Aromatic amine contents, component distributions and risk assessment in sludge from 10 textile-dyeing plants

Low-cost optimization of industrial textile landfill sludge re-dewatering using ferrous sulfate and blast furnace slag

This study was based on an industrial sludge landfill with a scale of 1 million cubic meters, which had been filled for more than 10 years. It focused on the secondary dewatering of industrial textile landfill sludge (LS) with a total organic carbon (TOC) content greater than 50% and a volatile suspended solids to suspended solids (VSS/SS) ratio of 0.59. A response surface methodology (RSM) model was established using the coagulant ferrous sulfate (FeSO4) and conditioning agents such as hydrated magnesium oxide (MgO), blast furnace slag (BFS), and calcium oxide (CaO). By solving the RSM equations for the respective indicators, the optimal dosages of FeSO4, MgO, and BFS were determined to be 90 mg/g of dry sludge (DS), and for CaO 174.85 mg/g DS. Further examinations of the dewatering performance, apparent properties, extracellular polymeric substances (EPS) components, rheological characteristics, moisture distribution, and pollutant content variation led to the development of a green waste-based dewatering agent composed of FeSO4 and BFS. In small-scale diaphragm plate and frame filter press tests, the optimal water content (WC) was 69.11%. In the final production-scale experiments, it was 65.72%, with the actual application cost being only 13.07 $/ton DS. Additionally, when FeSO4 and BFS were used together, the combined action of Fe and Si could significantly reduce the biotoxicity of heavy metals (HMs), cut down 75.2% of the LS's TOC, and effectively reduced the leaching of organic substances from the leachate, which was beneficial for subsequent disposal. In conclusion, the combined use of FeSO4 and BFS for the secondary dewatering of industrial textile LS was economically efficient, effective in dewatering, and had significant harm reduction effects, making it a worthwhile for waste treatment.

Characteristics and health risks of population exposure to phthalates via the use of face towels

The production of face towels is growing at an annual rate of about 4% in China, reaching 1.13 million tons by 2021. Phthalates (PAEs) are widely used in textiles, and face towels, as an important household textile, may expose people to PAEs via the skin, further leading to health risks. We collected new face towels and analyzed the distribution characterization of PAEs in them. The changes of PAEs were explored in a face towel use experiment and a simulated laundry experiment. Based on the use of face towels by 24 volunteers, we calculated the estimated daily intake (EDI) and comprehensively assessed the hazard quotient (HQ), hazard index (HI), and dermal cancer risk (DCR) of PAEs exposure in the population. PAEs were present in new face towels at total concentrations of <MDL-2388 ng/g, with a median of 173.2 ng/g, which was a lower contamination level compared with other textiles. PAE contents in used face towels were significantly higher than in new face towels. The concentrations of PAEs in coral velvet were significantly higher than those in cotton. Water washing removed some PAEs, while detergent washing increased the PAE content on face towels. Gender, weight, use time, and material were the main factors affecting EDI. The HQ and HI were less than 1, which proved PAEs had no significant non-carcinogenic health risks. Among the five target PAEs studied, DEHP was the only carcinogenic PAE and may cause potential health risks after long-term exposure. Therefore, we should pay more attention to DEHP.

Nanobiohybrids: Synthesis strategies and environmental applications from micropollutants sensing and removal to global warming mitigation

Micropollutants contamination and global warming are critical environmental issues that require urgent attention due to natural and anthropogenic activities posing serious threats to human health and ecosystems. However, traditional technologies (such as adsorption, precipitation, biodegradation, and membrane separation et al.) are facing challenges of low utilization efficiency of oxidants, poor selectivity, and complex in-situ monitoring operations. To address these technical bottlenecks, nanobiohybrids, synthesized by interfacing the nanomaterials and biosystems, have recently emerged as eco-friendly technologies. In this review, we summarize the synthesis approaches of nanobiohybrids and their utilization as emerging environmental technologies for addressing environmental problems. Studies demonstrate that enzymes, cells, and living plants can be integrated with a wide range of nanomaterials including reticular frameworks, semiconductor nanoparticles and single-walled carbon nanotubes. Moreover, nanobiohybrids demonstrate excellent performance for micropollutant removal, carbon dioxide conversion, and sensing of toxic metal ions and organic micropollutants. Therefore, nanobiohybrids are expected to be environmental friendly, efficient, and cost-effective techniques for addressing environmental micropollutants issues and mitigating global warming, benefiting both humans and ecosystems alike.

