Characterization of individual fly ash particles emitted from coal- and oil-fired power plants

Individual particles from coal- and oil-fired power plants were analyzed by scanning electron microscope equipped with an energy dispersive X-ray spectrometer to investigate size, morphology, and composition. Samples were collected on filters by dichotomous sampler in the fine ( <2.5 μm aerodynamic diameter) and coarse (2.5 to 5–10 μm) fractions. In both fractions coal fly ash particles were predominantly ( > 95%) smooth, mineral spheres. No cenospheres (perforated hollow spheres) were detected, and almost 90% of the mass concentrations occurred in the coarse fraction. Sulfur as lared as a surface layer on the mineral core; the abundances of Fe and S were highly variable. The Al/Si ratio was fairly constant for most of the spheres but not for the relatively few Fe-rich or non-spherical coal fly ash particles. Over 90% of the mass of oil fly ash occurred in the fine fraction. The size distribution of chemical and morphological properties of individual oil fly ash particles was found to be trimodal. Oil fly ash particles smaller than 0.7 μ (geometric diameter) were non-spherical and relatively pure in sulfate, and 90% of such particles were smaller than 0.5 μm; V or Ni could be detected in 50% to 60% of such particles larger than 0.3 μm. Those particles in the 0.7–3 μm range of geometric diameters were predominantly spherical and of mineral composition, highly variable in Al, Si, P, Ca, Ti and Fe; 50–60% of them contained detectable amounts of V or Ni. Larger oil fly ash particles had a lacy morphology and consisted of carbonaceous material and sulfur.     

An analysis of extinction coefficients of particles and water moisture in the stack after flue gas desulfurization at a coal-fired power plant

Two important factors that affect in-stack opacity--light extinction by emitted particles and that by water moisture after a flue gas desulfurization (FGD) unit--are investigated. The mass light extinction coefficients for particles and water moisture, k(p) and k(w), respectively, were determined using the Lambert-Beer law of opacity with a nonlinear least-squares regression method. The estimated k(p) and k(w) values vary from 0.199 to 0.316 m2/g and 0.000345 to 0.000426 m2/g, respectively, and the overall mean estimated values are 0.229 and 0.000397 m2/g, respectively. Although k(w) is 3 orders of magnitude smaller than k(p), experimental results show that the effect on light extinction by water moisture was comparable to that by particles because of the existence of a considerable mass of water moisture after a FGD unit. The mass light extinction coefficient was also estimated using Mie theory with measured particle size distributions and a complex refractive index of 1.5-ni for fly ash particles. The k(p) obtained using Mie theory ranges from 0.282 to 0.286 m2/g and is slightly greater than the averaged estimated k(p) of 0.229 m2/g from measured opacity. The discrepancy may be partly due to a difference in the microstructure of the fly ash from the assumption of solid spheres because the fly ash may have been formed as spheres attached with smaller particles or as hollow spheres that contained solid spheres. Previously reported values of measured k(p) obtained without considering the effects of water moisture are greater than that obtained in this study, which is reasonable because it reflects the effect of extinction by water moisture in the flue gas. Additionally, the moisture absorbed by particulate matter, corresponding to the effect of water moisture on the particulates, was clarified and found to be negligible.     

An Analysis of Extinction Coefficients of Particles and Water Moisture in the Stack after Flue Gas Desulfurization at a Coal-Fired Power Plant

ABSTRACT

Two important factors that affect in-stack opacity—light extinction by emitted particles and that by water moisture after a flue gas desulfurization (FGD) unit—are investigated. The mass light extinction coefficients for particles and water moisture, k _p and k _w, respectively, were determined using the Lambert-Beer law of opacity with a nonlinear least-squares regression method. The estimated k _p and k _w values vary from 0.199 to 0.316 m²/g and 0.000345 to 0.000426 m²/g, respectively, and the overall mean estimated values are 0.229 and 0.000397 m²/g, respectively. Although k _w is 3 orders of magnitude smaller than k _p, experimental results show that the effect on light extinction by water moisture was comparable to that by particles because of the existence of a considerable mass of water moisture after a FGD unit. The mass light extinction coefficient was also estimated using Mie theory with measured particle size distributions and a complex refractive index of 1.5-ni for fly ash particles. The k _p obtained using Mie theory ranges from 0.282 to 0.286 m²/g and is slightly greater than the averaged estimated k _p of 0.229 m²/g from measured opacity. The discrepancy may be partly due to a difference in the microstructure of the fly ash from the assumption of solid spheres because the fly ash may have been formed as spheres attached with smaller particles or as hollow spheres that contained solid spheres. Previously reported values of measured k _p obtained without considering the effects of water moisture are greater than that obtained in this study, which is reasonable because it reflects the effect of extinction by water moisture in the flue gas. Additionally, the moisture absorbed by particulate matter, corresponding to the effect of water moisture on the particulates, was clarified and found to be negligible.

