEOs)	26027-38-3	Extremely toxic to aquatic organisms
Stain removers	Carbon tetrachloride	56-23-5	Harmful effect on the liver, central nervous system, and kidneys; extended exposure can cause coma and fatality
Softener	Silicones and amino silicones with APEO emulsifier	63148-62-0; 63148-62-9	Chronic respiratory effects; extremely toxic to aquatic organisms
Dyes	Azo dyes (Remazol Brilliant Blue R)	12222-67-8	Carcinogenic, skin irritation, aquatic toxicity, persistent in ecosystems
	Reactive dyes (Procion blue)	12236-36-4	Skin irritation, allergic reactions, aquatic toxicity
	Acid dyes (Cibacron fuchsia)	6105-59-9	Skin irritation, heavy metal contamination, water pollution
	Basic dyes (crystal violet)	548-62-9	Dermatitis, respiratory irritation, aquatic toxicity
	Disperse dyes (Disperse Blue 1)	12222-72-5	Allergic dermatitis, suspected carcinogen, water pollution
	Sulphur dyes (sulphur black)	1326-97-6	Skin irritation, respiratory issues, aquatic toxicity
	Vat dyes (indigo)	482-89-3	Respiratory irritation, water toxicity, persistent pollutants
	Pigments (titanium dioxide)	13463-67-7	Heavy metal toxicity, carcinogenic, non-biodegradable
Heavy metals	Copper (Cu)	7440-50-8	Inhalation and respiratory problems; fever; nausea; vomiting
	Lead (Pb)	7439-92-1	Affects the central nervous system, causing coma, convulsions, and death
	Mercury (Hg)	7439-97-6	Adverse effects on the nervous, digestive, and immune systems
	Cadmium (Cd)	7440-43-9	Harmful to lungs, bones, and kidneys
	Chromium (Cr)	7440-47-3	Pulmonary sensitisation; causes lung, nasal, and sinus cancer; severe dermatitis and painless skin ulcers
	Arsenic (As)	7440-38-2	Affects organs such as the eyes, skin, liver, kidneys, and lungs; causes cancer
Carriers in dyeing	Dichlorobenzene	25321-22-6	Kidney and liver cancer
	Trichlorobenzene	12002-48-1	Skin, eye, nose, and throat irritation
Oxidation in dyeing	Sodium dichromate	10588-01-9	Causes asthma; damages the liver and kidneys
Pigment printing and dye-fixing	Kerosene	8008-20-6	Dizziness, headache, and vomiting
	Formaldehyde	50-00-0	Skin and eye irritation; coughing; wheezing; nausea; burning sensations in the nose and throat
Finishing	Cationic surfactants (cetyltrimethylammonium bromide)	57-09-0	Skin irritation
	Functional synthetic finish (perfluorooctanoic acid)	335-67-1	Environmental risks; toxic to aquatic organisms

).

The textile industry is a significant consumer of water and chemicals, with an average plant using approximately 1.6 million litres of water daily to produce 8000 kg of fabric [4]. The dyeing and finishing processes contribute to 17–20% of the industry’s water pollution [14]. Textile wastewater is burdened with a range of toxic chemicals, including azo dyes like Remazol Brilliant Blue R, which are carcinogenic, cause skin irritation, and are persistent in ecosystems. Other common pollutants include formaldehyde, used in size preservatives and coating processes, which causes skin and eye irritation, and copper, a heavy metal found in textile effluents that can cause respiratory problems [15]. Additionally, per- and polyfluoroalkyl substances (PFASs), including perfluorooctanoic acid (PFOA), used in textile finishing for its water- and stain-repellent properties, are highly persistent and bioaccumulative, posing serious risks to human health and the environment [16,17]. These pollutants are stable in the environment and resistant to conventional treatment methods, emphasising the need for more effective and sustainable treatment technologies. Other toxic substances like tributyltin oxide, sodium hypochlorite, and nonylphenol ethoxylates are commonly found in textile wastewater. These substances pose significant risks to both human health and the environment, with many being difficult to degrade using conventional wastewater treatment methods [17]. This highlights the urgent need for more effective and sustainable treatment solutions to address the growing environmental challenges in the textile industry.

3.1. Microbial Remediation of Textile Effluents

Microbial remediation is a process that uses microorganisms—such as bacteria, fungi, and algae—to degrade or detoxify pollutants in the environment, converting harmful substances into less toxic or non-toxic forms [18]. This approach offers an environmentally friendly and cost-effective alternative to traditional methods of waste treatment, which can often be inefficient, costly, and environmentally harmful [19]. Microorganisms, including bacteria, fungi, and algae, possess natural abilities to degrade various pollutants, including textile dyes [20,21,22].

Table 3. Comparison of fungi, bacteria, and algae in terms of efficiency, advantages, limitations, and applications for textile effluent bioremediation.

Textile Effluent Remediation	Fungi	Bacteria	Algae
Efficiency	- High ability to degrade a wide range of dyes - Effective in removing heavy metals such as chromium and copper - High tolerance to toxic compounds	- Efficient in decolourising dyes and removing textile pollutants - Faster growth rate compared to fungi - Can be engineered for enhanced degradation	- Effective in removing dye pollutants through biosorption and bioaccumulation - Can absorb heavy metals from effluent
Advantages	- High degradation potential - Efficient in breaking down complex dyes and pollutants - Can be used in both solid-state and liquid-state remediation	- Fast growth rate and ability to adapt to changing conditions - Can be used in both aerobic and anaerobic environments - Lower nutrient requirements	- Easy to cultivate in large quantities - Can be used in combination with other microorganisms - Cost-effective
Limitations	- Slow growth rate - Requires specific conditions - May need additional treatment to handle residual metabolites	- Sensitive to toxic concentrations of pollutants - May require genetic modification for enhanced degradation	- Limited to certain types of dyes - Requires light for photosynthesis - Growth is sensitive to environmental changes
Applications	- Bioremediation of textile wastewater - Removal of toxic dyes and heavy metals from effluents	- Biodegradation of textile dyes and chemicals - Treatment of wastewater with high concentrations of pollutants	- Bioremediation of dyes and heavy metals - Integrated treatment systems with fungi and bacteria
Reference	[21,23]	[24,25]	[24,26]

compares the efficiency, advantages, limitations, and applications of fungi, bacteria, and algae in the bioremediation of textile effluents.

These microorganisms can be harnessed in bioreactors or other bioremediation systems to treat textile effluents effectively. The microbial remediation process typically involves the breakdown of chromophoric groups, which are the coloured part of the dye molecules, followed by the mineralisation of the dye into non-toxic by-products [20]. The use of microbial remediation techniques in textile wastewater treatment minimises the need for harmful chemicals, reduces pollution, and promotes sustainability in the textile industry.

3.1.1. Fungal Bioremediation

Fungi are particularly effective in the biodegradation of textile dyes due to their ability to produce extracellular enzymes capable of breaking down complex organic molecules. Species like Phanerochaete chrysosporium, Trichoderma harzianum, Aspergillus oryza, and Cunninghamella elegans have been extensively studied for their potential in decolourising textile effluents [27]. Phanerochaete chrysosporium, for example, produces enzymes like lignin peroxidase, manganese peroxidase, and laccase that can degrade a wide variety of dyes, including polycyclic aromatic hydrocarbons found in wastewater from textile and pulp industries [28,29]. Similarly, Trichoderma harzianum has shown remarkable efficiency in degrading dyes like Congo red and Bromophenol blue, with studies highlighting the role of fungal biomass in absorbing and breaking down toxic dye molecules [30]. Corso et al. demonstrated that Aspergillus oryzae in its pellet form effectively biosorbs and reduces the toxicity of azo dyes like Direct Red 23 and Direct Violet 51, offering a sustainable solution for industrial wastewater treatment [31]. Non-lignin-degrading fungi like Cunnighamella elegans degrade dyes such as malachite green via cytochrome P450 activity and can simultaneously remove hexavalent chromium, achieving 95% removal of dye and metal over 19 cycles in a semi-continuous process [32]. The combination of aerobic and anaerobic microbial treatment has also proven effective in enhancing the degradation of dyes, as seen in the case of Aspergillus strains, which can decolourise dyes like orange 3R under specific conditions [33]. Fungal bioremediation is advantageous due to the fast growth, high biomass production, and wide hyphal networks of many fungal species.

