Sung-Hyun Kwon

Correlation of Releases of Nutrient Salts in Sediment with Vicinal Oxic Conditions

Abstract The aim of this paper is to correlate the release characteristics of marine and lake sediment with their vicinal oxic conditions. We performed lab-scale simulation experiments using field sediment and water in order to compare the release concentrations and the release rates one another. To provide a few different kinds of oxic environments we used natural air flow and some oxygen releasing compounds such as CaO 2 and MgO 2 . In case of phosphates, in each oxic condition, removal of phosphorus via biological activity and that via salt precipitation with the metal ions lowered the release rates. The behavior of the nitrogen-origin salts seemed to greatly depend on the typical biological actions - growth of biomass, nitrification, and partial denitrification. Generally speaking, the control of releases of NH 3 -N, PO 4 -P, T-N and T-P was successful under the oxic conditions meanwhile COD, nitrates and nitrites were difficult to reduce the releases into the bulk water because of the considerable microbial oxidation. Based on typical diffusive mass transfer kinetics the changes of concentrations of the nutrients were computed for qualitative and quantitative comparisons.

Degradation of ammonium dinitramide (ADN) in digested sewage sludge under strict anaerobic conditions

The biodegradation of one popular nitramine energetics, ammonium dinitramide (ADN) by mixture of denitrifying bacterial species was investigated. ADN was observed to be effectively mineralized in the anaerobic mixed culture. The initial ADN concentration of 250 mg/L was reduced to non‐detectable levels (> 99% removal efficiency) in 5 days of incubation under anaerobic conditions. Final products generated from anaerobic degradation of nitramine energetics by anaerobic metabolism were NH4 +, CH4, and CO2 that were released to the environment with the denitrifiers’ growth. In addition, it was found that the activity of denitrifiers was inhibited by high concentration of ammonia generated through the degradation reactions of energetic nitrites.

A biological approach in the treatment of TNT wastewater

A mixed microbial population in digested sewage culture under strict anaerobic conditions degraded TNT (2,4,6‐trinitrotoluene) effectively. An initial concentration of 110 mg/L of TNT was reduced to a non‐detectable amount (> 99% removal) in 6 days of incubation. Red color due to the electron charge of NO2 groups becomes colorless after 6 days of incubation, while the autoclave control remained red in color. Further stepwise deamination and subsequent mineralization by ring cleavage occurred by mixed nitroreductase which is available from many of the denitrifying bacteria predominantly in sewage culture.

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.

Influence of Effective Microorganisms on Polluted Marine Sediment and Its Microbial Community

Lactobacillus sp., Acetobacter sp. and yeast were the most dominant organisms in the EM stock culture and subculture product. Lactic acid bacteria and yeast were able to grow in the fermentation process utilizing seawater. EM treatment of higher concentrations using EM stock culture and EM clay balls (1% or 4%) contributed to an early removal of malodor and an increase of DO in the polluted sediments, indicating an odor-removing activity of EM. The EM treatment of higher concentrations (1% or 4%) somewhat appeared to modify the microbial communities within the sediments, which was confirmed by existence of a few unique fragments from the stock culture based on PCR-DGGE. It still remains to be elucidated that EM cultures were directly involved in the malodor removal and potential sediment bioremediation.

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.

A new bioremediation approach in the treatment of petroleum‐contaminated groundwater

The objective of this research is to determine the feasibility of enhanced bioremediation with oxygen‐releasing compound (ORC) of petroleum‐contaminated groundwater. Total petroleum hydrocarbon (TPH) and its most important components benzene, toluene, ethylbenzene and xylene (BTEX) may be degraded via biological activities under aerobic conditions. The ORC can supply oxygen when needed, as can other chemical oxygen sources like hydrogen peroxide and calcium peroxide, but the ORC has several important advantages. The concentrations of TPH and BTEX were reduced to almost 99% of the original in the ORC batch due to high microbial activity. In contrast, only a 18.9% reduction of TPH and a 2.1 % reduction of the total BTEX were found in the control batch after two weeks of incubation. It is suggested that this improved biodégradation process, which poses high treatment efficiency in a short period, may be a good approach for field applications such as soil and groundwater remediation.

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.

Characteristics of electricity production by metallic and nonmetallic anodes immersed in mud sediment using sediment microbial fuel cell

Abstract Sediment microbial fuel cell (SMFC), equipped with Zn, Al, Cu, Fe or graphite felt (GF) anode and marine sediment, was performed. Graphite felt was used as a common cathode. SMFC was single chambered and did not use any redox mediator. The aim of this work was to find efficient anodic material. Oxidation reduction potential (ORP), cell voltage, current density, power density, pH and chemical oxygen demand (COD) were measured for SMFC’s performance.. The order of maximum power density was 913 mWm -2 for Zn, 646 mWm -2 for Fe, 387.8 mWm -2 for Cu, 266 mWm -2 for Al, and 127 mWm -2 for graphite felt (GF). The current density over voltage was found to be strongly correlated with metal electrodes, but the graphite felt electrode, in which relatively weaker electricity was observed because of its bio-oriented mechanism. Metal corrosion reactions and/or a complicated microbial electron transfer mechanism acting around the anodic compartment may facilitate to generate electricity. We presume that more sophisticated selection of anodic material can lead to better performance in SMFC.