Numerical studies of the heterogeneous combustion of char using detailed chemistry

The oxidation of graphite is used as a model system for the combustion of char. In order to understand this oxidation process a stagnation-point flow of an oxygen stream on a graphite surface is investigated numerically. The chemical reactions in the gas phase as well as on the surface are modelled by a series of elementary steps. The surface reactions take into consideration the different surface complexes formed, the influence of the geometry of the graphite surface and the interaction of gas-phase molecules with surface complexes. The rate coefficients used are estimated by applying methods of the microkinetic analysis of heterogeneous catalytic reactions. The mechanism is used to simulate the combustion rate of a graphite surface and the ratio of CO to CO2 formed on the surface. The simulation results are compared with experimental data and a good agreement is achieved. Furthermore, the fraction of char-bound nitrogen converted to N2 and N2O is calculated.     

造纸废水混凝处理中SFT助凝替代性研究

中小造纸厂废水处理常用PAC作混凝剂 ,PAM作助凝剂。由于PAM成本很高 ,影响了处理设备的投运率。用超细滑石粉 (SFT)替代PAM助凝 ,与混凝剂PAC配合 ,其混凝处理效果基本相当 ,但是处理成本降低 0 .10元 /m3 。由于SFT属环境无害材料 ,不会给排泥带来二次污染     

Evaluation of a simplified top-down model for the spatial assessment of hot traffic emissions in mid-sized cities

Traffic emission estimation in developing countries is a key-issue for air pollution management. In most cases, comprehensive bottom-up methodologies cannot be applied in mid-sized cities because of the resource cost related to their application. In this paper, a simplified emission estimation model (SEEM) is evaluated. The model is based on a top-down approach and gives annual global hot emission. Particular attention is paid to the quality of the input traffic data. The quality of results is assessed by application of the SEEM model in the Chilean Gran Concepción urban area and by comparison with a bottom-up approach that has been led for the year 2000. The SEEM model estimates emissions with an accuracy of about $20\%$ and is related to important resource savings. The results of the SEEM model are then distributed in space with a disaggregation approach and using GIS techniques. The relevancy of the disaggregation approach is evaluated among several possibilities through statistical methods. A spatial disaggregation using principal roads density gives the best results in terms of emissions repartition and gives a globally accurate image of the distribution of hot emissions in a mid-sized city.     

混凝试验搅拌器的研制

影响混凝效果的因素众多,混凝沉淀烧杯试验是进行水的混合、絮凝、沉淀工艺研究、设计和生产指导的最有效方法之一,阐述了智能型混凝试验搅拌器的设计原理和技术性能.     

Determination of the required surface area of a final clarifier for an activated-sludge system.

A generic methodology for determining the required surface area of a final clarifier is presented. Clarification and thickening requirements are integrated to form a unified procedure for final clarifier design. The new method is based on results obtained by Yuen (2002) on the solids flux theory for a secondary clarifier; it does not require the specification of recycle rate, which is computed as an output of the method. The author shows that there is a minimum required surface area (A(m)) for a final clarifier under the thickening requirement when the designed recycle rate is set at the maximum allowable value (FR)m (at the critical state). The designed surface area and the return activated sludge pumping capacity can be determined by applying a safety factor to A(m) and (FR)m, respectively. The method is shown to conform to conventional design criteria under typical design conditions.     

Theoretical study of the dechlorination reaction pathways of octachlorodibenzo-p-dioxin

The dechlorination reaction pathways of 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (OCDD) by the hydrogen atom are investigated by the density-functional theory B3PW91 method. The dechlorination reactions have large exothermicity and small activation energies. The activation energies (approximately 5 kcal/mol) of the sigma-complex formation due to the hydrogen addition are lower than those (approximately 9 kcal/mol) of the direct chlorine abstraction. It is suggested that the sigma-complex plays an important role in the reactions, although it has scarcely been shown in previous studies of the dechlorination of dioxins. The sigma-complex formation is favored at low temperatures and the chlorine abstraction is favored at high temperatures. Furthermore, it is found that the lateral positions have a marginal preference over the longitudinal positions. The dechlorination of OCDD by the hydrogen atom is thus not likely to result in a dominant formation of the laterally substituted toxic congeners.     

Growth of Zostera japonica in different sediment habitats of the Yellow River estuary in China

Environmental Science and Pollution Research - The estuarine delta of the Yellow River is a region of strong land-ocean-human interactions that undergoes a unique evolutionary process. The delta is...     

