81. 题目: Immobilization of exopolymeric substances from bacteria for metal removal: A study on characterization, optimization, reusability and toxicity
This study investigated the immobilization of exopolymeric substances (EPS) from Bacillus cereus using sodium alginate to form EPS beads for metal removal. The EPS beads were characterized and their optimum biosorption conditions established (biosorbent dosage, initial metal concentration and pH of metal solutions). The EPS beads were also tested for reusability by using them continuously for five metal removal cycles with desorption process in between cycles. The toxicity of the treated metal solutions was tested by phytotoxicity tests. Results revealed that EPS beads demonstrated significantly higher metal removal efficiency (Pb: 99.26%, Cr: 50.73%, Cu: 48.94%, Zn: 29.81%, Cd: 20.29%) compared to plain alginate beads (without EPS) (Pb: 84.45%, Cu: 31%, Cr: 28.37%, Zn: 11.91%, Cd: 9.37%). SEM-EDX analysis detected Cu, Pb, Zn, Cd and Cr on the surface of EPS beads. Optimum conditions for Pb removal by EPS beads were from the use of 0.1 g of biosorbent at 100 mg/L initial metal concentration and pH 5. By contrast, Cu, Zn, Cd and Cr were optimally removed by 0.3 g of biosorbent at 25 mg/L initial metal concentration and pH 5. EPS beads can be reused up to five times while maintaining a high rate of metal removal efficiency (Pb- 99.52%, Cr- 89.23%, Cu- 89.17%, Zn-52.52%, Cd-39.12%). This was achieved through desorption with nitric acid that consistently recovered 76–93% of the metal adsorbed. FTIR analysis reveals that nitric acid is capable of restoring the functional groups present within EPS beads, allowing it to bind with metal ions in repeated cycles. Metal solutions treated with EPS beads were less toxic as seedling shoots (pre-treated: 0–10 cm, post-treated: 1.2–18.1 cm) and roots (pre-treated: 0–7.8 cm, post-treated: 0.8–15.1 cm) grew well, which suggested that reduced levels of metals led to reduced phytotoxicity. This study provides an insight into the use of EPS beads for metal removal, highlighting the benefits and reusability of the beads for future wastewater treatment.
82. 题目: Citric acid secretion from rice roots contributes to reduction and immobilization of Cr(VI) by driving microbial sulfur and iron cycle in paddy soil
Root exudates released by plants can promote microbial growth and activity, thereby affecting the transformation and availability of soil pollutants. However, the effects of the root exudates of rice plants on chromium (Cr) transformation in paddy soils and the underlying mechanisms are yet to be elucidated properly. The present study investigated how rice root exudates interact with rhizosphere microorganisms to influence the transformation of Cr and explored the key components in root exudates that affect Cr(VI) reduction. The results showed that the addition of root exudate and citric acid markedly decreased soil pH and increased dissolved organic carbon content that created favorable conditions and provided sufficient electron donors for Cr(VI) reduction, thereby greatly facilitating the reduction of Cr(VI) and the transformation of HOAc-extractable Cr into more stable oxidizable and residual Cr. Additionally, Desulfovibrio-related sulfate-reducing bacteria, Thiobacillus-related sulfide-oxidizing bacteria, and Geobacter-related Fe(III)-reducing bacteria were enriched with the addition of root exudate and citric acid. Among them, sulfate would be reduced by Desulfovibrio to sulfide, which would be further utilized by Thiobacillus to reduce Cr(VI), thereby enabling the continuous reduction of Cr(VI); simultaneously, Geobacter would sustain the reduction of Cr(VI) by reducing Fe(III) to Fe(II). Furthermore, based on the high-level secretion of citric acid in response to Cr(VI) exposure and the similar effects of root exudates and citric acid on Cr(VI) reduction, it is proposed that citric acid is the key component in rice root exudates that affects Cr(VI) reduction. These results suggest that root exudates (citric acid as the key component) contribute to the reduction and immobilization of Cr(VI) by driving microbial S and Fe cycles, with Desulfovibrio, Thiobacillus, and Geobacter being the keystone genera. The study provides a novel insight into the Fe/S/Cr co-transformation processes with microbial involvement, and the artificial root exudate mixtures designed to reduce Cr(VI).
