Evaluation of mercury speciation and removal through air pollution control devices of a 190 MW boiler

Air pollution control devices (APCDs) are installed at coal-fired power plants for air pollutant regulation. Selective catalytic reduction (SCR) and wet flue gas desulfurization (FGD) systems have the co-benefits of air pollutant and mercury removal. Configuration and operational conditions of APCDs and mercury speciation a ect mercury removal e ciently at coal-fired utilities. The Ontario Hydro Method (OHM) recommended by the U.S. Environmental Protection Agency (EPA) was used to determine mercury speciation simultaneously at five sampling locations through SCR-ESP-FGD at a 190 MW unit. Chlorine in coal had been suggested as a factor a ecting the mercury speciation in flue gas; and low-chlorine coal was purported to produce less oxidized mercury (Hg2+) and more elemental mercury (Hg0) at the SCR inlet compared to higher chlorine coal. SCR could oxidize elemental mercury into oxidized mercury when SCR was in service, and oxidation e ciency reached 71.0%. Therefore, oxidized mercury removal e ciency was enhanced through a wet FGD system. In the non-ozone season, about 89.5%–96.8% of oxidized mercury was controlled, but only 54.9%–68.8% of the total mercury was captured through wet FGD. Oxidized mercury removal e ciency was 95.9%–98.0%, and there was a big di erence in the total mercury removal e ciencies from 78.0% to 90.2% in the ozone season. Mercury mass balance was evaluated to validate reliability of OHM testing data, and the ratio of mercury input in the coal to mercury output at the stack was from 0.84 to 1.08.     

Bioaccumulation of cadmium bound to humic acid by the bivalve Meretrix meretirx Linnaeus from solute and particulate pathways

Humic acid is an important pool of heavy metals in sediments.Generally,the presence of refractory humic matter in aquatic systems would decrease the bioavailability of Cd and hence control the bioaccumulation of Cd in benthic animals.In the present work,we applied a suspending system to determine the relative importance of particulate and dissolved fractions of humic acid as Cd sources for the bivalve Meretrix meretrix and to investigate the difference of bioaccumulation characteristics of Cd adsorbed on di...     

Effects of sediment dredging on water quality and zooplankton community structure in a shallow of eutrophic lake

Effects of suction dredging on water quality and zooplankton community structure in a shallow of eutrophic lake,were evaluated.The results showed that a decreasing trend for levels of phosphorus,organic matter,total suspended solids,Chlorophyll a and Secchi transparency in the water column was found,while levels of water depth,electrical conductivity,total dissolved solids and NO 3--N concentration increased markedly post-dredging.The effects of dredging on dissolved oxygen,pH value and temperature were alm...     

Comparative study of microbial community structure in di erent filter media of constructed wetland

Comparisons of microbial community structure, in eight filter media of zeolites, anthracite, shale, vermiculite, ceramic filter media, gravel, steel slag and bio-ceramic, were undertaken by analyzing the phospholipid fatty acid (PLFA) composition. A total of 20 fatty acids in the range of C11 to C20 were determined but only 13 PLFAs were detected in steel slag. They consist of saturated fatty acids, branched fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids. The variation of fatty acids was revealed in the relative proportions of these fatty acids in di erent media. The aerobic prokaryotes were the predominant group in all media. The PLFA composition showed significant di erences among the eight di erent media by Tukey’s honestly test. It was found that steel slag was significantly di erent in the microbial community as compared to other filter media, probably due to its alkaline e uent. Steel slag alone is probably not a good choice of substratum in constructed wetlands. The principle components analysis (PCA) showed that zeolites, bio-ceramic, shale and vermiculite had a similar microbial community structure while steel slag and ceramic filter media were distinct from other media.     

Thermal stabilization of chromium slag by sewage sludge: Effects of sludge quantity and temperature

To investigate the feasibility of detoxifying chromium slag by sewage sludge,synthetic chromium slag containing 3% of Cr(VI) was mixed with sewage sludge followed by thermal treatment in nitrogen gas for stabilizing chromium.The effects of slag to sludge ratio(0.5,1 and 2) and temperature(200,300,500,700 and 900°C) on treatment efficiency were investigated.During the mixing process before thermal treatment,59.8%-99.7% of Cr(VI) was reduced,but Cr could be easily leached from the reduction product.Increasing heating temperature and decreasing slag to sludge ratio strengthened the reduction and stabilization of Cr(VI).When the slag to sludge ratio was 0.5 and thermal treatment temperature was 300°C,the total leached Cr and Cr(VI) declined to 0.55 mg/L and 0.17 mg/L respectively,and 45.5% of Cr in the thermally treated residue existed as residual fraction.A two-stage mechanism was proposed for the reduction and stabilization of Cr.     

