Purification of dye wastewater using bicarbonate activated hydrogen peroxide: Reaction process and mechanisms

Insights into the efficient mineralization of antibiotic trimethoprim in aqueous media by Fe2+ catalytically enhanced vacuum-UV irradiation: Kinetics, mechanisms, and toxicity evaluation

The widespread existence of antibiotics in the environment has attracted growing concerns regarding the potential adverse effects on aquatic organisms, ecosystems, and human health even at low concentrations. Extensive efforts have been devoted to developing new methods for effective elimination of antibiotics from wastewater. Herein, a novel process of Fe2+ catalytically enhanced vacuum ultraviolet (VUV) irradiation was proposed as a promising approach for the removal of antibiotic trimethoprim (TMP) in water. Compared with UVC photolysis, VUV photolysis, and UVC/Fe2+, VUV/Fe2+ could increase the pseudo-first-order reaction rate constant of TMP removal by 6.6-38.4 times and the mineralization rate by 36.5%-59.9%. The excellent performance might originate from the synergistic effect of VUV and Fe2+, i.e., VUV irradiation could effectively split water and largely accelerate the Fe3+/Fe2+ cycle to generate more reactive oxygen species (ROS). EPR results indicated that •OH and O2•- were identified as the main ROS in the UVC/Fe2+ and VUV/Fe2+ processes, while •OH, O2•-, and 1O2 were involved in the VUV process. The operating parameters, such as Fe2+ dosage and initial TMP contents, were evaluated and optimized. Up to 8 aromatic intermediates derived from hydroxylation, demethylation, carbonylation, and methylene group cleavage were identified by UPLC-QTOF-MS/MS technique, the possible pathways of TMP degradation were proposed. Finally, the acute and chronic toxicity of intermediates formed during TMP degradation in the VUV/Fe2+ process were also evaluated.

Enhanced activation of persulfate by modified red mud biochar for degradation of dye pollutant: Resource utilization and non-radical activation

The substantial development of the dyeing and printing industry has resulted in an increased discharge of dye wastewater containing a large amount of recalcitrant organic pollutants. Furthermore, the landfill disposal of red mud has led to significant environmental pollution such as soil erosion and groundwater contamination. Therefore, this study aimed to promote the resource utilization of red mud by preparing advanced oxidation catalyst, resulting in effective treatment of dye wastewater, and the primary reaction mechanism was revealed. In this study, biochar-loading red mud (RBC) was applied to activate persulfate (PDS) for the degradation of acid orange 7 (AO7) with the initial concentration of 50 mg L-1. The maximum removal rate of 2.45 mg L·min-1 was achieved in 20 min and corresponding with the removal ratio of 98.0% under the PDS concentration of 20 mM (4.76 g L-1). Eventually, the removal ratio of 99.2% was attained within 60 min. The high catalytic efficiency was probably ascribed to the singlet oxygen (1O2) dominant non-radical pathway and RBC-mediated electron transfer mechanism. It was found that Fe(II), specific surface areas and functional groups on the catalyst were highly related to its catalytic efficiency and passivation. RBC had better reusability due to the loading of biochar and the reduction of zero-valent iron. The non-radical pathway mechanism and electron transfer mechanism were proposed for the activation of PDS, and non-radical pathway played a dominant role. Besides, the degradation pathways and toxicity assessment were analyzed. This research proposed a new electron transfer mechanism for activation process of PDS, which can provide a theoretical support for further studies. Overall, this study demonstrated that catalysts synthesized from red mud and biomass exhibit highly efficient activation in degrading the model pollutant AO7 through PDS activation. The catalyst displayed promising reusability and practical applicability, offering potential advancements in both the resource utilization and reduction of red mud.