IMPLICATIONS In-stack opacity is used as a surrogate for particle concentration and can be measured using light transmission meters as part of a continuous emission monitoring system. Because emission standards have become increasingly strict, FGD with wet scrubbing is generally used for coal-fired power plants. However, after a FGD unit with wet scrubbing is set up, the concentration of water moisture increases, affecting the measured opacity. This study evaluates the contributions of particles and water moisture to opacity. The results should provide useful information and can be utilized for modifying measurements for monitoring particulate emissions using opacity.     

Study of PCDD/Fs distribution in fly ash,ash deposits,and bottom ash from a medical waste incinerator in China

Over the past decades in China, the number of medical waste incinerators (MWIs) has been rising rapidly, causing emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). In this study, samples of fly ash, ash deposits, and bottom ash from typical MWIs were analyzed for PCDD/Fs and their distribution characteristics. Results showed international toxic equivalent (I-TEQ) values in the range of 6.9–67 ng I-TEQ/g in fly ash and ash deposits, whereas the concentration in bottom ash was extremely low (only 1.33 pg I-TEQ/g), yet the generation of PCDD/Fs was mostly de novo synthesis in fly ash and ash deposits according to the ratio of PCDFs to PCDDs; the major distribution differences of PCDD/Fs in fly ash was manifested by the content of toxic furan 2,3,7,8-TCDF, but other toxic PCDD/Fs showed similar distribution. Other findings are that 2,3,4,7,8-PeCDF had the most contribution to TEQ concentration, and that the most abundant toxic furan congener is 1,2,3,4,6,7,8-HpCDF. Correlation analysis showed that there was no significant correlation between PCDD/Fs concentration and several other physical and chemical parameters.

Implications: This paper is of interest because it presents the emission performances of PCDD/Fs in ash from medical waste incineration in China. PCDD/F contents in fly ash and ash deposits vary between 6.9 and 67.3 ng I-TEQ/g. However, the concentration in bottom ash was extremely low (only 1.33?×?10^?3 ng I-TEQ/g). The fingerprints of PCDD/Fs in fly ash are almost similar, except for 2,3,7,8-TCDF. There is no marked correlation between PCDD/Fs and other physicochemical properties.

Supplemental Materials: Supplemental materials are available for this paper. Go to the publisher's online edition of the Journal of the Air & Waste Management Association.     

Characteristics of Individual Particles at a Rural Site in the Eastern United States

To determine the nature of aerosol particles in a rural area of the eastern United States, aerosol samples were collected at Deep Creek Lake, Maryland, on various substrates and analyzed by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). SEM analysis of particles larger than 2.5 μm collected on Nuclepore filters revealed the following: clay minerals, quartz, gypsum, and calcite comprised 50 percent of the particles analyzed; spores, pollen, and plant debris comprised 25 percent; 9 percent were fly ash; 11 percent were sulfates; 5 percent were unidentified. Particles ranging from 0.3 to 2 μm were collected in a cascade impactor on grid-supported carbon films and analyzed by TEM for decomposition rate as well as for reaction with the barium chloride and nitron (C₂₀H₁₆N₄) films that were applied after sampling. The TEM analyses indicated that as much as 95 percent of the particles in the 0.3- to 2-μm diameter range were pure ammonium sulfate or acidic ammonium sulfate; they contained essentially no insoluble or nonvolatile matter. About 5 percent of the particles were fly ash spheres. When replicas of particles collected on Nucleopore filters were analyzed by TEM, we observed agglomerates of particles smaller than 0.1 μm.     

Joint US/USSR Test Program for Reducing Fly Ash Resistivity

An electrostatic precipitator preceded by a wet scrubber was tested at the Reftinskaya Power Station. The unit collects a high resistivity fly ash from the combustion of low sulfur Ekibastuz coal. The operating parameters of the precipitator were measured as well as the mass emissions and the in-situ electrical resistivity of the fly ash. Density, particle size distribution, electrical resistivity, and chemical composition were determined for collected samples of the fly ash. The fly ash was also characterized by x-ray diffraction and scanning electron microscopy. When a centrifugal wet wall scrubber was installed ahead of the electrostatic precipitator, the temperature of the flue gas entering the precipitator was decreased and the moisture content increased. The electrical resistivity of the fly ash was attenuated a decade, but not enough to overcome the adverse effects of back corona in the precipitator. Lowering the flue gas temperature to about 85°C by the addition of a venturi scrubber ahead of the centrifugal scrubber reduced the electrical resistivity of the fly ash another decade and allowed the operation of the precipitator without back corona.     

