Reduction of tar using cheap catalysts during sewage sludge gasification

Solid-fuel conversion or gasification study of sewage sludge and energy recovery has become increasingly important because energy recovery and climate change are emerging issues. Various types of catalysts, such as dolomite, steel slag and calcium oxide, were tested for tar reduction during the sewage sludge gasification process. For the experiments on sewage sludge gasification reactions and tar reduction using the catalysts, a fixed bed of laboratory-scale experimental apparatus was set up. The reactor was made of quartz glass using an electric muffle furnace. The sewage sludge samples used had moisture contents less than 6%. The experimental conditions were as follows: sample weight was 20 g and reaction time was 10 min, gasification reaction temperature was from 600 to 800°C, and the equivalence ratio was 0.2. The quantity of catalysts was 2–6 g, and temperatures of catalyst layers were 500–700°C. As the reaction temperature increased up to 800°C, the yields of gaseous products and liquid products increased, whereas char and tar products decreased, showing effects on gas product compositions. These results were considered to be due to the increase of the water-gas reaction and Boudouard reaction. In the case of experiments with catalysts, dolomite (4 g), steel slag (6 g) and calcium oxide (6 g) were used. When the temperature of catalysts increased, the weight of the tar produced decreased with different cracking performances by different catalysts. Reforming reactions were considered to occur on the surface of dolomite, steel slag and calcium oxide, causing cracking of the hydrocarbon structure, which eventually showed reduced tar generation.     

COMPLEX I and II Model Performance Evaluation in Nevada and New Mexico

The COMPLEX I and COMPLEX II Gaussian dispersion models for complex terrain applications have been made available by EPA. Various terrain treatment options under IOPT(25) can be selected for a particular application, one of which [IOPT(25) = 1] is an algorithm similar to that of the VALLEY model. A model performance evaluation exercise involving three of the available options with both COMPLEX models was carried out using SF⁶ tracer measurements taken during worst-case stable impaction conditions in complex terrain at the Harry Allen Plant site in southern Nevada. The models did not reproduce observed concentrations on an event by event basis, as correlation coefficients for 1-h concentrations of 0-0.3 were exhibited. When observed and calculated cumulative frequency distributions for 1-h and 3-h concentrations were compared, a close correspondence between observations and concentrations calculated with COMPLEX I, IOPT(25) = 2 or 3 was noted; both options consistently overestimated observed concentrations. With IOPT(25) = 1, upper percentile (maximum) values in the calculated frequency distribution exceeded the corresponding IOPT(25) = 2 or 3 value by roughly a factor of 2, and observed values by 2.5-5. COMPLEX II typically produced maximum values 2-4 times as great as COMPLEX I for the same terrain treatment option. From these results it is concluded that: 1) the physically unrealistic sector-spread approach used in VALLEY and COMPLEX I under stable impaction conditions is a surrogate for wind direction variation, and 2) the doubling of the plume centerline concentration due to ground reflection under terrain impingement conditions that is included in IOPT(25) = 1 is inappropriate.

These findings were found to be consistent with an analysis of noncurrent observed and calculated SO₂ χ/Q frequency distributions for 1, 3, and 24 hours near the Four Corners Plant in New Mexico. The comparison involved a four-year calculated χ/Q data set and a two-year observed χ/Q data set at the worst-case high terrain impact location near the plant.     

Revised relative potency values for PCDDs, PCDFs, and non-ortho-substituted PCBs for the optimized H4IIE-luc in vitro bioassay

While the World Health Organization 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalency factors are useful estimates of relative potencies of mixtures when conducting risk assessments, they are not useful when comparing the results of bioassays such as the H4IIE-luc to concentrations of TCDD equivalents calculated from instrumental analyses. Since there are thousands of dioxin-like compounds (DLCs), one use of screening assays is to determine if all of the aryl hydrocarbon receptor (AhR) active DLCs in a mixture have been accounted for in instrumental analyses. For this purpose, bioassay-specific relative potency (ReP) values are needed. RePs of 21 polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and dioxin-like polychlorinated biphenyls that exhibit effects mediated through the AhR were determined by use of the H4IIE-luc assay. Different values of RePs are derived, depending on the statistical, curve-fitting methods used to derive them from the dose–response relationships. Here, we discuss the various methods for deriving RePs from in vitro data and their assumptions and effects on values of RePs. Full dose–response curves of 2,3,7,8-TCDD and other representative DLCs were used to estimate effective concentrations at multiple points (e.g., EC20-50-80), which were then used to estimate ReP of each DLC to 2,3,7,8-TCDD.     

