• Journal of Environmental Science International
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• v.4 no.4
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• pp.367-377
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• 1995

The study of flocculation kinetics is of fundamental interest in the field of water treatment, because rational study of the factors affecting the coagulation process should be based on the rate of particle growth. The effect of sulfate on flocculation kinetics were examined using ferric nitrate as a coagulant to coagulate kaolin clay in water under several experimental conditions. Both the particle size distribution data obtained from the AIA and the on-line measurement of turbidity fluctuation by the PDA were used to measure flocculation kinetics. Results show that sulfate ion added to the kaolin suspension played an important role in the flocculation process, not only improving flocculation kinetics at more acidic pH levels but also changing surface charge of particles. The kinetics of flocculation were improved mainly by the enhanced rate and extent of Fe(III) precipitation attributed to the addition of sulfate, and thereby, better interparticle collision frequency, but little by the charge reductions resulting from the sulfate addition. The increase in sulfate concentration beyond $3\times10^{-4}M (up to 2\times10^{-3}M)$ did not induce further improvement in flocculation kinetics, although the higher concentrations of sulfate ion substantially increased the negative ZP value of particles. Key Words : Flocculation Kinetics, Fe(III) Coagulant, Sulfate ion, Turbidity Fluctuation.

• Carbon letters
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• v.8 no.4
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• pp.326-334
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• 2007

In this study, graphite composites were fabricated by warm press molding method to realize commercialization of PEM fuel cells. Graphite composites have been considered as alternative economic materials for bipolar plate of PEM fuel cells. Graphite powder that enables to provide electrical conductivity was selected as the main substance. The graphite powder was mixed with phenolic resin and the mixture was pressed using a warm press method. First of all, the graphite powder was pulverized with a ball mill for the dense packing of composite. As the ball milling time increases, the average size of particles decreases and the size distribution becomes narrow. This allows for improvement of the uniformity of graphite composite. However, the surface electrical resistivity of graphite composite increases as the ball milling time increases. It is due to that graphite particles with amorphous phase are generated on the surface due to the friction and collision of particles during pulverizing. We found that the contact electrical resistivity of graphite particles increases as the particle size decreases. The contact electrical resistivity of graphite powders was reduced due to high molding pressure by warm press molding. This leads to improvement of the mechanical properties of graphite composite. Hydrogen gas impermeability was measured with the graphite composite, showing a possibility of the application for bipolar plate in fuel cell. And, I-V curves of the graphite composite bipolar plate exhibit a similar performance to the graphite bipolar plate.

• Membrane Journal
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• v.24 no.1
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• pp.20-30
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• 2014

A membrane-coupled sequencing batch reactor (MSBR) was used for the advanced treatment of rural village sewage which is very low C/N ratio. The effect of powdered activated carbon, aeration rate, and external organic material loadings on the treatment efficiency and filtration performance were investigated in sequencing batch reactor, in which a flat-sheet type microfiltration membrane with a pore size of $0.4{\mu}m$ was submerged. At the initial operation (within 54 days) MLSS concentration, and the removal efficiencies of COD, T-N, and T-P were increased with the increase of C/N ratio. After 89 days the removal efficiencies of COD, T-N, and T-P were 97.1%, 75.0%, and 48.3%, respectively. Suspended solid-free effluent was obtained by membrane filtration. The T-P removal was relatively low because of depending on the amount of excess sludge wasting. During the operation of MSBR with powdered activated carbon, the particle size of the sludge reduced by the increase of collision frequency and mixing intensity. In comparison with MSBR without powdered activated carbon, TMP of MSBR with that was significantly elevated.

• Nuclear Engineering and Technology
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• v.19 no.2
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• pp.85-98
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• 1987

To analyze the aerosol dynamics in severe accidents of LMFBR, a new computer code entitled MCAD (Multicomponent Aerosol Dynamics) has been developed. The code can treat two component aerosol system using relative collision probability of each particles as sequences of accident scenarios. Coagulation and removal mechanisms incorporating Brownian diffusion and gravitational sedimentation are included in this model. In order to see the effect of particle geometry, the code makes use of the concept of density correction factor and shape factors. The code is verified using the experimental result of NSPP-300 series and compared to other code. At present, it fits the result of experiment well and agrees to the existing code. The input variables included are very uncertain. Hence, it requires uncertainty and sensitivity analysis as a supplement to code development. In this analysis, 14 variables are selected to analyze. The input variables are compounded by experimental design method and Latin hypercube sampling. Their results are applied to Response surface method to see the degree of regression. The stepwise regression method gives an insight to which variables are significant as time elapse and their reasonable ranges. Using Monte Carlo Method to the regression model of LHS, the confidence level of the results of MCAD and their variables is improved.