Investigating Bio-Inspired Degradation of Toxic Dyes Using Potential Multi-Enzyme Producing Extremophiles

Biological treatment methods overcome many of the drawbacks of physicochemical strategies and play a significant role in removing dye contamination for environmental sustainability. Numerous microorganisms have been investigated as promising dye-degrading candidates because of their high metabolic potential. However, few can be applied on a large scale because of the extremely harsh conditions in effluents polluted with multiple dyes, such as alkaline pH, high salinity/heavy metals/dye concentration, high temperature, and oxidative stress. Therefore, extremophilic microorganisms offer enormous opportunities for practical biodegradation processes as they are naturally adapted to multi-stress conditions due to the special structure of their cell wall, capsule, S-layer proteins, extracellular polymer substances (EPS), and siderophores structural and functional properties such as poly-enzymes produced. This review provides scientific information for a broader understanding of general dyes, their toxicity, and their harmful effects. The advantages and disadvantages of physicochemical methods are also highlighted and compared to those of microbial strategies. New techniques and methodologies used in recent studies are briefly summarized and discussed. In particular, this study addresses the key adaptation mechanisms, whole-cell, enzymatic degradation, and non-enzymatic pathways in aerobic, anaerobic, and combination conditions of extremophiles in dye degradation and decolorization. Furthermore, they have special metabolic pathways and protein frameworks that contribute significantly to the complete mineralization and decolorization of the dye when all functions are turned on. The high potential efficiency of microbial degradation by unculturable and multi-enzyme-producing extremophiles remains a question that needs to be answered in practical research.

Oxidation of simulated wastewater by Fe2+-catalyzed system: The selective reactivity of chlorine radicals and the oxidation pathway of aromatic amines

Aromatic amines (AAs), a characteristic pollutant with electron-donating groups in textile industry, having high reactivity with reactive chlorine free radicals, is probably the precursor of chlorinated aromatic products in advanced oxidation treatment. In this study, Fe2+/peroxydisulfate (PDS)/Cl- and Fe2+/H2O2/Cl-systems were used to treat four kinds of AAs (5-Nitro-o-toluidine (NT), 4-Aminoazobenzol (AAB), O-Aminoazotoluene (OAAT), 4,4'-Methylene-bis(2-chloroaniline) (MBCA)) in simulated wastewater, and the selectivity of various reactive species to AAs, the oxidation law and pathway of AAs were explored. The results showed that dichloride anion radical (Cl2·-) could effectively oxidize four AAs, and chlorine radical (·Cl) was strongly reactive to AAB and MBCA, especially MBCA. The largest f - (Fukui function) of MBCA is 0.0822, which is the lowest of the four AAs, so ·Cl might be more sensitive to electrophilic point than hydroxyl radical (·OH). The oxidation pathway of NT and MBCA showed that ·Cl mainly played the role of electron transfer to AAs instead of generating chlorinated products, but the addition of ·OH to -NH2 generated aromatic nitro compounds with higher toxicity than NT and MBCA. Therefore, the electron transfer of ·Cl and Cl2·- could not only improve the removal of AAs but also reduce the generation of toxic products. This study found that the reactivity of reactive chlorine free radicals was not necessarily related to chlorination, which provided a theoretical basis for the further studies into the formation mechanism of chlorination products.

