Net Waste Reduction Analysis Applied to Air Pollution Control Technologies

Post-combustion air pollution control technologies were evaluated to determine total waste produced by the operation of these systems. A continuum of air pollution control technology choices providing increasing levels of control is presented and the quantity of waste produced by each air pollution control option has been calculated. In addition, this analysis accounts for waste produced indirectly by the generation of energy required for operation of the control technologies. This type of analysis can be used to select optimal control levels and to demonstrate why a goal of zero air emissions may not be environmentally desirable.     

The Spanish dioxin inventory part I: Incineration as municipal waste management system

The main objectives of the Spanish dioxin inventory and the incidence of municipal waste incinerators in the PCDD/Fs releases in the period from January 1997-November 1999 are presented. Preliminary data about the stack emission levels, fly ashes and slags as solid residues and the PCDD/Fs input in the USW are also presented to elaborate an initial balance for the incineration sector. A great decrease, from 20 to 1.2 g I-TEQ/y, from incineration gas emissions has been observed since 1996. The preliminary balance in the MWI sector suggests an overall PCDD/Fs destruction. The calculated emission factor, 1.06 microg I-TEQ/Mg, indicates a high quality of the air pollution control systems. The assumption of PCDD/Fs in the USW permits an initial evaluation of other waste management systems.     

Wind Roses for Florida

A three-dimensional Joint frequency distribution (3DJFD) map of Florida is developed based upon wind rose data available for 10 cities. This map may be used in conjunction with the analytic polar coordinate Gaussian Plume Model or conventional dispersion models to calculate the approximate incremental pollution concentration contours associated with an emission source at any site in Florida. Possible means of generalizing the work to other geographic regions, to stack height altitudes, and to incorporate time dependence are discussed.     

An Efficient Gaussian-Plume Multiple-Source Air Quality Algorithm

The information presented in this paper is directed to air pollution scientists with an interest in applying air quality simulation models. RAM is the three letter designation for this efficient Gaussian-plume multiple-source air quality algorithm. RAM is a method of estimating short-term dispersion using the Gaussian steady-state model. This algorithm can be used for estimating air quality concentrations of relatively stable pollutants for averaging times from an hour to a day in urban areas from point and area sources. The algorithm is applicable for locations with level or gently rolling terrain where a single wind vector for each hour is a good approximation to the flow over the source area considered. Calculations are performed for each hour. Hourly meteorological data required are wind direction, wind speed, stability class, and mixing height. Emission information required of point sources consists of source coordinates, emission rate, physical height, stack gas volume flow and stack gas temperature. Emission information required of area sources consists of south-west corner coordinates, source area, total area emission rate and effective area source height. Computation time is kept to a minimum by the manner in which concentrations from area sources are estimated using a narrow plume hypothesis and using the area source squares as given rather than breaking down all sources to an area of uniform elements. Options are available to the user to allow use of three different types of receptor locations: 1 ) those whose coordinates are input by the user, 2) those whose coordinates are determined by thé model and are downwind óf significant point and area sources where maxima are likely to occur, and 3) those whose coordinates are determined by the model to give good area coverage of a specific portion of the region. Computation time is also decreased by keeping the number of receptors to a minimum.     

In-stack emissions of heavy metals estimated by moss biomonitoring method and snow-pack analysis

Data from the chemical analysis of moss growing close to a thermal power station and snowpack have been used for the estimation of heavy metal deposition close to the point pollution sources. A semi-empirical model was proposed to describe atmospheric trace metal deposition close to the point pollution source. Model parameters were derived from experimental data, and nickel and vanadium quantities, washed out with snow and rain, were calculated. Using long-term meteorological observation data of rain and snow duration and metal uptake efficiencies in moss, the average emission rates of vanadium and nickel from the stack were calculated. The coincidence between data from emission inventory and model results was within 25%. It was estimated that in the vicinity of pollution source (within 30 km) about 15% out of total emitted metals were washed out by rain and snow events. Metal concentrations in the environment become indistinguishable from the background at a distance of about 20 km from the stack.     

Water flume study of the enhancement of buoyant rise in pairs of merging plumes

When multiple stacks are grouped or ganged together at a site, the effluent plumes are often observed to merge downwind, forming a single buoyant plume whose rate of rise is enhanced relative to the rise of the plumes individually. The magnitude of this rise enhancement depends on many factors, and the few available models for rise enhancement do not always agree with one another. In the present study the rise behaviour of pairs of merging, buoyant plumes was studied by physical modelling in a water flume at 1:500 scale. The experiments were conducted at several stack separation distances and various exit velocity ratios for stack pairs aligned with, or perpendicular to, the ambient flow. Limited experiments were also done with the stacks aligned at other angles to the flow. The stack releases were made buoyant by heating the source water, and the resulting plumes were measured with an array of sensitive temperature probes. From these measurements it was possible to determine the plume structure and rise rates. For small stack separations when the stacks are aligned with the ambient flow, the experimental results show that the enhanced rise is close to, and sometimes above, the maximum theoretical rise enhancement factor of 2^1/3. For the perpendicular orientation there is little or no rise enhancement. The rise enhancement for other stack orientations is somewhere between these two extremes. A plausible physical explanation for the observed behaviour is given, based on initial momentum shielding and line vortex dynamics in the merging plumes.     

