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Ozonation pretreatment is typically implemented to improve algal cell coagulation. However, knowledge on the effect of ozonation on the characteristics and coagulation of associated algal organic matter, particularly cellular orga...
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Ozonation pretreatment is typically implemented to improve algal cell coagulation. However, knowledge on the effect of ozonation on the characteristics and coagulation of associated algal organic matter, particularly cellular organic matter (COM), which is extensively released during algal bloom decay, is limited. Hence, this study aimed to elucidate the impact of ozonation applied before the coagulation of dissolved COM from the cyanobacteria Microcystis aeruginosa. Additionally, the degradation of microcystins (MCs) naturally present in the COM matrix was investigated. A range of ozone doses (0.1-1.0 mg O-3/mg of dissolved organic carbon - DOC) and ozonation pH values (pH 5, 7 and 9) were tested, while aluminium and ferric sulphate coagulants were used for subsequent coagulation. Despite negligible COM removal, ozonation itself eliminated MCs, and a lower ozone dose was required when performing ozonation at acidic or neutral pH (0.4 mg O-3/mg DOC at pH 5 and 7 compared to 0.8 mg O-3/mg DOC at pH 9). Enhanced MC degradation and a similar pattern of pH dependence were observed after preozonation-coagulation, whereas coagulation alone did not sufficiently remove MCs. In contrast to the benefits of MC depletion, preozonation using >= 0.4 mg O-3/mg DOC decreased the coagulation efficiency (from 42%/48% to 28%-38%/41%-44% using Al/Fe-based coagulants), which was more severe with increasing ozone dosage. Coagulation was also influenced by the preozonation pH, where pH 9 caused the lowest reduction in COM removal. The results indicate that ozonation efficiently removes MCs, but its employment before COM coagulation is disputable due to the deterioration of coagulation. (C) 2020 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
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Concentration distribution of two fractions of glass-bead (ballotini) particles (medium size 0.44 and 0.53mm, respectively) in flows of heterogeneous slurry was measured in a laboratory pipe of the internal diameter of 100mm using...
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Concentration distribution of two fractions of glass-bead (ballotini) particles (medium size 0.44 and 0.53mm, respectively) in flows of heterogeneous slurry was measured in a laboratory pipe of the internal diameter of 100mm using a radiometric device. Particles in such flows are supported by both interparticle contacts and turbulent eddies and the solids load must be considered as combined load composed of both contact and suspended load. Flows tend to be partially stratified and if high concentrated (mean volumetric concentration of solids higher than approximately 20%) they exhibit a sliding bed. It appears that two most common methods to calculate concentration profiles in settling-slurry flows are not able to handle the sliding bed adequately. A comparison of the test results with the Gillies-Shook model for combined-load flows shows that the modeling approach requires further refinements. An application of the more recent Kaushal-Tomita model based on the turbulent-diffusion concept is inappropriate in high-concentrated slurries composed of medium-to-coarse grains. A simple one-dimensional model is proposed that takes conditions for an existence of a sliding bed into account and predicts a simplified concentration profile in stratified flows composed of a sliding bed and a transport layer above the bed.
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Constitutive models that complete the set of equations describing the flow of polymer melts should respect objective thermodynamics and stability conditions ensuring their validity in the whole range of possible deformation flow. ...
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Constitutive models that complete the set of equations describing the flow of polymer melts should respect objective thermodynamics and stability conditions ensuring their validity in the whole range of possible deformation flow. However, in practice, a very good description of flow situations can be achieved with the models not complying with the physical assumptions in all respects. Analogously to the term characterizing yield stress in empirical viscoplastic models, the term represented by the Gordon-Schowalter (GS) derivative in the differential constitutive models contributes to better fitting the experimental data, especially shear thinning. Efficiency of the recently presented modified eXtended Pom-Pom model (just one non-linear parameter per mode) implementing the GS derivative term (one additional non-affine motion parameter per mode) is improved (documented on LDPE, HDPE, and polyvinyl butyral (PVB) materials), and a comparison with the exponential Phan-Tien-Tanner (PTT) and PTT-XPP models (a priori containing the GS derivative term) are presented.
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This study focuses on the description of soil water dynamics at four sites with different land cover types, namely beech forest, conifer forest, meadow and clipped grass. The analysis was based on soil tensiometer measurements fro...
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This study focuses on the description of soil water dynamics at four sites with different land cover types, namely beech forest, conifer forest, meadow and clipped grass. The analysis was based on soil tensiometer measurements from five consecutive vegetation seasons (comprising both wet and dry years). We investigated both column average pressure heads and also their vertical distribution. The soil water balance was studied by the HYDRUS-1D model.
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The removal of algal organic matter (AOM) is a growing concern for the water treatment industry worldwide. The current study investigates coagulation of non-proteinaceous AOM (AOM after protein separation), which has been minimall...
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The removal of algal organic matter (AOM) is a growing concern for the water treatment industry worldwide. The current study investigates coagulation of non-proteinaceous AOM (AOM after protein separation), which has been minimally explored compared with proteinaceous fractions. Jar tests with either aluminum sulphate (alum) or polyaluminium chloride (PACT) were performed at doses of 0.2-3.0 mg Al per 1 mg of dissolved organic carbon in the pH range 3.0-10.5. Additionally, non-proteinaceous matter was characterized in terms of charge, molecular weight and carbohydrate content to assess the treatability of its different fractions. Results showed that only up to 25% of non-proteinaceous AOM can be removed by coagulation under optimized conditions. The optimal coagulation pH (6.6-8.0 for alum and 7.5-9.0 for PACl) and low surface charge of the removed fraction indicated that the prevailing coagulation mechanism was adsorption of non-proteinaceous matter onto aluminum hydroxide precipitates. The lowest residual Al concentrations were achieved in very narrow pH ranges, especially in the case of PACl. High-molecular weight saccharide- like organics were amenable to coagulation compared to low-molecular weight (<3 kDa) substances. Their high content in non-proteinaceous matter (about 67%) was the reason for its low removal. Comparison with our previous studies implies that proteinaceous and nonproteinaceous matter is coagulated under different conditions due to the employment of diverse coagulation mechanisms. The study suggests that further research should focus on the removal of low-molecular weight AOM, reluctant to coagulate, with other treatment processes to minimize its detrimental effect on water safety. (C) 2018 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.
