6 research outputs found

    Stepwise Adsorption of Phenanthrene at the Fly Ash–Water Interface as Affected by Solution Chemistry: Experimental and Modeling Studies

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    Fly ash (FA) is predominantly generated from coal-fired power plants. Contamination during disposal of FA can cause significant environmental problems. Knowledge about the interaction of FA and hydrophobic organic pollutants in the environment is very limited. This study investigated the adsorption of phenanthrene at the interface of FA and water. The performance of phenanthrene adsorption on FA and the effects of various aqueous chemistry conditions were evaluated. The adsorption isotherms exhibited an increasing trend in the adsorbed amounts of phenanthrene, while a stepwise pattern was apparent. A stepwise multisite Langmuir model was developed to simulate the stepwise adsorption process. The adsorption of phenanthrene onto FA was noted to be spontaneous at all temperatures. The thermodynamic results indicated that the adsorption was an exothermic process. The adsorption capacity gradually decreased as pH increased from 4 to 8; however, this trend became less significant when pH was changed from 8 to 10. The binding affinity of phenanthrene to FA increased after the addition of humic acid (HA). The pH variation was also responsible for the changes of phenanthrene adsorption on FA in the presence of HA. High ionic strength corresponded to low mobility of phenanthrene in the FA–water system. Results of this study can help reveal the migration patterns of organic contaminants in the FA–water system and facilitate environmental risk assessment at FA disposal sites

    Removal of Tannin from Aqueous Solution by Adsorption onto Treated Coal Fly Ash: Kinetic, Equilibrium, and Thermodynamic Studies

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    The study investigated the performance of tannin adsorption on treated coal fly ash. The adsorption capacity of coal fly ash could be enhanced through appropriate pretreatment by acid. There was an apparent increase of tannin adsorption when fly ash dosage changed from 0 to 20 g/L. The adsorption isotherm data fitted to Freundlich and Langmuir models. The adsorption process followed pseudo-second-order kinetics. The adsorption processes presented a two-stage pattern, a rapid adsorption process followed by a slow adsorption process. The adsorbed amount of tannin was higher at 20 °C than other temperature levels. The thermodynamic studies indicated the adsorption of tannin onto fly ash was exothermic in nature and the entropy of the system decreased during adsorption process. The removal efficiency of tannin adsorption onto fly ash decreased when NaCl concentration ranged from 0 to 0.4 mol/L

    Unveiling Antibacterial and Antibiofilm Mechanisms of Methyleugenol: Implications for Ecomaterial Functionalization

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    Bacterial resistance evolution necessitates the continuous adaptation of antimicrobial agents. In this study, we systematically investigated the antibacterial and biofilm-inhibition mechanisms of plant extracts, including methyleugenol and eugenol, and further explored their potential for immobilization in practical applications. Our findings revealed that eugenol exhibited robust antibacterial activity by disrupting bacterial redox balance and membrane permeability. Methyleugenol, on the other hand, efficiently mitigated biofilm formation by inhibiting the quorum sensing (QS) system and depolarizing the cell membrane. Through gene expression analysis and molecular docking studies, we confirmed that methyleugenol suppressed the transcriptional expression of QS regulatory genes by competitively binding to the RhlR receptor protein, thereby reducing the secretion of extracellular polymeric substances and inhibiting the biofilm formation. Furthermore, we observed an upregulation of multiple efflux pump MexAB-OprM as a response to bacterial reductive stress during compound exposure. To expand the practical utility of these findings, we successfully grafted methyleugenol onto glass surfaces using the atom transfer radical polymerization method, demonstrating enduring antibacterial and antibiofilm properties. Overall, our study offers a comprehensive understanding of the antibacterial and antibiofilm mechanisms of methyleugenol and eugenol, with promising applications for enhancing ecomaterial functionalization

    Unveiling the Vertical Migration of Microplastics with Suspended Particulate Matter in the Estuarine Environment: Roles of Salinity, Particle Properties, and Hydrodynamics