A contact sex pheromone component of the emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)

Analyses of the elytral hydrocarbons from male and female emerald ash borer, Agrilus planipennis Fairmaire, that were freshly emerged vs. sexually mature (>10 days old) revealed a female-specific compound, 9-methyl-pentacosane (9-Me-C₂₅), only present in sexually mature females. This material was synthesized by the Wittig reaction of 2-decanone with (n-hexadecyl)-triphenylphosphonium bromide followed by catalytic reduction to yield racemic 9-Me C₂₅, which matched the natural compound by gas chromatography/mass spectrometry (retention time and EI mass spectrum). In field bioassays with freeze-killed sexually mature A. planipennis females, feral males spent significantly more time in contact and attempting copulation with unwashed females than with females that had been washed in n-hexane to remove the cuticular lipids. Hexane-washed females to which 9-Me-C₂₅ had been reapplied elicited similar contact time and percentage of time attempting copulation as unwashed females, indicating that 9-methyl-pentacosane is a contact sex pheromone component of A. planipennis. This is the first contact sex pheromone identified in the Buprestidae.     

A new approach to predicting the maximum temperature in dry drilling based on a finite element model

A new analysis approach is developed to predict the temperature in dry drilling. The working rake angle and the working relief angle which the effect of feed is considered at an arbitrary point in the leading cutting edge of a twist drill are developed for the equivalent model. Then finite element models are developed to predict the drilling temperature based on the equivalent model. Commercial finite element codes Abaqus, Deform 2D and Third Wave Systems AdvantEdge have been used. In simulations, different chip separation models and material models are applied in the three codes. And the effect of the laws of drilling velocities and feed rates on the temperature are investigated by the finite element method. Predicted results of the maximum temperatures by three codes are compared with experiments, respectively. Results indicate that the drilling temperature results of simulations have good agreement to the experimental ones, and the errors are all less than 15%.     

雨水管道沉积物对径流初期冲刷的影响

为了避免汇水面源头以及分流制雨水管道系统中沉积的大量污染物在降雨时随雨水径流被冲刷进入水体,从而控制径流对水环境构成的冲击性污染,从理论和试验2方面分析了管道径流污染物(汇水面和管道沉积物2个来源)的流失规律.结果表明,汇水面源头污染物流失较符合源头冲刷的指数衰减模型,管道内沉积物流失可用流量曲线模型计算;管道内沉积物占管道径流污染物的比例越大,管道径流的初期冲刷现象越不明显.为了提高径流污染控制设施的效率,宜在源头进行分散控制,并加强雨水管网系统清洁维护,避免污染物的积累.     

Efficient Delineation of Nested Depression Hierarchy in Digital Elevation Models for Hydrological Analysis Using Level‐Set Method

In terrain analysis and hydrological modeling, surface depressions (or sinks) in a digital elevation model (DEM) are commonly treated as artifacts and thus filled and removed to create a depressionless DEM. Various algorithms have been developed to identify and fill depressions in DEMs during the past decades. However, few studies have attempted to delineate and quantify the nested hierarchy of actual depressions, which can provide crucial information for characterizing surface hydrologic connectivity and simulating the fill‐merge‐spill hydrological process. In this paper, we present an innovative and efficient algorithm for delineating and quantifying nested depressions in DEMs using the level‐set method based on graph theory. The proposed level‐set method emulates water level decreasing from the spill point along the depression boundary to the lowest point at the bottom of a depression. By tracing the dynamic topological changes (i.e., depression splitting/merging) within a compound depression, the level‐set method can construct topological graphs and derive geometric properties of the nested depressions. The experimental results of two fine‐resolution Light Detection and Ranging‐derived DEMs show that the raster‐based level‐set algorithm is much more efficient (~150 times faster) than the vector‐based contour tree method. The proposed level‐set algorithm has great potential for being applied to large‐scale ecohydrological analysis and watershed modeling.     

Motorcycle safety among motorcycle taxi drivers and nonoccupational motorcyclists in developing countries: A case study of Maoming,South China

Objective: An increasing number of motorcycle taxis have been involved in traffic crashes in many developing countries. This study examines the characteristics of both motorcycle taxi drivers and nonoccupational motorcyclists, investigates the risks they pose to road safety, and provides recommendations to minimize their risks.

Methods: Based on the data collected from a questionnaire survey of 867 motorcycle taxi drivers and 2,029 nonoccupational motorcyclists in Maoming, South China, comparisons were made to analyze differences of personal attributes, attitudes toward road safety, and self-reported behavior of the 2 groups.

Results: Results of the chi-square tests show that not only motorcycle taxi drivers but also nonoccupational motorcyclists in Maoming held poor attitudes toward road safety and both groups reported unsafe driving behavior. There is much room for improving local road safety education among all motorcyclists in Maoming. Yet, motorcycle taxi drivers were more likely to pose road safety risks than nonoccupational motorcyclists under some circumstances, such as speeding late at night or early in the morning, not requiring passengers to wear helmets, and running a red light. The results of the binary logistic regression model show that possessing a vehicle license for a motorcycle or not was the common significant predictor for unsafe driving behavior of motorcycle taxi drivers and nonoccupational motorcyclists. Therefore, enforcement against all motorcyclists not showing vehicle licenses for their motorcycles should be stepped up.

Conclusion: Motorcycle safety is largely poor in Maoming. Therefore, efforts to improve motorcycle safety should be strengthened by targeting not only motorcycle taxi drivers but also nonoccupational motorcyclists.