Catalytic destruction of dichloromethane using perovskite-type oxide catalysts

Dichloromethane (DCM, also known as methylene chloride [CH2Cl2]) is often present in industrial waste gas and is a valuable chemical product in the chemical industry. This study addresses the oxidation of airstreams that contain CH2Cl2 by catalytic oxidation in a tubular fixed-bed reactor over perovskite-type oxide catalysts. This work also considers how the concentration of influent CH2Cl2 (Co = 500-1000 ppm), the space velocity (GHSV = 5000-48,000 1/hr), the relative humidity (RH = 10-70%) and the concentration of oxygen (O2 = 5-21%) influence the operational stability and capacity for the removal of CH2Cl2. The surface area of lanthanum (La)-cobalt (Co) composite catalyst was the greatest of the five perovskite-type catalysts prepared in various composites of La, strontium, and Co metal oxides. Approximately 99.5% CH2Cl2 reduction was achieved by the catalytic oxidation over LaCoO3-based perovskite catalyst at 600 degrees C. Furthermore, the effect of the initial concentration and reaction temperature on the removal of CH2Cl2 in the gaseous phase was also monitored. This study also provides information that a higher humidity corresponds to a lower conversion. Carbon dioxide and hydrogen chloride were the two main products of the oxidation process at a relative humidity of 70%.     

Fe (III) supported on resin as effective catalyst for the heterogeneous oxidation of phenol in aqueous solution

FeIII supported on resin as an effective catalyst for oxidation was prepared and applied for the degradation of aqueous phenol. Phenol was selected as a model pollutant and the catalytic oxidation was carried out in a batch reactor using hydrogen peroxide as the oxidant. The influent factors on oxidation, such as catalyst dosage, H2O2 concentration, pH, and phenol concentration were examined by considering both phenol conversion and chemical oxygen demand (COD) removal. The FeIII-resin catalyst possesses a high oxidation activity for phenol degradation in aqueous solution. The experimental results of this study show that almost 100% phenol conversion and over 80% COD removal can be achieved with the FeIII-resin catalyst catalytic oxidation system. A series of prepared resin were investigated for improving the oxidation efficiency. It was found that the reaction temperature and initial pH in solution significantly affected both of phenol conversion and COD removal efficiency. The activity of the catalyst significantly decreased at high pH, which was similar to the Fenton-like reaction mechanism. Results in this study indicate that the FeIII-resin catalytic oxidation process is an efficient method for the treatment of phenolic wastewater.     

A modal approach to vehicular emissions and fuel consumption model development

This study reports on the analysis of emissions and fuel consumption from motor vehicles using a modal approach. The four standard driving modes are idling, accelerating, cruising, and decelerating. On-road data were collected using instrumented test vehicles traveling many times through the urban areas of Hong Kong. A model was developed for estimating vehicular fuel consumption and emissions as a function of instantaneous speed and driving mode. Piecewise interpolation functions were proposed for each nonidling driving mode. Idling emission and fuel consumption rates were estimated as negative exponential functions of idling time. Preliminary modeling results showed good agreements for the test vehicles and indicated that the on-road measurements are feasible for the development of modal emission and fuel consumption models.     

Receptor modeling for analyzing PCDD/F and dioxin-like PCB sources in Hong Kong

A total of 96 ambient air samples were collected from January 2004 to December 2004 for the investigation of dioxins (polychlorinated dibenzo-para-dioxins and polychlorinated dibenzofurans [PCDD/Fs]) and dioxin-like profile for polychlorinated biphenyls (PCBs) in the atmosphere of Hong Kong. Two-day back-trajectories were obtained using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model from National Oceanic and Atmospheric Administration (NOAA) Air Resources Laboratory. Receptor models – potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) – were built based on the measured PCDD/Fs and dioxin-like PCBs total toxic equivalent (TEQ) concentrations. Both models were modified in this study so as to integrate the information obtained from three sampling sites in Hong Kong. The PSCF modeling resolved two main PCDD/F and dioxin-like PCB polluting paths from Mainland China. In line with previous studies, the northerly path around the Pearl River Delta might be one of the pollution sources of Hong Kong air. On the other hand, the receptor models also indicated another potential northeasterly source from Yangtze River Delta, which was seldom mentioned as the source region of Hong Kong air. Results from the CWT modeling suggested that the most toxic air mass affecting Hong Kong is probably attributable to the northeast path rather than the north path.     