3.1.2. Bacterial Bioremediation

Bacteria are also powerful agents in bioremediation, particularly in the degradation of azo dyes, which are commonly used in the textile industry. Azo dyes contain the characteristic azo group (-N=N-), which can be biodegraded by bacteria through the enzymatic activity of azoreductases, leading to a reduction in azo bonds under anaerobic conditions and the subsequent formation of colourless aromatic amines [34]. These metabolites are further degraded aerobically or anaerobically, making bacterial bioremediation an efficient method for decolourising and detoxifying textile effluents. The degradation of azo dye is often facilitated by specific bacterial strains capable of breaking the azo bonds, such as Klebsiella pneumoniae GM-04, which demonstrated a 95% colour removal efficiency for Disperse Blue 284 (DB 284) dye under anaerobic conditions at pH 7, 37 °C, and an initial dye concentration of 200 mg/L after 24 h [35]. Similarly, Acinetobacter baumannii effectively decolourised 98.8% of Reactive Black 5, 96% of Reactive Red 120, and 96.2% of Reactive Blue 19 under optimal conditions of pH 7, temperature 37 °C, 500 ppm dye concentration, 48 h incubation, and anaerobic conditions [36]. Kishor et al. demonstrated that the lignocellulosic enzyme-producing bacterium Bacillus albus MW407057 effectively biodegraded methylene blue dye, achieving 93.8% colour removal, 86.02% reduction in BOD, and 77.35% reduction in COD within 48 h [37]. Acidithiobacillus thiooxidans removes up to 91.4% of Sulphur Blue 15 dye via biosorption and further biodegrades 50% of the remaining dye under optimised conditions [38]. Pseudomonas stutzeri SPM-1 decolourised Procion Red-H3B dye (50 mg/L) in 20 h under microaerophilic conditions, reducing BOD, COD, and TOC by 85%, 90%, and 65%, respectively. The strain showed significant activities of azoreductase (95%), laccase (76%), and NADH-DCIP reductase (88%), with GC-MS/FT-IR analyses confirming its effective dye degradation, highlighting its potential for textile wastewater bioremediation [39]. Mixed bacterial cultures such as Providencia rettgeri strain HSL1 and Pseudomonas sp. SUK1 achieved 98–99% decolourisation and 62–72% TOC reduction in various azo dyes (Disperse Red 78, Direct Red 81, Reactive Black 5, Reactive Orange 16) under sequential aerobic and microaerophilic or vice versa at 30 °C for 12–30 h, demonstrating their effectiveness for treating complex textile industry effluents [40]. This highlights the advantages of using mixed cultures over isolated single-bacterial strains.

Table 4. Bacterial bioremediation of textile dyes.

Bacterial Species	Dye	% Degradation	Degradation Conditions (Dye conc., pH, Temp., Inc. Time)	Enzyme Involved	Reference
Isolated single culture
Actinomycetes strains	Orange dye	85	50 mg/L, pH 7.2, 37 °C, 48 h	Not identified	[41]
Aeromonas hydrophila	Crystal violet	99	100 mg/L, pH 7, 35 °C, 8 h	Laccase, lignin peroxidase	[42]
Alcaligenes sp. TEX S6	Direct Red 28	86	150 mg/L, pH 7, 37 °C, 48 h	Not identified	[43]
Bacillus lentus BI377	Reactive Red 141, Reactive Red 2	99.11	500 mg/L, pH 8, 40 °C, 6 h	Superoxide dismutase, peroxidase	[44]
Bacillus megaterium KY848339	Acid Red 337	91	500 mg/L, pH 7, 30 °C, 24 h	Azoreductase	[45]
Bacillus sp.	Direct Red 81	-	100 mg/L, pH 7, 30 °C, 24 h	Azoreductase, laccase	[46]
Klebsiella pneumoniae	Methyl orange	83	20 μM, pH 8, 40 °C, 10 min	Azoreductase	[47]
Marinobacter sp. HBRA	Direct Blue 1	100	100 mg/L, pH 8, 37 °C, 6 h	Oxidases (not identified)	[48]
Shewanella sp.	Reactive Black-5, Direct Red-81, Acid Red-88	96.9	200 mg/L, pH 8.5, 35 °C, 12 h	Azoreductase	[49]
Bacillus sp. strain CICC 23870	Methyl orange, Black 5, Acid Blue 113, methyl red	97.87	32.7 mg/L, pH 7, 35 °C, 24 h	Azoreductase	[50]
Mixed culture
Brevibacillus aydinogluensis, Geobacillus thermoleovorans, Anoxybacillus flavithermus, Bacillus thermoamylovorans	Direct Black G, Direct Black 38, Congo red, methyl orange	97	600 mg/L, pH 8, 55 °C, 8 h	Azoreductase, laccase, lignin peroxidase, manganese peroxidase	[51]
Enterococcus sp. L2 and Mycobacterium vaccae	Reactive Violet 5R	97.6	100 mg/L, pH 6.8, 8 h	Azoreductase, formate dehydrogenase	[52]
Lysinibacillus sp., Raoultella sp., Enterococcus spp., Citrobacter sp., Lysinibacillus sp.	Reactive Black 1	99	100 mg/L, pH 7, 37 °C, 8 h	Azoreductase, lignin peroxidase	[53]

lists the degradation of textile dyes by various isolated and mixed cultures.

Bacterial degradation offers several advantages, including growing rapidly and adapting to different environmental conditions. Additionally, bacteria can be genetically engineered to enhance their dye-degrading capabilities, improving the efficiency of the bioremediation process [34].

3.1.3. Algal Bioremediation

Algae are known for their extensive surface area and can effectively remove dyes from water by adsorbing pollutants onto their biomass or metabolising dye chromophores into non-toxic products [54]. Alvarez et al. identified three mechanisms underlying algal dye decolourisation: (1) utilisation of chromophores for algal biomass production, releasing CO₂ and H₂O; (2) conversion of chromophores into non-chromophoric materials; and (3) adsorption of residual chromophores onto algal biomass [55]. For instance, Devi et al. demonstrated the effectiveness of freshwater algae (Spirulina platensis) and seaweed (Gracilaria edulis) in removing Reactive Blue 19 (RB 19) using batch adsorption techniques [56]. Both algae and cyanobacteria exhibit promising potential in textile wastewater treatment due to their ability to degrade recalcitrant azo dyes and other pollutants. While algae like Chlorella pyrenoidosa utilise intracellular laccase enzymes for effective dye degradation [57], cyanobacteria such as Phormidium autumnale UTEX1580 demonstrate complete breakdown of dyes like indigo, producing non-toxic metabolites [58]. Together, these microorganisms offer eco-friendly solutions for the decolourisation and detoxification of industrial effluents.

In conclusion, microbial remediation offers an eco-friendly, cost-effective, and sustainable alternative to conventional methods for treating textile wastewater. With the ability to break down complex and persistent pollutants, microorganisms provide an efficient solution for long-term environmental management. Advancing research in this field underscores its potential to reduce the environmental impact of the textile industry and support sustainability.

4. Enzymatic Innovations in Textile Processing and Effluent Treatment

The textile industry is a significant contributor to global pollution, making the adoption of green alternatives crucial for sustainable practices. The use of enzymes or non-toxic chemical substitutes in textile processing represents a transformative approach, replacing hazardous chemicals and reducing associated health risks [10,59]. Among the various stages of textile production, wet processing and fabric finishing are particularly harsh and benefit greatly from enzymatic interventions. Enzymes such as amylases for desizing, pectinases for bioscouring, cellulase for stonewashing and biopolishing, and catalase for bleaching and bleach clean-up are integral to greener processing methods [5]. These enzymatic treatments minimise environmental impact and enhance the final product’s quality and sustainability [59].

Table 5. Green alternatives replacing existing harmful chemicals in the textile industry.

Textile Process	Existing Harmful Chemicals	Green Chemical Substitute	Enzymatic Alternative	Reference
Sizing	Polyvinyl alcohol	Potato starch; carboxymethylcellulose	-	[60]
Desizing	Mineral acids (acid-based desizing)	-	Amylase; xylanase	[12]
Scouring	Sodium hydroxide (caustic soda)	-	Pectinase (pectin lyase); xylanase	[61]
Stonewashing and polishing	Nonylphenol–ethylene oxide adducts [alkylphenol polyethoxylates (APEOs)]	Fatty alcohol–ethylene oxide adducts; alkyl polyglycosides	Cellulase	[62]
Bleaching	Calcium and sodium hypochlorite; other chlorine oxidising chemicals	Hydrogen peroxide; ozone at cold	Glucose-oxidase; laccase; ligninase (lignin peroxidase); arylesterase	[63,64]
Bleach clean-up	Thiosulfates	-	Catalase	[65]
Dyeing and printing	Kerosene; formaldehyde; dichlorobenzene; trichlorobenzene	Water-based thickener; polycarboxylic acids; non-formaldehyde products; butyl benzoate; benzoic acid	Ligninase (lignin peroxidase)	[5]
Finishing and effluent treatment	Silicone-based softeners; formaldehyde-based resins; heavy metals	Natural oils (e.g., soybean, castor, or palm oils); formaldehyde-free resins; eco-friendly coagulants	Proteases; lipases; laccase	[3,64]

outlines green chemical substitutes and enzyme-aided steps as viable substitutes for harmful chemicals in textile processing. Green alternatives to harmful chemicals in the textile industry offer sustainable solutions across processing stages. In sizing, polyvinyl alcohol is replaced with potato starch or carboxymethylcellulose [60]. Desizing substitutes mineral acids with enzymes like amylase and xylanase, while scouring uses pectinase and xylanase instead of sodium hydroxide [12,61]. Stonewashing and polishing shift from nonylphenol–ethylene oxide adducts to fatty alcohol–ethylene oxide adducts or alkyl polyglycosides, with cellulase as an enzymatic alternative [62]. Bleaching avoids chlorine-based chemicals by using hydrogen peroxide, ozone, or enzymes like glucose–oxidase, laccase, and ligninase [63,64]. Catalase replaces thiosulfates for bleach clean-up [65]. Dyeing and printing eliminate harmful carriers like kerosene and formaldehyde, using water-based thickeners, polycarboxylic acids, and enzymatic options like ligninase [5]. For finishing and effluent treatment, silicone softeners and formaldehyde resins are replaced with natural oils, formaldehyde-free resins, and eco-friendly coagulants, supported by enzymes such as proteases, lipases, and laccase [3,64].