• Journal of Korean Elementary Science Education
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• v.42 no.1
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• pp.161-177
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• 2023

Scientific explanation is composed of various representations such as texts, diagrams, and graphs, and each representation contributes to expanding scientific meaning by connecting similar but slightly different meanings as a 'mode'. Based on this perspective of social semiotics, we aimed to identify the characteristics of meaning formation demonstrated in students' science writing (verbal mode) and science drawing (visual mode) and to discuss the pedagogical use of multimodal representations. To that end, 18 science drawings and 18 scientific writings constructed by science-gifted elementary students on air pressure were collected. The characteristics of the drawn and written explanations were then analyzed from the affordance perspective in social semiotics. In science drawing, students showed a tendency to use the affordance of the visual mode to infer concrete changes from the particle view, such as the movement of air particles, the number of air particles, and the collision of particles. In science writing, students used the affordance of the verbal mode mainly to infer the causal relationship between the concept of air pressure and other related factors at an abstract level. Based on those results, we discuss the educational implications and provide concrete examples of how to use the unique affordances of each form to complement one another.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.5
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• pp.448-454
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• 2000

This study was to examine the physicochemical characteristics of coagulation reaction between ignited oyster shell powder (IOSP) and red tide organisms (RTO), and its feasibility, in developing a technology for the removal of RTO bloom in coastal sea,IOSP was made from oyster shell and its physicochemical characteristics were examined for particle size distribution, surface characteristic by scanning electron microscope, zeta potential, and alkalinity and pH variations in sea water. Two kinds of RTO that were used in this study, Cylindrotheca closterium and Skeletonema costatum, were sampled in Masan bay and were cultured in laboratory. Coagulation experiments were conducted using various c(Incentrations of IOSP, RTO, and a jar tester. The supernatant and RTO culture solution were analyzed for pH, alkalinity, RTO cell number, IOSP showed positive zeta potentials of $11.1{\~}50.1\;mV\;at\;pH\;6.2{\~}12.7$, A positive zeta potential of IOSP slowly decreased with decreasing pNa 4,0 to 2,0. When pNa reached zero, the zeta potential approached zero, When a pMg value was decreased, the positive zeta potential of IOSP increased until pMg 3.0 and decreased below pMg 3.0. IOSP showed 4.8 mV of positive zeta potential while RTO showed -9.2 mV of negative zeta potential in sea water. A positive-negative EDL (electrical double-layer) interaction occurred between $Mg(OH)_2$ adsorption layer of IOSP and RTO in sea water so that EDL attractive force always worked between them. Hence, their coagulation reaction occurred at primary minimum on which an extreme attractive force acted because of charge neutralization by $Mg(OH)_2$ adsorption layer of IOSP. As a result, the coagulation reaction was rapidly processed and was irreversible according to DLVO (Deriaguin-Landau-Verwey-Overbeek) theory. Removal rates of RTO were exponentially increased with increasing both IOSP concentration and G-value. The removal rates were steeply increased until 50 mg/l of IOSP and reached $100{\%}\;at\;400\;mg/l$ of IOSP. Removal rates of RTO were $70.5,\;70.5,\;81.7,\;85.3{\%}$ for G-values of $1,\;6,\;29,\;139\;sec^(-1)$at IOSP 100 mg/l, respectively. This indicated that mixing (i.e., collision among particles) was very important for a coagulation reaction.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.5
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• pp.455-462
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• 2000

The objective of this study was to examine the physicochemical characteristics of coagulation reaction between loess and red tide organisms (RTO) and its feasibility, in developing a technology for the removal of RTO bloom in coastal sea. The physicochemical characteristics of loess were examined for a particle size distribution, surface characteristics by scanning electron microscope, zeta potential, and alkalinity and pH variations in sea water. Two kinds of RTO that were used in this study, Cylindrothen closterium and Skeietonema costatum, were sampled in Masan bay and were cultured in laboratory. Coagulation experiments were conducted using various concentrations of loess, RTO, and a jar tester. The supernatant and RTO culture solution were analyzed for pH, alkalinity, RTO cell number. A negative zeta potential of loess increased with increasing pH at $10^(-3)M$ NaCl solution and had -71.3 mV at pH 9.36. Loess had a positive zeta potential of +1,8 mV at pH 1.98, which resulted in a characteristic of material having an amphoteric surface charge. In NaCl and $CaCl_2$, solutions, loess had a decreasing negative zeta potential with increasing $Na^+\;and\;Ca^(+2)$ ion concentration and then didn't result in a charge reversal due to not occurring specific adsorption for $Na^+$ ion while resulted in a charge reversal due to occurring specific adsorption for $Ca^(+2)$ ion. In sea water, loess and RTO showed the similar zeta potential values of -112,1 and -9.2 mV, respectively and sea sand powder showed the highest zeta potential value of -25.7 mV in the clays. EDLs (electrical double-layers) of loess and RTO were extremely compressed due to high concentration of salts included in sea water, As a result, there didn't almost exist EDL repulsive force between loess and RTO approaching each other and then LVDW (London-yan der Waals) attractive force was always larger than EDL repulsive force to easily form a floe. Removal rates of RTO exponentially increased with increasing a loess concentration. The removal rates steeply increased until $800 mg/l$ of loess, and reached $100{\%}$ at 6,400 mg/l of loess. Removal rates of RTO exponentially increased with increasing a G-value. This indicated that mixing (i.e., collision among particles) was very important for a coagulation reaction. Loess showed the highest RTO removal rates in the clays.