83. 题目: Lignin-oxidizing and xylan-hydrolyzing Vibrio involved in the mineralization of plant detritus in the continental slope
A large amount of terrigenous organic matter (TOM) is constantly transported to the deep sea. However, relatively little is known about the microbial mineralization of TOM therein. Our recent in situ enrichment experiments revealed that Vibrio is especially enriched as one of the predominant taxa in the cultures amended with natural plant materials in the deep sea. Yet their role in the mineralization of plant-derived TOM in the deep sea remains largely unknown. Here we isolated Vibrio strains representing dominant members of the enrichments and verified their potential to degrade lignin and xylan. The isolated strains were closely related to Vibrio harveyi, V. alginolyticus, V. diabolicus, and V. parahaemolyticus. Extracellular enzyme assays, and genome and transcriptome analyses revealed diverse peroxidases, including lignin peroxidase (LiP), catalase-peroxidase (KatG), and decolorizing peroxidase (DyP), which played an important role in the depolymerization and oxidation of lignin. Superoxide dismutase was found to likely promote lignin oxidation by supplying H2O2 to LiP, DyP, and KatG. Interestingly, these deep-sea Vibrio strains could oxidize lignin and hydrolyze xylan not only through aerobic pathway, but also through anaerobic pathway. Genome analysis revealed multiple anaerobic respiratory mechanisms, including the reductions of nitrate, arsenate, tetrathionate, and dimethyl sulfoxide. The strains showed the potential to anaerobically reduce sulfite and metal oxides of iron and manganese, in contrast the non-deep-sea Vibrio strains were not retrieved of genes involved in reduction of metal oxides. This is the first report about the lignin oxidation mechanisms in Vibrio and their role in TOM mineralization in anoxic and oxic environments of the marginal sea.
84. 题目: Closing in on the last frontier: C allocation in the rhizosphere
85. 题目: Implications of Free and Occluded Fine Colloids for Organic Matter Preservation in Arable Soils
86. 题目: Source identification and chemical compositions of particulate and mineral-associated organic matter in the deposited sediments of a dam-controlled watershed
Understanding the soil fraction controls on the source and chemical composition of soil organic matter (SOM) in buried sediments is essential for revealing the underlying mechanisms of deposited carbon (C) fate and stabilization on the earth. In this study, we fractionated the bulk SOM into particulate organic matter (POM) and mineral-associated organic matter (MAOM) in deposit profiles trapped by check dam on the Chinese Loess Plateau and then attempted to explore the sources and chemical compositions of the POM and MAOM fractions by combining physical fractionation with elemental, isotopic, and spectroscopic analyses. The results showed that the main C source of deposited SOM from upland soils varied with soil fractions. The primary contributor of the POM fraction in deposited sediments originated from grassland and the gully’s contribution was minimal, whereas the cropland was the main contributor to the MAOM fraction and the lowest contribution was from forest. The relative enrichments of δ13C and δ15N and the lower C/N ratio in the MAOM fraction indicated that it had undergone more microbial processing than the POM had. Moreover, the specific peak data of Fourier Transform Infrared spectra (FTIR) demonstrated that there were higher proportions of the labile functional groups (i.e., alcohol COH/CNH, polysaccharide CO, and aliphatic CH) than the recalcitrant functional group (i.e., aromatic CC/CN) in the POM fraction in entire deposit profiles. The poor relationships between 13CSOC and log-transformed SOC in different soil fractions further confirmed a lower decomposition rate of MAOM compared to the POM. The results indicate that the POM fraction might have a faster SOM biogeochemical cycling than the MAOM fraction in buried sediments. Our results provide important implications for accurately estimating the nature and persistence of the deposited OM retained by check dams.
