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411.
Atmospheric deposition of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in urban and suburban areas of Korea 总被引:1,自引:0,他引:1
Bulk atmospheric samples (wet and dry) were collected monthly throughout a year at urban and suburban areas of Korea to assess the deposition flux and seasonal variations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). The PCDDs/DFs deposition fluxes ranged from 1.0 to 3.7 ng TEQ/m2/year in the urban area and from 0.5 to 4.6 ng TEQ/m2/year in the suburban area. The deposition fluxes of PCDDs/DFs in this study were comparable to or lower than those previously reported at different locations. The atmospheric deposition fluxes of particles and PCDDs/DFs in winter tended to be higher than those in summer. However, monthly variations between particle and PCDDs/DFs deposition fluxes were small, and the correlation coefficients between the deposition fluxes of air particles and each homologue group of PCDDs/DFs varied according to the degree of chlorination of the homologue group. The deposition velocity of PCDDs/DFs in the urban area was estimated at 0.04 cm/s, which is a lower value than those found in other studies. The two most likely factors affecting the monthly variation of deposition fluxes are the ambient temperature and the amount of precipitation. In particular, the ambient temperature had an influence on the lower chlorinated homologues of PCDDs/DFs while precipitation had an influence on the higher chlorinated PCDDs/DFs. The PCDDs/DFs profiles in atmospheric deposition bulk samples showed a similar pattern at the urban and suburban sites. The possibility of the loading of PCDDs/DFs by Asian dust events could be partly confirmed by investigation of homologue profiles. 相似文献
412.
This paper describes a method for predicting local scour around bridge piers using an artificial neural network (ANN). Methods for selecting input variables, calibrations of network control parameters, learning process, and verifications are also discussed. The ANN model trained by laboratory data is applied to both laboratory and field measurements. The results illustrate that the ANN model can be used to predict local scour in the laboratories and in the field better than other empirical relationships that are currently in use. A parameter study is also carried out to investigate the importance of each input variable as reflected in data. 相似文献
413.
Pt/CeO2–ZrO2–SnO2/γ-Al2O3 catalysts were prepared by co-precipitation and wet impregnation methods for catalytic oxidation of acetaldehyde to acetic acid in water. In the present catalysts, Pt and CeO2–ZrO2–SnO2 were successfully dispersed on the γ-Al2O3 support. Dependences of platinum content and reaction time on the selective oxidation of acetaldehyde to acetic acid were investigated to optimize the reaction conditions for obtaining both high acetaldehyde conversion and highest selectivity to acetic acid. Among the catalysts, a Pt(6.4 wt.%)/Ce0.68Zr0.17Sn0.15O2.0(16 wt.%)/γ-Al2O3 catalyst showed the highest acetaldehyde oxidation activity. On this catalyst, acetaldehyde was completely oxidized after the reaction at 0°C for 8 hr, and the selectivity to acetic acid reached to 95% and higher after the reaction for 4 hr and longer. 相似文献
414.
415.
W. Jutidamrongphan K. Y. Park S. Dockko J. W. Choi S. H. Lee 《Environmental Chemistry Letters》2012,10(1):21-28
This report shows that silica sulfate is removing phosphate from wastewater very efficiently. Phosphorus removal and recovery
from wastewater is a worldwide issue due to pollution of natural waters by phosphate and depletion of phosphate ores. Adsorption
is a process that can remove phosphate at low concentrations. Adsorption also allows the recovery of phosphate for possible
re-use. Here, we studied the adsorption of phosphate from wastewater using commercial Zr ferrite, Zr-MCM 41 and silica sulfate.
We calculated equilibrium isotherms, kinetic models and thermodynamic effects under conditions similar to real wastewaters.