The enzymatic alternatives employed at various stages of processing cotton, silk, wool, and synthetic fibres are illustrated in Figure 2. In cotton processing, cellulases enhance fabric smoothness through biopolishing, while amylases remove starch-based sizing agents [12,62]. Protease enzymes are essential in silk degumming, preserving strength and sheen, while in wool processing, they soften fibres and reduce prickle. Lipases are employed to eliminate grease and oils. For synthetic fibres, enzymes break down lubricants, improve dye uptake, and enhance fabric properties [66]. This enzymatic approach not only improves product quality but also reduces energy, water usage, and pollution, supporting sustainable practices in textile manufacturing [10].

4.1. Amylases in Desizing

Amylase is a key biocatalyst that catalyses the hydrolysis of starch into sugars. Bacteria, fungi, and plants are the major producers of amylases. Additionally, amylases are present in the saliva of humans and other mammals, where they initiate the digestion process [67]. All amylases belong to the hydrolase class of enzymes and are broadly classified as glycosidases, as they cleave the α-1,4-glycosidic bonds in starch, particularly in amylose. There are three types of amylases: α-amylases (which act randomly on starch and require Ca²⁺ for activity), β-amylases (which act from the non-reducing end and also depend on Ca²⁺), and γ-amylases (which cleave both α-1,4 and α-1,6-glycosidic bonds from the non-reducing end). Among these, α-amylase is the fastest-acting and most widely used type [68]. Due to its industrial potential, amylases are widely employed in industries such as textiles, food, pharmaceuticals, and detergents [69].

In textile processing, fabrics are often coated with starch-based sizing materials to strengthen them during weaving. This sizing must be removed before subsequent processes like dyeing, printing, and polishing. Enzymatic desizing using amylases is the most commonly employed method, producing short-chain sugars such as dextrin, maltose, and glucose as byproducts of starch breakdown. This method improves fabric quality and uniform wettability, essential for further processing. Rehman et al. demonstrated the effective and eco-friendly desizing of textiles using amylase produced by an indigenous Bacillus cereus strain, optimising desizing conditions to achieve complete starch removal within 15 h at 60 °C with minimal fabric damage [70]. Singh et al. identified Aspergillus fumigatus NTCC1222 as an efficient producer of α-type amylase (341.7 U/mL) under optimised solid-state fermentation conditions using wheat bran, with promising potential for cost-effective textile applications [71]. The enzyme α-amylase was evaluated for its desizing efficiency on starch-sized cotton fabrics under the influence of ultrasound. Although ultrasound reduced enzyme activity on soluble starch, it enhanced desizing efficiency through intensified hydrophobic interactions, with simultaneous ultrasound application yielding superior results by improving mixing, substrate modification, catalytic activity, and product removal [72]. Metal-independent α-amylase from Bacillus sp., exhibited optimal activity at 75–80 °C and pH 4.0–6.0, with its activity and thermal stability unaffected by the presence of Ca²⁺, EDTA, or calcium absence, demonstrating its robustness for industrial applications [73]. The industrial-level production of α-amylase using Bacillus sp. KR-8104 was optimised for simultaneous enzyme production and desizing of cotton fabric. The highest enzyme yield was achieved at 45 °C, pH 5.0–6.0, using media with novel nitrogen sources, such as soya powder and chicken excrement, while desizing efficiency peaked at 40–45 °C, pH 5.0–6.0, over 10–24 h [74]. Similarly, the large-scale production of a highly thermostable α-amylase from Thermotoga petrophila, cloned into E. coli, was optimised for industrial applications as a textile desizer. Maximum enzyme yield (22.08 U mL⁻¹ min⁻¹) was achieved in ZBM medium with lactose (200 mM) as an inducer under specific fermenter conditions, including 70% medium volume, 2.0 vvm air supply, 20% dissolved oxygen, and 200 rpm agitation. The enzyme demonstrated optimal desizing activity at 85 °C, pH 6.5, and 150 U mL⁻¹ concentration, showcasing its potential for efficient textile processing [75]. These fermentative desizing processes, employing inexpensive raw materials, offer a promising, cost-effective, and environmentally sustainable solution for the textile industry.

4.2. Pectinases in Scouring and Degumming

The primary non-cellulosic impurities in fabrics, particularly cotton, consist of pectins, which bind cellulosic and non-cellulosic polymers. The decomposition of pectins is critical for the removal of non-cellulosic substances from fabrics. Traditional scouring methods using sodium hydroxide (NaOH) can damage textiles due to their harsh alkaline treatments. Enzyme-aided scouring offers a safer, eco-friendly alternative for delicate textiles like silk, wool, and cashmere, effectively removing pectins without causing fabric damage, thus meeting the demands of sustainable textile processing [76,77]. Also, non-ionic surfactants are often employed to enhance enzyme penetration by lowering the surface tension of fibres and facilitating the removal of wax and grease during scouring. This step is essential for preparing textiles for further industrial processing [77]. Pectinases, or pectinolytic enzymes, are the biocatalysts responsible for pectin degradation. This group includes polygalacturonase, pectin lyase, pectate lyase, and pectin esterase, which decompose pectins through glycolysis, hydrolysis, and deesterification [78]. These enzymes are primarily produced by saprophytic and plant-pathogenic microorganisms, including bacteria, yeasts, and fungi [79].

The application of scouring and degumming on various fibres using pectinase has been studied under different conditions, with fungal enzymes from Aspergillus niger being commercially significant and widely utilised across industries. For textile applications, a new prescription process for pectinase production by Aspergillus niger using solid fermentation was developed, optimising the culture substrate and temperature treatments, with the optimal formula consisting of rice dextrose, wheat bran, ammonium sulphate, and water, resulting in a pectinase activity of 36.3 IU/g dry mass [80]. Vigneswaran et al. used a commercial pectinase enzyme for scouring cotton at a pH range of 8.5–9, a temperature of 60 °C, and an enzyme dose of 6% for 1 h [81]. In another study by Rajendran et al. (2011), Fusarium sp. pectinase was applied for cotton scouring at a pH of 8, a temperature of 40 °C, and an enzyme dose of 2% for 0.33 h [82]. For degumming of ramie, Guo et al. (2013) applied Bacillus sp. pectate lyase at pH 8.5 for 2.4 h at 50 °C with an enzyme dose of 40 U/g and a fabric-to-moisture ratio of 1:13 [83]. Zheng et al. (2001) applied a combination of pectate lyase, polygalacturonase, xylanase, and cellulase from Bacillus sp. for degumming ramie at pH 10 for 5 h at 40 °C [84].

The use of mixed enzyme systems has proven highly effective in bioscouring, integrating multiple textile processes into a single step. These systems typically combine pectinase with cellulases, xylanases, cutinases, lipases, or proteases. Such combined processes offer significant advantages, including water and energy conservation [85,86]. For example, desizing, bioscouring, and bleaching can be performed in a single bath, minimising water and energy consumption. Alkaline pectinases are particularly compatible with other enzymes, such as α-amylase and glucose oxidase, and are suitable for simultaneous H₂O₂ bleaching and reactive dyeing [86,87]. Enzymatic scouring not only meets the demand for sustainable textile processing but also enhances fabric quality while reducing environmental impact, making it a preferred choice in modern textile industries.

4.3. Cellulases in Stonewashing and Finishing

Cellulases are enzymes that hydrolyse the β-1,4 linkages of cellulose, resulting in the release of degraded products such as glucose, cellobiose, and oligosaccharides of varying lengths. These enzymes are produced by various microorganisms, including bacteria and fungi, and have significant industrial applications [88]. Microbial cellulases, particularly those from Cellulomonas sp., Clostridium sp., Thermomonospora sp., Aspergillus sp., and Trichoderma sp., are produced in large quantities and are widely used in different commercial sectors [89]. Cellulase enzymes can be classified into three types: endoglucanase (which hydrolyses internal O-glycosidic bonds), exoglucanase (which hydrolyses cellulose from the ends), and β-glucosidase (which hydrolyses non-reducing β-D-glucosyl residues from the terminals) [89,90].

In the textile industry, cellulases are employed in various processes, such as the pretreatment of fibres, biowashing, mixed enzymatic scouring, stone finishing, and biopolishing [91]. Natural fibres like jute, cotton, ramie, and flax typically contain 15–30% non-cellulosic impurities, which can be efficiently removed by pre-treating the fibres with mixed enzymatic systems [92]. As an eco-friendly alternative, cellulase enzymes are used in biostoning to achieve a washed-out look like traditional stonewashing. This method reduces water consumption, waste, and energy use, while enhancing fabric softness and fade effects. Unlike pumice stones, which can damage machinery and contaminate wastewater, enzymatic biostoning offers a sustainable solution, adding value to denim without the environmental impact of conventional stonewashing [93]. Cellulases are extensively utilised in textiles to enhance fabric softness, smoothness, and lustre, while also creating a distinctive stonewashed effect on denim [94]. For effective fibre pretreatment, cellulases work in conjunction with other enzymes (such as hemicellulases, proteases, and pectinases) to target and remove fibre impurities [94,95]. For example, in mixed enzymatic scouring, cellulases penetrate the outer cuticle layer of the textile fibres, creating space for pectinases to act on the primary wall and hydrolyse pectin [96].