Formation of organic chloride in the treatment of textile dyeing sludge by Fenton system

In the oxidation treatment of textile dyeing sludge, the quantitative and transformation laws of organic chlorine are not clear enough. Thus, this study mainly evaluated the treatment of textile dyeing sludge by Fenton and Fenton-like system from the aspects of the influence of Cl^-, the removal of polycyclic aromatic hydrocarbons (PAHs) and organic carbon, and the removal and formation mechanism of organic chlorine. The results showed that the organic halogen in sludge was mainly hydrophobic organic chlorine, and the content of adsorbable organic chlorine (AOCl) was 0.30 mg/g (dry sludge). In the Fenton system with pH=3, 500 mg/L Cl^-, 30 mmol/L Fe²⁺ and 30 mmol/L H₂O₂, the removal of phenanthrene was promoted by chlorine radicals (•Cl), and the AOCl in sludge solid phase increased to 0.55 mg/g (dry sludge) at 30 min. According to spectral analysis, it was found that •Cl could chlorinate aromatic and aliphatic compounds (excluding PAHs) in solid phase at the same time, and eventually led to the accumulation of aromatic chlorides in solid phase. Strengthening the oxidation ability of Fenton system increased the formation of organic chlorines in liquid and solid phases. In weak acidity, the oxidation and desorption of superoxide anion promoted the removal and migration of PAHs and organic carbon in solid phase, and reduced the formation of total organic chlorine. The Fenton-like system dominated by non-hydroxyl radical could realize the mineralization of PAHs, organic carbon and organic chlorines instead of migration. This paper builds a basis for the selection of sludge conditioning methods.

Aromatic amines leachate from cigarette butts into aquatic environments: Is there risk for water organisms?

There are many toxics, such as aromatic amines (AAs), in cigarette butts (CBs). As CBs are the most abundant litter worldwide, these chemicals may leach into water bodies. In the present work, for the first time, the levels of AAs leachates from CBs in distilled water (DW) and river water (RW) samples were evaluated at different exposure times ranging from 15 min to 30 days. The mean leachate levels of AAs in DW and RW samples were in the range of 0.2-566 and 0.2-596 ng L^-1, respectively, with overall mean values of 569 and 556 ng L^-1. There was no significant difference (p > 0.05) between the total AAs levels as well as the level of each examined AA in DW and RW samples. Aniline (ANL) had the highest leaching rate from CBs into water. The mean leachates of AAs from CBs into water were ranked as: ANL> 1-naphthylamine (1-NA)> 2-naphthylamine (2-NA) > 2,6-dimethylaniline (2, 6-DMA)> ∑toluidine (∑TOL)> o-anisidine (o-ASD)> ∑aminobiphenyl (∑ABP). Ecological risk assessment showed that ∑7AAs, ANL, p-TOL, o-TOL, 2-NA, and ∑ABP had medium risks to sensitive crustaceans and fish. As AAs are not the only hazardous chemicals which may leach from CBs into aquatic environments, restrictions on littering CBs into the environment are required due to the release of different toxics ultimately causing adverse effects on aquatic organisms.

Occurrence of primary aromatic amines and nicotine in sediments collected from the United States

Despite extensive use of primary aromatic amines (AAs) in consumer products, little is known about their occurrence in the environment. In this study, we investigated the occurrence of 14 AAs and nicotine in 75 sediment samples collected from seven estuarine and freshwater ecosystems in the Unites States. Additionally, risk quotients (RQs) were calculated to assess potential risks of these chemicals to aquatic organisms. Of the 14 AAs analyzed, seven of them were found in sediments. The sum concentrations of seven AAs in sediments were in the range of 10.2 to 1810 ng/g, dry wt (mean: 388 ng/g). Aniline was the most abundant compound, accounting for, on average, 53 % of the total concentrations. Nicotine was found in sediments at a concentration range of <LOQ to 1340 ng/g, dry wt (mean: 119 ng/g). Among the seven sampling locations studied, AAs and nicotine concentrations were the highest in sediment from Altavista wastewater lagoon in Virginia (AV, mean: 1700 ng/g) followed in descending order by Chicago Sanitary and Ship Canal (CSSC, mean: 807 ng/g), Indiana Harbor and Ship Canal (IHSC, mean: 698 ng/g) and New Bedford Harbor (NBH, mean: 482 ng/g). Sediments from the upper Mississippi River (MISS, mean: 63.4 ng/g) and Tittabawassee River (TBR, mean: 52.3 ng/g) contained the lowest concentrations. The RQ values for AAs in sediment ranged from 0 to 733 and that for nicotine ranged from 0 to 2060. Among AAs, the highest RQ value was found for 4-chloroaniline. Nicotine exhibited notable RQ values, which suggested risk from this chemical to aquatic organisms. This is the first study to report the occurrence of AAs in sediments and our results suggest the need for further investigations on the sources and ecological impacts of these chemicals in aquatic ecosystems.