87. 题目: Exceptional molecular preservation in the Late Jurassic Claudia palaeo-geothermal field (Deseado Massif, Patagonia, Argentina)
Gas chromatography–mass spectrometry was applied to samples collected from an exceptionally well-preserved Late Jurassic (∼150 Ma) sinter complex of the Claudia palaeo-geothermal field, Deseado Massif geological province, Argentinean Patagonia, which, despite its age, has never been deeply buried. Results indicate that the distal sinter apron has a much higher preservation potential for indigenous organic matter (OM) than the more proximal (vent area) facies of this palaeo-geothermal field. Specifically, homohopane ratios show that the OM of the proximal apron is of mixed thermal maturities and is in low abundance. In contrast, the OM extracted from the distal apron contains highly abundant, thermally immature biomarkers, the presence of which are consistent with the lower original fluid temperatures of the distal spring facies. Moreover, despite indications of the presence of some thermally mature aromatic compounds, hopane and sterane ratios confirm that the distal apron samples are extremely thermally immature and thereby constitute an area of exceptional molecular preservation. From an astrobiological viewpoint, these results suggest that silica sinter can preserve abundant organics over millions of years in palaeoenvironmentally conducive settings, and that sample-site selection within a hot spring facies-model framework may be critical in the successful search for ancient extra-terrestrial life.
88. 题目: High nitrogen addition after the application of sewage sludge compost decreased the bioavailability of heavy metals in soil
Nitrogen (N) fertilizer is highly significant in agricultural production, but long-term N addition causes changes in quality indicators, such as soil organic matter (SOM), thus affecting the absorption and accumulation of organic pollutants. Therefore, paying more attention to organic fertilizers in the development of green agriculture is necessary. However, the accumulation of heavy metals (HMs) contained in organic fertilizers (especially sewage sludge compost (SSC)) in the soil can cause environmental contamination, but how this cumulative reaction changes with the long-term N addition remains unclear. Here the SSC impact on the bioavailability of five typical HMs (cadmium–Cd, chromium–Cr, copper–Cu, lead–Pb, arsenic–As) in the soil-plant system without and after SSC application was demonstrated through a field study in soils with different application rates of 0, 100 and 300 kg N ha−1yr−1, respectively. Our results showed that SSC application increased the concentration of most HMs in soil profiles and plant systems (wheat roots and grains), but the accumulation rate of HMs and most bioaccumulation values (BAC–bioaccumulation coefficient and BCF–bioconcentration factor) in plant systems were both lower in high-N addition soil than that in the low-N group. Moreover, speciation distribution results further indicated that SSC application increased the LB (liable available form, including F1–water soluble, F2–ion exchangeable, and F3–bound to carbonates) form of HMs and decreased the PB (potentially available form, including F4–humic acids and F6–fraction bound to organic matter) form of HMs in high-N addition soil, respectively. Those results suggested that HM bioavailability in high-N addition soil was lower than that in low-N addition soil when applied with SSC. Overall, this study found that increasing soil N content can inhibit the bioavailability of HMs when applying SSC, providing suggestions for optimizing the trialability and risk assessment of SSC application.
89. 题目: Application of chitosan- and alginate-modified biochars in promoting the resistance to paddy soil acidification and immobilization of soil cadmium
To develop more green, practical and efficient biochar amendments for acidic soils, chitosan-modified biochar (CRB) and alginate-modified biochar (ARB) were prepared, and their effects on promoting soil pH buffering capacity (pHBC) and immobilizing cadmium (Cd) in the paddy soils were investigated through indoor incubation experiments. The results of Fourier transform infrared spectroscopy and Boehm titration indicated that the introduction of chitosan and sodium alginate effectively amplified the functional groups of the biochar, and improved acid buffering capacity of the biochar. Since there was a plateau region between pH 4.5 and 5.5 in acid-base titration curve of the CRB, adding this biochar to acidic paddy soils apparently improved the pHBC and enhanced the acidification resistance of the paddy soils. The addition of ARB enhanced the reduction reactions during submerging and weakened the oxidation reactions during draining, thus retarded the decline of paddy soil pH during drainage. Furthermore, the pH of the paddy soils with ARB addition was higher at the end of draining, which reduced the activity of soil Cd. Considering the environmental sustainability of chitosan and sodium alginate and convenience of preparation method, biochars modified with these two materials provided alternatives for acidic paddy soil amelioration and heavy metal immobilization. However, the additional experiments should be conducted under field conditions to confirm practical application effects in the future.