Cellulases are extensively utilised in textiles for their ability to enhance fabric softness, smoothness, and lustre, while also imparting a distinctive stonewashed effect on denim. They are most frequently applied in stonewashing or finishing processes, where they partially hydrolyse colours or dyes from the surface of denim and heavy cotton twills without compromising fabric strength [97]. In biopolishing, cellulases eliminate surface microfibrils on fabrics like cotton, linen, and viscose through controlled hydrolysis, creating a fibre-free surface that improves brightness, texture, luminosity, and softness [96]. Additionally, cellulases reduce pilling in viscose and fibrillation in lyocell, though their effects are less pronounced on cellulose acetate. Among fabrics, linen is the most susceptible to enzymatic hydrolysis, followed by viscose, cotton, and lyocell [98]. The benefits of using cellulases in textile processing over traditional chemical treatments are numerous, including improved textile quality, greener pretreatment methods, eco-friendliness, less damage to garments, reduced wastewater generation, enhanced biodegradability of wastewater, and reduced equipment load [99]. These advantages make cellulases an important component in sustainable textile manufacturing processes.

4.4. Glucose–Oxidases in Textile Bleaching

Many studies have demonstrated that hydrogen peroxide (H₂O₂) is a safer and more environmentally friendly alternative to traditional chlorine-based oxidising agents in textile bleaching. Hydrogen peroxide is particularly attractive because it decomposes into water and oxygen, making it less harmful to the environment compared to chlorine [100]. Glucose oxidase is an enzyme naturally produced by certain fungi (such as Penicillium glaucum and Aspergillus niger) that can be used to enzymatically produce hydrogen peroxide [101]. Glucose oxidase is a highly stable flavin adenine dinucleotide (FAD)-dependent enzyme that catalyses the oxidation of glucose into gluconic acid, simultaneously producing hydrogen peroxide in the presence of oxygen [29]. This hydrogen peroxide can then be used for biobleaching, a more sustainable method of fabric whitening.

Glucose oxidase is most effective in producing hydrogen peroxide at acidic to neutral pH levels and lower temperatures. However, traditional bleaching processes often require alkaline pH and higher temperatures for optimal results [102]. This mismatch between enzyme activity conditions and the bleaching requirements presents a challenge. To address this, Davulcu et al. employed ultrasound energy to enhance the enzymatic reaction, which improved fabric whiteness without the need for harsh alkaline conditions or high temperatures [103]. Sonicated bleaching with glucose oxidase significantly enhanced fabric whiteness and lightness through enzymatic generation of H₂O₂, while the application of ultrasound power beyond 150 W offered no further improvement in bleaching efficiency and resulted in a reduction in tensile strength [104]. This innovative approach allows for a more energy-efficient and environmentally friendly bleaching process.

Many researchers have explored the use of combined one-bath systems for desizing and bleaching, where the degradation products of starch (such as glucose) are reused to generate hydrogen peroxide [105,106]. For example, studies have shown that glucose derived from starch degradation can be utilised for hydrogen peroxide formation in a combined process [106]. Recently, Mojsov developed an efficient multi-enzyme one-bath system for treating sized cotton fabric. This system uses enzymes such as amylase, amyloglucosidase, pectinase, and glucose oxidase to convert starch into hydrogen peroxide through a series of reactions [107]. This enzymatic approach not only produces hydrogen peroxide for bleaching but also offers significant advantages in terms of reducing waste generation and water consumption in textile processing.

4.5. Catalase in Bleach Cleanup

Catalase plays a pivotal role in the textile industry, particularly in the bleach cleanup process, where it effectively removes residual hydrogen peroxide from fabrics. This enzymatic treatment ensures that textiles are peroxide-free and ready for subsequent processes such as dyeing. The term “bleach cleanup” was originally coined by Novo Nordisk to describe this specific enzymatic application [108]. Hydrogen peroxide is widely used as a bleaching agent due to its effectiveness in whitening fabrics. However, residual peroxide left on the fabric after bleaching can interfere with the dyeing process, causing uneven colour absorption and diminished fabric quality [109]. Catalase addresses this issue by catalysing the decomposition of hydrogen peroxide into water and oxygen, two environmentally benign byproducts [110].

Sooch et al. isolated a thermophilic strain of Geobacillus (BSS-7) that produced exceptionally high levels of intracellular catalase, demonstrating strong potential for hydrogen peroxide (H₂O₂) degradation. The strain effectively removed H₂O₂ in a packed bed reactor and has bleach cleanup applications [111]. Czyzewska et al. proposed the chemical immobilisation of catalase on membranes from psychrotolerant bacteria, enhancing its performance under textile conditions through membrane deposition. The catalytic properties of the immobilised catalase demonstrated its efficiency in decomposing hydrogen peroxide waste from textile bleaching processes [112]. Recently, Sheer et al. investigated recombinant manganese catalases from Geobacillus thermopakistaniensis, demonstrating their superior performance in hydrogen peroxide removal for sustainable textile processing. The manganese–catalase showed high activity, thermostability, and alkalinity, offering significant advantages by reducing water consumption, eliminating extensive rinsing, and operating under mild conditions [113,114]. Therefore, catalases are eco-friendly enzymes that leave no harmful residues, preserve fabric integrity, and enhance dye uptake while promoting environmentally sustainable practices in textile manufacturing [115].

4.6. Laccases in Textile Bleaching and Dye Decolourisation

Laccase is one of the most abundant oxidoreductase enzymes in nature, being widely distributed in microorganisms, including bacteria and fungi (e.g., Trametes versicolour, Pycnoporus cinnabarinus, and Bacillus subtilis). It is capable of oxidising phenols and aromatic amines by reducing molecular oxygen (O₂) to water (H₂O) through the action of multiple copper ions in its catalytic pocket [32]. In addition to the enzyme itself, the entire redox mediator system of laccase has been applied in various industrial processes. Laccase plays a significant role in several commercial sectors, including textiles, cosmetics, food, and the paper and pulp industries [116]. In textile processing, the use of laccase has gained considerable attention due to its two key applications: (i) textile bleaching and (ii) effluent dye decolourisation. Laccases are used in textile bleaching to modify fabric surfaces and enhance the whiteness of textiles, significantly reducing the amount of hydrogen peroxide (H₂O₂) required during the bleaching process [117]. Kim et al. demonstrated that laccases can effectively bleach textiles while minimising H₂O₂ dosages [118]. Additionally, Abou-Okeil et al. found that the combined effect of laccase and H₂O₂, assisted by ultrasonication, resulted in effective bleaching with less fibre damage. Ultrasound treatment helps to de-aggregate the enzyme, improving its activity and facilitating its diffusion into fibres, enhancing the overall bleaching efficiency [104]. Laccase, when combined with glucose oxidase in a dual-enzyme system, effectively removes lignin, enhancing linen bleaching. The combination demonstrated superior performance compared to individual enzymes, improving the surface properties and whiteness of the treated fibres [119].

Laccase plays a significant role in enhancing the whiteness of fabrics by improving the efficiency of hydrogen peroxide bleaching, leading to similar or better results than conventional methods with lower environmental impact [120]. For instance, Pereira et al. isolated a laccase from Trametes hirsuta, which effectively oxidised various flavonoids, improving the whiteness of cotton fabrics [121]. Furthermore, during the finishing stage of textile processing, laccase can transform toxic chemicals or dyes into non-toxic forms in a more eco-friendly and economical manner, helping reduce environmental pollution. For instance, Neifar et al. screened the salt-tolerant bacterium Pseudomonas extremorientalis BU118 for laccase production, achieving high enzymatic activity (7000 U/L) and demonstrating its potential for decolourising the textile azo dye Congo red under optimised conditions [122]. Similarly, the laccase from Streptomyces cyaneus CECT 3335 decolourised azo dyes like methyl orange and Orange II by 90% with acetosyringone as a mediator [123]. The laccase showed excellent colour removal capabilities across various dye and salt concentrations, highlighting its biotechnological potential in textile effluent treatment.

Laccase from Trametes versicolour has been successfully used in denim finishing, where it efficiently degrades indigo dye without the need for a redox mediator [124]. This application has proven to be a highly effective method for environmentally friendly denim processing. In addition to denim, the economic colouring of wool can be achieved using laccase, which requires less dye and demonstrates enhanced fixation capabilities compared to conventional methods. Laccase from Sclerotium rolfsii has also been used for wool dye decolourisation [125]. Overall, laccase is a promising biocatalyst in textile processing, offering an eco-friendly alternative to harmful chemicals and contributing to more sustainable methods due to its versatility and environmentally beneficial properties.