Synergistic role of bacterial consortium to biodegrade toxic dyes containing wastewater and its simultaneous reuse as an added value

The current environmental research has fascinated the sustainable exploitation of mix bacterial consortium to biodegrade the environmentally-related toxic compounds, including hazardous synthetic dyes. Based on the existing literature evidence, textile and other industrial waste effluents pollute the natural water bodies. Textile effluent contains synthetic dyes which are liberated in the environment without proper treatment. The presence of toxic dyes added to the textile effluents undoubtedly affects the flora and fauna as that untreated water is used for irrigation by local farmers. Many conventional and biological methods are in action for the treatment of wastewater. Physical and chemical processes are expensive as compared to microbial treatments. The use of microbial consortia generates efficient results. Wastewater is a valuable resource, however, up to 80% of wastewater is released to different water matrices. This discernment needs to change for a better tomorrow. In this context, herein, we present a robust microbial-assisted treatment and simultaneously reuse of the treated wastewater as an added value to induce plant growth. Thus, the microbial approach for textile waste treatment release by-product after degradation should be non-toxic for the environment. In the present study, the toxicity of synthetic textile dye named Reactive Red 120, Reactive Orange 122, Reactive Yellow 160, and Reactive Blue 19 was investigated using a bioassay method with plant species namely Sorghum bicolor. Plate and Pot experiment was conducted with respect to untreated Azo dyes, degraded metabolites obtained from single bacteria, and consortium. Efficient Seed germination (89%), shoot length (12.4 cm), root length (15.6 cm) of the plants were observed for bacterial consortium degraded metabolites exposed seeds after comparing with the control. The degraded metabolite also increases protein (45.56 mg/g) and sugar (3.15 mg/g) contents. Bioremediation of various textile industrial effluents saves the ecosystem from the harmful effects of hazardous dyes. The biological decolorization of the textile azo dyes was investigated under co-metabolic conditions. The degraded metabolites can be used to enhance crop productivity and for commercial application. This mandates the current and future research to develop economically feasible and environmentally sustainable wastewater treatment practices.

Managing water sustainability in textile industry through adaptive multiple stakeholder collaboration

Textile manufacturing poses pressing challenges on water sustainability characterized by intensive chemical consumption and waterborne pollution. Industrial clustering is a hallmark of textile industry development, featuring a two-stage wastewater treatment system consisting of in-plant and centralized treatment facilities. Driven by increasingly stringent wastewater discharge limits, three pillar stakeholders in textile industrial clusters, the local government, enterprises and environmental utility operators, seek for systematic countermeasures by balancing contradictory interests. This study presents a trilateral game model to uncover the economic and environmental tradeoffs among the three stakeholders targeting the optimization of wastewater systems. The model is solidified by a representative textile industrial cluster and is then extrapolated to 242 large-scale Chinese textile clusters to quantify the benefits. The key finds are (1) the in-use wastewater systems in many clusters function with low eco-efficiency; (2) the optimal paradigm is to adaptively leave room at half- to onefold for discharge limits from in-plant to centralized treatment facilities; (3) the environmental and economic benefits thereof are 24∼x223C61% and 6%, respectively, after retrofitting to the optimal paradigm for the Chinese textile clusters.

Coagulated Mineral Adsorbents for Dye Removal, and Their Process Intensification Using an Agitated Tubular Reactor (ATR)

