Emission of particulate and gaseous pollutants from household laser processing machine

Indoor air quality (IAQ) directly affects the health of occupants. Household manufacturing equipment (HME) used for hobbies or educational purposes is a new and unexplored source of air pollution. In this study, we evaluated the characteristics of particulate and gaseous pollutants produced by a household laser processing equipment (HLPE). Various target materials were tested using a commercial HLPE under various operating conditions of laser power and sheath air flow rate. The mode diameters of the emitted particles gradually decreased as laser power increased, while the particle number concentration (PNC) and particle emission rate (PER) increased. In addition, as the sheath air flow rate quadrupled from 10 to 40 L/min, the mode diameter of the emitted particles decreased by nearly 25%, but the effect on the PNC was insignificant. When the laser induced the target materials at 53 mW, the mode diameters of particles were <150 nm, and PNCs were >2.0 × 10⁴ particles/cm³. Particularly, analyses of sampled aerosols indicated that harmful substances such as sulfur and barium were present in particles emitted from leather. The carcinogenic gaseous pollutants such as acrylonitrile, acetaldehyde, 1,3-butadiene, benzene, and C₈ aromatics (ethylbenzene) were emitted from all target materials. In an actual indoor environment, the PNC of inhalable ultrafine particles (UFPs) was >5 × 10⁴ particles/cm³ during 30 min of HLPE operation. Our results suggest that more meticulous control methods are needed, including the use of less harmful target materials along with filters or adsorbents that prevent emission of pollutants.     

A study on torrefaction characteristics of waste sawdust in an auger type pyrolyzer

Torrefaction is thermo-chemical process which can improve solid fuel quality as well as grindability. In previous studies, torrefaction has been studied mainly for removal of moisture and for improving grindability. In this experiment, the characteristics of torrefied waste sawdust were studied especially for its energy yield. Hence, torrefaction was performed on varying reaction temperatures (200, 220, 240, 260, 280, 300 °C) and solid residence time (10, 30, 60 min). The results indicated that the yield of torrefaction decreases with increasing temperature and residence time. It was found that above 280 °C, the yield got remarkably decreased. The lowest yield was obtained at the residence time of 60 min. It was also noticed that the HHV of torrefied samples increases with increasing temperature. The highest HHV was found to be 26.09 MJ/kg which was obtained at 60 min and 300 °C. However, the highest energy yield was obtained to be 104.17 % which was noticed at 30 min and 260 °C.     

Diurnal vertical migration of Cochlodinium polykrikoides during the red tide in Korean coastal sea waters

The diurnal vertical migration of Cochlodinium polykrikoides (C. polykrikoides), which caused a red tide in the Korean coastal waters of the East Sea/Sea of Japan in September 2003, was examined by determining the time-dependent changes in the density of living cells in relation to the depth of the water column. The ascent of this species into the surface layer (depth of water 2 m) occurred during 1400-1500. The descent started at 1600 and a high distribution rate (86%) at 15-20 m was observed at 0300. During the ascent, the cells were widely distributed at each depth level from 0600 hr and at 0800-1100, the cells were primarily distributed in the middle layer (0-6 m). The concentration of dissolved inorganic nitrogen was generally < or = 2.86 micromol l(-1), but at 1400-1500, the concentration in the surface layer reduced to < or = 0.14 micromol l(-1). Moreover, the concentration gradually increased as the depth increased to > or = 5 m. These results showed that the nutrient-consumption rate associated with the proliferation of C. polykrikoides during a red tide is more influenced by the inorganic-nitrogen resources ratherthan the inorganic-phosphorus compounds.     

Evaluation of SWAT sub-daily runoff estimation at small agricultural watershed in Korea

