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1.
There seems to be a general impression on the part of the public and many technical people that dust collecting systems on the open hearth furnace are simply a matter of giving a contract for a duplicate system to that previously installed; signing a check for a sum to cover the cost of the cleaning equipment itself, pressing the start-up button and then sitting back to receive the plaudits of a grateful community. This paper will briefly present some of the problems common to all of the installations to date. It will also explain why the cost of the cleaning equipment itself is such a small portion of the total cost.  相似文献   

2.
Regional haze regulations require progress toward reducing atmospheric haze as measured by particle scattering coefficient of visible light. From a practical perspective, this raises the following question: Given a decrease in extinction, what is the probability that people will notice an improvement in visibility? This paper proposes a quantitative definition of the probability of a perceptible increase in visibility given a decrease in light extinction and a general method to estimate this probability from perception measurements made in the field under realistic conditions. Using data from a recent study of visibility perception by 8 observers, it is estimated that a 2-4 deciview change gives a 67% maximum probability of detecting the improvement. Stated another way, the odds of seeing a difference are at most 2:1 for a change of 2-4 deciviews. A 90% probability requires a change of at least 3.5-7.0 deciviews. The limitations and possible bias in the results of this study are discussed. These results may have a major effect on the cost-benefit analysis of regulatory actions to improve visibility.  相似文献   

3.
A rapid spectrophotometric determination of persulfate anion in ISCO   总被引:10,自引:0,他引:10  
Due to a gradual increase in the use of persulfate as an in situ chemical oxidation (ISCO) oxidant, a simple measurement of persulfate concentration is desirable to analyze persulfate distribution at designated time intervals on/off a site. Such a distribution helps evaluate efficacy of ISCO treatment at a site. This work proposes a spectrophotometric determination of persulfate based on modification of the iodometric titration method. The analysis of absorption spectra of a yellow color solution resulting from the reaction of persulfate and iodide in the presence of sodium bicarbonate reveals an absorbance at 352 nm, without significant interferences from the reagent matrix. The calibration graph was linear in the range of persulfate solution concentration of 0-70 mM at 352 nm. The proposed method is validated by the iodometric titration method. The solution pH was at near neutral and the presence of iron activator does not interfere with the absorption measurement. Also, analysis of persulfate in a groundwater sample using the proposed method indicates a good agreement with measurements by the titration method. This proposed spectrophotometric quantification of persulfate provides a simple and rapid method for evaluation of ISCO effectiveness at a remediation site.  相似文献   

4.
Abstract

The objective of this research was to investigate a sequentially loaded and regenerated granular activated carbon (GAC) biofilter system and to determine whether regenerative ozonation/advanced oxidation could improve the removal and biodegradation of a volatile organic compound from a contaminated airstream. Bench-scale reactors were constructed to operate in a manner analogous to a commercially available system manufactured by Terr-Aqua Environmental Systems (only with longer contact time). The GAC system consisted of two GAC biofilter beds that operated in a cyclical manner. On a given day, the first GAC bed adsorbed methyl isobutyl ketone from a simulated waste airstream, while the second bed underwent regeneration; then on the next day, the second bed was in the adsorption mode while the first was regenerated.

Three bench-scale systems were used to compare the performance under three operating conditions: (1) ozone/ associated oxidant regeneration of a GAC biofilter system that was seeded with microorganisms from a field site, (2) a humid air regeneration of a seeded GAC biofilter, and (3) a humid air regeneration of an unseeded GAC biofilter. For the advanced oxidant regenerated GAC biofilter, a maximum removal efficiency of >95% was achieved with an empty bed contact time of 148 sec and an influent concentration of 125 ppm methyl isobutyl ketone, and 90–95% was achieved at 148-sec empty bed contact time and a 1150-ppm influent.  相似文献   

