Catalytic reduction of sulfur dioxide with carbon monoxide over tin dioxide for direct sulfur recovery process

SO(2) reduction by CO over SnO(2) catalyst was studied in this work. The parameters were the reaction temperature, space velocity (GHSV) and [CO]/[SO(2)] molar ratio. The optimal temperature, GHSV and [CO]/[SO(2)] molar ratio were 550 degrees C, 8000 h(-1) and 2.0, respectively. Under these conditions, the SO(2) conversion and sulfur selectivity were about 78% and 68%, respectively. The following reaction pathway involving two mechanisms was proposed in SO(2) reduction by CO over SnO(2) catalyst: in the first step involving Redox mechanism, the elemental sulfur was produced by the mobility of the lattice oxygen between SO(2) and SnO(2) surface. In the second step, COS was formed by the side reaction between elemental sulfur and CO or metal sulfide and CO. In the third step involving COS intermediate mechanism, the abundant elemental sulfur was produced by the SO(2) reduction by COS which was produced in the second step and was more effective reducing agent than CO.     

Stressor identification and health assessment of fish exposed to wastewater effluents in Miho Stream, South Korea

This study evaluated the effects of an industrial wastewater treatment plant (IWTP) and a municipal wastewater treatment plant (MWTP) effluents on a variety of bioindicators ranging from biochemical, organism, and population-level responses in pale chub (Zacco platypus) and fish community structure. The Index of Biotic Integrity (IBI) indicated that the site upstream of these wastewater treatment plant discharges is in fair–good condition and downstream of the plant is in poor condition. The EROD (ethoxyresorufin-O-deethylase) activity, condition factor, and liver somatic index were significantly increased at the downstream site compared to those of the upstream site. The most significant change observed in pale chub population in the downstream site of the Miho Stream, relative to the upstream population, was the total absence of an younger age group. Stressors impacting the downstream site were identified as mostly organic or nutrient enrichment and habitat degradation associated with wastewater treatment plants. The results of causal analysis suggest that the primary causes affecting fish population in the downstream site are through both size-selective mortality caused by ammonia toxicity and recruitment failure caused by habitat degradation and reproduction problem due to an IWTP and MWTP effluents.     

Cell-wall morphology correlated with vertical migration in the non-motile marine dinoflagellate Pyrocystis noctiluca

 We report an ultrastructural study of the morphological changes in cells of the marine dinoflagellate Pyrocystis noctiluca Murray, which correlate with its vertical migration pattern. Cells alternate between a large, highly vacuolated, positively buoyant, vegetative cyst surrounded by a dinosporin-containing wall and a smaller, more compact, negatively buoyant, cellulose-bounded cell. The cyst wall is composed of two layers: a thin smooth outer layer, thought to be composed of dinosporin, and a thick inner layer that likely to be cellulosic. One or two thecate cells are formed from within the cysts. Thecate cells are smaller, more compact and contain many small translucent bodies. They are surrounded by a typical dinoflagellate amphiesmal layer composed of membranes and cellulose plates. The amphiesmal layer appears only in recently divided cells and exists for only one night. By the following day, the cellulose wall has been replaced by a new dinosporin wall synthesized from beneath the cellulose thecal layer. The cyst stage is suggested as being optimized for photosynthesis, whereas the compact, negatively buoyant, thecate form is thought to allow nutrient uptake in deeper waters. Vertical migration in this species is thus correlated with the presence of dinosporin wall during most of its stay in the upper waters, alternating with a brief thecate wall in deeper nutrient-rich waters. This is the first report correlating dinoflagellate vertical migration with changes in cell-wall composition. Received: 28 July 1999 / Accepted: 8 May 2000     