Treatment of textile wastewater using the Co(II)/NaHCO3/H2O2 oxidation system

Textile wastewater (TWW) is one of the most hazardous wastewaters for ecosystems when it is discharged directly into water streams without adequate treatment. Some organic pollutants, such as dyes in TWW, are considered refractory compounds that are difficult to degrade using conventional chemical and biological methods. The bicarbonate-activated peroxide (BAP) system is an advanced oxidation process (AOP) based on applying H2O2, which has been demonstrated to be a clean and efficient technology for dye degradation, with the advantage of operating under slightly alkaline pH conditions. In this study, response surface methodology (RSM) based on a central composite design (CCD) was used to optimize the degradation of TWW contaminated with the azo dye Acid Black 194 using the BAP system catalyzed with cobalt ions in solution (Co2+). The analysis of variance (ANOVA) technique was applied to identify significant variables and their individual and interactive effects on the degradation of TWW. The optimum reagent concentrations for degrading TWW at 25 °C and with 45 μM Co2+ were 787.61 and 183.34 mM for H2O2 and NaHCO3, respectively. Under these conditions, complete decolorization (≥99.40), 32.20 % mineralization, and 52.02 % chemical oxygen demand removal were achieved. Additionally, the acute toxicity of textile wastewater before and after oxidation was evaluated with guppy fish (Poecilia reticulata), showing a total reduction in mortality after treatment with the Co2+-BAP system. The Co2+-BAP oxidation system is a potential method for textile wastewater treatment, which, in addition to achieving complete decolorization and partial mineralization, improves biodegradability and reduces the toxicity of the treated water.

Bicarbonate-Hydrogen Peroxide System for Treating Dyeing Wastewater: Degradation of Organic Pollutants and Color Removal

The textile industry is a global economic driving force; however, it is also one of the most polluting industries, with highly toxic effluents which are complex to treat due to the recalcitrant nature of some compounds present in these effluents. This research focuses on the removal of Chemical Oxygen Demand (COD), color, Total Organic Carbon (TOC), and Ammoniacal Nitrogen (N-NH₃) on tannery wastewater treatment through an advanced oxidation process (AOPs) using sodium bicarbonate (NaHCO₃), hydrogen peroxide (H₂O₂) and temperature using a central composite non-factorial design with a surface response using Statistica 7.0 software. All experiments used a 500 mL reactor with 300 mL of tannery wastewater from a company in Cúcuta, Colombia. The physicochemical characterization was done to determine the significant absorbance peaks about the color in the wavelengths between 297 and 669 nm. Statistical analysis found that the concentration of NaHCO₃ affects the removal of color and N-NH₃; however, it did not affect COD and TOC. The optimal process conditions for removing the different compounds under study were: NaHCO₃ 1 M, H₂O₂ 2 M, and 60 °C, with efficiencies of 92.35%, 31.93%, 68.85%, and 35.5% N-NH₃, COD, color, and TOC respectively. It can be concluded that AOPs using H₂O₂ and NaHCO₃ are recommended to remove color and N-NH₃.

Green Photocatalysis of Organic Pollutants by Bimetallic Zn-Zr Metal-Organic Framework Catalyst

A series of bimetallic Zn-Zr metal-organic frameworks (Zn-Zr MOFs) with different Zn:Zr molar ratios has been synthesized via a green hydrothermal method. The structures and morphologies of these photocatalysts have been characterized and analyzed by FTIR, XRD, SEM, and nitrogen adsorption-desorption. The prepared Zn-Zr MOFs had large specific surface areas and pore volumes, favoring the adsorption of pollutant molecules, which in turn led to an improved photocatalytic effect. The photocatalytic activities of the Zn-Zr MOFs under visible light irradiation have been studied towards rhodamine B (RhB) as a target pollutant. The extent of degradation of RhB in a 40 mg/L aqueous solution reached 97.4%. The optimal photocatalyst could also degrade other dyes, suggesting a certain degree of universality.

