Electrochemical stripping of cotton fabrics dyed with Reactive Black 5 in water and wastewater

Textile Recycling's Hidden Problem: Surface-Modified Fiber Fragments Emitted at Every Stage

Chemical recycling methods for post-consumer textile waste are effective for sustainable textile waste management. However, recycling synthetic and blended (cotton and synthetic) textiles can contribute to the release of microplastic fibers (MPFs) into the environment. This study investigated MPF release across different stages of two chemical recycling approaches, acid and alkaline hydrolysis, of polyester/cotton-blended textiles. Recycling involves various stages, including dye removal, treatment stage, and product. In the treatment stage, acid hydrolysis breaks down cotton into cellulose, leaving the polyester (PET) intact, whereas alkaline hydrolysis degrades PET, allowing cotton recovery. Across all stages, dye removal generated the highest MPF count, averaging nearly 10,055 MPFs g-1 of textile waste. Statistical analysis confirmed that the recycling approach significantly affected MPF release (p < 0.05), whereas the fabric type did not (p > 0.05). Alkaline hydrolysis reduced MPF release during the treatment stage by 87.55% compared to acid hydrolysis, indicating that recovering cotton and chemically degrading PET can significantly minimize MPF emissions during recycling. Ridge regression analysis identified the reaction conditions as key factors in MPF fragmentation, with blend ratios influencing the number of released MPFs. Surface characterization revealed treatment-induced fiber alterations, raising concerns regarding MPF emissions throughout the process. These findings highlight the textile recycling industries can be a source of MPF release into the environment, but recovering PET through degradation or dissolution can help minimize this impact of the treatment stage.

Electrocatalytic degradation of nitrogenous heterocycles on confined particle electrodes derived from ZIF-67

Nitrogen-containing heterocyclic compounds (NHCs) are hazardous, toxic, and persistent pollutants, thereby requiring urgent solutions. Herein, ZIF-67 was compounded with powder-activated carbon (PAC) to prepare Co/NC/PAC (NC i.e. nitrogen-doped carbon) particle electrodes for the electrocatalytic treatment of pyridine and diazines. Co/NC/PAC reflected the confinement of Co3O4/CoN/Co0 into the N-doped graphitic-carbon layer to generate both pyrrolic-N and graphitic-N active sites. Under the optimal conditions (0.3 A, 12 mL min-1, and initial pH 7.00), the degradation of four NHCs realized 90.2-93.7% efficiencies. The number and position of N atoms in NHCs directly affected the degradation efficiency. The following increasing order of facilitated degradation was recorded: pyridazine < pyrimidine < pyrazine < pyridine. The as-obtained Co/NC/PAC possessed the direct redox effect on NHCs, achieving fast electrocatalytic rate. Species like ·OH and H* were detected in Co/NC/PAC system with contributions to NHCs degradation estimated to 24% and 34%, respectively. Density functional theory (DFT) calculations revealed H* susceptible to attacking the N position, while the meta-position of C was subject to hydroxyl radical (·OH) addition. Overall, degradation of NHCs was achieved by hydro-reduction, oxidation, ring opening cleavage, hydroxylation, and mineralization. Ring-cleavage and mineralization of NHCs provided a novel electrochemical strategy to refractory wastewater treatment.

Variation of current density with time as a novel method for efficient electrochemical treatment of real dyeing wastewater with energy savings

Electro-oxidation is a promising technology for wastewater treatment with biorefractory organic and nitrogen pollutants; however, the high energy demand hinders its wide application. In this study, a novel method by regulating significant parameter during the electro-oxidation process in a timely manner for real dyeing wastewater treatment with energy savings was studied. Operating factors (i.e., flow rate, initial pH value, electrode distance, and current density) were investigated for chemical oxygen demand (COD) and ammonia removal, and the results indicated that current density was the key factor that obviously influenced the electrochemical performance. Indirect oxidation by active chlorine was then confirmed as the main reaction pathway for pollutant oxidation, and the relationship between the current density and the generation of active chlorine was established, suggesting that a large part of the generated active chlorine was not utilized effectively. Subsequently, a novel method of varying the current density in a timely manner based on the reaction mechanism was proposed; the results indicated that, with similar pollutant removal efficiencies, energy consumption could be reduced from 31.6 to 20.5 kWh/m3. Additionally, the novel system was further optimized by Box-Behnken design: The COD removal efficiency could reach 71.8%, and the energy demand could be reduced by 45.6%.

Environmental Profile Study of Ozone Decolorization of Reactive Dyed Cotton Textiles by Utilizing Life Cycle Assessment

Research approaches on the use of ecotechnologies like ozone assisted processes for the decolorization of textiles are being explored as against the conventional alkaline reductive process for the color stripping of the cotton textiles. The evaluation of these ecotechnologies must be performed to assess the environmental impacts. Partial “gate to gate” Life Cycle Assessment (LCA) was implemented to study the ozone based decolorization process of the reactive dyed cotton textiles. Experiments were performed to determine input and output data flows for decolorization treatment of reactive dyed cotton textile using the ozonation process. The functional unit was defined as “treatment of 40 g of reactive dyed cotton fabric to achieve more than 94% color stripping”. Generic and specific data bases were also used to determine flows, and International Life Cycle Data system (ILCD) method was selected to convert all flows into environmental impacts. The impact category “Water resource depletion” is the highest for all the ozonation processes as it has the greatest relative value after normalization amongst all the impact indicators. Electricity and Oxygen formation were found to be the major contributors to the environmental impacts. New experimental conditions have been studied to optimize the impacts.

Application of Ozone Treatment for the Decolorization of the Reactive-Dyed Fabrics in a Pilot-Scale Process—Optimization through Response Surface Methodology

The decolorization of a cotton fabric dyed with a reactive dye (C.I. Reactive Black 5) was studied using an optimized ozone-assisted process at pilot scale. Box–Behnken design was used to evaluate the effects of three parameters on the decolorization of the dyed textile, namely, pH of the treatment (3–7), ozone concentration (5–85 g/m3 of ozone), and treatment time (10–50 min). The fitted mathematical model allowed us to plot response surfaces as well as isoresponse curves and to determine optimal decolorization conditions. In this study, we have proposed a pilot-scale machine which utilizes ozone for the color stripping of the dyed cotton. This pilot-scale application opens up the route for application of ozone at an industrial scale for achieving sustainability in the textile industry.