4.7. Peroxidases in Dye Degradation and Effluent Treatment

Peroxidases are a group of enzymes that play a significant role in the textile industry, particularly in addressing environmental challenges associated with dye degradation and effluent treatment [126]. The textile industry generates substantial quantities of wastewater containing synthetic dyes, which are not only aesthetically displeasing but also toxic to aquatic ecosystems. Peroxidases, by catalysing oxidative reactions, offer an eco-friendly and efficient solution to degrading these persistent dyes and reducing their environmental impact [127]. They are derived from various sources, such as plants (e.g., horseradish peroxidase), fungi (e.g., lignin peroxidase), and bacteria, which can catalyse the breakdown of these dyes by generating highly reactive radicals in the presence of hydrogen peroxide. These radicals attack dye molecules, leading to their oxidation and eventual breakdown into less harmful or completely mineralised products like water, carbon dioxide, and simple organic acids [128].

In textile dyeing processes, synthetic dyes such as azo, anthraquinone, and reactive dyes are extensively used. These dyes often resist natural degradation due to their complex aromatic structures, making traditional wastewater treatment methods insufficient [129]. The application of peroxidases in effluent treatment has shown promising results in degrading a wide range of dye pollutants. For example, lignin peroxidase and manganese peroxidase from white-rot fungi (Phanerochaete chrysosporium) are particularly effective against recalcitrant dyes, such as azo and anthraquinone dyes. These enzymes operate under mild conditions and can break down dye molecules that are otherwise resistant to conventional chemical and biological treatments [130]. A dye-decolourising peroxidase from Bacillus amyloliquefaciens (BaDyP) demonstrated significant potential for bioremediation of industrial effluent by degrading Reactive Blue 19 and Reactive Black 5, and reducing COD, colour, and toxicity. Treated effluent showed enhanced seed germination and reduced bacterial inhibition, highlighting BaDyP as an efficient biocatalyst for pollutant mitigation [131]. Recently, Ilić Đurđić et al. improved the degradation of azo dyes (Amido Black 10B, Evans blue and Guinea green) using lignin peroxidase (LiP) from Phanerochaete chrysosporium through mutagenesis near the catalytic pocket and the application of enzyme-coated yeast cell walls. Mutants exhibited up to 13-fold higher catalytic activity, and LiP-coated cell wall fragments demonstrated enhanced stability, retaining activity across multiple reaction cycles [132]. Saha et al. demonstrated that a bacterial consortium (VITPBC6), comprising six Bacillus strains (B. flexus, B. paraflexus, B. megaterium, B. firmus, B. flexus, and B. aryabhattai), efficiently degraded Reactive Orange 16 (RO-16) through enzymatic action involving azoreductase, tyrosinase, laccase, lignin peroxidase, and manganese peroxidase. This enzymatic degradation significantly reduced the dye’s toxicity, showcasing the consortium’s potential for bioremediation of textile effluents. Additionally, peroxidases are capable of treating mixed dye effluents, making them versatile in real-world applications [133]. Hossain et al. demonstrated efficient dye degradation by Bacillus pseudomycoides and Acinetobacter haemolyticus, isolated from industrial effluents, targeting methylene green, basic violet, and acid blue dyes. These bacteria showed up to 82% degradation for mixed dye combinations, driven by peroxidase and azoreductase enzymes essential for breaking azo bonds. Molecular docking and dynamics studies confirmed strong enzyme-dye interactions, highlighting the potential of these strains for large-scale wastewater treatment [134].

One of the key advantages of using peroxidases is their ability to work in conjunction with other treatment processes. For instance, enzymatic dye degradation can be combined with coagulation, adsorption, or membrane filtration to enhance overall effluent treatment efficiency [19]. The enzymatic approach minimises the use of harsh chemicals, reduces sludge generation, and ensures the treated water meets environmental standards for discharge or reuse.

Peroxidases are emerging as powerful biocatalysts for dye degradation and effluent treatment in the textile industry, offering an enzymatic alternative to toxic chemicals and energy-intensive processes. Their ability to degrade synthetic dyes under ambient, environmentally benign conditions, combined with biodegradability, positions them as a sustainable solution for reducing the environmental impact of textile processing [135]. Advances in enzyme technology and process optimisation could further enhance their potential for eco-friendly textile manufacturing.

4.8. Esterases and Lipases in Pre-Treatment of Textile

Esterases and lipases are enzymes classified as carboxyl ester hydrolases, which are distinguished primarily by their substrate specificity. Esterases catalyse the hydrolysis of water-soluble short-chain acyl esters, while lipases are typically active on water-insoluble long-chain triacylglycerols [136]. These enzymes have found significant applications in textile processing, particularly in improving the dye uptake properties of polyester fabrics [137]. Esterases and lipases are used in cotton fabric pre-treatment to remove sizing lubricants, enhancing absorbency and enabling better dye fixation for vibrant colours. A study on lipase (lipolase) showed it effectively scours cotton by removing wax, pectin, and protein, improving hydrophilicity, whiteness, and dyeing performance. Combining lipase with pectinase further enhanced scouring efficiency, reduced treatment time, and produced superior fabric properties comparable to conventional alkali methods [138]. Another study demonstrated that lipases are particularly effective in removing both natural and added fats/greases from cotton fabrics [139]. This was achieved through a mixed enzymatic bioscouring system that included lipase, along with other enzymes such as pectinase, cellulase, and protease. The combined effect of these enzymes in the bioscouring process helped to clean the cotton fabric more efficiently, enhancing its ability to absorb dye and improving the final quality of the textile [140]. Using esterases and lipases in textile pre-treatment offers several benefits, including improved dye uptake, enhanced fabric quality, and reduced environmental impact compared to traditional chemical treatments. These enzymes help ensure that the fabrics are more receptive to dyeing and promote eco-friendly processing by reducing the need for harsh chemicals and minimising water usage.

4.9. Arylesterases in Scouring and Bleaching

Arylesterases are enzymes classified under the hydrolase group, specifically responsible for catalysing the hydrolysis of carboxylic ester bonds [141]. In textile processing, arylesterases play a crucial role in the enzymatic scouring and bleaching of fabrics. Notably, they can catalyse the in situ production of peracetic acid from hydrogen peroxide (H₂O₂) under mild conditions, such as at neutral pH and a moderate temperature of 65 °C [142]. This ability to generate peracetic acid in situ makes arylesterases a valuable tool in sustainable textile processing, offering an effective alternative to traditional chemical bleaching methods. The application of arylesterases in the textile industry is particularly advantageous for scouring and bleaching processes, where the enzyme contributes to improving fabric characteristics such as absorbency, whiteness, and fibre tenacity. The enzymatic process is a one-step procedure that efficiently removes impurities from fibres, leading to cleaner textiles with enhanced quality. Studies have shown that enzymatic scouring and bleaching using arylesterases not only achieves high levels of whiteness but also results in minimal damage to the fibre structure, preserving the integrity and strength of the fabric [143,144]. Overall, arylesterases provide a sustainable solution for textile processing, improving dye uptake and uniformity while reducing environmental impact through minimised use of harsh chemicals, water, and energy.

4.10. Cutinases in Surface Modification of Synthetic Fibres

Cutinases are enzymes belonging to the hydrolase class, specifically responsible for hydrolysing cutin into cutin monomers. As serine esterases, cutinases contain a catalytic triad consisting of serine (Ser), histidine (His), and aspartic acid (Asp), which are essential for their hydrolytic activity [145]. Cutinases are used in textile processing to modify synthetic fibres by degrading complex polyesters like cutin, improving fabric properties. PET hydrolases, designed to degrade PET plastics, also play a role in recycling and modifying synthetic textiles by breaking down PET into monomers. These enzymes, isolated from various bacterial (Ideonella sakaiensis and Thermobifida fusca) and fungal (Aspergillus oryzae and Fusarium solani) species, offer diverse potential for textile surface modification and bioremediation applications [146]. Beyond their biological role, cutinases have become useful in the surface modification of synthetic fibres such as polyester, polyamide, and polyacrylonitriles [147]. For instance, in a heterogeneous system, the combined use of Candida antarctica lipase A and Fusarium solani pisi cutinase showed different degradation modes of poly(ε-caprolactone) (PCL), with lipase leading to higher mass loss and a significant decrease in crystallinity. While cutinase degradation maintained thermal stability and one-step decomposition, lipase hydrolysis resulted in reduced thermal stability and multi-step degradation [148]. Similarly, Carniel et al. demonstrated that lipase from Candida antarctica (CALB) and cutinase from Humicola insolens (HiC) work synergistically to hydrolyse poly(ethylene terephthalate) (PET) into terephthalic acid (TPA), with CALB converting bis-(hydroxyethyl) terephthalate (BHET) to TPA even at high concentrations. This combination enhanced PET depolymerisation, achieving a 7.7-fold increase in yield and a TPA mole fraction of up to 0.88, with potential applications in the surface modification of synthetic fibres and PET recycling [149]. Cutinases, when combined with other enzymes like pectin lyase, have been used to improve the wetting properties of cotton fibres, enhancing their water absorption [85]. Their application in synthetic fibre surface modification improves wettability, dye uptake, and functionality, offering an eco-friendly alternative to harsh chemical treatments in sustainable textile processing.