Accelerated Fenton degradation of azo dye wastewater via a novel Z-scheme CoFeN-g-C3N4 heterojunction photocatalyst with excellent charge transfer under visible light irradiation

A schematic illustration of the photo-Fenton degradation of azo dyes by a Z-scheme CFN-CN1 heterojunction under visible light irradiation.

Rapid SERS inspection of carcinogenic aromatic amines in textiles by using liquid interfacial assembled Au array

Wide uses of azo dyes produce a great risk of high residuals of carcinogenic aromatic amines, and hence it is important to rapidly analyze these carcinogenic compounds in the textile products to guarantee product safety. In the present work, a surface enhanced Raman spectroscopic (SERS) method was developed for rapid detection of carcinogenic aromatic amines in textiles. In this method, target aromatic amines are extracted from textiles, and then gold nanoparticles are added to the organic extractant, which assemble into closely packed Au array at liquid interface in situ. Finally, fingerprint SERS signals of the target aromatic amines are detected on the generated Au array on the basis of strong chemical interaction between the aromatic amines and the Au surface. The proposed method provided good reproducibility with a relative standard deviation of 3.5% for ten parallel tests of benzidine. It was applied to analyze 70 textile products. To strengthen the spectroscopic data processing, a cluster analysis model was established with 50 samples to automatically identify the spectra based on the good signal reproducibility. The other 20 samples were used as test sets to validate this model. It was found that all the positive samples were successfully identified with false positive rate of 20%. With the addition of the Artificial Intelligence step, the reliability of the discriminant results can be ensured.

Remediation of organophosphorus pesticide polluted soil using persulfate oxidation activated by microwave

Contaminated sites from pesticide industry have attracted global concern due to the characteristics of organic pollution with high concentrations and complete loss of habitat conditions. Remediation of organophosphorus pesticide polluted soil using microwave-activated persulfate (MW/PS) oxidation was investigated in this study, with parathion as the representative pesticide. Approximately 90 % of parathion was degraded after 90 min of MW/PS oxidation treatment, which was superior to those by single PS or MW treatment. Relatively greater performances for parathion degradation were obtained in a relatively larger PS dosage, higher microwave temperature, and lower organic matter content. Appropriate soil moisture favored parathion degradation in soil. SO₄^-, OH, O₂^-, and ¹O₂ generated in the MW/PS system all contributed to parathion degradation. Multiple spectroscopy analyses indicated that PO and PS bonds in parathion were destroyed after MW/PS oxidation, accompanied by generation of hydroxylated and carbonylated byproducts. The soil safety after parathion degradation was assessed via model prediction. Furthermore, MW/PS oxidation also exhibited great performance for degradation of other organophosphorus pesticides, including ethion, phorate, and terbufos.

Oxygen doped graphitic carbon nitride nanosheets for the degradation of organic pollutants by activating hydrogen peroxide in the presence of bicarbonate in the dark

The development of novel wastewater treatment processes that use heterogeneous catalysts to activate hydrogen peroxide (H2O2) with bicarbonate (HCO3 -) has been a subject of great interest in recent years; however, significant challenges remain, despite research into numerous metal-based catalysts. The work presented herein employed oxygen-doped graphitic carbon nitride (O/g-C3N4) as a non-metal catalyst for activating H2O2 in the presence of HCO3 -, and this method represented the first system capable of removing organic pollutants in the dark, to our knowledge. The catalysts were characterized using several microscopic imaging, spectroscopic, electrochemical, and crystallographic techniques, as well as N2-physorption procedures. Analysis of the results revealed that the O/g-C3N4 catalyst possessed a high specific surface area and many defect sites. Various operational parameters, including the relative amounts of HCO3 -, H2O2, and O/g-C3N4, were systemically investigated. A clear performance enhancement was observed in the degradation of organic contaminants when subjected to the HCO3 --H2O2-O/g-C3N4 system, and this result was ascribed to the synchronous adsorption and chemical oxidation processes. The novel system presented herein represented a new water treatment technology that was effective for removing organic contaminants.