Effect of fly ash on metsulfuron-methyl sorption and leaching in soils

This investigation was undertaken to determine the effect of amendment of two fly ashes [Kota and Inderprastha (IP)] on sorption behavior of metsulfuron-methyl in three Indian soil types. Kota fly ash (5%) did not show any effect on herbicide sorption while IP fly ash significantly enhanced the sorption. Further studies on metsulfuron-methyl sorption-desorption behavior in 0.5, 1, 2, and 5% IP fly ash-amended soils suggested that effect of fly ash varied with soil type and better effect was observed in low organic carbon content soils. The sorption-desorption isotherms fitted very well to the Freundlich sorption equation and, in general, slope (1/n) values less than unity were observed. Metsulfuron-methyl sorption in the IP fly ash-amended soils showed strong correlation with the fly ash content and compared to the Freundlich sorption constant (K _f), K _FA values (sorption normalized to fly ash content) showed less variation. Metsulfuron-methyl leaching studies suggested greater retention of herbicide in the application zone in IP fly ash-amended soils, but effect varied with soil type and no herbicide leaching was observed in 5% fly ash-amended soils. The study suggested that all coal fly ashes are not effective in enhancing the sorption of metsulfuron-methyl in soils. However, one which enhanced herbicide sorption, could play an important role in reducing its leaching losses.     

Immobilization and volume reduction of heavy metals in municipal solid waste fly ash using nano-size calcium and iron-dispersed reagent

This study was conducted to examine the synthesis and application of novel nano-size calcium/iron-based composite material as an immobilizing and separation treatment of the heavy metals in fly ash from municipal solid waste incineration. After grinding with nano-Fe/Ca/CaO and with nano-Fe/Ca/CaO/[PO₄], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash). Heavy metals in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized, respectively. Additionally, scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM-EDS) observations indicate that the main fraction of enclosed/bound materials on treated fly ash includes Ca/PO₄-associated crystalline complexes. After nano-Fe/Ca/CaO/[PO₄] treatment, the heavy metal concentrations in the fly ash leachate were much lower than the Japan standard regulatory limit for hazardous waste landfills. These results appear to be extremely promising. The addition of a nano-Fe/Ca/CaO/PO₄ mixture with simple grinding technique is potentially applicable for the remediation and volume reduction of fly ash contaminated by heavy metals.

Implications: After grinding with nano-Fe/Ca/CaO and nano-Fe/Ca/CaO/[PO₄], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash), whereas heavy metals either in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized. These results appear to be very promising, and the addition of nano-Fe/Ca/CaO/PO₄ mixture with simple grinding technique may be considered potentially applicable for the remediation and volume reduction of contaminated fly ash by heavy metals.     

Mercury Balance on a Large Pulverized Coal-Fired Furnace

This paper presents results of a survey of mercury concentrations in coal, ash, water, fly ash, and flue gas discharges from a 5.5 × 10⁶ Ib/hr steam generator serving a 775 MW (net) turbine-generator set. Representative composite or grab samples were obtained for inlet coal and outlet ash and water. Stack samples were obtained for fly ash and mercury vapor emissions while the unit was operated at 660 MW (net) (85% of full load). Samples were analyzed by anodic stripping voltammetry, plasma emission spectroscopy, and neutron activation analysis to determine mercury concentration entering the furnace in the coal and leaving the furnace in the flue gas, fly ash, bottom and hopper ash, and water. Method inter-comparisons are discussed. A material balance for mercury has been calculated from fuel, ash, and stack gas flow rates. About 90% of the mercury in the coal is released and appears as vapor discharged in the stack gas while 10% remains in the residual ash. For a 700 MW (net) unit, about 5 lb/day of mercury vapor is released to the atmosphere.     