The aim of this study was to understand the efficacy of widely available minerals as dual-function adsorbers and weighter materials, for the removal of toxic azo-type textile dyes when combined with coprecipitation processes. Specifically, the adsorption of an anionic direct dye was measured on various mineral types with and without the secondary coagulation of iron hydroxide (‘FeOOH’) in both a bench-scale stirred tank, as well as an innovative agitated tubular reactor (ATR). Talc, calcite and modified bentonite were all able to remove 90–95% of the dye at 100 and 200 ppm concentrations, where the kinetics were fitted to a pseudo second-order rate model and adsorption was rapid (<30 min). Physical characterisation of the composite mineral-FeOOH sludges was also completed through particle size and sedimentation measurements, as well as elemental scanning electron microscopy to determine the homogeneity of the minerals in the coagulated structure. Removal of >99% of the dye was achieved for all the coagulated systems, where additionally, they produced significantly enhanced settling rates and bed compression. The greatest settling rate (9 mm min−1) and solids content increase (450% w/w) were observed for the calcium carbonate system, which also displayed the most homogenous distribution. This system was selected for scale-up and benchmarking in the ATR. Dye removal and sediment dispersion in the ATR were enhanced with respect to the bench scale tests, although lower settling rates were observed due to the relatively high shear rate of the agitator. Overall, results highlight the applicability of these cost-effective minerals as both dye adsorbers and sludge separation modifiers to accelerate settling and compression in textile water treatment. Additionally, the work indicates the suitability of the ATR as a flexible, modular alternative to traditional stirred tank reactors.

Treatment of simulated textile sludge using the Fenton/Cl- system: The roles of chlorine radicals and superoxide anions on PAHs removal

The main content of this work is to investigate the removal of polycyclic aromatic hydrocarbons (PAHs: phenanthrene, anthracene, and fluoranthene) from simulated sludge solid phase employing an Fenton/Cl^- system under various Cl^- contents and pH values. The steady-state concentrations of the hydroxyl, chlorine, and dichloride anion radicals ([·OH]_ss, [·Cl]_ss, and [Cl₂^·-]_ss) in heterogeneous system were first measured using tert-butanol, nitrobenzene, and benzoic acid. The outcomes exhibited that increasing the Cl^- content from 50 to 2000 mg/L (pH = 3.0) or raising the pH from 3.0 to 5.0 (1000 mg/L Cl^-) caused [·OH]_ss to continuously decrease and [Cl₂^·-]_ss and the concentration of superoxide anions (HO₂·/O₂^·-) to continuously increase. When the pH was 3.0 and the Cl^- concentration was 1000 mg/L, [·Cl]_ss had a maximum value of 9.27 × 10^-14 M. Combining the results of PAH removal, radical quenching, and product analysis, it was found that ·Cl in the Fenton/Cl^- system promoted the oxidative degradation of phenanthrene without forming chlorination byproducts. Furthermore, HO₂·/O₂^·- was helpful in removing anthracene and fluoranthene. Under the environment of high Cl^- content (≥1000 mg/L), PAHs could be removed more effectively by using HO₂·/O₂^·-. This investigation underpins further study on the regulation of reactive species and the efficient degradation of target organic matter in Fenton/Cl^- system, and provides a basis for studying the formation of chlorinated or toxic byproducts in the process of treating textile dyeing sludge by Fenton.

Integrated fate assessment of aromatic amines in aerobic sewage treatment plants

The fate and exposure of chemicals in sewage treatment plants (STPs) are major considerations in risk assessment and environmental regulation. The biodegradability and removal of seven aromatic amines were systematically evaluated using a three-tiered integrated method: a standard ready biodegradability test, an aerobic sewage treatment simulation method, and model prediction. In tier 1, the seven aromatic amines were not readily biodegraded after 28 days. In adapted aerobic active sludge, 4-isopropyl aniline, 2,4-diaminotoluene, and 4-nitroaniline among them exhibited the degradation half-life time less than 20 h, the other four aromatic amines exhibited persistent with degradation half-life of > 60 h. In tier 2 of the aerobic sewage treatment simulation testing, 2,4-diaminotoluene, 4-nitroaniline, and 4-isopropylaniline demonstrated moderately to high overall removal. Hydraulic retention time (HRT) affects the removal with the optimum HRT was determined to be 12 h to 24. 2,6-Dimethyl aniline, 2-chloro-4-nitroaniline, 2,6-diethylaniline, and 3,4-dichloroaniline were not removed during the test, indicting these four aromatic amines will enter surface water and hence pose a potential risk to aquatic ecology. Considering the lack of an STP model in China for regulation purposes, in tier 3, we developed a Chinese STP (aerobic) (abbreviated as C-STP(O)) model that reflects a universal scenario for China to predict the fate. The predicted degradation, volatilization, and absorption showed a close relationship to the physicochemical properties of the chemicals, and had same tendency with tier 2 simulation test. The prediction showed that biodegradation rather than absorption or volatilization was the main removal process of aromatic amines in aerobic STP. With the combination of modified kinetics test with C-STP (O) model, the chemical fate can be more accurately predicted than using only the readily biodegradation result.