5.
The objective of this research was to investigate a sequentially loaded and regenerated granular activated carbon (GAC) biofilter system and to determine whether regenerative ozonation/advanced oxidation could improve the removal and biodegradation of a volatile organic compound from a contaminated airstream. Bench-scale reactors were constructed to operate in a manner analogous to a commercially available system manufactured by Terr-Aqua Environmental Systems (only with longer contact time). The GAC system consisted of two GAC biofilter beds that operated in a cyclical manner. On a given day, the first GAC bed adsorbed methyl isobutyl ketone from a simulated waste airstream, while the second bed underwent regeneration; then on the next day, the second bed was in the adsorption mode while the first was regenerated. Three bench-scale systems were used to compare the performance under three operating conditions: (1) ozone/ associated oxidant regeneration of a GAC biofilter system that was seeded with microorganisms from a field site, (2) a humid air regeneration of a seeded GAC biofilter, and (3) a humid air regeneration of an unseeded GAC biofilter. For the advanced oxidant regenerated GAC biofilter, a maximum removal efficiency of >95% was achieved with an empty bed contact time of 148 sec and an influent concentration of 125 ppm methyl isobutyl ketone, and 90-95% was achieved at 148-sec empty bed contact time and a 1150-ppm influent.  相似文献   

6.
The future for electrocoagulation as a localised water treatment technology   总被引:1,自引:0,他引:1  
Electrocoagulation is an electrochemical method of treating polluted water whereby sacrificial anodes corrode to release active coagulant precursors (usually aluminium or iron cations) into solution. Accompanying electrolytic reactions evolve gas (usually as hydrogen bubbles) at the cathode. Electrocoagulation has a long history as a water treatment technology having been employed to remove a wide range of pollutants. However electrocoagulation has never become accepted as a 'mainstream' water treatment technology. The lack of a systematic approach to electrocoagulation reactor design/operation and the issue of electrode reliability (particularly passivation of the electrodes over time) have limited its implementation. However recent technical improvements combined with a growing need for small-scale decentralised water treatment facilities have led to a re-evaluation of electrocoagulation. Starting with a review of electrocoagulation reactor design/operation, this article examines and identifies a conceptual framework for electrocoagulation that focuses on the interactions between electrochemistry, coagulation and flotation. In addition detailed experimental data are provided from a batch reactor system removing suspended solids together with a mathematical analysis based on the 'white water' model for the dissolved air flotation process. Current density is identified as the key operational parameter influencing which pollutant removal mechanism dominates. The conclusion is drawn that electrocoagulation has a future as a decentralised water treatment technology. A conceptual framework is presented for future research directed towards a more mechanistic understanding of the process.  相似文献   

7.
This paper focusses on a conceptual overview of ways to address a comprehensive analysis of ecosystem services (ES) in a country as large and heterogeneous as Russia. As a first step, a methodology for assessing the services for the federal subjects of Russia was chosen, i.e., its constituent provinces and similar entities, in physical terms. Russia harbors a great diversity of natural conditions and ecosystems which are suppliers of ES, and likewise a variety of the socio-economic conditions that shape the demand for these services and their consumption. The methodological approach described permits several important tasks to be addressed: the evaluation of the degree of satisfaction of people’s needs for ES, the identification of ecological donor and acceptor regions, and zoning of the country’s territory for ES assessment. The next step is to prepare a prototype of a National Report on ES in Russia, for which we are presenting the planned structure.  相似文献   

8.
The optimization of the intermittent aeration in a full-scale biological reactor treating municipal and industrial wastewater has been studied by means of an experimental design, where the main factors considered have been the on-off period of aeration and the dissolved-oxygen set point. The objective of the work has been to determine the optimal configuration of the aeration control to achieve a simultaneous removal of carbon (expressed as chemical oxygen demand [COD]) and nitrogen. The results were obtained in a full-scale bioreactor located at the wastewater treatment plant of Sant Celoni (Barcelona, Spain), where a nitrogen removal based on a nitrification-denitrification process is being tested. It has been shown that the crucial parameter to ensure a complete removal of COD and nitrogen is to give the system a long time of on-off aeration to complete both the nitrification and the denitrification processes, whereas the dissolved-oxygen set point has a minor influence on the overall performance. The results presented can be applied to a great number of similar systems, in which a nitrogen removal, based on a nitrification-denitrification scheme, is currently being tested or implemented.  相似文献   

