Exploring Textile Effluent treatment Techniques to make Water drinkable

The Indian textile industry plays a vital role in the supply chain and marketing of garments and diverse handloom products, thereby strengthening India's commercial position in the global market. The exceptional performance of textiles in the regions of Gujarat, Tamil Nadu, Maharashtra, Rajasthan, Madhya Pradesh, and Punjab in terms of woollen production facilities. According to the Annual Survey of Industries (ASI), 23.6% of the textile sector in Gujarat exhibits high levels of production. 

 

 

Textile industries generate a large volume of complex effluents during the processing of clothes, and before discharging, which is a high organic and inorganic effluent load on the environment. Azo, Benzo, Cationic, Xanthene, a group of dyes that are effective in our humanity and the abiotic life cycle. According to the Central Pollution Control Board (CPCB) survey, 92 million tons of effluent were generated in FY23-24. This wastewater often shows high TDS, salinity, alkalinity, and electrical conductivity, primarily originating from salt-intensive dyeing processes. Additionally, textile wastewater contains heavy metals (Cr, Cu, Ni, Zn), formaldehyde-based resins, and chlorinated compounds, posing ecotoxicological and human health risks. Some of the most carcinogenic groups of dyes are the reactive dyes, which are harmful and highly soluble in water molecules, for example, RB21 (Reactive Turquoise Blue 21) dye. The general molecule's formula is C₄₀H₂₅CuN₉O₁₄S₅, represents a copper phthalocyanine reactive dye with multiple functional groups (nitrogen heterocycles, sulfonic groups) around a central Cu atom. Typically contains reactive vinyl sulfonyl (–SO₂–CH=CH₂) or sulfatoethylsulphonyl groups that can form covalent bonds with hydroxyl (–OH) groups of cellulose fibres during the dying process. One of the most advanced research studies was successfully published in a reputed journal, which one is the advance solutions to degrade this carcinogenic pollutant by using the AOPs (Advance Oxidation Processes) technique. 

Catalyst is the altering the rate of the reaction. One of the most susceptible, highly active, emerging, and advanced materials in the presence of visible light also enhances COD, BOD, and DO rates to make water drinkable. Recent breakthroughs to mineralise faster RB21 with the combination of materials with hybrid techniques like Photocatalyst+Ultrasonication, UV+Ozonation,  Corona Discharge Plasma with Fe2+ addition,n etc. 

    

Method	Approx. RB21 Removal	Notes
Corona plasma + Fe²⁺	~100% color removed, ~83 % COD ↓	Advanced oxidation
Photo‑ozonation	~99 %	Very short reaction times
SmFeO₃‑rGO + ultrasound	High degradation (faster)	Effective on the actual effluent
Fly ash adsorption	Moderate capacity (~105 mg g⁻¹)	Very low cost
Photocatalysis with MgFe2O4	93 %  removal rate	AOP, low cost

Figure 1: Advance Oxidation Process (AOPs) Techniques performance over RB21 dye degradation (Predictive analysis) (a) Various AOPs Utilised for RB21 dye (b) Concentration variation over RB21 with Vis. + H2O2

Figure 1 assumes a RB21 dye concentration of 25 ppm, utilising AOPs techniques, including ozonation, photocatalysis, photo-Fenton, and UV and Vis light irradiation with H₂O₂ as an oxidant to break the interaction between the dye and H₂O molecules. 

Azo bond is extremely ozone-sensitive -N=N- bond undergoes rapid cleavage, R-N=N-R + Ozone to form aromatic amines with smaller fragments. When using ozonation, one ozone molecule can break chromophoric structure, leading to rapid decolourisation, but at high concentrations of RB21,

Ozone ​+ OH− → •OH + O2​

$$•OH + \text{RB21} \rightarrow \text{fragmented intermediates}$$

$$\text{Why its happening, ozonation destroys chromophores first, and some aromatic fragments remain due to not destroyed completely, like sulfonated benzene/naphthalene derivatives. It becomes colourless but lack of degradation onto benzene rings. Why aromatic fragments are hard to remove becausethey have resonance stability and can react with ozone slowly in the presence of hydroxyl radicals. }$$

An Innovative Plant-Based Hydrogel Module Employing a Bio-Authentic Strategy for Agricultural Waste Reduction

The title outlines a study focused on developing a sustainable system for creating high-performance hydrogel modules from agricultural waste, such as rice straw, sugarcane bagasse, and maize stover, to achieve better water retention and nutrient delivery, a design concept known as the "Bio-Authentic Strategy" imitates natural biological systems, such as the plant's own vascular system.

1. Core Concept: The "Bio-Authentic" Strategy

Petroleum-based polymers are frequently used in conventional synthetic hydrogels. Two things are given priority in a bio-authentic approach: replicating the three-dimensional structure of plant tissues (xylem/phloem) to enable effective capillary action, and water storage is known as structural mimicry.

Utilising naturally occurring polymers, primarily cellulose, hemicellulose, and lignin, derived from waste materials, ensures the complete biodegradability and chemical compatibility of the final product with the soil ecosystem.

2. Transforming Agricultural Waste

The module examines the "waste to wealth" cycle by processing standard field residues.