Dissipation pattern and pre-harvest residue limit of abamectin in perilla leaves

The pre-harvest residue limit (PHRL) of abamectin (abamectin B1a and B1b) in Perilla frutescens leaves grown under greenhouse conditions were investigated using high-performance liquid chromatography with a fluorescence detector. Samples were extracted with acetonitrile. The extract was purified through a solid phase extraction procedure. Then the purified extract was derivatized with trifluoroacetic anhydride and N-methylimidazole to form a strong stable fluorescent derivative of abamectin. Finally, derivatized abamectins were conveyed to the detector via an Atlantis C₁₈ column, with water and methanol as a mobile phase. Calibration curves were linear over the calibration ranges with coefficients of determinants r ²?≥?0.999. The limits of detection and quantification were 0.0033 and 0.01 mg kg^?1 for abamectin B_1a and B_1b, respectively. Recovery was assessed in a control matrix at two different fortification concentrations, with three replicates for each concentration. Good recoveries were obtained for the target analytes and ranged from 82.11 to 93.03 %, with relative standard deviations of less than 8 %. The rate of disappearance of total abamectin on perilla leaves for recommended and double the recommended doses was described as first-order kinetics with a half-life of 0.7 days. Using the PHRL curve, we could predict the residue level of total abamectin to be 0.92 mg kg^?1 at 7 days before harvest or 0.26 mg kg^?1 at 4 days before harvest, which would be below the provisional MRL designed by the Korea Food and Drug Administration.     

Transportation noise and exposed population of an urban area in the Republic of Korea

Using noise prediction models, we explored the transportation noise levels of Youngdeungpo-gu, an urbanized area of Seoul Metropolitan City in the Republic of Korea. In addition, we estimated the population exposed to transportation noise levels and determined how many people are vulnerable to noise levels that would cause serious annoyance and sleep disturbance. Compared with the World Health Organization [WHO] recommended levels, the daytime and nighttime transportation noise levels were still high enough to have the two psychosocial effects on people when considering the recommended levels of the World Health Organization (WHO; 55 decibels [dB[A]] and 40 dB[A] for daytime and nighttime, respectively). Particularly, nighttime transportation noise was discovered to be harmful to a wider area and more people than daytime noise. Approximately 91% of the Youngdeungpo-gu area experienced nighttime transportation noise levels exceeding those recommended by WHO. It was estimated that as much as 80% of the people in the study area were exposed to transportation noise levels >40 dB[A] during nighttime. Taking this into account, there is an urgent need to control and reduce transportation noise levels in Seoul, to protect residents against the potential ill health effects caused by urban transportation.     

Field application of electrokinetic remediation for multi-metal contaminated paddy soil using two-dimensional electrode configuration

In this study, we evaluated the feasibility of in situ electrokinetic remediation for arsenic (As)-, copper (Cu)-, and lead (Pb)-contaminated soil, in a pilot-scale field application with two-dimensional electrode configurations. Square and hexagonal configurations with different electrode spacing, 1 m and 2?m, were investigated under a constant 100 V. A square configuration with electrode spacing of 2 m removed 61.5 % of As, 11.4 % of Cu, and 0.9 % of Pb, respectively, and a hexagonal configuration with the same spacing showed a higher removal efficiency in top (59 % of As, 0–0.5 m) and middle (53 % of As, 0.5–1.0 m) layers, but much lower removal efficiency in the bottom layer (1–1.5 m), which was thought to be due to groundwater flow through periodic rise and fall of tides. Fractionation analysis showed that As bound to Fe–Mn oxyhydroxide was the main form of As removed by the electrokinetic process. The two-dimensional configuration wasted less electrical energy by Joule heating, and required fewer electrode installations, compared to the one-dimensional electrode configuration.     