Determination of aromatic hydrocarbons in submicrogram quantities in aqueous systems by means of high performance liquid chromatography

One liter of the water sample is extracted with 1,1,2-trichlorotrifluoroethane. This non-polar solvent with a low boiling point is then concentrated and a portion of the concentrated extract is injected in a high performance liquid chromatography system. Polar material is separated from the hydrocarbons by means of a silica gel column. The detector measures the UV absorbance at 254 nm at which wavelength aromatic compounds absorb especially well. The quantitative values are given as phenanthrene equivalents and amounts as small as 20 ng/l can be detected. The standard deviation of the method is ± 50 ng/l. Both these values can be improved with a limited amount of difficulty. A concentrated sample extract can be injected and evaluated in less than 6 minutes, and the method is simple enough to have been used at sea.     

Degradation and photodegradation of tetraacetylethylenediamine (TAED) in the presence of iron (III) in aqueous solution

The dark degradation of tetraacetylethylenediamine (TAED) was investigated. It is a slow process which is favored in acidic medium. There is a hydrolysis of an imide group with the scission of the C---N bond giving rise to the triacetyl derivative (TAED'). When allowed to stand for longer times a second acetyl group is eliminated with the formation of the symetric diacetyl derivative (DAED). The degradation of TAED photoinduced by iron (III) was also investigated. It appears a faster degradation which does not lead to the same products. The process only involves ^•OH radicals formed upon photolysis of aquocomplex of iron (III). They preferentially abstract a hydrogen from the methylene group. The degradation is then assisted by oxygen and leads to the formation of carbonylated oxidation products.     

Effect of Plantings on Radiation of Highway Noise

The body of information presented in this paper is directed to those individuals concerned with the location of highways relative to either existing or planned residential communities. The paper treats in depth the expected attenuation of automobile and particularly diesel tractor-trailer generated hoise by the interposition of extensive and dense planting of trees and shrubs between the highway and the community. The results of research, by the author and others cited in the paper, gives clear indication that a belt of dense man-made growth of tall trees and underbrush can give as much as 5 to 8 dB truck/car noise reduction per 100 ft of planting depth. Natural growth of deep forests were measured to give from 3 to 5 dB attenuation per 100 ft of planting depth. Planting depth of at least 100 ft is required to give reliable results, with tree heights of 40-50 ft desirable and densities of 50-70 ft visibility needed for good effect.

The paper provides considerable experimental verification by an analysis of the current literature. The types of noise sources in cars and trucks are briefly treated as are community reactions to noise from such sources. The dBA is used as the accepted measure for characterizing truck and automobile noise. Both spherical and cylindrical radiation of sound are discussed for low density and high density traffic, respectively.

The paper concludes with an example of attenuation of a typical truck noise by spherical and cylindrical radiation for low- and high-density traffic and a 200-ft deep planting of dense, mature forest. It is concluded that a mature belt of either coniferous or deciduous forest with underbrush can produce barely acceptable noise levels in the community which is separated by such a noise barrier from a heavily traveled highway.     

Methodologies for incorporation of synergistic effects in the calculation of the Pollutant Standards Index

The United States Environmental Protection Agency (EPA) developed the Pollutant Standards Index (PSI) in order to provide the public with an overall assessment of daily air quality. PSI values are determined from measured concentrations of five criteria air pollutants carbon monoxide, nitrogen dioxide, ozone, sulfur dioxide, and particulate matter (PM-10). In general, the PSI can be considered a useful tool in the assessment of air quality as it relates to health effects. However, the current method of PSI calculation is subject to certain inherent limitations. These limitations include the fact that the PSI neglects the role of synergism between the individual pollutants in affecting air quality and health. It is very likely that the combination of certain pollutants is more harmful than each acting individually. Since the general population is exposed to more than one of the criteria pollutants at a given time, revising the current PSI methodology to account for such synergism would be useful and helpful to the public. In the current work, two methodologies for synergistic PSI calculation have been evaluated. The first option (Option 1) is dominated by the principle of threshold levels. When further research determines more accurate levels, the methodology may be of value for future synergistic PSI evaluations. The second option (Option 2) is an attempt to incorporate the correlation of pollutant concentrations with health effects (as determined by increased hospital admissions) into the synergism evaluation. The underlying philosophy of this methodology holds the most promise for accurate synergistic PSI calculation. Comprehensive research and experimentation would be beneficial in creating a more accurate PSI function equation. The main advantage of these hypothetical methodologies is that the current PSI method would still be valid for initial PSI calculation. The dissimilarity is in the calculation of the critical (i.e. reportable) PSI value. It is no longer a matter of the highest PSI value among the pollutants being an accurate representative of air quality. Instead, each of the PSI values obtained is applied to a separate equation to determine a synergistic PSI. When above-average pollutant concentrations are recorded, the possibility of synergistic behavior increases and would be demonstrated with the application of both options. The advantage of Option 1 (versus Option 2) is that the equation was derived from a recognized approach to synergism in combination with the ideas of threshold levels. The advantage of Option 2 is that it is an attempt to correlate concentration levels with health effects observed in the health industry. It is possible that a combination of both philosophies will eventually lead to the development of a synergistic PSI methodology worthy of approval by the EPA.     