Bioelectricity generation from the decolorization of reactive blue 19 by using microbial fuel cell

Microbial fuel cell (MFC) was compared to conventional biological techniques for decolorization of anthraquinone dye, reactive blue 19 (RB19) with simultaneous electricity generation. With 50 mg/L of RB19 in the anode chamber as a fuel, the MFC achieved 89% decolorization efficiency of RB19 within 48 h, compared with 51 and 55% decolorization efficiency achieved by aerobic and anaerobic techniques, respectively. The cyclic voltammetry results showed that RB19 could promote the electron transfer and redox reaction on the surface of anode. The RB19 decolorization process can be described by first-order kinetics, and the decolorization rate decreased with the increase of RB19 concentration. The high-throughput 16S rRNA sequencing analysis indicated significant microbial community shift in the MFC. At phylum level, the majority of sequences belong to Proteobacteria, accounting from 23 to 84% of the total reads in each bacterium community. At genus level, the MFC contained two types of microorganisms in general such as electrochemically active and decolorization bacteria. Overall, MFC is an effective method for anthraquinone dye treatment with simultaneous energy recovery. The 16S rRNA revealed that there were two major functioning microbial communities in the MFC such as electricity-producing and RB19-degrading bacteria which synergistically worked on RB19 degradation.

Treatment of 3,3'-dimethoxybenzidine in sludge by advance oxidation process: Degradation products and toxicity evaluation

Studies on the oxidation products of organic pollutants and their toxicity in textile dyeing sludge after the sludge was treated by the advance oxidation processes were limited, since textile dyeing sludge was a complicated mixture. For the first time, simulated sludge was used to study the degradation mechanism of 3,3'-dimethoxybenzidine (DMB) during the combined ultrasound-Mn(VII) treatment. The toxicity of DMB and its products was also evaluated. The results indicated that the compositions and microstructures of polyaluminium chloride (PAC)- and polyferric sulphate (PFS)-based simulated sludge were similar to those of real textile dyeing sludge. The optimum conditions of ultrasound-Mn(VII) treatment were: a KMnO₄ dosage of 40 μM, an ultrasound power density of 0.36 W cm^-3, and a reaction time of 20 min. 98.24% of DMB and 63.04% of total organic carbon (TOC) in the simulated sludge were removed. Six products, that is, 2-nitroanisole, 3-methoxy-4-nitrophenol, vanillylmandelic acid, vanillyl alcohol, m-anisic acid, and benzoic acid, were identified by GC-MS and LC-MS-MS. It was noted that all of these identified products were also detected in the real textile dyeing sludge after the ultrasound-Mn(VII) treatment. All of them were less toxic than DMB. Moreover, 53.30% and 54.80% of toxicity toward the alga Desmodesmus subspicatus and the bacterium Vibrio fischeri were removed in simulated sludge, respectively. Therefore, simulated sludge was helpful for studying a pollutant's degradation mechanism in the complex sludge mixtures. The results would also provide some useful suggestions for the sludge disposal after the sludge was treated by the advance oxidation processes.

Homologous-heterogeneous structure control and intelligent adsorption effect of a polycationic gel for super-efficient purification of dyeing wastewater

A homologous-heterogeneous polycationic gel (HPCG) system was constructed by a waste-free synthesis process, to be used as a super-efficient adsorbent material for purifying dyeing wastewater. It is the first discovery of a new intelligent adsorption effect occurring in HPCG adsorption by detecting the homologous-heterogeneous structure transformations in HPCG adsorption using optical microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analysis technologies. The adsorption capacities of HPCG products were 532.55-605.45 times higher than that of the widely-used activated carbon, thereby being the greatest improvement of the adsorption ability for HPCG versus this existing adsorbent. Meanwhile, the adsorption capacities of HPCG were also improved by 3.67-46.05 times compared to that of all the similar polycationic cotton adsorbents reported in our previous serial works, demonstrating more efficient purification of dyeing wastewater than we could do before. In addition, through studying the adsorption models, it was further discovered that HPCG adsorption followed the new two-segment adsorption process, i.e. including a speed control segment and an acceleration segment, also confirming the existence of the intelligent adsorption effect for HPCG adsorption.

