33 research outputs found
Water-Soluble Synthetic Polymers: Their Environmental Emission Relevant Usage, Transport and Transformation, Persistence, and Toxicity
Water-soluble synthetic polymers
(WSPs) are distinct from insoluble
plastic particles, which are both critical components of synthetic
polymers. In the history of human-made macromolecules, WSPs have consistently
portrayed a crucial role and served as the ingredients of a variety
of products (e.g., flocculants, thickeners, solubilizers, surfactants,
etc.) commonly used in human society. However, the environmental exposures
and risks of WSPs with different functions remain poorly understood.
This paper provides a critical review of the usage, environmental
fate, environmental persistence, and biological consequences of multiple
types of WSPs in commercial and industrial production. Investigations
have identified a wide market of applications and potential environmental
threats of various types of WSPs, but we still lack the suitable assessment
tools. The effects of physicochemical properties and environmental
factors on the environmental distribution as well as the transport
and transformation of WSPs are further summarized. Evidence regarding
the degradation of WSPs, including mechanical, thermal, hydrolytic,
photoinduced,
and biological degradation is summarized, and their environmental
persistence is discussed. The toxicity data show that some WSPs can
cause adverse effects on aquatic species and microbial communities
through intrinsic toxicity and physical hazards. This review may serve
as a guide for environmental risk assessment to help develop a sustainable
path for WSP management
Reducing N<sub>2</sub>O Emission from a Domestic-Strength Nitrifying Culture by Free Nitrous Acid-Based Sludge Treatment
An increase of nitrite
in the domestic-strength range is generally
recognized to stimulate nitrous oxide (N<sub>2</sub>O) production
by ammonia-oxidizing bacteria (AOB). It was found in this study, however,
that N<sub>2</sub>O emission from a mainstream nitritation system
(cyclic nitrite = 25–45 mg of N/L) that was established by
free nitrous acid (FNA)-based sludge treatment was not higher but
much lower than that from the initial nitrifying system with full
conversion of NH<sub>4</sub><sup>+</sup>-N to NO<sub>3</sub><sup>–</sup>-N. Under dissolved oxygen (DO) levels of 2.5–3.0 mg/L, N<sub>2</sub>O emission from the nitritation stage was 76% lower than that
from the initial stage. Even when the DO level was reduced to 0.3–0.8
mg/L, N<sub>2</sub>O emission from the nitritation stage was still
40% lower. An investigation of the mechanism showed that FNA treatment
caused a shift of the stimulation threshold of nitrite on N<sub>2</sub>O emission. At the nitritation stage, the maximal N<sub>2</sub>O
emission factor occurred at ∼16 mg of N/(L of nitrite). However,
it increased with increasing nitrite in the range of 0–56
mg of N/L at the initial stage. FNA treatment decreased the biomass-specific
N<sub>2</sub>O production rate, suggesting that the enzymes relevant
to nitrifier denitrification were inhibited. Microbial analysis revealed
that FNA treatment decreased the microbial community diversity but
increased the abundances of AOB and denitrifiers
Polyaspartic Acid Concentration Controls the Rate of Calcium Phosphate Nanorod Formation in High Concentration Systems
Polyelectrolytes
are known to greatly affect calcium phosphate
(CaP) mineralization. The reaction kinetics as well as the CaP phase,
morphology and aggregation state depend on the relative concentrations
of the polyelectrolyte and the inorganic ions in a complex, nonlinear
manner. This study examines the structural evolution and kinetics
of polyaspartic acid (pAsp) directed CaP mineralization at high concentrations
of polyelectrolytes, calcium, and total phosphate (19–30 mg/mL
pAsp, 50–100 mM Ca<sup>2+</sup>, Ca/P = 2). Using a novel combination
of characterization techniques including cryogenic transmission electron
microscopy (cryo-TEM), spectrophotometry, X-ray total scattering pair
distribution function analysis, and attenuated total reflectance Fourier
transform infrared spectroscopy (ATR-FTIR), it was determined that
the CaP mineralization occurred over four transition steps. The steps
include the formation of aggregates of pAsp stabilized CaP spherical
nanoparticles (sNP), crystallization of sNP, oriented attachment of
the sNP into nanorods, and further crystallization of the nanorods.