Decomposition of 2-nitrophenol in aqueous solution by ozone and UV/ozone processes.

The decomposition of 2-nitrophenol in aqueous solutions by ozone and UV/ozone processes was found to be technically feasible under adequate experimental conditions. Formation of nitrate ions was observed following the decomposition of 2-nitrophenol by ozone and UV/ ozone processes. Increasing ozone dosage and UV light intensity accelerated the decomposition rate of 2-nitrophenol in an aqueous solution. The species distribution of 2-nitrophenol under various solution conditions plays a significant role in determining decomposition behavior. In most experiments conducted in this study, the decomposition of 2-nitrophenol by ozone and UV/ozone processes was favored to occur in alkaline conditions. The addition of 2-butanol accelerated the rate of gaseous ozone transfer to an aqueous phase by reducing the surface tension of aqueous solution and therefore enhancing the decomposition rate of 2-nitrophenol by ozone and UV/ozone processes.     

Use of regenerated ferric oxide for CO destruction and suppressing dioxin formation in flue gas in a pilot-scale incinerator

Catalytic destruction of chlorinated compounds is one of the key methods in reducing pollutant emissions. For the purpose of utilizing waste materials, a catalyst was regenerated from ferric ion sludge, obtained from the addition of iron salts to precipitate heavy metals. The sludge was dewatered, heated (800 degrees C for 4 h), and ground into smaller particles. The regenerated ferric oxide particles were then used as the oxidation catalyst to destroy CO formation during the combustion of three chlorinated solvents and to suppress dioxin formation in flue gas in a real waste solvent. In the presence of catalyst, the combustion efficiency (ratio of CO(2) to the sum of CO(2) and CO) for chlorobenzene was more than 98% at 850 degrees C in a pilot-scale incinerator. The destruction and removal efficiencies of chlorobenzene, 2,4-dichlorophenol and trichlorofluoroethane were more than three nines. In the absence of catalysts, the flue gas emission from a real waste could not meet the regulatory dioxin standard of 0.1 ng-TEQ/Nm(3) even with the powdered activated carbon injection. The use of catalyst at either 100 or 300 g/h, however, was able to meet the emission standard.     

Enrichments of Trace Metals in Particulate Matter From the Southern East China Sea,North of Taiwan

Abstract

This study investigates the distributions and enrichments of trace metals in suspended and sinking particulate matter from southern East China Sea (ECS) north of Taiwan during the period April 1992 to April 1993. According to these results, concentration of suspended particulate matter in the inner shelf of southern China Sea, the upwellinginfluenced shelf break, and in Kuroshio water are 1.30 (surface)–4.2 (bottom) mg1^?1, ca. 0.4 mg1^?1 and 0.1–0.2 mg1^?1, respectively, reflecting various influences of terrestrial inputs. A benthic nepheloid layer (BNL), apparently owing to resuspension of local and/or remote bottom sediments, formed over the shelf region. Temporal variations in trace metal contents and enrichments in suspended matter from the shelf region reflect the variation of metal inputs from Chinese rivers, particularly from the Changjiang runoff. the enriched metals are more likely to be derived from anthropogenic input, rather than from biological accumulation. in addition, a decrease in metal contents and an increase in salinity confirm the transport of suspended particulate metals from the East China Sea shelf to the open ocean. the feature of metal plume in the intermediate layer (550–800m) of Kuroshio water also verifies this occurrence. Moreover, the sinking particles collected from a sediment trap on the upper slope are relatively enriched in lithogenic matter and trace metals, suggesting the deposit of anthropogenic metals in the slope area.     