The effect of improved nowcasting of precipitation on air quality modeling

The predictive potential of air quality models and thus their value in emergency management and public health support are critically dependent on the quality of their meteorological inputs. The atmospheric flow is the primary cause of the dispersion of airborne substances. The scavenging of pollutants by cloud particles and precipitation is an important sink of atmospheric pollution and subsequently determines the spatial distribution of the deposition of pollutants. The long-standing problem of the spin-up of clouds and precipitation in numerical weather prediction models limits the accuracy of the prediction of short-range dispersion and deposition from local sources. The resulting errors in the atmospheric concentration of pollutants also affect the initial conditions for the calculation of the long-range transport of these pollutants. Customary the spin-up problem is avoided by only using NWP (Numerical Weather Prediction) forecasts with a lead time greater than the spin-up time of the model. Due to the increase of uncertainty with forecast range this reduces the quality of the associated forecasts of the atmospheric flow.In this article recent improvements through diabatic initialization in the spin-up of large-scale precipitation in the Hirlam NWP model are discussed. In a synthetic example using a puff dispersion model the effect is demonstrated of these improvements on the deposition and dispersion of pollutants with a high scavenging coefficient, such as sulphur, and a low scavenging coefficient, such as cesium-137. The analysis presented in this article leads to the conclusion that, at least for situations where large-scale precipitation dominates, the improved model has a limited spin-up so that its full forecast range can be used. The implication for dispersion modeling is that the improved model is particularly useful for short-range forecasts and the calculation of local deposition. The sensitivity of the hydrological processes to proper initialization implies that the spin-up problem may reoccur with changes in the model and increased model resolution. Spin-up should be an ongoing concern for atmospheric modelers.     

Analysis of chemical and physical effects of ultraviolet bulbs on cooking emissions

There is a growing recognition of the risks to health, fire hazard, and air quality from cooking emissions. Recent research has identified what is emitted when foods are cooked. Some of the emitted mass is captured in the exhaust system. The balance is expelled into the atmosphere. The outlet of the exhaust system is a demarcation point-upstream the captured mass is the operator or building owner's concern, whereas downstream into the atmosphere, it affects air quality. Building codes have long required operators to deal with the upstream section. More recently, regulations are being placed on what kitchens can emit to the atmosphere. The industry is responding to this challenge with product innovations. Recently gained understanding of cooking emissions supports much of the innovation-but not all. This paper evaluates the purported benefit of adding better filtration and ultraviolet C (UVC) bulbs in kitchen hoods. A "UV hood" claims a two-step process to reduce emissions: better filters capture more emitted mass, and UVC photons and ozone drive photo-decomposition and oxidation reactions of some of the remaining greasy constituents. Adding UV to a hood at least doubles the cost compared to an equivalent non-UV hood. There is evidence that UV hoods do reduce some emissions. The essential question is whether improved performance is due to UV or relatively inexpensive, improved filters. Experimentation exposed an oleic acid aerosol, representative of cooking emissions, to UVC energy and ozone at higher concentrations and for longer exposure times than can occur in a UV hood. Particle-size and chemical changes were measured on samples collected with UV bulbs off and on. Results strongly indicate little change is happening and most emission reductions are caused by better filtration and not UV. The conclusion is that UV hoods fall short of claimed performance, and unreacted ozone may increase air pollution.     

Adsorption-oxidation of hydrogen sulfide on activated carbon fibers: effect of the composition and the relative humidity of the gas phase

The removal of hydrogen sulfide by oxidation-adsorption on two type carbon fibers, Actitex FC1201 and RS1301, was studied. Two kinetic steps where identified. During the first step, the degradation appears to be limited by the oxidation reaction. In the second kinetic step, the by-products inhibit the hydrogen sulfide degradation. This leads to a limitation in the carbon site's accessibility and to a lower kinetic. The Langmuir-Hinshelwood model was used to correlate the experimental results and to estimate the kinetic (k) and the Langmuir adsorption (K) constants. For FC1201 fibers, the kinetic constant (k) is five time higher and the adsorption constant is five time lower compared to the RS1301 fibers. The role of the humidity was found to be highly beneficial for the removal of hydrogen sulfide. Especially in the second kinetic step, where it removes the by-product formed and therefore delays the occurrence of this low kinetic step. The kinetic constant (k) is strongly influenced by humidity while the Langmuir adsorption constant (K) seems independent. The effect of the nature of the gas phase on the reaction kinetic was also studied. Under a dry atmosphere, we note that the oxidation-reaction occurs even if the gaseous oxygen is not present. This oxidation is due to the oxygen surface function of the carbon fibers. Moreover, the degradation kinetic is faster under a dry nitrogen atmosphere. The presence of water traces leads to the acidification of the carbon surface, under oxygen or carbon dioxide atmospheres, and hence limits the hydrogen sulfide dissociation. In a humid atmosphere, the oxygen or carbon dioxide leads to a faster reaction kinetic. The acidification of the carbon surface is largely counterbalanced by the dissolution of the by-products.     