4.11. Proteases in Scouring

Proteases are enzymes produced by microorganisms (Bacillus subtilis, Bacillus licheniformis, and Aspergillus niger) that break down proteins into smaller peptides and amino acids. Fungal proteases typically activate in a pH range of about 4 to 8, while bacterial proteases work best at a pH of 7 to 8. In the textile industry, proteases subtilisin and keratinase are used in processes like enzyme-based biopolishing, degumming of silk, wool finishing, and denim stonewashing, enhancing fabric softness, improving dyeing properties, and reducing the need for harsh chemicals and water consumption, making the process more eco-friendly [150,151]. Protease enzymes from Bacillus subtilis 168 E6-5 and commercial enzymes were tested on wool fabric to modify its surface and prevent felting. The results showed that the protease from B. subtilis enhanced the physical properties of wool, including tear strength and whiteness, more effectively than the commercial enzyme [152]. In the degumming of silk, proteases break down the sericin protein, enhancing the fabric’s softness, sheen, and mechanical properties. Enzymatic degumming under optimal conditions improves silk’s physical properties and serves as an eco-friendly alternative to traditional soap treatments [153]. Sreelakshmi et al. demonstrated that acidic proteases from Bacillus licheniformis and Bacillus cereus have potential for scouring cotton fabrics, with B. licheniformis showing superior efficiency in weight loss, absorbency, and impurity removal. Protease-treated samples exhibited reduced tear strength compared to alkali scouring, while FTIR analysis confirmed the removal of protein-related compounds, retaining wax and pectin residues [154]. Proteases, in combination with cellulases, are also used for optimised bioscouring. For instance, a study has shown that mixing proteases (such as those from Bacillus) with cellulase results in successful scouring, dye removal, and improved water absorbency, although some fibre damage can occur with cellulase presence. For denim stonewashing, proteases break down protein-based impurities, achieving the desired faded look without damaging fabric strength. Proteases combined with commercial enzymes have been optimised using artificial neural network (ANN) techniques to enhance absorbency and remove pectin, improving overall fabric quality [155]. Another study revealed that protease treatment of wool fabric at various concentrations (1–5 g/L) improved physical properties such as softness, absorbency, and surface smoothness, while reducing weight loss and enhancing dyeability and colour fastness compared to untreated wool. The 4 g/L protease concentration showed the best results in improving the fabric’s handle, tensile strength, and overall quality [156]. Therefore, proteases in textile processing provide an eco-friendly alternative, enhancing absorbency and cleaning while reducing chemicals and water usage.

5. Improving Enzymes for Textile Applications

This section covers recombinant and engineered enzymes, immobilised enzymes, and extremozymes—robust biocatalysts essential for the harsh processes of textile applications. Improving enzymes for textile applications involves designing recombinant and engineered enzymes with enhanced specificity, activity, and stability tailored to industrial needs [157]. Immobilised enzymes, fixed on solid supports, offer reusability and operational stability, reducing costs and environmental impact in processes like bioscouring and degumming [158,159]. Extremozymes, derived from extremophiles, are robust biocatalysts with resilience to extreme conditions such as high temperature and pH, making them ideal for harsh textile processing environments [160].

5.1. Recombinant and Engineered Enzymes

Recombinant enzymes for textile processing have significantly advanced industrial biotechnology by enabling the production of tailored enzymes with enhanced properties. Native enzymes often fail to meet industrial yield demands, necessitating heterologous expression in mesophilic hosts. Host selection depends on genome compatibility, metabolism, growth rate, and culture conditions. While E. coli is a preferred host due to its ease of manipulation and rapid growth, its limitations include codon bias, inclusion body formation, and lipopolysaccharide contamination [161]. Alternative hosts, such as Bacillus subtilis, Saccharomyces cerevisiae, and Trichoderma reesei, offer efficient systems for protein expression. Codon harmonisation algorithms effectively address codon bias, enhancing protein expression [162,163].

Advances in enzyme production focus on achieving stability under extreme conditions, such as high or low temperatures, salinity, pressure, and pH variations. For instance, cold-adaptive lipases, such as LSK25 from Pseudomonas sp., have been expressed in E. coli BL21 (DE3) as inclusion bodies, which enhance proteolytic resistance and enable industrial-scale production. These enzymes, with optimal activity at 30 °C and pH 6, are valuable for cold washing and other temperature-sensitive industrial processes [164]. Similarly, thermostable xylanases derived from metagenomics have been expressed in E. coli, achieving yields of ~100 mg/L with optimal activity at 80 °C and pH 7. Metal ions such as Ni, Zn, and Mg enhance activity by up to 55% [165]. Recombinant production of other enzymes, such as cold-adaptive endoxylanases in Pichia pastoris and thermophilic endoglucanases from Sulfolobus shibatae, demonstrates the versatility of heterologous systems [166]. These enzymes exhibit optimal activity under industrially relevant conditions. Using hosts like Bacillus subtilis and Aspergillus spp. for extracellular enzyme production eliminates the need for cell disruption, reducing production costs [167]. In another example, Yu et al. optimised recombinant alkaline catalase (KatA) production in E. coli BL21 under ethanol stress, achieving a high yield of 78,762 U/mL with an extracellular ratio of 92.5%. The purified KatA exhibited stability at 50 °C and pH 6–10, efficiently removing residual H₂O₂ and reducing water, steam, and energy consumption by 25%, 12%, and 16.7%, respectively, without compromising fabric quality [168].

Enzyme engineering has emerged as a keystone of sustainable biotechnology, particularly in textile processing and waste treatment, by enabling the development of highly efficient, environmentally friendly enzymes. Figure 3A illustrates various enzyme engineering strategies. Modern approaches include directed evolution, site-directed mutagenesis, in silico enzyme design, enzyme truncation or fusion, and integrated combined mutagenesis, each playing a vital role in optimising enzyme functionality for industrial applications [169]. Directed evolution, using techniques like error-prone PCR and DNA shuffling, enhances enzyme traits such as stability, efficiency, and substrate specificity, making them suitable for harsh industrial conditions. Site-directed mutagenesis and in silico enzyme design further refine enzyme activity through precise modifications and computational predictions, while truncation and fusion improve adaptability. Combining these approaches produces engineered enzymes with superior thermal stability, pH resistance, and catalytic performance for industrial applications like textile effluent treatment. For industrial bioscouring applications, enzymes must be stable under elevated temperatures and alkaline pH conditions [170]. The efficiency of pectin removal varies depending on the enzyme, with optimal conditions generally involving 0.05–2% pectinase at temperatures of 30–80 °C and pH levels of 3–9 [171]. Solbak et al. reported a novel pectate lyase mutant with eight mutations (A118H, Y190L, A197G, S208K, S263K, N275Y, Y309W, S312V) that improved the enzyme’s thermal stability by 16 °C, enabling efficient high-temperature bioscouring with lower enzyme dosages [172]. Recently, Li et al. enhanced the activity and alkali resistance of alkaline pectate lyase BspPel from Bacillus RN.1 through loop replacement, achieving a 4.4-fold increase in specific activity (139.4 U/mg) and improved stability at pH 11.0 and 60 °C. The modified enzyme, with enhanced affinity for apple pectin, shows significant potential for industrial applications, including bioscouring in textile processing [173]. Khan et al. employed a rational protein engineering approach to enhancing the thermostability and activity of Bacillus subtilis lipase, generating mutants (F41K, W42E, P119E, Q121K, V149K, Q150E) that exhibited improved activity at 60 °C and pH 10, and successfully removing up to 90% fats/grease from the fabric [139]. In another study, Saha et al. compared the desizing efficiency of full-length and C-terminal truncated α-amylases from Bacillus subtilis on starch-coated polystyrene, silk, and cotton fabrics, with truncated α-amylases achieving up to 85% efficiency on polystyrene fabrics, highlighting their potential for textile applications [12]. Therefore, enzyme engineering in textile processing and waste treatment not only enhances efficiency and sustainability but also supports the transition towards greener, more eco-friendly industrial practices, benefiting both production processes and environmental health.

5.2. Immobilised Enzymes

Enzyme immobilisation has transformed industrial biocatalysis by enabling enzymes to retain their catalytic activity while being reused continuously. Immobilisation involves attaching enzymes to support materials, restricting their mobility to create heterogeneous catalysts suitable for diverse applications. The success of immobilisation depends on the choice of support materials and immobilisation methods, both of which critically influence enzyme performance [174]. Enzyme immobilisation methods include surface attachment, encapsulation, and cross-linking (Figure 3B). Surface attachment involves physical adsorption, ionic bonding, or covalent bonding. Physical adsorption is simple and reversible but can result in desorption under changing conditions. Ionic bonding relies on electrostatic interactions, offering moderate binding strength with activity retention, although it is sensitive to pH and ionic strength variations. Covalent bonding forms stable, irreversible links between the enzyme and carrier, enhancing stability but potentially causing activity loss due to structural changes. Encapsulation confines enzymes within semi-permeable matrices such as alginate beads, protecting them from environmental factors while allowing substrate and product diffusion, albeit with potential mass transfer limitations. Cross-linking aggregates enzyme molecules using reagents like glutaraldehyde, creating a carrier-free immobilisation system with enhanced stability but potentially reduced activity due to rigidity [175,176].

Immobilisation affects enzyme properties like activity, stability, pH and temperature optima, substrate specificity, and kinetics. Efficiency depends on yield, specific activity, stability, and reusability. Yield includes bound enzymes and retained activity, while specific activity reflects reaction rate. Stability and reusability are assessed under operational and storage conditions [177].