Dioxins and their fingerprint in size-classified fly ash fractions from municipal solid waste incinerators in China—Mechanical grate and fluidized bed units

The distribution of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), in brief dioxins, has seldom been addressed systematically in fly ash from municipal solid waste incinerators (MSWIs). This study shows the amount and fingerprint of PCDD/Fs in fly ash from four different Chinese MSWIs, that is, three mechanical grate units and one circulating fluidized bed unit. In these fly ash samples, dioxins-related parameters (international toxic equivalent quantity, total amount of PCDD/Fs, individual isomer classes, and 17 toxic 2,3,7,8-substituted congeners) all tend to increase with decreasing particle size for mechanical grate incinerators, yet only for the finest fraction for fluidized bed units. Moreover, the fluidized bed incinerator seems superior to grate incineration in controlling dioxins, yet a comparison is hampered by internal differences in the sample, for example, the fluidized bed fly ash has much lower carbon and chlorine contents. In addition, the presence of sulfur from mixing coal as supplemental fuel to the MSW may poison the catalytic steps in dioxins formation and thus suppress the formation of dioxins. With more residual carbon and chlorine in the fly ash, it is easier to form dioxins during cooling. Nevertheless, there is no apparent relation between Fe, Cu, and Zn contents and that of dioxins in fly ash.

Implications This paper is of interest because it presents the amounts and distribution of PCDD/Fs in fly ash samples from some typical waste incineration plants in China, featuring distinct incinerator types, combustion conditions, fuel composition, or residual carbon, chloride, and heavy metal contents in fly ash.     

Performance of a Pulse-Jet Filter at High Filtration Velocity I. Particle Collection

The fly ash collection characteristics of a pulse-jet fabric filter have been studied. Fly ash penetration was found to decrease as the dust deposit increased from 0 to 60 micrometers in thickness, to increase as face velocity through the bags increased from 5 to 15 cm/s, and to remain relatively constant for particles from 0.3 to 4.0 µm in diameter. Experiments employing chemically tagged fly ash were performed to investigate three dust penetration mechanisms. On resumption of filtering after cleaning, penetration by straight through dust loss declined rapidly from its maximum, reached a minimum, and then increased. Seepage of dust through the fabric was found to be constant throughout the filtration cycle. Dust lost as pinhole plugs increased after cleaning, passed through a maximum, and then declined. The pinholes appeared to open the way for further penetration by the straight through mechanism.     

粉煤灰对水溶液中磷的吸附性能及机理

以粉煤灰为吸附剂去除溶液中的磷,考察了其吸附除P动力学特征、热力学特征以及溶液初始pH和粉煤灰投加量对吸附除P效果的影响,并对其吸附除P机理做了初步探讨。结果表明,在给定实验条件下,粉煤灰对P具有较好的去除效果,随着初始P浓度从10 mg/L升高到80 mg/L,平衡吸附量为0.46～2.44 mg P/g粉煤灰,吸附效率从92.2%降低至61.1%;对不同浓度的含P溶液,粉煤灰最适用量为0.6～1.5 g粉煤灰/mg P;相同反应条件下,当温度由25℃升高到45℃时,P初始吸附速率提高了3倍;粉煤灰对P的吸附过程能够较好地拟合Langmuir、Freundlich及D-R吸附等温模型,相关系数均在0.98以上。通过对吸附饱和的粉煤灰进行解析实验发现,初始P浓度较低(<50 mg/L)时,以化学吸附为主,而在初始P浓度较高(>80 mg/L)时,则以物理吸附为主。     

Comparison of CaO’s effect on the fate of heavy metals during thermal treatment of two typical types of MSWI fly ashes in China

Both grate and fluidized bed incinerators are widely used for MSW incineration in China. CaO addition for removing hazardous emissions from MSWI flue gas changes the characteristics of fly ash and affects the thermal behavior of heavy metals when the ash is reheated. In the present work, two types of MSWI fly ashes, sampled from both grate and fluidized bed incinerators respectively, were thermal treated at 1023–1323 K and the fate of heavy metals was observed. The results show that both of the fly ashes were rich in Ca and Ca-compounds were the main alkaline matter which strongly affected the leaching behavior of heavy metals. Ca was mostly in the forms of Ca(OH)₂ and CaCO₃ in the fly ash from grate incinerator in which nascent fly ash particles were covered by Ca-compounds. In contrast, the content of Ca was lower in the fly ash from fluidized bed incinerator and Ca was mostly in the form of CaSO₄. Chemical reactions among Ca-compounds caused particle agglomeration in thermal treated fly ash from grate incinerator, restraining the heavy metals volatilization. In thermal treated fly ash from fluidized bed incinerator, Ca was converted into aluminosilicates especially at 1323 K which enhanced heavy metals immobilization, decreasing their volatile fractions as well as leaching concentrations. Particle agglomeration hardly affected the leaching behavior of heavy metals. However, it suppressed the leachable-CaCrO₄ formation and lowered Cr leaching concentration.     