A study was undertaken for the prediction of runoff flow from 0.8 ha field-sized agricultural watershed in South Korea using Soil and Water Assessment Tool (SWAT) sub-daily. The SWAT model with sub-daily configuration predicted flow from the watershed within the range of acceptable accuracy. The SWAT sub-daily simulations were carried out for a total of 18 rainfall events, 9 each for calibration and validation. Overall trend and extent of matching simulated flow for the rainfall events in 2007-2008 with measured data during the calibration process were coefficient of determination (R²) value of 0.88 and Nash and Sutcliffe Efficiency (E_NS) value of 0.88. For validation, R² and E_NS values were 0.9 and 0.84, respectively. Whereas R² and E_NS values for simulation results using daily rainfall data were 0.79 and -0.01, respectively, that were observed to be out of acceptable limits for the model simulation. The importance of higher time resolution (hourly) precipitation records for flow simulation were evaluated by comparing R² and E_NS with 15 min, 2 h, 6 h and 12 h precipitation data, which resulted in lower statistics with increases in time resolution of precipitation data. The SWAT sub-daily sensitivity analysis was performed with the consideration of hydraulic parameter and was found as in the rank order of CN2 (curve number), ESCO (soil evaporation compensation factor), GW_DELAY (ground water delay time), ALPHA_BF ( base flow alpha factor), GWQMN ( a threshold minimum depth of water in the shallow aquifer required for return flow to occur) , REVAPMN (minimum depth of water in shallow aquifer for re-evaporation to occur) , LAT_TIME (lateral flow travel time) respectively. These sensitive parameters were evaluated at 10% higher and lower values of the parameters, corresponding to 70.5% higher and 23.2% lower in simulated flow out from the SWAT model. From the results obtained in this study, hourly precipitation record for SWAT sub-daily with Green-Ampt infiltration method was proven to be efficient for runoff estimation at field sized watershed with higher accuracies that could be efficiently used to develop site-specific Best Management Practices (BMPs) considering rainfall intensity, rather than simply using daily rainfall data.     

AUTOMATED WEB GIS BASED HYDROGRAPH ANALYSIS TOOL,WHAT1

The separation of the base flow component from a varying streamflow hydrograph is called “hydrograph analysis.” In this study, two digital filter based separation modules, the BFLOW and Eckhardt filters, were incorporated into the Web based Hydrograph Analysis Tool (WHAT) system. A statistical component was also developed to provide fundamental information for flow frequency analysis and time series analysis. The Web Geographic Information System (GIS) version of the WHAT system accesses and uses U.S. Geological Survey (USGS) daily streamflow data from the USGS web server. The results from the Eckhardt filter method were compared with the results from the BFLOW filter method that was previously validated, since measured base flow data were not available for this study. Following validation, the two digital filter methods in the WHAT system were run for 50 Indiana gaging stations. The Nash‐Sutcliffe coefficient values comparing the results of the two digital filter methods were over 0.91 for all 50 gaging stations, suggesting the filtered base flow using the Eckhardt filter method will typically match measured base flow. Manual separation of base flow from streamflow can lead to inconsistency in the results, while the WHAT system provides consistent results in less than a minute. Although base flow separation algorithms in the WHAT system cannot consider reservoir release and snowmelt that can affect stream hydrographs, the Web based WHAT system provides an efficient tool for hydrologic model calibration and validation. The base flow information from the WHAT system can also play an important role for sustainable ground water and surface water exploitation, including irrigation and industrial uses, and estimation of pollutant loading from both base flow and direct runoff. Thus, best management practices can be appropriately applied to reduce and intercept pollutant leaching if base flow contributes significant amounts of pollutants to the stream. This Web GIS based system also demonstrates how remote, distributed resources can be shared through the Internet using Web programming.     

Cell-recycle fed-batch production of a highly unsaturated polyhydroxyalkanoate from 1,3-butanediol byPseudomonas sp. A33

The recently isolatedPseudomonas sp. A33 was investigated for the production of a highly unsaturated polyhydroxyalkanoate (PHA) containing various alkyl and alkenyl pendent groups from 1,3-butanediol in a cell-recycle fed-batch production mode. The monomer composition and degree of unsaturation in PHA were dependent on the environmental conditions. The production temperature markedly influenced the content, composition, and degree of unsaturation of PHA. As the production temperature decreased from 30 to 10°C, the degree of unsaturation and content of PHA were increased, while the mole percentage of 3-hydroxybutyrate (3HB) was decreased. These temperature effects on the composition of PHA imply that the production can be used as a control variable for the biosynthesis of a highly unsaturated PHA and for the specific regulation of the composition of PHA. The biosynthetic pathway for a highly unsaturated PHA which is based on de novo fatty acid biosynthetic pathway is proposed. For the enhanced production of this functional PHA, a high cell density was achieved by cell-recycle continuous culture at 30°C, and then a large amount of PHA was accumulated at 15°C by fed-batch addition of the feeding solution containing excess 1,3-butanediol. The structures of monomer constituents of polymer were confirmed by gas chromatography—mass spectrometric analysis of trimethylsiyl derivatives of 3-hydroxyalkanoic acids methyl esters.     