For example, a catalase from Bacillus sp. was covalently immobilised on silanised alumina, showing higher stability at alkaline pH and temperatures compared to the free enzyme. The immobilised catalase demonstrated improved stability (214 h at pH 11, 30 °C), but its activity was inhibited by anionic stabilisers or surfactants in the hydrogen peroxide substrate solution [178]. Another study by Costa et al. revealed the covalent immobilisation of commercial catalase (Terminox Ultra 50L) on alumina using glutaraldehyde for the recycling of textile bleaching effluents in dyeing processes. The immobilised enzyme retained 44% of its activity at pH 11 and 30 °C, and 90% at 80 °C and pH 7. Furthermore, the half-life of the immobilised catalase was extended to 2 h at pH 12 and 60 °C [179]. The immobilisation of Bacillus subtilis MTCC 2414 laccase using sodium alginate was optimised for dye degradation studies. The immobilised laccase exhibited higher degradation of Yellow GR dye (81.72%) compared to free laccase (74.69%) and culture filtrate (72.16%), with maximum activity at pH 7 and 35 °C [180].

Table 6. Examples of immobilised enzymes used for textile applications.

Immobilisation Method	Enzyme	Carrier/Support	Improvement	Stability/Reusability	Reference
Adsorption	Cellulase	Ca alginate starch bead	Lower weight loss, minimal tensile strength reduction (67–98.35%), and improved whiteness index	-	[181]
	Cellulase	Epoxy resin	Maximum activity was used on cotton fabric for biopolishing	Reuse up to 6 cycles	[182]
	Cellulase	PVA coated chitosan	pH optimum of enzyme shifted from 4.0 to 7.0 and showed better stability at neutral pH	Stability of 52% after 8 cycles	[183]
	Laccase	TiO2–ZrO2–SiO2	100% alizarin red S removal	90% stable after 20 days	[184]
Adsorption and covalent bonding	Cellulase	Kaolin	Minimised tensile strength loss, enzyme reusability, improved product quality, and reduced polishing costs	Better recovery and reuse for 3 cycles	[185]
Covalent binding	Laccase	Green coconut fibre	Enhanced thermal stability at 50 °C and high efficiency in continuous reactive dye decolourisation	Stability retained 45–50% after 4 cycles	[186]
	Laccase	Glycidyl methacrylate functionalised polyacrylamide alginate	55% dye removal	50% stability remained after 5 cycles	[187]
	Manganese peroxidase	Fe3O4/chitosan	98% Reactive Orange 16 and 96% methylene blue removal	86% stable after 5 cycles and 60% after 14 days	[188]
Covalent/cross-linking	Protease (esperase)	Eudragit S-100	Operational stability at 60 °C improved 1.7-fold	Activity of 72% after 5 cycles	[189]
Cross-linking	Keratinase	Chitosan-β-cyclodextrin	Enhanced optimal activity at pH 11 and 70–75 °C with superior thermo-stability	Storage stability of ~53% after 30 days	[190]
	Laccase	Cu(II) ion chelated chitosan	43% removal of methyl orange, 69% removal of Cibacron blue and 87% removal of Reactive Black 5	81% stable after 20 uses	[191]
	Manganese peroxidase	Chitosan beads	97% dye removal	60% stable after 10 cycles	[192]
Entrapment	Laccase	Alginate beads	66% dye removal	95% stable after 15 days	[193]
Non-covalent binding	Cellulase	Eudragit S-100 and Eudragit L-100	Improved fabric softness while minimising weight and tensile strength loss to the surface fibres	Stability of 51% and 42% after 3 cycles	[194]

presents more examples of immobilised enzymes based on different immobilisation methods used in various textile processing and waste management applications.

5.3. Extremozymes—Robust Biocatalysts

Extremozymes are specialised enzymes produced by extremophiles—microorganisms that thrive in extreme environments such as high/low temperatures, acidic/alkaline conditions, high salinity, or extreme pressures [195]. These enzymes have evolved unique molecular mechanisms that enable them to function under harsh conditions, where standard enzymes from mesophilic organisms would typically be denatured, with their biochemical properties adapted to ensure stability under environmental stress. For example, thermophilic enzymes often have a large hydrophobic core, which minimises flexibility and helps maintain protein stability at high temperatures. The increased number of disulfide bonds and specific amino acid compositions (e.g., more hydrophobic and aromatic residues) contribute to their heat tolerance. Psychrophiles, on the other hand, have enzymes with greater flexibility due to a reduced number of proline residues, which increases protein mobility and allows them to function effectively at low temperatures [160,195].

Extremozymes play a crucial role in both industrial wastewater treatment and textile processing, particularly in the textile industry, where effluents are often rich in salts, dyes, and chemicals. These enzymes are utilised in key processes such as desizing, bioscouring, biostoning, biobleaching, and biopolishing, where they improve fabric quality, reduce energy consumption, and minimise the use of chemicals [196]. Halophilic extremozymes are highly effective in decolourising azo dyes and degrading a range of chemical pollutants found in textile effluents. Strains like Halogeometricum borinquense and Halomonas sp. have demonstrated exceptional ability to break down dyes even under high-salinity conditions, further enhancing the sustainability of textile wastewater treatment [197]. A thermostable, mildly alkalophilic recombinant laccase from Thermus thermophilus, produced in E. coli, exhibited optimal activity at ~90 °C for short reactions and efficiently decolourised up to six industrial dyes (orange dye, green dye, acid red dye, Naphthol Brilliant Blue, Remazol Brilliant Blue, and Congo red), demonstrating potential for various redox applications [198].

A study on thermostable Bacillus licheniformis α-amylase optimised for desizing cotton fabrics focused on reducing sugars, absorbency, flexural rigidity, and weight loss. The optimal conditions for desizing were 3.0 g/L enzyme concentration, pH 6.0, 40 min treatment, and 85 °C, resulting in improved fabric absorbency and lower residual matters compared to acid desizing [199]. Similarly, a highly thermostable and alkaline α-amylase from Bacillus sp. AB68, isolated from Van soda lake, exhibited activity between 20 °C and 90 °C, with optimal activity at pH 10.5 and 50 °C, maintaining over 90% activity after 30 min at 80 °C [200]. Anish et al. demonstrated that an alkali-stable endoglucanase from Thermomonospora sp. effectively reduces back staining while enhancing softness and abrasion in denim biofinishing, offering a sustainable alternative to conventional acid and neutral cellulases [201].

The use of extremozymes in the textile industry improves process efficiency and fabric quality and contributes to more sustainable and cost-effective manufacturing practices. With ongoing research and technological advancements, extremozymes have the potential to revolutionise industrial processes further, offering a greener alternative to traditional chemical methods.

6. Strategies for Reducing Textile Waste

The textile industry is a significant source of environmental pollution, driven by its high consumption of water, energy, and chemicals during production. To mitigate its environmental footprint, a range of strategies has been developed, focusing on different stages of production [202]. These include preparation, dyeing, finishing, and overarching general practices aimed at promoting sustainability (Figure 4).

The preparation stage involves recovery systems, waste steam reuse, chemical substitutions, and alternative processing methods, all of which play a crucial role in reducing waste and enhancing sustainability in textile production. Recent studies highlight the use of recycled fibres from textile waste in composite materials to promote eco-sustainability and circular economy practices in textile manufacturing [203]. Textile waste management currently relies on incineration for energy recovery, reuse, and recycling, with emerging technologies like mechanical recycling, such as SOEX’s process, which transforms 15,000 tons of clothing annually into insulation materials [204]. Recovery systems such as membrane filtration and centrifugation reclaim valuable materials like sizing agents and caustic soda, minimising waste and reducing resource demand. The environmental impact of textile production, the issue of solid textile waste, and strategies for recycling fibres into thermoplastic polymers, resins, natural constituents, and concrete are also discussed [205]. Waste steam from processes like desizing and scouring can be redirected to other heating applications, conserving energy and water and reducing greenhouse gas emissions [203,206]. Chemical substitutions, such as using enzymes or biodegradable surfactants instead of harsh alkalis, can improve wastewater quality by reducing toxicity. Despite these alternatives, textile auxiliaries like alkyl phenol ethoxylates (APEOs), nonylphenol ethoxylates, sodium chloride, formaldehyde, and perfluoroalkyl chains are commonly used, contributing to environmental and health risks due to their toxicity, slow degradation, and hormone disruption. The diverse and often secretive nature of textile chemical formulations complicates efforts to mitigate their impact, even as alternative chemicals and improved practices help reduce harm [203]. Additionally, innovative methods like enzymatic desizing, ultrasonic washing, and plasma treatment offer resource-efficient and eco-friendly alternatives to traditional techniques, advancing sustainability in textile processing [207].

Reconstituting and reusing dye baths conserve water and dyes by purifying and adjusting them for reuse, ensuring consistent colour quality while reducing resource consumption. Replacing synthetic dyes and traditional mordants with biodegradable or plant-based alternatives minimises the release of harmful chemicals into wastewater [208]. Advanced dyeing techniques, such as digital printing, cold pad batch dyeing, and supercritical CO₂ dyeing, significantly reduce water use, eliminate toxic substances, and enhance energy efficiency. Synthetic dyes, however, continue to pollute water bodies due to weak fabric binding and untreated effluent discharge, causing toxicity, mutagenicity, and environmental degradation [19]. The biodegradation of dyes by microbes depends on the dye structure, with synthetic azo dyes being more readily degraded due to their azo bonds (-N=N-), which can be reduced or oxidised by aerobic or anaerobic bacteria. In contrast, natural colourants are more complex, making them less susceptible to microbial breakdown [209]. Eco-friendly wastewater treatment technologies and the adoption of biomordants derived from natural sources offer sustainable solutions, though challenges like scalability and cost remain. By embracing these innovative approaches, the textile industry can mitigate environmental impacts while meeting consumer demand for sustainable products [210].