Analysis of spatial and seasonal distributions of MODIS aerosol optical properties and ground-based measurements of mass concentrations in the Yellow Sea region in 2009

Satellite-retrieved data on aerosol optical depth (AOD) and Ångström exponent (AE) using a moderate resolution imaging spectrometer (MODIS) were used to analyze large-scale distributions of atmospheric aerosols in East Asia. AOD was relatively high in March (0.44?±?0.25) and low in September (0.24?±?0.21) in the East Asian region in 2009. Sandstorms originating from the deserts and dry areas in northern China and Mongolia were transported on a massive scale during the springtime, thus contributing to the high AOD in East Asia. However, whereas PM10 with diameters ≤10 μm was the highest in February at Anmyon, Cheongwon, and Ulleung, located leeward about halfway through the Korean Peninsula, AOD rose to its highest in May. The growth of hygroscopic aerosols attendant on increases in relative humidity prior to the Asian monsoon season contributed to a high AOD level in May. AE typically appears at high levels (1.30?±?0.37) in August due to anthropogenic aerosols originating from the industrial areas in eastern China, while AOD stays low in summer due to the removal process caused by rainfall. The linear correlation coefficients of the MODIS AOD and ground-based mass concentrations of PM10 at Anmyon, Cheongwon, and Ulleung were measured at 0.4~0.6. Four cases (6 days) of mineral dustfall from sandstorms and six cases (12 days) of anthropogenically polluted particles were observed in the central area of the Korean Peninsula in 2009. PM10 mass concentrations increased at both Anmyon and Cheongwon in the cases of mineral dustfall and anthropogenically polluted particles. Cases of dustfall from sandstorms and anthropogenic polluted particles, with increasing PM10 mass concentrations, showed higher AOD values in the Yellow Sea region.     

Evaluation of the use of diffusive air samplers for determining temporal and spatial variation of volatile organic compounds in the ambient air of urban communities

The Houston-Galveston metropolitan area has a relatively high density of point and mobile sources of air toxics, and determining and understanding the relationship between emissions and ambient air concentrations of air toxics is important for evaluating potential impacts on public health and formulating effective regulatory policies to control this impact, both in this region and elsewhere. However, conventional ambient air monitoring approaches are limited with regard to expense, siting limitations, and representative sampling necessary for adequate exposure assessment. The overall goal of this multiphase study is to evaluate the use of simple passive air samplers to determine temporal and spatial variability of the ambient air concentrations of selected volatile organic compounds (VOCs) in urban areas. Phase 1 of this study, reported here, was a field evaluation of 3M organic vapor monitors (OVMs) involving limited comparisons with commonly used active sampling methods, an assessment of sampler precision, a determination of optimal sampling duration, and an investigation of the utility of a simple modification of the commercial sampler. The results indicated that a sampling duration of 72 hr exhibited generally low bias relative to automated continuous gas chromatography measurements, good overall precision, and an acceptable number of measurements above detection limits. The modified sampler showed good correlation with the commercial sampler, with higher sampling rates, although lower than expected.     

Environmental estrogenic effects and gonadal development in wild goldfish (Carassius auratus)

Serum vitellogenin (VTG) contents of wild goldfish (Carassius auratus) were investigated as a sensitive biomarker for artificial estrogenic compounds in aquatic environments. Goldfish was sampled from a pristine area, a river situated 5 km downstream from a sewage treatment works (STW), and also from the Young-San River in Korea. The female yolk precursor protein VTG was not detected when gonadosomatic index (GSI) was less than 0.85%, while VTG levels of >10 microg/ml were found in males whose GSI was less than 1.53%. In male goldfish sampled from STW and the Young-San River, the higher VTG corresponded to lower GSI. This study suggested a trend that gonad development was connected to VTG levels in both sexes, and the application of GSI and histological analysis provide an attractive possibility that it could be included in the panel of markers used for estrogenic activity investigation of aquatic environments.     