Distribution of mercury in the combustion products from coal-fired power plants in Guizhou,southwest China

Method 30B and the Ontario Hydro Method (OHM) were used to sample the mercury in the flue gas discharged from the seven power plants in Guizhou Province, southwest China. In order to investigate the mercury migration and transformation during coal combustion and pollution control process, the contents of mercury in coal samples, bottom ash, fly ash, and gypsum were measured. The mercury in the flue gas released into the atmosphere mainly existed in the form of Hg°. The precipitator shows a superior ability to remove Hg^p (particulate mercury) from flue gas. The removal efficiency of Hg²⁺ by wet flue gas desulfurization (WFGD) was significantly higher than that for the other two forms of mercury. The synergistic removal efficiency of mercury by the air pollution control devices (APCDs) installed in the studied power plants is 66.69–97.56%. The Hg mass balance for the tested seven coal-fired power plants varied from 72.87% to 109.67% during the sampling time. After flue gas flowing through APCDs, most of the mercury in coal was enriched in fly ash and gypsum, with only a small portion released into the atmosphere with the flue gas. The maximum discharge source of Hg for power plants was fly ash and gypsum instead of Hg emitted with flue gas through the chimney into the atmosphere. With the continuous upgrading of APCDs, more and more mercury will be enriched in fly ash and gypsum. Extra attention should be paid to the re-release of mercury from the reutilization of by-products from APCDs.

Implications: Method 30B and the Ontario Hydro Method (OHM) were used to test the mercury concentration in the flue gas discharged from seven power plants in Guizhou Province, China. The concentrations of mercury in coal samples, bottom ash, fly ash, and gypsum were also measured. By comparison of the mercury content of different products, we found that the maximum discharge source of Hg for power plants was fly ash and gypsum, instead of Hg emitted with flue gas through the chimney into the atmosphere. With the continuous upgrading of APCDs, more and more mercury will be enriched in fly ash and gypsum. Extra attention should be paid to the re-release of mercury from the reutilization of by-products from APCDs.     

Dioxin contents in fly ash from large-scale MSW incinerators in Taiwan

In this study, fly ash samples were collected from three municipal waste incinerators (MWI) in Taiwan. These MWIs investigated are equipped with different air pollution control devices (APCDs). Preliminary results indicated that 2,3,7,8-PCDD/Fs homologue patterns of various types of fly ash were quite similar for all three MWIs. Concentrations of higher-chlorinated congeners of PCDDs and PCDFs were remarkably higher than those of lower-chlorinated congeners. In the case of MSW-A, the PCDD/PCDF ratios of ashes were found in the decreasing order for cyclone, boiler and baghouse. The PCDD/PCDF ratios in various types of fly ash of MWI-B was boiler-A < boiler-B < ESP < boiler-C. As for MSW-C, no obvious trend has been observed for PCDD/PCDF ratio. However, the ratio in boiler ash was higher than that in baghouse ash of MWI-A. The dioxin contents in fly ash would increase as the fly ash passed through APCD zones. In other words, the environmental conditions of APCD may actually cause the increase of the dioxin contents in fly ash. The trend for dioxin contents in fly ash collected from three MSW incinerators investigated was MSW-C < MSW-A < MSW-B.     

Removal of PCDDs/DFs and dl-PCBs in MWI fly ash by heating under vacuum

Temperature dependence of PCDD/DF and dioxin-like polychlorinated biphenyl (dl-PCB) concentrations in fly ash from a municipal waste incinerator (MWI) heated under vacuum has been investigated as a function of sample temperature ranging from T(s)=425 to 800 K to find out if PCDDs/DFs in fly ash evaporate and are trapped in a liquid nitrogen-cooled trap. The results show that more than 99.98% of PCDDs/DFs in TEQ is removed from fly ash by vacuum heat treatment at T(s)>650 K for 4 h. Almost no PCDDs/DFs were detected in the liquid nitrogen-cooled trap. Homologue distributions indicate that dechlorination/hydrogenation (DCH) reactions proceed in fly ash at T(s)>450 K. Arrhenius rate parameters for the DCH reactions have been determined for each homologue assuming that only DCH reactions occur. The fly ash heated under vacuum at 650 or 800 K was reheated at 573 K (300 degrees C) in a stream of dry or humid air to see how much PCDDs/DFs and dl-PCBs are regenerated. We have found that (1) PCDDs/DFs are regenerated in both 650 K and 800 K treated fly ash, whereas dl-PCBs are regenerated in 650 K treated fly ash, (2) formation of PCDFs predominates over that of PCDDs or dl-PCBs, and (3) less chlorinated homologues are abundant for PCDDs/DFs and dl-PCBs.     