9.
Loss of filtration efficiency in a fabric filter baghouse is typically caused by bag failure, in one form or another. The degree of such failure can be as minor as a pinhole leak or as major as a fully involved baghouse fire. In some cases, local air pollution regulations or federal hazardous waste laws may require estimation of the total quantity of particulate matter released to the environment as a result of such failures. In this paper, a technique is presented for computing the dust loading in the baghouse exhaust when one or more bags have failed. The algorithm developed is shown to be an improvement over a previously published result, which requires empirical knowledge of the variation in baghouse pressure differential with bag failures. An example calculation is presented for a baghouse equipped with 200 bags. The prediction shows that a small percentage of failed bags can cause a relatively large proportion of the gas flow to bypass the active bags, which, in turn, leads to high outlet dust loading and low overall collection efficiency from the baghouse.  相似文献   

10.
11.
The following results provide a comparison between net airborne contamination produced by the traditional form of kiln used in Northern Mexico and by those modified according to a design by Dr. Robert Marquez. What has become known as the MK style kiln was intended to significantly reduce contaminant emissions. The concept involves covering the kiln with a dome and channeling the output of an active kiln through a second, identical loaded kiln for its additional filtration of the effluents. Kilns of a pair are connected via clay brick channels. The roles are reversed after the initial kiln is refilled. Significant reductions in the particulate and gaseous emissions were achieved in the prototype system, but a connectional problem with recent kiln pairs has also limited the degree of operational success. The problem did not mask the potential of the MK kiln, as will be shown. Additional anticipated benefits to the owners of MK kilns, such as reduced operating cycles and decreased quantities of fuel, also have been verified. Key measurements made during all of the burns were of aerosol densities and buoyancies in the flues, kiln temperatures, and, on a number of occasions, chemical analyses of both aerosol and gaseous effluents. Continuous time histories of aerosol densities for most burns (of a total of -40) provide a basis for examining features and the effects of differing styles of operation with respect to burn efficiency and net contaminant masses. Covering the active kiln with a dome produces a net reduction in dry aerosol effluent mass of a factor between 5 and 10, whereas the addition of a filter kiln produces a net reduction of about a factor of 2. The use of used motor oil as a fuel further reduced aerosol contamination by -1 order of magnitude.  相似文献   

12.
ABSTRACT

Researchers have applied open path optical sensing techniques to a variety of workplace and environmental monitoring problems. Usually these data are reported in terms of a path-average (or path-integrated) concentration. When assessing potential human exposures along a beam path, this path-average value is not always informative, since concentrations along the path can vary substantially from the beam average. The focus of this research is to arrive at a method for estimating the upper-bound in contaminant concentrations over a fixed open beam path. The approach taken here uses a statistical model to estimate an upper-bound concentration based on a combination of the path-average and a measure of the spatial variability computed from point samples along the beam path. Results of computer simulations and experimental testing in a controlled ventilation chamber indicate that the model produced conservative estimates for the maximum concentration along the beam path. This approach may have many applications for open path monitoring in workplaces or wherever maximum concentrations are a concern.  相似文献   

13.
Eulerian derivation of the fractional advection-dispersion equation   总被引:4,自引:0,他引:4  
A fractional advection-dispersion equation (ADE) is a generalization of the classical ADE in which the second-order derivative is replaced with a fractional-order derivative. In contrast to the classical ADE, the fractional ADE has solutions that resemble the highly skewed and heavy-tailed breakthrough curves observed in field and laboratory studies. These solutions, known as alpha-stable distributions, are the result of a generalized central limit theorem which describes the behavior of sums of finite or infinite-variance random variables. We use this limit theorem in a model which sums the length of particle jumps during their random walk through a heterogeneous porous medium. If the length of solute particle jumps is not constrained to a representative elementary volume (REV), dispersive flux is proportional to a fractional derivative. The nature of fractional derivatives is readily visualized and their parameters are based on physical properties that are measurable. When a fractional Fick's law replaces the classical Fick's law in an Eulerian evaluation of solute transport in a porous medium, the result is a fractional ADE. Fractional ADEs are ergodic equations since they occur when a generalized central limit theorem is employed.  相似文献   