Sono-advanced Fenton-like degradation of aromatic amines in textile dyeing sludge: efficiency and mechanisms

In this paper, a novel strategy integrating ultrasound (US) with a Fenton-like (zero-valent iron/EDTA/air, ZEA) process was proposed for the removal of the refractory and carcinogenic aromatic amines (AAs) in textile dyeing sludge for the first time. The operating condition was optimized as 1.08 W/cm³ ultrasonic density, 15 g/L ZVI, and 1.0 mM EDTA, which could reach degradation efficiencies of 51.79% in US, 72.88% in ZEA, and 92.40% in US/ZEA system after 90-min reaction. Quenching experiments showed that electron transfer reactions generated by the iron ligands in ZEA brought about various reactive oxidative species (ROS), in which Fe (IV), O₂˙^-, and ˙OH dominated the degradation. US induced sludge disintegration by ultrasonic shear, proven by particle size decrease and supernatant organic matter upsurge, which helps ROS contact with those pollutants in the sludge cavities. Besides, US facilitated the iron redox cycle for oxygen activation by promoting the corrosion of ZVI and stripping considerable ferric ions from sludge iron oxides which were verified by SEM, XRF, and XPS. Graphical abstract.

Aromatic amines equilibrium sorptive interaction with synthesized silica based mesoporous MCM-41: Physicochemical evaluation and isotherm modeling

Present study reports the adsorption of aromatic amine, 4-chloro-o-toluidine (4-COT), onto synthesized mesoporous Mobil Composition of Matter No. 41 (MCM-41) silica nanoparticles, in batch mode. Synthesized MCM-41 was characterized by XRD, BET, FTIR, SEM and TEM analysis. The effects of pH, MCM-41 dose, 4-COT concentration, contact time and temperature were studied, and interaction of 4-COT with the surface of MCM-41 and adsorption process controlling mechanism were investigated. BET analysis of MCM-41 showed 502.77 m² g^-1 of surface area. Kinetic experimental data were well represented by the pseudo-second order kinetic model. Freundlich and Temkin isotherm models well represented the adsorption equilibrium isotherm data.

Combined ultrasound with Fenton treatment for the degradation of carcinogenic polycyclic aromatic hydrocarbons in textile dying sludge

To develop an effective method to remove the toxic and carcinogenic polycyclic aromatic hydrocarbons (CPAHs) from textile dyeing sludge, five CPAHs were selected to investigate the degradation efficiencies using ultrasound combined with Fenton process (US/Fenton). The results showed that the synergistic effect of the US/Fenton process on the degradation of CPAHs in textile dyeing sludge was significant with the synergy degree of 30.4. During the US/Fenton process, low ultrasonic density showed significant advantage in degrading the CPAHs in textile dyeing sludge. Key reaction parameters on CPAHs degradation were optimized by the central composite design as followed: H₂O₂ concentration of 152 mmol/L, ultrasonic density of 408 W/L, pH value of 3.7, the molar ratio of H₂O₂ to Fe²⁺ of 1.3 and reaction time of 43 min. Under the optimal conditions of the US/Fenton process, the degradation efficiencies of five CPAHs were obtained as 81.23% (benzo[a]pyrene) to 84.98% (benz[a]anthracene), and the benzo[a]pyrene equivalent (BaP_eq) concentrations of five CPAHs declined by 81.22-85.19%, which indicated the high potency of US/Fenton process for removing toxic CPAHs from textile dyeing sludge.