90. 题目: Composition of organic matter in soils from tidal marshes around the Chesapeake Bay, USA, as revealed by lipid biomarkers and stable carbon and nitrogen isotopes
The ability of tidal marshes to maintain their elevation despite rising sea levels depends on the accumulation of organic matter (OM) from estuarine particulate matter and in situ marsh plant production. Although previous studies have examined carbon in marshes, few have used the source composition of OM in marsh soils to provide insight into the processes controlling the delivery, transformation, and fate of carbon within marshes. This study used multiple geochemical tools (i.e., n-alkanes, fatty acids (FA), sterols, and stable carbon and nitrogen isotopes) to characterize the sources of OM in surface (0–10 cm) and subsurface (30–40 cm) soils collected along transects from the marsh edge to the low marsh/high marsh transition in tidal marshes around the Chesapeake Bay. Four study sites were selected for their different physical settings and soil types, allowing us to characterize the dominant OM sources in the soils and identify factors that contributed to differences in marsh OM composition. Contributions of OM from estuarine (i.e., short-chain FA, brassicasterol, cholesterol), marsh plant (i.e., long-chain FA, mid- and long-chain n-alkanes, sitosterol, taraxerol), and microbial (i.e., branched fatty acids, ergosterol) sources were identified in all soils. Results from a stable isotope mixing model allowed us to quantify the relative contributions of these OM sources to the marsh soils and indicated that soil OM was comprised of 29.0 ± 9.0% estuarine POM, 22.7 ± 5.5% riverine POM, 22.1 ± 11.3% C3 marsh plant OM, and 37.9 ± 13.8% C4 marsh plant OM. Relative contributions from these sources varied depending on location in the marsh with estuarine OM contributing a greater fraction of OM near the marsh edge and to surface soils while marsh plants contributed larger amounts of OM to soils in the marsh interior and in the sub-surface. Our results suggest that long-term carbon sequestration in marsh soils in controlled by the marsh plant community, and that changes to a marsh's physical setting or plant community in response to changing climate or human activity could alter the sequestration of carbon in marshes.
91. 题目: Influence of thermally activated peroxodisulfate pretreatment on gaseous emission, dissolved organic matter and maturity evolution during spiramycin fermentation residue composting
Aerobic composting combined with appropriate pretreatment is promising to achieve the utilization of antibiotics fermentation residues (AFRs). This research studied the effect of thermally activated peroxodisulfate (TAP) pretreatment on greenhouse gas (GHGs) emission, dissolved organic matter (DOM) and maturity evaluation during spiramycin fermentation residue (SFR) composting. Three treatments were conducted from co-composting of SFR and wheat straw, while 90% and 99.9% residual spirmycin removal pretreatment SFR by TAP were provided and compared with raw SFR. The cumulative CO2 and NH3 emissions increased by 17.2% and 30.8% after TAP pretreatment removed 99.9% residual spiramycin in SFR, while the cumulative CH4 and N2O emission decreased by 34.0% and 5.27%, respectively. The dissolved organic matter (DOM), humic acid (HA)/fulvic acid (FA) and NH4+/NO3- analysis confirmed that the composting maturity was improved with the increasing of HA and NO3- content by TAP pretreatment.