Harmonization of methods for impact assessment

Some aspects of a number of different techniques for environmental decision support, in particular risk assessment (RA) and life-cycle assessment (LCA), are briefly discussed. The importance of a coherent framework, the use of common data sets, and harmonization of methods is emphasized. The latter leads to a discussion of a fundamental difference between techniques that assess continuous emission fluxes, like RA, and techniques that assess discrete emission pulses, like LCA. The question whether it is possible to apply the same types of impact assessment models is positively answered for most models. The implications are threefold: It is allowed to employ the much easier steady-state models in pulse-oriented techniques, there exist often postulated but not yet rigidly proven equivalency factors for use in e.g. life-cycle assessment, and it is possible to harmonize the models as used in pulse-oriented and in flux-oriented models.     

Fractional calculus applied to the analysis of spectral electrical conductivity of clay-water system

The analysis of the low-frequency conductivity spectra of the clay-water mixtures is presented. The frequency dependence of the conductivity is shown to follow the power-law with the exponent n=0.67 before reaching the frequency-independent part. When scaled with the value of the frequency-independent part of the spectrum the conductivity spectra for samples at different water content values are shown to fit to a single master curve. It is argued that the observed conductivity dispersion is a consequence of the anomalously diffusing ions in the clay-water system. The fractional Langevin equation is then used to describe the stochastic dynamics of the single ion. The results indicate that the experimentally observed dielectric properties originate in anomalous ion transport in clay-water system characterized with time-dependent diffusion coefficient.     

Persistence of the mixture of chlorfenvinphos and cypermethrin (Survan) in citrus fruits

The Survan (a mixture of the insecticides chlorfenvinphos and cypermethrin) persistence in lemon citrus fruits, verna variety, is studied. In all the cases, residues of both compounds have been detected in the juices of the fruits treated. When the mixture of the insecticides is used at a concentration of 0.20%, the levels of chlorfenvinphos after 14 days is not higher than 0.14 ppm; however, when it is used at a 0.15% concentration, this value is overpassed in all the samples. The residues of the cypermethrin component are not higher than 0.35 ppm throughout the whole experiment.     

Evaluation of fecal pollution of river sediment by detection of urobilin

In this study, we attempted to establish a new indicator for fecal pollution of river sediment using a sensitive detection method for urobilin. Urobilin contained in sediment was extracted with an alkaline buffer solution. The suitable buffer solution for extraction of urobilin consisted of 0.1 M Tris-HCl buffer (pH 10.0) containing 0.1 m sodium chloride. The ratio of sediment to buffer was 1:10. The distribution of urobilin in river sediment was studied by this method. The amount of urobilin in the river sediment of Tokyo (urban) and the Miura peninsula (rural) area was surveyed. Large quantities of urobilin were detected in the sediments of the urban rivers, but it was scarce in the rural rivers. Urobilin showed a higher content in sediment than in water. Urobilin in river sediment is distributed in large amounts in the lower reaches, where the water is polluted with domestic sewage and industrial waste, but is scarce in the upper streams. The amount of urobilin decreases to the lower layers.     

Vacuum-ultraviolet (VUV) photolysis of water: Mineralization of atrazine

The versatility and efficiency of the VUV photolysis of water as an “Advanced Oxidation Procedure” for the light-induced oxidative degradation of atrazine as a pollutant of surface and ground waters is evaluated. The oxidation of atrazine using TiO₂ as a photocatalyst has been reported to produce almost stoichiometric amounts of cyanuric acid. Mineralization to CO₂, water and inorganic nitrogen containing ions occurred to a very low extent implying that cyanuric acid is resistant to further degradation under the chosen experimental conditions. Our present results show that in oxygen saturated solutions 50% of the initial atrazine is converted to cyanuric acid, whereas only 10% of the initial atrazine is isolated as cyanuric acid in argon saturated solutions. The results indicate that mineralization is more efficient in not strictly oxidative reaction media.