Structural effect of the in situ generated titania on its ability to oxidize and capture the gas-phase elemental mercury

Structural effect of the in situ generated TiO(2) sorbent particle was examined for its ability to capture elemental mercury under UV irradiation in a simulated combustion flue gas. Titania particles were prepared by thermal gas-phase oxidation of Titanium (IV) isopropoxide (TTIP) using a high temperature electric furnace reactor. The structural characteristics of the in situ generated TiO(2) at various synthesis temperatures were investigated; size distribution and the geometric mean diameter were measured using a scanning mobility particle sizer, while fractal dimension and radius of gyration were evaluated from the transmission electron microscopy images. Results from the Hg(0) capture experiment show that with increasing titania synthesis temperature, the overall aggregate size increases and the morphology becomes more open-structured to gas-phase Hg(0) and UV light, resulting in the improved mercury removal capability.     

Mass Load-Based Pollution Management of the Han River and Its Tributaries, Korea

Spatio-temporal variations of biochemical oxygen demand (BOD) and total coliform (TC) in the Han River, Korea, were investigated in terms of concentration-based and mass loading-based approaches. Considering the river water quality criteria regulated by the Ministry of Environment in Korea, the tributaries linked to the mainstream of the Han River were found to be highly contaminated with respect to both BOD and TC and, in fact, most of the tributaries exceeded the maximum water quality criteria. To evaluate the pollution impact of tributaries on the mainstream, the monthly water quality monitoring data for six years (from 1995 to 2000) were collected from the Han River basin, and statistically analyzed using Pearson’s correlation coefficient. The results revealed that mass loading-based approach was superior to the concentration-based approach for effective Han River watershed management. Overall results supported that the mass loading-based approach associated with total maximum daily loads (TMDL) management would be a useful and suitable protocol in watershed management for improving the water quality of the Han River and protecting public health. Therefore, this study supporting TMDL management can be applicable to a wide array of contaminants and watershed settings in Korea.     

Occurrence and ecological hazard assessment of selected veterinary medicines in livestock wastewater treatment plants

The occurrence of some veterinary medicines in the livestock wastewater plants (WWTPs) was investigated. This investigation represented the occurrence of veterinary medicines to treat in the livestock WWTPs or be discharged into the water system in Korea since the sampling sites were widely distributed across the nation and samples were collected from the 11 livestock WWTPs. Nine antibiotics, two analgesics, and two disinfectants occurred in the livestock wastewater plants (WWTPs). From 11 livestock WWTP influents, chlortetracycline, oxytetracycline, acetylsalicylic acid, and disinfectants frequently occurred with the high concentrations. Meanwhile, sulfamethoxazole, erythromycin-H₂O, and trimethoprim did not occur during sampling periods. The values for log Kow of each chemical showed a high correlation with the number of hydrogen bonding acceptors and were important parameters to estimate and understand the biodegradability and toxicity of a compound in the environment. The biodegradability of each compound was proportional to the hydrophilicity of each compound and the toxicity was proportional to the number of hydrogen bonding acceptors of each compound. The expected introductory concentration (EIC), predicted exposure concentration (PEC), and hazard quotient showed that the livestock WWTP effluents were hazardous to ecosystems.     

Synthesis of mesoporous magnesium oxide: Its application to CO2 chemisorption

Mesoporous magnesium oxide (MgO) was synthesized using mesoporous carbon CMK-3 obtained from mesoporous SBA-15 as exotemplate. P123 was used as the structure-directing template and rice husk ash (RHA) as the silica source for the synthesis of SBA-15, which was subsequently treated with sucrose and sulphuric acid to obtain mesoporous carbon (CMK-3). X-ray powder diffraction (XRD) results and the type-IV adsorption isotherm with H1 hysteresis obtained by N₂ adsorption/desorption study for SBA-15, CMK-3 and mesoporous MgO suggests its resemblance with materials synthesized using conventional silica sources. Mesoporous MgO was subjected for CO₂ adsorption study in TGA; adsorption was 8 and 10 wt% at 25 and 100 °C, respectively. Finally, mesoporous MgO is selective to CO₂ gas, thermally stable and regenerable. Thus, this study contributes a better route to enhance CO₂ gas adsorption and use ecological waste rice husk for the synthesis of such efficient mesoporous materials.