Ecological Survey of Coastal I Water Adjacent to Nuclear Power I Plants in Taiwan

A total of six nuclear reactors installed in three power plants, two along the northern and one along the southern coasts of Taiwan, started their operations one after another since October 1977. Owing to the large quantities of cooling water intake into and discharge from the plants, some environmental factors such as water temperature, chlorine, environmental radioactivity and nearshore currents may be significantly changed. Variations of these abiotic environmental factors may influence the biological activities in the ecosystem, particularly doing some kinds of damage to marine biological resources. Therefore, the possible environmental impact upon the biological systems including the fishery resources along the northern and southern coasts of Taiwan should be studied before and during the plant operation.

We have started the long-term programmes of biological, chemical and hydro-graphical surveys of the nuclear power plant sites on both northern (since July 1974) and southern (since July 1979) coasts of Taiwan. the survey items include ocean currents, physical and chemical properties of sea water, primary productivity, specific compositions and interspecific relationships among phyto- and zooplankton, algae, invertebrates, corals, and fishes; and radionuclides in water and biological specimens, and fishery statistics. in general, except for a few events, the operations of the six units of nuclear power plants have not produced detectable effects on the marine ecosystem. Radio activity levels and radionuclides in water and the biological specimens remained the same as background levels throughout the survey period. However, the events of coral bleaching and fish body anomalies caused by thermal discharges were observed respectively along the outlets of third and second Nuclear Power Plants. the purposes of this paper are to report and evaluate these two events during the operations of nuclear power plants in Taiwan.     

Inter-laboratory comparison study on measuring semi-volatile organic chemicals in standards and air samples

Measurements of semi-volatile organic chemicals (SVOCs) were compared among 21 laboratories from 7 countries through the analysis of standards, a blind sample, an air extract, and an atmospheric dust sample. Measurement accuracy strongly depended on analytes, laboratories, and types of standards and samples. Intra-laboratory precision was generally good with relative standard deviations (RSDs) of triplicate injections <10% and with median differences of duplicate samples between 2.1 and 22%. Inter-laboratory variability, measured by RSDs of all measurements, was in the range of 2.8-58% in analyzing standards, and 6.9-190% in analyzing blind sample and air extract. Inter-laboratory precision was poorer when samples were subject to cleanup processes, or when SVOCs were quantified at low concentrations. In general, inter-laboratory differences up to a factor of 2 can be expected to analyze atmospheric SVOCs. When comparing air measurements from different laboratories, caution should be exercised if the data variability is less than the inter-laboratory differences.     

Air pollution modeling at road sides using the operational street pollution model--a case study in Hanoi, Vietnam

In many metropolitan areas, traffic is the main source of air pollution. The high concentrations of pollutants in streets have the potential to affect human health. Therefore, estimation of air pollution at the street level is required for health impact assessment. This task has been carried out in many developed countries by a combination of air quality measurements and modeling. This study focuses on how to apply a dispersion model to cities in the developing world, where model input data and data from air quality monitoring stations are limited or of varying quality. This research uses the operational street pollution model (OSPM) developed by the National Environmental Research Institute in Denmark for a case study in Hanoi, the capital of Vietnam. OSPM predictions from five streets were evaluated against air pollution measurements of nitrogen oxides (NO(x)), sulfur dioxide (SO2), carbon monoxide (CO), and benzene (BNZ) that were available from previous studies. Hourly measurements and passive sample measurements collected over 3-week periods were compared with model outputs, applying emission factors from previous studies. In addition, so-called "backward calculations" were performed to adapt the emission factors for Hanoi conditions. The average fleet emission factors estimated can be used for emission calculations at other streets in Hanoi and in other locations in Southeast Asia with similar vehicle types. This study also emphasizes the need to further eliminate uncertainties in input data for the street-scale air pollution modeling in Vietnam, namely by providing reliable emission factors and hourly air pollution measurements of high quality.