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Low molecular weight algal organic matter (AOM), as a frequent water contaminant with poor coagulation efficiency, adversely affects the quality of produced water and serves as a source of potentially carcinogenic disinfection by-...
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Low molecular weight algal organic matter (AOM), as a frequent water contaminant with poor coagulation efficiency, adversely affects the quality of produced water and serves as a source of potentially carcinogenic disinfection by-products. AOM removal from water is inevitable to eliminate the negative health and environmental impacts. This research evaluates the removal of arginine, phenylalanine and aspartic acid, which are amino acids abundant in AOM. Adsorption experiments were performed at 10, 18 and 25 degrees C and pH 5, 7 and 9 using two different activated carbons (FTL, PIC). Amino acids showed endothermic adsorption behaviour, with a higher removal at higher temperature. Higher temperature increased the diffusion of amino acid molecules, reduced the solution viscosity, or enhanced the hydrophobic interactions contributing to adsorption. The effect of temperature manifested differently during experiments depending on the chemical nature of the amino acids, the pH value and the surface properties of the carbon. Phenylalanine isotherms showed specific waves (Langmuir type 4). pH had a greater effect on arginine adsorption than did temperature. Aspartic acid isotherms exhibited a decrease in adsorption at higher pH values and higher temperatures. The principal mechanisms involved in amino acid adsorption were hydrophobic interactions, electrostatic interactions or hydrogen bonds.
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The method of preparation of polymer solutions significantly influences the quality of the corresponding electrospun nanofibrous webs. However, this factor is often ignored, and in a majority of presentations concerning the electr...
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The method of preparation of polymer solutions significantly influences the quality of the corresponding electrospun nanofibrous webs. However, this factor is often ignored, and in a majority of presentations concerning the electrospinning process, the applied method is not mentioned. This paper compares the influence of magnetic stirring, vibrational shaking and ultrasonication on a solution of poly(ethylene oxide) in distilled water. Along with the methods of preparation, other parameters were altered such as concentration, intensity of mixing and molecular weight. The best results from the viewpoint of electrospinning were achieved with moderate magnetic stirring.
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To evaluate the lowest polymer concentration within a solvent from which there appears beadless nanofibres during the process of electrospinning, is rather complicated. A widely used method is based on a determination of so called...
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To evaluate the lowest polymer concentration within a solvent from which there appears beadless nanofibres during the process of electrospinning, is rather complicated. A widely used method is based on a determination of so called entanglement concentration c(e) and the onsets of beadless nanofibres are characterized by multipliers of c(e) subjected to used materials. However, a determination of c(e) as an intersection point of two linear segments (in log-log coordinates specific viscosity vs. concentration) in a semi-dilute region is not applicable for all materials as for instance a solution of poly(ethylene oxide) (PEO) in water does not exhibit 'classical' three linear segments within the dilute and semi-dilute regions determining overlap and entanglement concentrations. For such cases a new approach for the evaluation of an initial concentration from which beadless nanofibres are produced is proposed. This method does not use the terms overlap and entanglement concentrations. The procedure is demonstrated using four PEO solutions differing in molecular weight. The relationship expressing initial concentration in dependence on PEO molecular weight containing no adjustable parameters is proposed.
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Extreme precipitation intensities derived from temporally aggregated time series can be considerably underestimated. Therefore, some form of correction is appropriate prior to their usage e.g. for the derivation of idf curves. The...
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Extreme precipitation intensities derived from temporally aggregated time series can be considerably underestimated. Therefore, some form of correction is appropriate prior to their usage e.g. for the derivation of idf curves. The correction is usually performed in a multiplicative manner, using the coefficient obtained as a mean ratio of real to aggregated extremes. In this paper a novel correction approach is derived, allowing an individual treatment of each aggregated extreme. The precipitation time series from Prague (central Europe) are used for the assessment of newly introduced method. The comparison with the standard approach shows that the new method reaches better results as it reduces an undesirable overestimation of the corrected extremes. Moreover, the effect of data aggregation on extreme precipitation intensities is evaluated as well as the effect on quantiles of the generalized extreme value (GEV) distribution. The results are compared to those published for other climatic conditions.
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Many studies have overlooked the role of pH in optimizing coagulation. Herein, the authors emphasize the importance of pH value in coagulation during the production of drinking water. We investigate the influence of pH value on th...
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Many studies have overlooked the role of pH in optimizing coagulation. Herein, the authors emphasize the importance of pH value in coagulation during the production of drinking water. We investigate the influence of pH value on the surface charges and forms of coagulants and impurities intended for removal. A methodology is suggested for optimizing key parameters for efficient coagulation - coagulant dosage and pH value. The study points out that various optimal pH ranges are required for coagulation of specific impurities and their mixtures. For natural organic matter of both humic and algogenic origin, acidic pH values are favourable for their removal through charge neutralization mechanism. Algal cells are effectively coagulated at slightly acidic to neutral pH values due to interactions with coagulant hydroxide precipitates. Inorganic particles are eliminated preferably at around neutral pH values. When mixtures of impurities are coagulated, mutual interaction between the impurities may impact dose of coagulant and also optimal pH ranges.
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