Removal of polycyclic aromatic hydrocarbons (PAHs) from textile dyeing sludge by ultrasound combined zero-valent iron/EDTA/Air system

This paper proposes a combined ultrasound (US) and zero-valent iron/EDTA/Air (ZEA) system to remove polycyclic aromatic hydrocarbons (PAHs) from textile dyeing sludge. The removal efficiencies of 16 PAHs using ZEA, US/Air (air injected into the US process), and US/ZEA treatments were investigated, together with the effects of various operating parameters. The enhanced mechanisms of US and the role of reactive oxygen species (ROS) in removing PAHs in the US/ZEA system were explored. Results showed that only 42.5% and 32.9% of ∑16 PAHs were removed by ZEA and US/Air treatments respectively, whereas 70.1% were removed by US/ZEA treatment, (with favorable operating conditions of 2.0 mM EDTA, 15 g/L ZVI, and 1.08 w/cm³ ultrasonic density). The US/ZEA system could be used with a wide pH range. US led to synergistic improvement of PAHs removal in the ZEA system by enhancing sludge disintegration to release PAHs and promoting ZVI corrosion and oxygen activation. In the US/ZEA system, PAHs could be degraded by ROS (namely OH, O₂^-/HO₂, and Fe(IV)) and adsorbed by ZVI, during which the ROS made the predominant contribution. This study provides important insights into the application of a US/ZEA system to remove PAHs from sludge.

Selective hydrogenation of nitroarenes using an electrogenerated polyoxometalate redox mediator

The 2-electron reduced form of the polyoxometalate silicotungstic acid (H₄[SiW₁₂O₄]) is shown to be an effective and selective hydrogenation agent for a range of nitroarenes without the need for any co-catalyst.

Degradation of aromatic amines in textile-dyeing sludge by combining the ultrasound technique with potassium permanganate treatment

This paper reports, for the first time, a combined technique of ultrasound (US) with KMnO4 degradation of aromatic amines in a textile-dyeing sludge. The reaction mechanisms and the degradation kinetics of aromatic amines at various operating parameters (KMnO4 dosage, US power density and pH) were systematically examined by the combined system of US-KMnO4. The results indicated that there was a synergistic effect between US and KMnO4, as US greatly enhanced KMnO4 in the degradation of aromatic amines and exhibited apparent sludge disintegration and separated pollutants from the sludge. In addition to accelerating the Mn(VII) reaction with pollutants in the filtrate, US also caused Mn(VII) to enter the porous sludge and sufficiently facilitated the reaction of the strongly absorbed aromatic amines. The combined treatment of US-KMnO4 was effective in the degradation of aromatic amines in textile-dyeing sludge. On average, 58.7% of monocyclic anilines, 88.3% of other forms of aromatic amines, and 24.0% of TOC were removed under the optimal operating conditions of a KMnO4 dosage of 12mM, an US power density of 1.80W/cm(3) and pH 5. The present study proposed US-KMnO4 treatment as a practical method for the disposal of aromatic amines in textile-dyeing sludge.

Degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge with ultrasound and Fenton processes: Effect of system parameters and synergistic effect study

To establish an efficient oxidation process for the degradation of polycyclic aromatic hydrocarbons (PAHs) in textile dyeing sludge, the effects of various operating parameters were optimized during the ultrasound process, Fenton process and the combined ultrasound-Fenton process. The results showed that the ultrasonic density of 1.80w/cm(3), both H2O2 and Fe(2+) dosages of 140mmol/L and pH 3 were favorable conditions for the degradation of PAHs. The degradation efficiency of high molecular weight PAHs was close to or even higher than that of light molecular weight PAHs. The highest degradation efficiencies of Σ16 PAHs were obtained within 30min in the order of: Fenton (83.5%) >ultrasound-Fenton (75.5%) >ultrasound (45.5%), then the efficiencies were decreased in the other of: ultrasound-Fenton (73.0%) >Fenton (70.3%) >ultrasound (41.4%) in 60min. The extra PAHs were released from the intracellular substances and the cavities of sludge due to the disruption of sludge during the oxidation process. Also, the degradation of PAHs could be inhibited by the other organic matter in the sludge. The combined ultrasound-Fenton process showed more efficient than both ultrasound process and Fenton process not only in the surface of sludge but also in the sludge interior.