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    The estuary is an energetic area connecting the inland, river, and ocean. The migration of microplastics (MPs) in this highly complex area is tied to the entire ecosystem. In this study, the effects of cohesive SPM (clay) and noncohesive SPM (sand) on the vertical migration of positively buoyant MPs, polyethylene (PE), and negatively buoyant MPs, polytetrafluoroethylene (PTFE), in the estuarine environment under hydrodynamic disturbances were investigated. The settling of positively buoyant MPs was more reliant on the cohesive SPM compared to the settling of negatively buoyant MPs. Moreover, MPs interacting with the SPM mixture at a clay-to-sand ratio of 1:9 settled more efficiently than those interacting with clay alone. A significant positive correlation was observed between MP settling percentage and the salinity level. MP settling percentage was significantly negatively correlated with fluid shear stress for both types of MPs, meanwhile, negatively buoyant MPs were able to resist greater hydraulic disturbances. In the low-energy mixing state, for both types of MPs, the settling percentage reached about 50% in only 10 min. The resuspension process of MPs under hydrodynamic disturbances was also uncovered. Additionally, the migration and potential sites of MPs were described in the context of prevalent environmental phenomena in estuaries

    Removal of Sulfonated Humic Acid through a Hybrid Electrocoagulation–Ultrafiltration Process

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    This study investigated the removal of sulfonated humic acid (SHA) from water through a hybrid electrocoagulation–ultrafiltration treatment process. The effects of major operating parameters including electrocoagulation time, current density, and initial pH on the electrocoagulation performance were evaluated. The increase in current density and operating time as well as decrease of pH improved the SHA removal efficiency. The operating conditions of electrocoagulation process were optimized through Box–Behnken design to maximize SHA removal. The optimum conditions for electrocoagulation included time of 7 min, current density of 10 mA/cm<sup>2</sup>, and pH of 5. Effective SHA removal was further achieved in the hybrid electrocoagulation–ultrafiltration treatment process. The performances of three molecular weight cutoff membranes were examined. The results showed that the SHA removal efficiency increased with the increasing initial concentration of SHA and decreased with the increasing transmembrane pressure. The SHA removal efficiency was more than 95% by 5 kDa membrane. The SHA removal efficiency by different membranes from high to low in turn was: 5 kDa > 8 kDa > 10 kDa. The results will have significant implications for the treatment of complex drilling and hydraulic fracturing wastewater through electrocoagulation–ultrafiltration process

    Insights into the Toxicity of Triclosan to Green Microalga <i>Chlorococcum sp.</i> Using Synchrotron-Based Fourier Transform Infrared Spectromicroscopy: Biophysiological Analyses and Roles of Environmental Factors

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    This study investigated the toxicity of triclosan to the green microalga <i>Chlorococcum sp.</i> under multiple environmental stressors. The interactions between triclosan and environmental stressors were explored through full two-way factorial, synchrotron-based Fourier transform infrared spectromicroscopy and principal component analyses. Phosphorus concentration, pH * phosphorus concentration, and temperature * pH * NaCl concentration were the most statistically significant factors under triclosan exposure. The variation of those factors would have a huge impact on biophysiological performances. It is interesting to find <i>Chlorococcum</i> sp. may become more resistant against triclosan in phosphorus-enriched environment. Besides, particular significant factors from multiple environmental stressors showed the impacts of triclosan on the corresponding response of <i>Chlorococcum</i> sp. owing to the specific structure and performance of biomolecular components. Moreover, two high-order interactions of temperature * pH * NaCl concentration and temperature * pH * NaCl concentration * phosphorus concentration had more contributions than others at the subcellular level, which could be attributed to the interactive complexity of biomolecular components. Due to cellular self-regulation mechanism and short exposure time, the biophysiological changes of <i>Chlorococcum sp.</i> were undramatic. These findings can help reveal the interactive complexity among triclosan and multiple environmental stressors. It is suggested that multiple environmental stressors should be considered during ecological risk assessment and management of emerging pollutants
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