The intermediate aggregate sizes and the reaction kinetics were found
to be highly polymer concentration dependent while the sizes of the
particles were not concentration dependent. This study demonstrates
the complex role of pAsp in controlling the mechanism as well as the
kinetics of CaP mineralization
Kinetics of Aggregation and Crystallization of Polyaspartic Acid Stabilized Calcium Phosphate Particles at High Concentrations
Bone is an important material to
study due to its exceptional mechanical
properties and relevance with respect to hard tissue regeneration
and repair. A significant effort has been directed toward understanding
the bone formation process and the production of synthetic bone mimicking
materials. Here, the formation and structural evolution of calcium
phosphate (CaP) was investigated in the presence of relatively high
concentrations of calcium, phosphate, and polyaspartic acid (pAsp)
using dynamic light scattering (DLS) and cryo-transmission electron
microscopy (cryo-TEM). The incipient CaP aggregates were comprised
of spherical nanoparticles (diameter ≈ 3–4 nm); they
became preferentially aligned over time and eventually transformed
into nanorods. The nanorods remained stable in suspension with no
signs of further aggregation for at least four months. Detailed cryo-TEM
suggested that the CaP nanorods formed through an oriented attachment
mechanism. These results show that the reaction concentration greatly
influences the mechanism and final properties of CaP. Mechanistic
insights gained from this study will facilitate better design and
fabrication of bioinspired materials
CART analyses of the relationships between biome and environmental factors along the gradients of precipitation and temperature in the Hulunbuir grasslands.
<p>The key environmental factors were screened in panels A (AGB), B (BGB) and C (R/S). Branches are labeled with criteria used to segregate data. Values in terminal nodes represent mean vegetation biomass of sites grouped within the cluster. n = number of plots in the category. The below corresponding panels were structural complexity (cp value) of trees. All designations are the same as those in the footnotes below <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102344#pone-0102344-t001" target="_blank">Table 1</a>.</p
Frequency distribution curves of the AGB, BGB and R/S; the samples were collected across the Hulunbuir grasslands.
<p>All designations are the same as those in the footnotes below <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102344#pone-0102344-t001" target="_blank">Table 1</a>.</p
Internal uniform reliability and correlation coefficient of the SF-36 questionnaire.
<p><sup>*</sup><i>P</i> < 0.01. PF, physical function; RP, role-physical; BP, bodily pain; GH, general health; VT, vitality; SF, social function; RE, role-emotional ; MH, mental health.</p
Comparison of hypothetical and actual factor loadings.
<p>Correlation coefficient (<i>r</i>): <i>r</i> ≥ 0.70; * 0.70 > <i>r</i> > 0.30; <b><i>–</i></b><i>r</i> ≤ 0.30</p><p>PCS, physical component summary; MCS, mental component summary; PF, physical function; RP, role-physical; BP, bodily pain; GH, general health; VT, vitality; SF, social function; RE, role-emotional ; MH, mental health.</p
Short-Chain Fatty Acid Production from Different Biological Phosphorus Removal Sludges: The Influences of PHA and Gram-Staining Bacteria
Recently,
the reuse of waste activated sludge to produce short-chain fatty acids
(SCFA) has attracted much attention. However, the influences of sludge
characteristics, especially polyhydroxyalkanoates (PHA) and Gram-staining
bacteria, on SCFA production have seldom been investigated. It was
found in this study that during sludge anaerobic fermentation not
only the fermentation time but also the SCFA production were different
between two sludges, which had different PHA contents and Gram-negative
bacteria to Gram-positive bacteria (GNB/GPB) ratios and were generated
respectively from the anaerobic/oxic (AO) and aerobic/extended-idle
(AEI) biological phosphorus removal processes. The optimal fermentation
time for the AEI and AO sludges was respectively 4 and 8 d, and the
corresponding SCFA production was 304.6 and 231.0 mg COD/g VSS (volatile
suspended solids) in the batch test and 143.4 and 103.9 mg COD/g VSS
in the semicontinuous experiment. The mechanism investigation showed
that the AEI sludge had greater PHA content and GNB/GPB ratio, and
the increased PHA content accelerated cell lysis and soluble substrate
hydrolysis while the increased GNB/GPB ratio benefited cell lysis.
Denaturing gradient gel electrophoresis profiles revealed that the
microbial community in the AEI sludge fermentation reactor was dominated
by <i>Clostridium sp.</i>, which was reported to be SCFA-producing
microbes. Further enzyme analyses indicated that the activities of
key hydrolytic and acids-forming enzymes in the AEI sludge fermentation
reactor were higher than those in the AO one. Thus, less fermentation
time was required, but higher SCFA was produced in the AEI sludge
fermentation system
The establishment of a structural equation model for A) aboveground biomass (AGB), B) belowground biomass (BGB) and C) root to shoot ratio (R/S).
<p>Each line represents a direct linear causal relationship. The arcs show the correlation between two variables. Values on lines are path coefficients. The asterisks are significant at <i>P</i> = 0.05 level. The coefficients that are not statistically significant are shown by dashed arrows. All values are standardized. All designations are the same as those in the footnotes below <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102344#pone-0102344-t001" target="_blank">Table 1</a>.</p