We found that the equilibrium data for the adsorption of phosphate were best fitted to the Freundlich model. The results show
that the maximum uptake of phosphate was 3.36 mg g−1 for Zr-MCM, 27.73 mg g−1 for Zr ferrite and 46.32 mg g−1 for silica sulfate. The kinetic results of the three adsorbents were satisfactorily predicted using a pseudo-second-order
model. We found that silica sulfate provided excellent characteristics in terms of the maximum adsorption and rate constant
for the adsorption of phosphate. The thermodynamic data showed that increasing the temperature enhanced the adsorption of
phosphate onto silica sulfate. Our findings will help to define efficient methods to remove phosphate from wastewater. 相似文献
416.
Marla C. MANIQUIZ Lee-Hyung KIM Soyoung LEE Jiyeon CHOI 《Frontiers of Environmental Science & Engineering》2012,6(5):612-619
A structured stormwater infiltration system was developed and constructed at a university campus and monitoring of storm events was performed during a one-year operation period. The flow and pollutant mass balances were analyzed and the overall efficiency of the system was assessed. While significant positive correlations were observed among rainfall, runoff and discharge volume (R 2= 0.93-0.99; p <0.05), there was no significant correlations existed between rainfall, runoff, discharge volume and pollutant load. The system was more effective in reducing the runoff volume by more than 50% for small storm events but the difference between the runoff and discharge volume was significant even with rainfall greater than 10 mm. Results showed that the pollutant reduction rates were higher compared to the runoff volume reduction. Average pollutant reduction rates were in the range of 72% to 90% with coefficient of variation between 0.10 and 0.46. Comparable with runoff reduction, the system was more effective in reducing the pollutant load for small storm events, in the range of 80% to 100% for rainfall between 0 and 10 mm; while 65% to 80% for rainfall between 10 and 20 mm. Among the pollutant parameters, particulate matters was highly reduced by the system achieving only a maximum of 25% discharge load even after the entire runoff was completely discharged. The findings have proven the capability of the system as a tool in stormwater management achieving both flow reduction and water quality improvement. 相似文献
417.
Effect of activated sludge properties and membrane operation conditions on fouling characteristics in membrane bioreactors 总被引:2,自引:0,他引:2
Biofouling control is considered to be a major challenge in operating membrane bioreactors (MBRs) for the treatment of wastewater. This study examined the impact of biological, chemical, and physical properties of activated sludge on membrane filtration performance in laboratory-scale MBRs. Sludges with different microbial communities were produced using pseudo-continuous stirred-tank reactors and pseudo-plug flow reactors treating a synthetic paper mill wastewater. Various filtration resistances were used to investigate membrane fouling characteristics, and molecular biology tools targeting 16S ribosomal DNA gene sequences were used to identify predominant bacterial populations in the sludges or attached to the fouled membranes. Filtration experiments using axenic cultures of Escherichia coli, Acinetobacter calcoaceticus, and Gordonia amarae were also performed to better understand the initiation and development of biofouling. The results showed that the tendency of membranes to biofoul depended upon membrane operating conditions as well as the properties of the activated sludge in the MBR systems. Specific bacterial populations, which were not dominant in the activated sludges, were selectively accumulated on the membrane surface leading to the development of irreversible biofouling. 相似文献
418.
419.
420.
PCB levels and congener patterns from Korean municipal waste incinerator stack emissions 总被引:1,自引:0,他引:1
Congener specific polychlorinated biphenyl (PCB) data from the stack gas of nine Korean municipal waste incinerators was used to determine characteristic congener patterns of emitted PCBs. Principal component analysis revealed three classes of incinerators according to their pattern of PCB congener emissions: those resembling the background sampling material; those producing large quantities of a few tetra-chlorinated congeners; those producing large proportions of mono (MO-) and non-ortho (NO-) congeners relative to di-ortho (DO-) levels. Also, correlations between individual PCB congeners and polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) were discovered for several NO-PCBs and tetra and penta chlorinated PCDFs. Full PCB congener data is presented along with operating conditions for each incinerator. 相似文献