92. 题目: Respiration regimes in rivers: Partitioning source-specific respiration from metabolism time series
93. 题目: Fertilization regime shifts the molecular diversity and chlorine reactivity of soil dissolved organic matter from tropical croplands
Soil-derived dissolved organic matter (SDOM) is an important site-specific disinfection byproduct (DBP) precursor in watersheds. However, it remains unclear how fertilization regime shifts the molecular diversity and chlorine reactivity of SDOM in cropland-impacted watersheds. Here, we analyzed the spectroscopic and molecular-level characteristics of the SDOM from croplands that had different fertilization regimes (i.e., non-fertilization, chemical fertilization, straw return, and chemical fertilization plus straw return) for 5 years and evaluated the chlorine reactivity of the SDOM by determining the 24-h chlorine consumption and specific DBP formation potential (SDBP-FP). The SDOM level decreased by chemical fertilization and was not significantly altered by straw return alone or combined with chemical fertilizer. However, all fertilization regimes elevated the molecular diversity of SDOM by increasing the abundance of protein-, lignin-, and tannin-like compounds. The chlorine reactivity of SDOM was reduced by chemical fertilization, but was significantly increased by straw return. Typically, straw return increased the formation potential of specific trihalomethane and chloral hydrate by 339% and 56% via increasing the aromatics in SDOM, whereas chemical fertilization could effectively decrease about 231% of the increased specific trihalomethane formation potential caused by straw return. This study highlights that fertilization regime can significantly shape the molecular diversity and chlorine reactivity of the SDOM in croplands and that partially replacing chemical fertilizer with crop straw is an advantageous practice for reducing DBP risks in drinking water in cropland-impacted watersheds.
94. 题目: Electron transfer mechanism of chitosan-modified natural manganese ore-cornstalk biochar composites with activated peroxymonosulfate: The role of functional groups on the surface of biochar-based composites
Biochar-based composite-driven advanced oxidation processes have important applications in wastewater purification. However, due to the complex structure of biochar-based composites, the mechanism of the emerging nonradical pathway is unclear. In this study, the functional groups on the surface of biochar composites were modified by the addition of chitosan to natural manganese ore- cornstalk biochar composites (CMCCX). Besides, the intrinsic structure-property relationship of biochar-based composite activated peroxymonosulfate (PMS) for the nonradical oxidation of bisphenol A (BPA) via electron transfer were revealed. Correlation linear fits to functional group content revealed that C-C/C-H on CMCCX was the active site for the metastable PMS generation, C-OH inhibited the generation of metastable PMS. Also, Mn-O, carboxyl, and hydroxyl groups influenced the electron transfer process from BPA to metastable PMS. Overall, the study prepared environmentally friendly biochar-based composites by a simple method and provided a reference for the preparation of biochar-based composites with tunable redox capacity.
95. 题目: Floc formation and growth during coagulation removing humic acid: Effect of stirring condition
Number of studies have explored the mechanism of humic acid (HA) removal by coagulation, while studies on the formation and growth mechanism of HA-floc are still limited. In this study, a series of dynamically monitored experiments were carried out and floc characterization techniques were applied to investigate HA-floc growth mechanisms and properties under different stirring conditions. First, HA was removed in the early stages and varied insignificantly during floc growth, and the stirring condition did not affect the removal of HA. Moreover, HA hindered the effective collision, resulting in a slower floc growth rate and a lower fractal dimension. Although stirring condition did not markedly affect the HA removal performance, it had a remarkable effect on floc growth and structure. For example, gentle stirring resulted in larger floc d50 and pore size. Intense stirring accelerated the breakage or aging of flocs, resulting in a reduction in the final floc size at equilibrium. In particular, fast stirring in the early stage of coagulation advanced floc growth, but decreased the zeta potential and active sites of flocs, and reduced the capacity of the primary aggregates to grow into larger flocs. This study provides information on the floc formation and growth mechanism and the properties of flocs formed under different stirring conditions, which are helpful for optimizing the coagulation process on organic matter removal and guide the processes utilizing flocs.