Mass transport of organic contaminants through a self-sealing/self-healing mineral landfill liner

The self-sealing/self-healing (SS/SH) liner system is based on the fundamental principle that an impermeable seal is self-formed and self-healed by the pozzolanic reaction at the interface between two adjacent reactive layers. The objectives of this study were to evaluate the effect of contaminants on the performance of an SS/SH liner used as a hydraulic barrier, to understand mechanism of volatile organic compound (VOC) sorption on the SS/SH materials, and to estimate the mass transport parameters of contaminants through the SS/SH liner materials. The hydraulic conductivity of the liner material decreased continuously with time, and stabilized at less than 1 × 10^–7cm/s after approximately 15 days. It is known that the seal at the interface between two reactive layers is self-formed over time, and this contributes to the decrease in the hydraulic conductivity of such a liner system. The retardation of the seven target VOCs tested was greater in the SS/SH liner materials than in a clayey soil specimen owing to the higher sorption capacity. An analytical solution developed to test column equipment could reduce the time required to estimate the hydrodynamic dispersion coefficients of organic compounds by using the data on changes in concentration in the upper reservoir of the column.     

Effect of substrate feeding frequencies on the methane production and microbial communities of laboratory-scale anaerobic digestion reactors

Even though full-scale digesters have been designed based on laboratory-scale tests, the substrate feeding modes of laboratory-scale tests might be different from those of full-scale digesters. The effect of substrate feeding frequencies on the performance and microbial community of laboratory-scale anaerobic digestion reactors was investigated. Feeding frequencies of twice a day, once a day, and every two days were tested in three 2-L reactors with an organic loading rate of 0.5 g-glucose/L/day under mesophilic condition. According to the results of this study, all the reactors showed similar methane production rates and SCOD removal efficiencies after sufficient time of acclimation, but frequently feeding promoted more stable digestion. Although there was no significant difference in microbial diversities from pyrosequencing analyses, the changes of archaeal community composition were observed. The decrease in feeding frequency appeared to cause shifts from acetoclastic methanogens affiliated with Methanosaeta to H₂-utilizing methanogens. The increase of Methanosaeta at a frequently feeding might contribute to the stability of reactor operation. Since this study uses glucose as the substrate, there is still possibility of different results for more complex substrates, such as sludge, food waste, etc.     

The Characteristics of Tropospheric Ozone Seasonality Observed from Ozone Soundings at Pohang, Korea

This paper presents the first analysis of vertical ozone sounding measurements over Pohang, Korea. The main focus is to analyze the seasonal variation of vertical ozone profiles and determine the mechanisms controlling ozone seasonality. The maxima ozone at the surface and in the free troposphere are observed in May and June, respectively. In comparison with the ozone seasonality at Oki (near sea level) and Happo (altitude of 1840 m) in Japan, which are located at the same latitude as of Pohang, we have found that the time of the ozone maximum at the Japanese sites is always a month earlier than at Pohang. Analysis of the wind flow at the surface shows that the wind shifts from westerly to southerly in May over Japan, but in June over Pohang. However, this wind shift above boundary layer occurs a month later. This wind shift results in significantly smaller amounts of ozone because the southerly wind brings clean wet tropical air. It has been suggested that the spring ozone maximum in the lower troposphere is due to polluted air transported from China. However, an enhanced ozone amount over the free troposphere in June appears to have a different origin. A tongue-like structure in the time-height cross-section of ozone concentrations, which starts from the stratosphere and extends to the middle troposphere, suggests that the ozone enhancement occurs due to a gradual migration of ozone from the stratosphere. The high frequency of dry air with elevated ozone concentrations in the upper troposphere in June suggests that the air is transported from the stratosphere. HYSPLIT trajectory analysis supports the hypothesis that enhanced ozone in the free troposphere is not likely due to transport from sources of anthropogenic activity.