33 research outputs found

    Water-Soluble Synthetic Polymers: Their Environmental Emission Relevant Usage, Transport and Transformation, Persistence, and Toxicity

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    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

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    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

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    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

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    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.

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    <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.

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    <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.

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    <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.

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    <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

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    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).

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    <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
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