14.
This is an overview of the strategy used to describe the effects of a potential release from a radioactive waste repository on human exposure and future environments. It introduces a special issue of AMBIO, in which 13 articles show ways of understanding and characterizing the future. The study relies mainly on research performed in the context of a recent safety report concerning a repository for spent nuclear fuel in Sweden (the so-called SR-Site project). The development of a good understanding of on-site processes and acquisition of site-specific data facilitated the development of new approaches for assessment of surface ecosystems. A systematic and scientifically coherent methodology utilizes the understanding of the current spatial and temporal dynamics as an analog for future conditions. We conclude that future ecosystem can be inferred from a few variables and that this multidisciplinary approach is relevant in a much wider context than radioactive waste.  相似文献   

15.
In preparation for a field experiment where a NAPL will be injected into a fractured sandstone aquifer, a 2D invasion percolation model of DNAPL migration in a single horizontal fracture with varying aperture has been developed. This simulation investigated the effect of spatially correlated fracture aperture fields on pressure-saturation relationships as a function of variable aperture mean, standard deviation, and spatial correlation statistics under hydrostatic conditions. Results from spatially correlated variable aperture fields can be significantly different from random fields. Longer ranges decreased entry pressures and higher standard deviations decreased nonwetting phase saturations. Mean aperture is the major control on displacement pressure, entry pressure and the form of the pressure-saturation curve. Simulation results using statistical parameters for a variable aperture natural sandstone fracture as described by Yeo et al. [International Journal of Rock Mechanics and Mining Sciences 35 (1998) 1051] closely resemble a Brooks-Corey pressure-saturation function, and exhibit a distinct entry pressure followed by a rapid increase in nonwetting phase saturation. Graphical estimates of entry pressure provide a good approximation of the critical aperture controlling the formation of a continuous nonwetting phase pathway in a variable aperture fracture. Consequently, we show that multiphase flow concepts developed for porous media can successfully be applied to variable aperture fractures. Entry pressure correlates well to the mean aperture in these simulations when using a Gaussian distribution of fracture aperture. Interpreted aperture distributions from NAPL injection experiments do not fit the true distribution well at low nonwetting phase saturations, but do at higher saturations above the entry pressure. Consequently, true, mechanical aperture variation within a fracture plane cannot be determined from NAPL injection experiments either in the field or laboratory.  相似文献   

16.
A semianalytical soil-pesticide transport model is formulated based on a compartmental approach to determine spatial and temporal variations of pesticide residues across a soil profile. The compartmental model is implemented by drawing an analogy between a series of continuous-flow stirred tank reactors and a soil horizon that consists of multiple perfectly mixed compartments. The analogy is strengthened by exploiting a relation between the compartment series and the conventional convective-dispersive equation (CDE) for vertical transport in the soil. Consequently, the number of compartments in the model formulation is not free, but dictated as a function of transport parameters. The model formulation allows consideration of arbitrary boundary value specifications and also, for some cases, spatially varying initial concentration profiles. Sorption kinetics is represented via a two-site model that involves a linear sorption isotherm and a first-order irreversible sorption or a radial diffusive penetrating model. For these three cases, analysis of the compartmental model allows the resultant concentration profiles to be expressed in terms of the Poisson distribution. When a nonlinear kinetic sorption model is used to simulate the sorption processes, an analytical solution is not found and a numerical approach is required.  相似文献   

