Daechul Cho

EVALUATION OF PH CONTROL AGENTS INFLUENCING ON CORROSION OF CARBON STEEL IN SECONDARY WATER CHEMISTRY CONDITION OF PRESSURIZED WATER REACTOR

The effect of various pH agents on the corrosion behavior of carbon steel was investigated under a simulated secondary water chemistry condition of a pressurized water reactor (PWR) in a laboratory, and the steel’s corrosion performance was compared with the field data obtained from Uljin NPP unit 2 reactor. All tests were carried out at temperatures of 50oC ? 250oC and pH of 8.5 ? 10. The pH at a given temperature was controlled by adding different agents. Laboratory data indicate that the corrosion rate of carbon steel decreased as the pH increased under the test conditions and the highest corrosion rate was measured at 150oC. This high corrosion rate may be related to high dissolution and instability of Fe oxide (Fe3O4) at 150oC. It was also found that an addition of ethanolamine (ETA) to ammonia was more effectivefor anticorrosion than ammonia alone, and that mixed treatment reduced 50% of iron or more at pHs of 9.5 or higher, especially in the steam generator (SG) and the moisture separator & re-heater (MSR).

Kinetics ofin situ surfactant soil flushing at moderate washing conditions

Economicin situ soil flushing using common surfactants may be a good substitute for exhaustive, pressurized soil washing or bioremediation requiring high energy consumption or laborious technique. Two model surfactants, sodium dodecyl sulfate (SDS) and polyoxyethylene (20) sorbitan monooleate (Tween-80), were chosen as flushing agents. Those surfactant solutions were applied to clean hydrocarbon (motor oil) contaminated sand soil. A kinetic investigation such as order of reaction of pollutant compounds, flushing mode (semi-continuous and continuous), change of soil pore matrix, etc. comprised a main part of this work. We found that the hydrocarbon elution curves were dropping in an exponential way, which was stiffer with higher surfactant concentrations. Higher surfactant concentration, higher flow rate, and lower porosity guaranteed higher removal efficiency as well as higher removal rate. Strong initial lag phases were found for Tween-80 solutions. A modified Monod-type reaction model describing the removal kinetics was proposed to be the first-order reaction, which agreed well with most of the experimental results. The curve-fitted parameters, n, k0 and K1 were linear functions of surfactant concentration and reciprocal of soil porosity.

Optimal Culturing and Enhancement of Lipid Accumulation in a Microalga Botryococcus braunii

Several tests and experimental work have been done for identifying the best growth conditions and accumulated amount of lipid moiety in B. braunii, a microalga(UTEX 572) in terms of media composition. The specific growth rate was found to be the highest at 0.15 g/L-day when the phosphorus concentration was doubled with the other ingredients at the normal level. Experiments for varied media compositions revealed that the accumulation of lipid was the highest at 48% (dry cell weight based) in the nitrogen deficient medium and its corresponding specific growth rate was comparative to that in the normal BG 11 medium. In the bubble column experiments, carbon dioxide containing air produced four times more cell mass than air only. Light and glucose addition also enhanced cell mass with maximum, 1.8 g/L and accordingly 42% of lipid composition, which turned out to be a better strategy for higher lipid-producing microalgal culture.

Interaction of Β-cyclodextrin with lipophilic ring compounds deposited in a sandy soil matrix during flushing

Chemical soil flushing in a packed sandy soil matrix using a natural surfactant, Β-cyclodextrin (CD) was investigated via a fluorescence spectroscopy and a dye labeling. The contaminants are lipophilic ring compounds — phenanthrene and naphthalene. Sand type and flushing intensity (rate and concentration) are critical investigation variables. The removal efficiencies were proportional to flow rate, concentration, temperature of the flushing solution and voidity of the sand column. Initial sorption of the surfactant onto the soil matrix was found to be a key step while flow shear was more crucial in the later steps. From time delay experiments before flushing, we speculate that the complexation reaction appears to be rate-limiting in non-equilibrium washing schemes.

A Solution Approach to the Design of Multi-period, Multipurpose Batch Plants

A deterministic model for multipurpose, multiperiod batch plants was presented in a linearized form to predict the future design according to the change of demand by using a modified Benders’ Decomposition. The OSL code offered by the IBM corporation as optimizer was employed for solving several example problems. The decomposition method was successful, showing remarkable reduction in the computing times as compared with those of the direct solution method. Also the heuristic used as a solution approach for the multiperiod model provided an efficient methodology to the block-structured problem by dividing the large overall problem into the manageable single period blocks.

Formation and stability study of silver nano-particles in aqueous and organic medium

Colloidal silver nanoparticles were obtained by chemical reduction of silver nitrate in water and organic solvent with sodium borohydride. The effects of oxidant, reducing agent, stabilizer, and temperature, during the growth of silver nanoparticles were discussed. As the reaction proceeded in aqueous medium a characteristic plasmon absorption peak between 390-420 nm appeared as presence of silver nanoparticles. The peak intensities and shifting (blue or red) were altered in accordance with some applied factors. The formed silver nanoparticles were found to be with particles size range from 3 to 20 nm. The change rates of Ag+ ions to Ag0 in aqueous and organic solvent are strongly temperature dependent, although reduction can take place at room temperature. The silver nano-colloid with negative zeta potential also has been confirmed to be more stable. Obtained nanoparticles were characterized by UV-vis spectrophotometer, particle analyzer for zeta (ζ) potential, polydispersity index (PDI), and transmission electron microscope (TEM).