96. 题目: Accompanying effects of sewage sludge and pine needle biochar with selected organic additives on the soil and plant variables
The effects of synthetic fertilizer and nutrient leaching are causing serious problems impacting soil function and its fertility. Mitigation of nutrient leaching and use of chemical fertilizer is crucial as fertile land adds up sustainability to climate changes. Biochar produced from agricultural bio-waste and municipal solid waste has been used for crop production and when applied in combination with organic nutrients may support mitigation of nutrient loss and adverse effects of chemical fertilizers. Different types of biochar and their application for soil enhancement have been observed, pine needle and sewage sludge derived low-temperature biochar along with compost, organic fertilizer in the form of manure and microalgal biomass may interact with soil chemistry and plant growth to impact nutrient loss and compensate the hazardous effect of chemical fertilizer, but it has not been investigated yet. This present study elaborates application of sewage sludge and pine needle biochar produced at 400 °C in an application rate of 5 % w/w and 10 t h−1 in combination with compost, manure and microalgal biomasses of Closteriopsis acicularis (BM1) and Tetradesmus nygaardi (BM2) on the growth of Chickpea (Cicer arietinum) and Fenugreek (Trigonella foenum-graecum) crop assessed in a pot experiment over a two crop (Chickpea - Fenugreek) cycle in Pakistan. Results depict that the pine needle biochar with additives has increased plant height by 104.1 ± 2.76 cm and fresh biomass by 49.9 ± 1.02 g, buffered the soil pH to 6.5 for optimum growth of crops and enhance carbon retention by 36 %. This study highlights the valorization of sewage sludge and pine needle into biochar and the effect of biochar augmentation, its impact on soil nutrients and plant biomass enhancement. The greener approach also mitigates and helps in the sustainable management of solid wastes.
97. 题目: Machine learning estimation of biodegradable organic matter concentrations in municipal wastewater
This study investigates whether a novel estimation method based on machine learning can feasibly predict the readily biodegradable chemical oxygen demand (RB-COD) and slowly biodegradable COD (SB-COD) in municipal wastewater from the oxidation–reduction potential (ORP) data of anoxic batch experiments. Anoxic batch experiments were conducted with highly mixed liquor volatile suspended solids under different RB-COD and SB-COD conditions. As the RB-COD increased, the ORP breakpoint appeared earlier, and fermentation occurred in the interior of the activated sludge, even under anoxic conditions. Therefore, the ORP decline rates before and after the breakpoint were significantly correlated with the RB-COD and SB-COD, respectively (p < 0.05). The two biodegradable CODs were estimated separately using six machine learning models: an artificial neural network (ANN), support vector regression (SVR), an ANN-based AdaBoost, a SVR-based AdaBoost, decision tree, and random forest. Against the ORP dataset, the RB-COD and SB-COD estimation correlation coefficients of SVR-based AdaBoost were 0.96 and 0.88, respectively. To identify which ORP data are useful for estimations, the ORP decline rates before and after the breakpoint were separately input as datasets to the estimation methods. All six machine learning models successfully estimated the two biodegradable CODs simultaneously with accuracies of ≥0.80 from only ORP time-series data. Sensitivity analysis using the Shapley additive explanation method demonstrated that the ORP decline rates before and after the breakpoint obviously contributed to the estimation of RB-COD and SB-COD, respectively, indicating that acquiring the ORP data with various decline rates before and after the breakpoint improved the estimations of RB-COD and SB-COD, respectively. This novel estimation method for RB-COD and SB-COD can assist the rapid control of biological wastewater treatment when the biodegradable organic matter concentration dynamically changes in influent wastewater.
98. 题目: From biomass to humic acid: is there an accelerated way to go?
Acid hydrothermal treatment of biowaste is favorable for producing hydrochar and corresponding hydrothermal solution containing saccharides, furans and aromatic compounds, while the alkaline hydrothermal condition is beneficial for their humification to form hydrothermal humic acid (HHA). Herein, the humification potential of hydrochar, hydrothermal solution, and their mixture under alkaline hydrothermal conditions was compared to further reveal their contribution to HHA. The result showed the main source of HHA was hydrochar, occupying 70 wt% of total HHA yield from their mixture while hydrothermal solution only contributed 17 wt%. Moreover, the HHA that existed in hydrochar (denoted as HHAacid) was 32 wt% while the hydrochar-derived HHA obtained after alkaline hydrothermal treatment (denoted as HHAalk) increased to 65 wt%, close to that from commercial coal or lignite. The hydrochar was further separated into four components, i.e. hydrothermal fulvic acid (HFA), stable HHAacid (S-HHAacid) non-stable HHAacid (N-HHAacid) and remaining substance (RS), aiming to reveal the major pathway of the incremental HHA production under alkaline hydrothermal condition. Reactions of RS + HFA, RS + N-HHAacid and self-synthesizing of RS all contributed to the incremental HHAalk yield with the major contribution (75 C%) from the first combination (RS + HFA). The pathways of alkaline hydrothermal humification of hydrochar were revealed after analyzing the molecular level structure of HHAalk by UPLC-MS. This in-depth analysis fills the knowledge gap in the mechanism of hydrothermal humification of biowaste.
