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