Reusing residual finishing chemicals like softeners and resins through filtration and purification technologies reduces textile waste without compromising fabric quality, while substituting conventional agents with eco-friendly alternatives such as plant-based resins and natural softeners mitigates environmental harm [211]. Sustainable finishing methods, including enzymatic treatments, plasma technology, and UV curing, require fewer chemicals and less energy while maintaining or enhancing fabric properties. These advances align with the biodegradation of textile fibres, where enzymatic processes play a critical role. Natural fibres like cotton and linen degrade faster than synthetic blends, influenced by crystallinity, polymerisation, and microbial activity, with fungi (Aspergillus sp., Fusarium sp., Penicillium sp., and Trichoderma sp.) and bacteria (Bacillus sp., Cellulomonas sp., Cellvibrio sp., and Clostridium sp.) degrading fibres differently [212]. Enzymes such as cutinases and keratinases enhance the breakdown of synthetic fibres like linen/PET (polyethylene terephthalate) and natural proteins like wool keratin, offering innovative solutions for textile waste recycling and promoting sustainable material management [213].

Characterising waste streams is essential for designing targeted waste reduction strategies. By analysing the type and volume of waste generated, including wastewater, solid waste, and emissions, manufacturers can identify opportunities for recovery and reuse [214]. Choosing sustainable raw materials like organic cotton, recycled fibres, or biodegradable synthetics reduces environmental impact and production waste. Textile waste can be repurposed into lower-value materials such as insulation or gypsum composites, or synthesised into products like cellulose acetate and biofuels. Advanced recycling processes extract components like caprolactam for Nylon 6 or bioconvert cotton into value-added products like glucose syrup, though challenges remain in achieving high yields due to cotton’s compact crystalline structure [215]. Managing the fate of processing chemicals is another vital aspect. Closed-loop systems and advanced treatments allow for the recovery and neutralisation of chemicals, preventing their accumulation in the environment [216]. The equalisation of wastewater flows is achieved through specialised tanks that balance effluent loads, ensuring consistent flow and concentration levels. This enhances the efficiency of downstream wastewater treatment processes and contributes to overall waste reduction.

Adopting these approaches across all stages of textile production not only reduces waste but also conserves valuable resources and minimises the industry’s environmental footprint. As sustainability becomes increasingly important, continued innovation and the implementation of these practices will play a key role in achieving a greener textile industry.

7. Challenges and Benefits of Enzymatic Textile Processing

Enzymatic textile processing has emerged as a promising alternative to conventional chemical-based methods, offering numerous advantages, particularly regarding sustainability, fabric quality, and environmental impact [10,77,217]. However, despite these benefits, several challenges must be addressed for the efficacious use of enzymes in textile applications. One significant challenge lies in the extremely specific nature of enzymes. Enzymes are highly selective in their reactions, acting on only particular substrates, with minimal side effects. While advantageous for precise reactions, this specificity limits the enzyme’s versatility and requires careful selection for different textile processes [218].

Enzymes also operate under mild conditions, making them safe to handle and non-corrosive in their applications. They require low energy, and their use results in reduced chemical consumption, leading to lower loads on effluent treatment plants (ETPs). This is due to the fact that enzymes are biodegradable and produce fewer hazardous residues, reducing the chemical discharge and overall environmental impact of textile processing [219]. However, this advantage is tempered by the enzyme’s sensitivity to environmental conditions. While enzymes remain chemically stable under varying pH or temperature, their physical configuration can alter, leading to “denaturation” and a loss of activity. This presents a challenge, as enzymes must be maintained within an optimal temperature and pH range [220]. For example, live steam should never be added directly to an enzyme bath, and enzymes must be pre-diluted to preserve their functionality.

Another critical challenge in enzymatic textile processing is the compatibility of enzymes with surfactants. Enzymes often exhibit limited compatibility with ionic surfactants, which can affect their effectiveness. To ensure high working efficiency and uniform results, nonionic wetting agents with appropriate cloud points must be selected [221]. Additionally, enzymes are highly sensitive to pH fluctuations, heavy metal contamination, and the precise temperature range. These sensitivities require careful monitoring and intense caution during their use in textile processing.

The high cost of enzyme production is another major barrier to their widespread adoption. While technological advancements and large-scale production may reduce costs, feasible cost-control measures must also be explored. These measures include utilising recombinant DNA technology to engineer microorganisms for enhanced enzyme production, optimising fermentation processes, employing cost-effective raw materials as substrates, and recycling immobilised enzymes for multiple uses [222]. Such approaches can help mitigate enzyme costs and enhance their affordability for textile applications.

Despite these challenges, the advantages of enzymatic processes in textiles are clear. Enzymes contribute to a lower discharge of chemicals and wastewater, reducing the handling of hazardous chemicals by textile workers. This results in improved fabric quality, offering consumers more fashion choices and extending the life of garments due to reduced damage to the original fabric. Furthermore, enzymes are an eco-friendly alternative to traditional chemical methods, leading to reduced water and energy consumption, and ultimately promoting sustainability in textile manufacturing [221].

The properties of enzymes used in textiles further highlight their potential. Enzymes accelerate reactions by lowering the activation energy required, acting as catalysts that remain unchanged at the end of the reaction. This makes enzymes efficient and reusable. Additionally, enzymes work best under specific temperature and pH conditions, with their activity peaking at the optimum values. Beyond their efficiency, enzymes provide an alternative to polluting chemicals, as they do not produce toxic waste upon degradation. Furthermore, enzymes exhibit high specificity, catalysing only specific reactions or interacting with specific substrates [223]. For instance, desizing enzymes used in cotton processing do not affect the cellulose, preserving the strength of the fabric [12].

The ease of controlling enzyme activity is another advantage, as their performance can be managed by maintaining optimal conditions. Moreover, enzymes are biodegradable, meaning they do not contribute to pollution when their activity is complete, making them a cleaner, more sustainable choice for textile processing [220]. However, effective enzymatic textile processing requires careful attention to enzyme production, purification, and optimisation. Factors such as optimum temperature, pH, process time, enzyme dosage, ionic strength, and the use of co-substrates must be considered to ensure the highest efficiency and effectiveness [220,224].

Enzymatic textile processing presents a promising solution to reduce environmental impact, improve fabric quality, and promote sustainability. However, addressing the challenges related to enzyme specificity, sensitivity, and compatibility is crucial for maximising their potential. With proper optimisation and careful control, enzymatic processing can revolutionise the textile industry, providing an eco-friendly and efficient alternative to traditional chemical-based methods.

8. Conclusions and Future Perspectives

Enzymatic solutions present a compelling avenue for revolutionising the textile industry, offering a sustainable and eco-friendly alternative to traditional chemical treatments. Enzymes such as amylases, pectinases, cellulases, and oxidoreductases have demonstrated their ability to replace hazardous chemicals in critical stages of textile processing—desizing, scouring, bleaching, and finishing. These biocatalysts not only improve fabric quality by enhancing softness, appearance, and durability but also significantly reduce the environmental impact by minimising chemical usage, water consumption, and effluent pollution. Furthermore, enzymes catalyse specific reactions with high selectivity, which ensures precision in textile processing while preserving the integrity of the fabric.

Despite their potential, enzymatic treatments face challenges including substrate specificity and sensitivity to environmental factors like pH, temperature, and the presence of inhibitors, as well as limitations in compatibility with certain surfactants and other additives. Additionally, the high cost of enzyme production and purification remains a constraint, though ongoing advancements in recombinant DNA technology and protein engineering are progressively lowering these barriers. Optimisation of process parameters, such as enzyme concentration, pH, and temperature, is also critical for enhancing enzyme performance and industrial viability.

Future research in enzymatic textile processing holds significant promise for addressing current challenges and advancing the field. Genetic engineering techniques, such as directed evolution, site-directed mutagenesis, and enzyme truncation, offer opportunities to improve enzyme properties, including enhanced stability, thermostability, pH tolerance, surfactant resistance, and substrate specificity. The development of immobilisation technologies could further extend enzyme longevity, improve reusability, and enhance operational efficiency. Additionally, the integration of enzymatic processes with complementary eco-friendly technologies, such as membrane filtration and advanced oxidation processes, could significantly improve the sustainability of textile manufacturing, particularly in the context of wastewater treatment. These advancements would not only optimise the use of enzymes in textile processing but also contribute to a more sustainable and environmentally friendly industry.

Collaboration between academia, industry, and regulatory bodies, coupled with growing consumer demand for sustainable textile products, will accelerate the widespread adoption of enzyme-based technologies. With sustained innovation in enzyme engineering, process optimisation, and integration with complementary technologies, the textile industry has the potential to shift towards a more sustainable and circular economy, significantly reducing its environmental footprint while improving product quality and performance.