Effects of combustion and operating conditions on PCDD/PCDF emissions from power boilers burning salt-laden wood waste

This paper discusses the effects of combustion conditions on PCDD/PCDF emissions from pulp and paper power boilers burning salt-laden wood waste. We found no correlation between PCDD/PCDF emissions and carbon monoxide emissions. A good correlation was, however, observed between PCDD/PCDF emissions and the concentration of stack polynuclear aromatic hydrocarbons (PAHs) in the absence of TDF addition. Thus, poor combustion conditions responsible for the formation of products of incomplete combustion (PICs), such as PAHs and PCDD/PCDF precursors, increase PCDD/PCDF emissions. PAH concentrations increased with higher boiler load and/or low oxygen concentrations at the boiler exit, probably because of lower available residence times and insufficient excess air. Our findings are consistent with the current understanding that high ash carbon content generally favours heterogeneous reactions leading to either de novo synthesis of PCDD/PCDFs or their direct formation from precursors. We also found that, in grate-fired boilers, a linear increase in the grate/lower furnace temperature produces an exponential decrease in PCDD/PCDF emissions. Although the extent of this effect appears to be mill-specific, particularly at low temperatures, the results indicate that increasing the combustion temperature may decrease PCDD/PCDF emissions. It must be noted, however, that there are other variables, such as elevated ESP and stack temperatures, a high hog salt content, the presence of large amounts of PICs and a high Cl/S ratio, which contribute to higher PCDD/PCDFs emissions. Therefore, higher combustion temperatures, by themselves, will not necessarily result in low PCDD/PCDFs emissions.     

A Theory of Plume Rise Compared with Field Observations

A theory for the rise of a plume in a horizontal wind is proposed in which it is assumed that, for some distance downwind of a high stack, the effects of atmospheric turbulence may be ignored in comparison with the effects of turbulence generated by the plume. The theory, an extension of the local similarity ideas used by Morton, Taylor, and Turner,¹ has two empirical parameters which measure the rate that surrounding fluid is entrained into the plume. Laboratory measurements of buoyant plume motion in laminar unstratified cross flow are used to estimate the empirical parameters. Using this determination of the parameters in the theory, the trajectories of atmospheric plumes may be predicted. To make such a prediction, the observed wind velocity and temperature as functions of altitude, and flow conditions at the stack orifice, are used in numerically integrating the equations. The resulting trajectories are compared with photographs, made by Leavitt, et al.,² of TVA, of plumes from 500 to 600 ft high stacks. Within 10 stack heights downwind of the stack, the root mean square discrepancy between the observed height of the trajectory above ground level and the theoretical value is 14%, which is about the uncertainty in the observed height. The maximum plume rise within the field of observation is within 15% of that predicted by the present theory.     

Treatment Technologies For Hazardous Wastes: Part IV A Review of Alternative Treatment Processes for Metal Bearing Hazardous Waste Streams

The U.S. Congress and the U.S. Environmental Protection Agency believe that treatment and recovery techniques should be given maximum priority when considering methods for managing the nation's generated hazardous waste. A prohibition for the disposal of certain categories of hazardous wastes either directly onto or into the land without being treated to an accepted degree prior to such disposal practice has been promulgated.¹ Wastes containing toxic metals and cyanide complexes have been selected as a group to be restricted. Due to the high generation rate associated with this category, a large capacity of waste treatment processing will be required. Existing and emerging treatment alternatives which are or have the potential to be employed for waste treatment of metal bearing wastes are presented in this paper.     

Determining straining of Escherichia coli from breakthrough curves

Though coliform bacteria are used world wide as an indication of faecal pollution, the parameters determining the transport of Escherichia coli in aquifers are relatively unknown, especially for the period after the clean bed collision phase brought about by prolonged infiltration of waste water. In this research, the breakthrough curves of E. coli after total flushing of 50-200 pore volumes were studied for various influent concentrations in various sediments at different pore water flow velocities. The results indicated that straining in Dead End Pores (DEPs) was an important process that dominated bacteria breakthrough in fine-grained sediment (0.06-0.2 mm). The filling of the DEP space with bacteria took 5-65 pore volumes and was dependent on concentration. Column breakthrough curves were modelled and from this the DEP volumes were determined. These volumes (0.21-0.35% of total column volume) corresponded well with values calculated with a formula based on purely geometrical considerations and also with values calculated with a pore size density function. For this function the so-called Van Genuchten parameters of the sediments used in the experiments were determined. The results indicate that straining might be a dominant process affecting colloid transport in the natural environment and therefore it is concluded that proper knowledge of the pore size distribution is crucial to an understanding of the retention of bacteria.     