• Feedstock: Sugarcane bagasse, wheat straw, fruit peels, dry fruit peels, and other biomass-based materials, which are cellulosic, hemicellulosic, and lignin. 
• Extraction: Cellulose is isolated via alkali treatment or green solvents (ionic liquids).
• Synthesis: Biodegradable agents, such as citric acid, or physical methods, like freeze-thaw cycles, are employed to cross-link the cellulose, thereby yielding a porous and highly absorbent network.

3. Key Benefits in Agriculture

These plant-based modules act as "mini-reservoirs" buried near the root zone, providing several advantages.

4. Current State-of-the-Research (2024–2025)

Recent breakthroughs in this field focus on "smart" hydrogel in reports. These are designed to respond to specific environmental triggers:

• pH-Responsive: releasing stored water only when the soil reaches a certain acidity/alkalinity level.
• Temperature-triggered: expanding or contracting based on soil heat to manage moisture during heatwaves.
• Nano-Reinforcement: Adding nanocellulose (CNCs) to the module to increase its mechanical strength, allowing it to withstand the pressure of heavy soil without collapsing.
• Note on Sustainability: This strategy aligns with the Circular Bioeconomy, as it prevents the open burning of agricultural waste (reducing CO2 and particulate emissions) while simultaneously tackling water scarcity.

From a chemical standpoint, plant-based hydrogels exploit naturally occurring biopolymers—primarily cellulose, hemicellulose, pectin, starch, alginate, and lignin—which possess abundant hydroxyl (–OH), carboxyl (–COOH), and ether (–O–) functional groups. These functionalities enable crosslinking, swelling, ion exchange, and biodegradation, making them ideal matrices for waste reduction and reuse strategies.

Chemical Basis of Plant-Based Hydrogel Formation

2.1 Raw Material Chemistry

Agricultural residues (e.g., rice straw, sawdust, sugarcane bagasse, fruit peels) are chemically composed of:

• Cellulose (β-1,4-linked D-glucose units) – primary structural polymer
• Hemicellulose – branched polysaccharides enhancing flexibility
• Lignin (phenolic polymer) – contributes mechanical strength and hydrophobicity
• Pre-treatment methods such as alkaline treatment (NaOH), acid hydrolysis (H₂SO₄), or enzymatic delignification are used to expose reactive functional groups and improve polymer accessibility.

2.2 Hydrogel Network Formation

Hydrogel synthesis involves the creation of a three-dimensional polymeric network capable of retaining large volumes of water. This can be achieved via:

a) Physical Crosslinking 

• Hydrogen bonding
• Ionic interactions (e.g., Ca²⁺ crosslinking of alginate) - Freeze–thaw cycles

b) Chemical Crosslinking

• Esterification (citric acid, tartaric acid)
• Radical polymerisation (initiators such as APS)
• Schiff base reactions (–CHO and –NH₂ groups)
• A bio-authentic strategy emphasises non-toxic, biodegradable crosslinkers, avoiding synthetic agents like glutaraldehyde.

3. Experimental Methodology

3.1 Extraction of Biopolymers

• Mechanical size reduction of agricultural waste
• Chemical pretreatment (alkaline or acid hydrolysis)
• Washing and neutralisation
• Drying and pulverisation
• Polymer isolation (cellulose/pectin/starch extraction)

3.2 Hydrogel Synthesis

• A typical experimental route includes:
• Dissolution of plant-derived polymer in aqueous medium
• Controlled addition of natural crosslinker
• Heating or stirring under inert/ambient conditions
• Gelation and curing
• Washing to remove unreacted components
• The resulting hydrogel module can be moulded into films, beads, blocks, or layered composites, depending on the application.

4. Characterisation Techniques

• To validate chemical structure and performance:
• FTIR – confirmation of functional group interactions and crosslinking
• XRD – crystallinity changes after gel formation
• SEM – porous network morphology
• Swelling studies – water retention and kinetics
• Thermal analysis (TGA/DSC) – thermal stability
• Biodegradability tests – soil burial or enzymatic degradation

5. Agricultural Waste Reduction Mechanism

• The hydrogel module contributes to waste reduction through:
• Upcycling agricultural residues into value-added materials
• Water retention and controlled nutrient release in soil, reducing irrigation demand
• Carrier matrices for compost nutrients or microbial consortia
• Biodegradable soil amendments, eliminating secondary pollution
• As the hydrogel degrades, it releases organic carbon and nutrients, closing the agricultural material loop.

6. Bio-Authentic Strategy and Sustainability

• The bio-authentic approach ensures:
• Renewable feedstocks
• Green chemistry principles
• Non-toxic synthesis pathways
• Complete environmental assimilation after use
• This strategy aligns with circular economy models, where agricultural waste is not discarded but transformed into functional materials supporting sustainable farming systems.

7. Conclusion

The development of an innovative plant-based hydrogel module represents a chemically robust and experimentally viable solution for agricultural waste reduction. By integrating plant biopolymer chemistry with eco-friendly crosslinking and scalable experimental techniques, this approach offers a sustainable, biodegradable, and multifunctional platform with strong potential for agricultural and environmental applications.

Mo