17.
The long-term health consequences of exposure to phenoxyherbicides used in Vietnam has been a great concern to the veterans. In addition to the Air Force Ranch Hand personnel, Army Chemical Corps personnel who served in Vietnam are thought to have had some of the highest herbicide exposures. The Department of Veterans Affairs commenced a study of veterans who served in Vietnam as members of the Army Chemical Corps and a comparison cohort of Army Chemical Corps personnel who served elsewhere. A total of 2872 Vietnam veterans and 2737 non-Vietnam veterans who served in the Army Chemical Corps were identified for inclusion in a telephone health interview survey with a random 20% sample of veterans receiving serum dioxin and other congeners assessments. In a feasibility study which included 284 Vietnam veterans and 281 non-Vietnam veterans, 100 serum assessments were conducted of which 95 were included in the analysis. Vietnam veterans with a history of spraying herbicides were found to have a statistically significant elevation in their current serum 2,3,7,8-TCDD concentrations compared to non-Vietnam veterans without a spray history (P = 0.05). Other 2,3,7,8-substituted dioxins levels were comparable to the levels found in the non-Vietnam veterans. This feasibility study demonstrated that serum dioxin concentrations from a sample of the study participants can be used to identify exposure variables in the health survey that can serve as a surrogate measure of phenoxyherbicide exposure.  相似文献   

18.
Five different water sampling techniques have been compared in a series of lakes. In deep lakes, no significant differences were observed between mean summer nutrient concentrations measured in (i) a tube sample integrating over the photic zone taken from the deepest point; (ii) a surface dip sample taken at the deepest point; (iii) a surface dip sample taken by wading into the water's edge; (iv) a dip sample taken slightly further off shore by suspending a bottle below a buoy thrown out about 30 m from the shore; and (v) a sample taken along a short transect out from the shore using a model boat to transport the sample bottle. In shallower lakes the integrating tube sampler gave significantly higher estimates of mean concentrations than other methods due to the increase in volume of the unmixed hypolimnion which reduced the depth of the well mixed epilimnion to less than the tube length. For national survey purposes samples taken from the edge of the lake are the most cost effective.  相似文献   

19.
The occurrence of multiple steady states in a toluene biodegrading, diffusion-limited biofilm under aerobic conditions was investigated by computer models: one steady-state, and one nonsteady-state. Two stable and one unstable intermediate steady-state were identified in a narrow set of combinations of parameters values. The nonsteady-state model predicts conditions that evolve to a steady state that is within 0.02–1% of the solution of the steady-state model, depending on the number of grid points used, confirming the algorithms are valid. Multiple steady states occur if, (1) a biofilm is exposed to a constant gas-phase pollution concentration, which exceeds or undershoots a certain threshold, (2) in a narrow range of parameter values and (3) provided that the pollutant degradation follows Haldane kinetics. Such a biofilm displays half-saturation (i.e., Michaelis-Menten)-like apparent (“falsified”) kinetics from a concentration range starting at zero up to the occurrence of a second steady state. Multiple steady states and falsified kinetics can negatively affect a biofilter and the experimental determination of kinetic parameters, respectively.

Implications: The occurrence of multiple steady states in a VOC treating biofilm, shows the significant impact of degradation kinetics and diffusion limitation on the biofilm behavior. Moreover, the implied possible sudden drop of removal efficiency of a biofilter, based on the occurrence of multiple steady states lead to possible bottle-necks in biofilter application and operation.  相似文献   

20.
With landfill costs increasing and regulations on landfilling becoming more stringent, alternatives to conventional hazardous waste treatment strategies are becoming more desirable. Incineration Is presently a permanent, proven solution for the disposal of most organic contaminants, but also a costly one, especially in the case of solids which require some auxiliary fuel. The goal of this research is to develop an understanding of the phenomena associated with the evolution of contaminants from solids In the primary combustor of an Incineration system. A four-fold approach is being used. First, a bench-scale particle characterization reactor was developed to study the transport phenomena on a particle basis, where the controlling processes are mainly intraparticle. Second, a bed-characterization reactor was built to examine the controlling transport phenomena within a bed of particles, where the processes are primarily interparticle. The results of these studies can be applied to any primary combustor. A pilot-scale rotary kiln was developed to study the evolution of contaminants from solids within a realistic temperature and rotation environment. Finally, in situ measurements are being obtained from a full-scale rotary-kiln.

This paper describes results obtained in a study using a commercial sorbent contaminated with toluene. The data are from the particle-characterization reactor and the rotary-kiln simulator. The results show that the method of contamination and charge size do not have a large effect on desorption, while temperature and contaminant concentration are important parameters In the evolution of contaminants in a rotary kiln.  相似文献   

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