99. 题目: Role of organic nanoparticles on transport and fate of various dyes in aqueous solution
This work studies the interaction of organic nanoparticles (ON) with various dyes in aqueous solution, to elucidate the role of ON on transport and fate of dyes in the environment, and on dyes removal from wastewater. Studied dyes are Acid Red 66 (AR66), Methylene Blue (MB), Reactive Black 5 (RB5), and Reactive Violet 5 (RV5). ON are extracted from organic matter of anthropogenic origin through resuspension of its colloidal fraction, and successive filtration and dialysis of the obtained suspension. Mechanisms of interaction are investigated initially through three-dimensional excitation emission matrix (3DEEM) analysis. Obtained data indicate that dynamic interactions occur strongly between dye molecules and ON aggregates. 3DEEM spectra of mixed samples containing ON together with one of the tested dyes, present a shape similar to the one of ON alone, but each of them is characterized by specific differences in terms of peaks quenching and shift. The analysis of these singularities suggests that dye molecules are bound to the functional groups of ON through H-bonds, according to the following steps: i) dyes reach the surface of ON aggregates; ii) the molecules pass through the hydrophilic surface of ON aggregates, and reach their hydrophobic core; iii) the dyes are sequestrated into the hydrophobic core of ON aggregates. Nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopies analysis confirm the formation of supramolecular aggregates with stable micellar hydrophobic structure, mainly consisting of aliphatic fractions of ON, which explain the disappearance of aromatic groups signals from dyes.
100. 题目: Effect of biological polymers on mobility and run-out distance of cohesive and non-cohesive sediment gravity flows
Lock-exchange experiments were carried out to investigate the effect of biologically cohesive extracellular polymeric substances (EPS) on the mobility of sediment gravity flows laden with physically cohesive clay, non-cohesive coarse silt and non-cohesive fine sand. The results reveal significant differences in the head velocity, run-out distance and deposit shape of these flows related to differences in physical cohesion, particle size, and EPS content. These differences are captured in a three-way coupling model of turbulent forces, cohesive forces, and particle settling velocity. In general, biological cohesion reduces flow mobility, demonstrated most clearly by a progressive decrease in the run-out distance of the silt and clay flows, as the EPS concentration is increased. This reduction in flow mobility is caused by the dominance of cohesive forces over turbulent forces, which comprise turbulence attenuation and the bulk settling of a biologically cohesive gel in which EPS form a pervasive network of bonds between the sediment particles. However, sand-laden gravity flows were found to behave in a markedly different way, in that the head velocity and run-out distance first increase and then decrease, as the EPS concentration is increased. The increase in sand flow mobility is inferred to be caused by a reduction in the settling velocity of the sand particles, as the EPS cause an increase in flow viscosity at EPS concentrations that are sufficiently low to maintain turbulent flow. Once the EPS concentration is high enough for turbulence attenuation, the sand flows start to agree with the silt and clay flows in establishing a negative correlation between flow mobility and EPS concentration caused by gelling. The experimental data also uncovered that deposits formed by EPS-rich, turbulence-attenuated flows are shorter and thicker and have more abrupt terminations than deposits formed by EPS-free or EPS-poor turbulent flows. The larger thickness of these deposits is partly caused by the ability of EPS to retain water and form matrix-supported textures. Earlier work has shown that EPS is common in many sedimentary environments, including those where sediment transport takes place regularly by particulate density currents. Combined with the increasing rate at which man-made structures, such as pylons and communication cables, appear in these environments, we argue that there is a need to incorporate the results of this study in applied models that aim to mitigate damage to such structures by sediment gravity flows.