Distribution and pollution sources of polycyclic aromatic hydrocarbons (PAHs) in reclaimed tidelands and tidelands of the western sea coast of South Korea

The wide-scale reclamation of tidal flats distributed throughout the western and southern coastal areas in Korea has been completed, in an effort to expand the available arable land. The present studies were conducted in order to characterize the concentrations and compositional patterns of selected PAHs, in order to obtain more information regarding environmental risk assessments for sustainable and environment-friendly agriculture in reclaimed tidelands and tidelands in South Korea. The PAH contents were low to moderate, relative to other urbanized regions of the world. Sigma PAHs ranged from 69.8 to 1,175.2 ng g(-1) in dry weight, with a mean value of 394.4 ng g(-1). Differences were observed in the Sigma PAHs concentrations between industrial complex areas and rural regions. The two dominant PAHs were identified as fluoranthene and pyrene. These compounds constituted 1.4 to 55.0% (mean, 33.4%) and 2.7 to 45.6% (mean, 22.0%) of the Sigma PAHs. Our correlation analysis revealed that the Sigma PAHs contents were associated significantly with the organic carbon content (R(2) = 0.86, P < 0.01) and the cation exchange capacity (CEC; R(2) = 0.89, P < 0.01) in the reclaimed tidelands and tidelands.     

Dietary exposure to DDT of secondary school students in Hong Kong

The aim of this study was to determine the dietary exposure of DDT in foodstuffs consumed in Hong Kong by secondary school students in Hong Kong in 2005. Food samples of domestic or imported food were collected randomly from local markets for the determination of DDT. The analytical method for this survey was based on isotope dilution technique. DDT isomers were determined at parts per billion (mugkg(-1)) levels in foods by pressured fluid extraction followed by gel permeation column cleanup and gas chromatography with mass spectrometry detection. Among the 98 composite samples, 25 were found positive with DDT levels greater than the limit of quantitation (LOQ) (1mugkg(-1) for each isomer of DDT). Only two of the meat products were found to contain low levels of the metabolites of DDT. A number of fish and shellfish were found to contain not just the metabolites of DDT, but also parent DDT. The main contribution to DDT was from seafood. The dietary intake of DDT for an average and high secondary school student consumers were estimated to be 0.145 and 0.291mugkg(-1)bwd(-1), respectively. Both levels fell well below the Provisional Tolerable Daily Intake (PTDI) of 10mugkg(-1)bwd(-1) established by the Joint Food Agriculture Organization/World Health Organization Meeting on Pesticide Residues (JMPR). It was concluded that both the average and high secondary school student consumers were unlikely to experience major toxicological effects of DDT.     

Destruction of EDTA using Ce(IV) mediated electrochemical oxidation: a simple modeling study and experimental verification

Mediated electrochemical oxidation (MEO) is a recent development in the environmental research field for the complete destruction of organic pollutants. This study presents the destruction of EDTA by cerium(IV) MEO process in nitric acid medium. The destruction reaction was carried out in a continuous stirred tank reactor under various conditions. A simple kinetic model was developed to analyze and simulate the organic destruction in the MEO process. The model was based on the calculation of the total mass balance, the component mass balance, and the energy balance in the reactor and also in the heating jacket. The sensitivity to key operating conditions such as the initial EDTA concentration (50-200 mM), EDTA feeding time (30-180 min), reaction temperature (323-363 K), and the rate laws corresponding to zero-, first-, second-, and third-order reaction were analyzed. It was found that the model simulated agreed well with the experimental data for EDTA oxidation. The results obtained showed the suitability of the MEO process for the effective mineralization of high concentrations of EDTA.     

Modified grey model for estimating traffic tunnel air quality

This study compared three forecasting models based on the mean absolute percentage errors (MAPE) of their accuracy in forecasting air pollution in a traffic tunnel: the Grey model (GM), the combination model used four sample point and five sample point prediction with GM (1,1)(GM(1,1)^4 + 5), and the modified grey model (MGM). An MGM was combined using the four points of the original sequence using the original grey prediction GM (1,1) for short-term forecasting. The proposed method cannot only enhance the prediction accuracy of the original grey model, but can also solve the jump data forecasting problem something for which the original grey model is inappropriate. The MAPE was applied to the models, and the MGM found the proposed method to be simple and efficient. The MAPE of MGM, calculated over 3 h of forecasts, were as follows: 10.12 (Upwind), 10.07 (Middle) and 7.68 (Downwind) for CO; 10.79 (Upwind), 6.05 (Middle) and 5.98 (Downwind) for NO _x , and 11.67 (Upwind), 7.32 (Middle) and 4.56 (Downwind) for NMHC. The MGM model results reveal that the combined forecasts can significantly decrease the overall forecasting error. Results of this demonstrate that MGM can accurately forecast air pollution in the Kaohsiung Chung–Cheng Tunnel.