Medium-Sulfur Coal and Fly Ash Resistivity

Electric generating plants burning medium-sulfur coal need a way to predict when ESP performance will be limited by high electrical resistivity of the collected fly ash. The main uncertainty in mathematical predictions of fly ash resistivity lies in the marginal effect of naturally occurring SO₃ vapor in the flue gas. This paper results from a project to expand the data base of SO₃/SO₂ concentrations and fly ash resistivities measured in utility fly ash precipitators. Complete data sets are presented from three plants in the Southern Company electric system. In situ resistivity data are compared with laboratory measurements and with two different mathematical predictions of resistivity based on coal and ash analyses. The revised version of the resistivity predictor gives results in good agreement with resistivity values measured both in situ and in the laboratory.     

Chlorobenzenes removal from municipal solid waste incineration fly ash by surfactant-assisted column flotation

The organic contaminants in municipal solid waste incineration (MSWI) fly ash, including chlorinated aromatic compounds and polycyclic aromatic hydrocarbons, have high toxicity and a potential negative impact on the environment. An effective and low energy consumption technique to remove the organic contaminants from MSWI fly ash is required urgently. Organic contaminants, such as chlorobenzenes (CBzs), in MSWI fly ash are known to become enriched in the unburnt carbon (UC) fraction. It is proposed that removal of UC from fly ash will result in the effective removal of most organic micropollutants. In this research, we use a technique of surfactant-assisted column flotation to decontaminate MSWI fly ash by removal of the CBzs-enriched UC from MSWI fly ash. We find that 39.8% of CBzs can be removed from fresh MSWI fly ash with 61.7% UC removal efficiency, whereas only 33.2% of CBzs can be removed from weathered MSWI fly ash with a low UC removal efficiency of 33.7%. By adding a mixture of two kinds of surfactants: sorbitan mono-oleate and polyoxyethylene (20) sorbitan mono-oleate to the weathered fly ash, 47.0% of CBzs were removed at the hydrophile lipophile balance value of 13.5, while the UC removal efficiency increased to 49.0%. The results show that surfactants can enhance CBzs and UC removal efficiencies during the column flotation process. Higher CBzs and UC removal efficiencies can be expected by further optimizing the conditions of surfactant-assisted column flotation.     

An empirically tractable model of optimal oil spills prevention in Russian sea harbours

Based on previous theoretical work by Gottinger (1997, 1998), we propose a simple model of optimal monitoring of oil-related activities in harbour areas that is suitable for empirical estimation within the Russian— Ukrainian context, in spite of the poor availability of data in these countries. Specifically, the model indicates how to best allocate at the steady state a given monitoring budget between different monitoring activities. An approximate analytical solution to the optimisation problem is derived, and a simple procedure for estimating the model on the basis of the actually available data is suggested. An application using data obtained for several harbours of the Black and Baltic Seas is given. It suggests that the current Russian monitoring practice could be much improved by better allocating the available monitoring resources.     

An Assessment of the Significance of Mercury Release from Coal Fly Ash

Abstract

Some mercury (Hg) naturally present in coal is retained in the fly ash remaining after combustion. Concern has been raised regarding the potential for release of this Hg to the environment. The exchange of Hg between fly ash and the atmosphere was measured in the laboratory and in situ at a fly ash landfill. All samples of fly ash used in the laboratory study, with the exception of that derived from lignite-type coal, acted as a sink for atmospheric Hg. Deposition rates were found to increase as air Hg concentrations increased and to decrease with incident light and increased temperature. Addition of water to fly ash samples resulted in re-emission of deposited atmospheric Hg. Deposition was the dominant flux measured in situ at a fly ash landfill. Atmospheric Hg was deposited to all samples collected as part of two demonstration projects using carbon injection for enhanced Hg capture. Hg concentrations of extracts derived using U.S. Environmental Protection Agency Method 1312 (Synthetic Precipitation Leaching Procedure) were ≤14.4 ng/L. Data developed demonstrate that fly ash, including that collected from Hg removal projects, will release little Hg to the air or water, and under certain conditions, absorbs Hg from the air.