3 research outputs found
Effects of microplastics on substance transformation, sludge characteristics, toxicological effect, and microbial communities in different biochemical sludge systems: A review
In recent years, microplastics (MPs) have attracted worldwide attention as emerging pollutants, and wastewater treatment plants are among the environment’s most important sources of MPs. This study aimed to summarize MPs effects on various aspects of sludge systems. The results showed that MPs inhibited substance transformation in sludge systems, with greater inhibition observed at higher concentrations and smaller MP particle sizes. Moreover, low concentrations of MPs promote extracellular polymeric substance (EPS) secretion, whereas high concentrations suppress EPS secretion, destroying the sludge structure. Granular sludge systems exhibit higher resistance to MPs than activated sludge systems owing to their layered structures. Micrometer-sized MPs primarily inhibit the dewatering performance of activated sludge through physical crushing, while nano-sized MPs primarily affect sludge dewatering through biological effects. However, for granular sludge system, micrometer-sized MPs were unable to penetrate the granular sludge interior, their affinity and aggregation capabilities enabled them to accumulate on the sludge surface. In contrast, nano-sized MPs can enter the interior of granular sludge and impair mass-transfer pathways, ultimately resulting in toxic effects. Furthermore, MPs induce various toxic effects in sludge systems (single and combined toxic effects). These toxic effects affect the expression of key enzymes and functional genes, leading to changes in microbial communities. Because of the layered structure of granular sludge systems, MPs may initially affect the microbial community structure outside the granules, with less impact on the internal microorganisms. However, the specific mechanism still needs to be explored. Finally, this study presents research questions and directions that require further investigation.</p
Monitoring the Internal Structure of Poly(<i>N</i>‑vinylcaprolactam) Microgels with Variable Cross-Link Concentration
The combination of a set of complementary
techniques allows us
to construct an unprecedented and comprehensive picture of the internal
structure, temperature dependent swelling behavior, and the dependence
of these properties on the cross-linker concentration of microgel
particles based on <i>N</i>-vinylcaprolactam (VCL). The
microgels were synthesized by precipitation polymerization using different
amounts of cross-linking agent. Characterization was performed by
small-angle neutron scattering (SANS) using two complementary neutron
instruments to cover a uniquely broad Q-range with one probe. Additionally
we used dynamic light scattering (DLS), atomic force microscopy (AFM),
and differential scanning calorimetry (DSC). Previously obtained nuclear
magnetic resonance spectroscopy (NMR) results on the same PVCL particles
are utilized to round the picture off. Our study shows that both the
particle radius and the cross-link density and therefore also the
stiffness of the microgels rises with increasing cross-linker content.
Hence, more cross-linker reduces the swelling capability distinctly.
These findings are supported by SANS and AFM measurements. Independent
DLS experiments also found the increase in particle size but suggest
an unchanged cross-link density. The reason for the apparent contradiction
is the indirect extraction of the parameters via a model in the evaluation
of DLS measurements. The more direct approach in AFM by evaluating
the cross section profiles of observed microgel particles gives evidence
of significantly softer and more deformable particles at lower cross-linker
concentrations and therefore verifies the change in cross-link density.
DSC data indicate a minor but unexpected shift of the volume phase
transition temperature (VPTT) to higher temperatures and exposes a
more heterogeneous internal structure of the microgels with increasing
cross-link density. Moreover, a change in the total energy transfer
during the VPT gives evidence that the strength of hydrogen bonds
is significantly affected by the cross-link density. A strong and
reproducible deviation of the material density of the cross-linked
microgel polymer chains toward a higher value compared to the respective
linear chains has yet to be explained
Thermal Stability of Skyrmion Tubes in Nanostructured Cuboids
Magnetic skyrmions in bulk materials
are typically regarded as
two-dimensional structures. However, they also exhibit three-dimensional
configurations, known as skyrmion tubes, that elongate and extend
in-depth. Understanding the configurations and stabilization mechanism
of skyrmion tubes is crucial for the development of advanced spintronic
devices. However, the generation and annihilation of skyrmion tubes
in confined geometries are still rarely reported. Here, we present
direct imaging of skyrmion tubes in nanostructured cuboids of a chiral
magnet FeGe using Lorentz transmission electron microscopy (TEM),
while applying an in-plane magnetic field. It is observed that skyrmion
tubes stabilize in a narrow field-temperature region near the Curie
temperature (Tc). Through a field cooling
process, metastable skyrmion tubes can exist in a larger region of
the field-temperature diagram. Combining these experimental findings
with micromagnetic simulations, we attribute these phenomena to energy
differences and thermal fluctuations. Our results could promote topological
spintronic devices based on skyrmion tubes