A solid control strategy for preparation of silver nanoparticles in aqueous medium

Uniformly distributed, spherically shaped, mild concentrated silver nanoparticles with single-digit to hundreds nm size have been prepared by reducing silver nitrate with popular reducers like sodium borohydride or hydrazine in the presence of ordinary stabilizers such as SDS, PVP, Polysorbates and ultrasonication. Uv-visble spectroscopic analysis, particle size analysis, and particle-imaging through transmission electron microscopy (TEM) were used for nanoparticle characterization. Higher temperature accelerated the reduction rates, which follows the typical autocatalytic kinetics. Particularly, ultrasonication helped to facilitate the crucial stage of reduction phase to result in excellent quality of nanosolution, such as narrow distribution of particles and size uniformity. We found that initial location or arrangement of silver ions in clouds of stabilizers and ‘effectve mixing’ in the stage of reduction were vital for successful preparation of silver nanosolution. Also, reagent/stabilizer ratio, reducer input, solution environment such as pH, temperature, and stabilizer properties were optimized and discussed in detail. Proper selection of stabilizer and molar ratio to reagent and effective ‘mixing’ for preventing grain growth needs to be investigated more in the future work.

Electricity Generation and De-contamination Effect for Characteristic Electrode Material in a Microbial Fuel Cell System Using Bay Sediment

Sediment works as a resource for electric cells. This paper was designed in order to verify how sediment cells work with anodic material such as metal and carbon fiber. As known quite well, sediment under sea, rivers or streams provides a furbished environment for generating electrons via some electron transfer mechanism within specific microbial population or corrosive oxidation on the metal surfaces in the presence of oxygen or water molecules. We experimented with one type of sediment cell using different anodic material so as to attain prolonged, maximum electric power. Iron, Zinc, aluminum, copper, zinc/copper, and graphite felt were tested for anodes. Also, combined type of anodes-metal embedded in the graphite fiber matrix-was experimented for better performances. The results show that the combined type of anodes exhibited sustainable electricity production for ca. 600 h with max. 0.57 W/m 2 Al/Graphite. Meanwhile, graphite-only electrodes produced max. 0.11 W/m 2 along with quite stationary electric output, and for a zinc electrode, in which the electricity generated was not stable with time, therefore resulting in relatively sharp drop in that after 100 h or so, the maximum power density was 0.64 W/m 2 . It was observed that the corrosive reaction rates in the metal electrodes might be varied, so that strength and stability in the electric performances(voltage and current density) could be affected by them. In addition to that, COD(chemical oxygen demand) of the sediment of the cell system was reduced by 17.5∼36.7% in 600 h, which implied that the organic matter in the sediment would be partially converted into non-COD substances, that is, would suggest a way for decontamination of the aged, anaerobic sediment as well. The pH reduction for all electrodes could be a sign of organic acid production due to complicated chemical changes in the sediment.

Comparison of Cyanide Degrading Enzymes Expressed from Genes of Fungal Origin

A variety of fungal species are known to degrade cyanide through the action of cyanide hydratase, a specialized nitrilases which hydrolyze cyanide to formamide. This work is a report on two unknown and un-characterized members from Neurospora crassa and Aspergillus nidulans. Recombinant forms of three cyanide hydratases (CHT) originated from N. crassa, Gibberella zeae, and A. nidulans were prepared after their genes were cloned with N-terminal hexahistidine purification tags, expressed in E. coli and purified using immobilized metal affinity chromatography. These enzymes were compared according to their pH activity profiles, and kinetic parameters. Although all three were similar, the N. crassa CHT has the widest pH range of activity above 50% and highest turnover rate () among them. The CHT of A. nidulans has the highest Km value of the three nitrilases evaluated in here. Expression of CHT in both N. crassa and A. nidulans were induced by the presence of KCN, regardless of any presence of nitrogen sources. These data can be used to determine optimal procedures for the enzyme uses in the remediation of cyanide-containing wastes.

Sensitivity of veliger larvae of Mytilus edulis and mussel of various sizes to chlorination

The blue mussel Mytilus edulis is one of the dominant fouling organisms in cooling water systems. In this work, how veliger larvae and different size groups of the mussels responded against chlorine dosage was examined. Veliger larvae mortality was studied at different residual chlorine concentrations (0.05–0.5 mg L−1), and it was found that a chlorine dose of 0.5 mg L−1 is 4 times as effective as 0.05 mg L−1 and twice as effective as 0.1 mg L−1. Mortality of 100% for three size groups (1.4, 14, and 25 mm) and relative physiological activities of two size groups (14 and 25 mm) were observed. The exposure duration for 100% mortality of mussels decreased with the increasing residual chlorine concentration (0.1–4.0 mg L−1). Mussel size was also found to be an important factor, considering that the continuation times for mussel mortality were 28 h for the 1.4 mm and 410 h for the 25 mm size groups. All size groups showed progressive reduction in physiological activities, such as oxygen consumption, foot activity, and byssus thread production with increasing chlorine dose (0.05–1.0 mg L−1); the two data-sets were strongly correlated with each other. The results of this study should be of significance for optimizing the chlorine content, and minimize the environmental threat to industries where mussels are the dominant fouling organisms.