Reuse of Textile Dyeing Wastewater Treated by Electrooxidation

At a Glance

Metadata	Details
Publication Date	2022-03-29
Journal	Water
Authors	Cláudia Pinto, Annabel Fernandes, Ana Lopes, Maria João Nunes, Ana Baía
Institutions	University of Beira Interior
Citations	17
Analysis	Full AI Review Included

Executive Summary

This study validates the feasibility of using Electrochemical Oxidation (EO) with a Boron-Doped Diamond (BDD) anode to treat textile dyeing wastewater (TDW) for consecutive reuse, focusing on resource recovery and ecotoxicity reduction.

Core Value Proposition: The BDD EO process enables the reuse of TDW in subsequent dyeing baths while achieving complete recovery of the high sulfate salt content, eliminating the need for fresh salt addition.
Quality Achieved: Treated TDW met both moderate-quality (COD < 200 mg L^-1 @ 60 mA cm^-2) and high-quality (COD ≤ 50 mg L^-1 @ 100 mA cm^-2) requirements for textile reuse after 10 hours of treatment.
Dyeing Performance: Fabrics dyed using both moderate- and high-quality treated water achieved a Total Color Difference (ΔE*) of 1.0 or less, complying with the most restrictive industry controls.
Consecutive Reuse: The process proved effective for two consecutive reuse cycles. Higher organic load removal was observed during the second EO treatment due to increased initial organic concentration.
Ecotoxicity Mitigation: EO treatment resulted in a drastic ecotoxicity reduction towards Daphnia magna, achieving up to an 18.6-fold reduction, ensuring that toxicity does not accumulate severely across reuse cycles.
Efficiency Conclusion: High-quality water (COD ≤ 50 mg L^-1) is not strictly necessary; moderate-quality water (COD < 200 mg L^-1) is sufficient for effective wool dyeing reuse.

Technical Specifications

Parameter	Value	Unit	Context
Anode Material	Si/BDD	-	Commercial Boron-Doped Diamond
Cathode Material	Stainless Steel	-	-
Electrode Area	10	cm²	Immersed area per electrode
Inter-electrode Gap	1	cm	-
Applied Current Density (j)	60 and 100	mA cm^-2	EO treatment conditions
Treatment Duration	10	h	Per EO cycle
Initial TDW COD	5.8 x 10³	mg L^-1	Before 1^st EO treatment
Final COD (Moderate Quality)	159	mg L^-1	After 1^st EO @ 60 mA cm^-2
Final COD (High Quality)	46	mg L^-1	After 1^st EO @ 100 mA cm^-2
Max Ecotoxicity Reduction	18.6-fold	-	After 2^nd EO @ 100 mA cm^-2
Total Color Difference (ΔE*)	1.00 to 1.04	-	1^st Reuse Cycle (meets control requirement of 1.0)
Sulfate Ion Concentration	Unchanged	mg L^-1	Maintained across all EO treatments
Final pH (100 mA cm^-2)	11.4 ± 0.1	-	After 1^st EO treatment (Corrected to pH 4.5 for reuse)
Final Electrical Conductivity (100 mA cm^-2)	4.31 ± 0.03	mS cm^-1	After 1^st EO treatment (Salinity preserved)

Key Methodologies

The study utilized a two-cycle reuse strategy involving dyeing, EO treatment, and subsequent reuse, focusing on wool fabric and acid dyes.

Wastewater Source: TDW was generated from dyeing 100% wool twill fabric (351.6 g m^-2) using a trichromatic combination of Nylosan acid dyes (Red, Yellow, Blue) at a 1:50 fabric:bath ratio.
Dye Bath Composition: The bath included sodium sulfate (1 g L^-1), equalizer agent (Sarabid PAW), humectant agent (SERA WET C-NR), and was buffered to pH 4.5 using acetic acid/sodium acetate.
Electrochemical Setup: Treatment was conducted in a batch, undivided cylindrical cell (250 mL) with continuous stirring (300 rpm).
Electrode Configuration: A commercial Si/BDD anode and a stainless-steel cathode were used, each with an immersed area of 10 cm² and a 1 cm inter-electrode gap.
Treatment Conditions: EO was performed for 10 hours at two current densities: 60 mA cm^-2 and 100 mA cm^-2. Five assays were run for each condition, and the treated water was combined for reuse.
Reuse Cycle Preparation: The treated TDW was used to prepare the subsequent dyeing baths. Crucially, no additional sodium sulfate salt was added, relying entirely on the recovered salt content. Fresh water was only added to compensate for volume loss (adsorption/evaporation).
Analytical Assessment: Performance was monitored via COD, DOC, UV-vis spectrophotometry (for dye removal), ion chromatography (for sulfate), and ecotoxicity testing using the Daphnia magna acute immobilization test (OECD Guideline 202).
Fabric Quality Control: Dyed wool fabrics were evaluated using the CIELab system to determine Total Color Difference (ΔE*) relative to the control fabric (dyed with fresh water), and color fastness to washing (ISO standards).

Commercial Applications

The findings support the implementation of BDD-based EO systems in industrial settings focused on sustainability and resource efficiency.

Textile Industry (Wool/Acid Dyes): Direct implementation for treating and recycling dyeing wastewater, enabling significant water savings and achieving zero liquid discharge (ZLD) targets.
Salt Recovery and Cost Reduction: Applicable in processes requiring high salt concentrations (e.g., reactive dyeing), allowing complete recovery and reuse of expensive electrolytes (like sodium sulfate), reducing chemical purchasing and disposal costs.
High-Salinity Wastewater Treatment: BDD EO is highly effective for mineralizing complex organic pollutants in saline matrices where conventional biological treatments fail or struggle.
Ecotoxicity Management: Use as a final polishing step for industrial effluents to ensure compliance with strict environmental discharge limits regarding toxicity, even when treating complex, multi-component waste streams.
Advanced Oxidation Process (AOP) Systems: Commercialization of modular BDD reactor units for decentralized treatment of specific, highly contaminated waste streams within a factory (stream separation strategy).

View Original Abstract

Wastewater reuse has been addressed to promote the sustainable water utilization in textile industry. However, conventional technologies are unable to deliver treated wastewater with the quality required for reuse, mainly due to the presence of dyes and high salinity. In this work, the feasibility of electrooxidation, using a boron-doped diamond anode, to provide treated textile dyeing wastewater (TDW) with the quality required for reuse, and with complete recovery of salts, was evaluated. The influence of the applied current density on the quality of treated TDW and on the consecutive reuse in new dyeing baths was studied. The ecotoxicological evaluation of the process towards Daphnia magna was performed. After 10 h of electrooxidation at 60 and 100 mA cm−2, discolorized treated TDW, with chemical oxygen demand below 200 (moderate-quality) and 50 mg L−1 (high-quality), respectively, was obtained. Salt content was unchanged in both treatment conditions, enabling the consecutive reuse without any salt addition. For the two reuse cycles performed, both treated samples led to dyed fabrics in compliance with the most restrictive controls, showing that an effective consecutive reuse can be achieved with a moderate-quality water. Besides the water reuse and complete salts saving, electrooxidation accomplished an ecotoxicity reduction up to 18.6-fold, allowing TDW reuse without severe ecotoxicity accumulation.

Tech Support

Original Source

DOI: https://doi.org/10.3390/w14071084

References

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2018 - Application of a planar falling film reactor for decomposition and mineralization of methylene blue in the aqueous media via ozonation, Fenton, photocatalysis and non-thermal plasma: A comparative study [Crossref]
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