Polycyclic aromatic hydrocarbon emissions from clinical waste incineration

Since the introduction of the Environmental Protection Act in the UK, there are few reports of PAH emissions from clinical waste incinerators (CWIs) operating to improved performance standards. The main aim of this study is to determine PAH emissions from a state-of-the-art CWI focusing on the effects of reactive gases and operating variables on emissions. This was carried out by collection of stack samples over three phases of operation.

At stack conditions, most PAHs are predicted to be in the vapour phase. Reactive losses of PAHs were closely correlated by rank with expected reactivities from laboratory studies. Estimates of emissions incorporating sampling losses were derived, although no correlation was found between PAH losses and the modest levels of reactive stack gases. PAH concentrations were one to two orders of magnitude lower than earlier reports from incinerators without effective air pollution control equipment (APCE). The low levels of carbon monoxide recorded were not correlated with any PAHs.

This study demonstrates the impact of efficient combustion conditions and APCE on PAH emissions from a CWI.     

Establishing the propensity for dioxin formation using a plume temperature model for medical waste incinerator emissions in developing countries

Air pollution control devices (APCDs) are not compulsory for medical waste incinerators (MWIs) in developing countries. In South Africa, combustion gases are usually vented directly to the atmosphere at temperatures greater than the formation temperature of dioxin. The possibility of dioxin formation outside the incinerator stack has been hypothesized. A plume model has been developed and tested in the wind tunnel with a scale model of an incinerator stack. The plume temperature and trajectory predictions of the plume model were verified within a +/- 3% experimental accuracy. Using South African data, the plume model predicts that the residence time of gases in the temperature range of 150-450 degrees C in a plume is 1.3 sec on average for 5% of a year (18 days) at meteorological conditions resulting in wind speeds of less than 1 m/sec. Two published dioxin formation models were used to assess the probability of dioxin formation in the plume. The formation models predict that the average polychlorinated dibenzodioxins/furans (PCDD/Fs) formed in the plume will exceed the stack emission regulations in South Africa of 0.2 ng/Nm3 toxic equivalent quotient (TEQ) by between 2 and 40 times. The calculated concentrations do not include additional gaseous PCDD/F compounds that may be formed at high-temperature post-combustion zones through pyrosynthesis mechanisms.     

A Correlation of Field Observations of Plume Rise

Data from 137 sets of plume observations, comprising nearly 1 500 data points, are correlated with two simple formulae. These formulae, one for the buoyancy-dominated rise region and the other for the stratification-dominated levelled-off region of a plume, represent an approximate form of the entrainment theory of Hoult, et al. (1968)¹ for the case of uniform atmospheric stratification and zero wind shear. The observations, which are those of the Tennessee Valley Authority and of Bringfelt (1968),⁶ were made of plumes whose source strengths ranged from 0.4 to 111 Mw and which were emitted from stacks of heights between 21 and 183 m. The two formulae are found to correlate the data equally well over all values of the stack exit and meteorological parameters, provided only that the bulk mean velocity of the stack gases exceeds the mean wind speed by at least 20%. The ratio of observed to calculated plume rise is found to be distributed log normally about the mean value.

The median rise at large distances downstream was found to differ insignificantly from that given by the effective stack height formula recommended recently¹¹ for large buoyant plumes. Based upon the correlation, two formulae are recommended for computing median plume rise at all distances downstream of the stack. The formulae include an estimate of the expected uncertainty in the predicted rise.     

Interaction of Population Growth,Industrial Growth and Pollution Control

A model is developed which predicts the level of pollution as a function of time given the rate of waste production and the persistence of the pollutant. In general, waste production is a function of the population density and the degree of industrialization of a society. With pollution control programs it is possible to reduce the per capita waste production for a given degree of industrialization. The model demonstrates that in a growth economy such as that of the United States, pollution control programs by themselves only delay the inevitable increase in pollution levels. In the long run population and industrial growth are incompatible with pollution control.     

A model for the maximum credible hourly impact on any ground receptor from point sources with thermal plume rise

A pollutant dispersion model is developed, allowing fast evaluation of the maximum credible 1-h average concentration on any given ground-level receptor, along with the corresponding critical meteorological conditions (wind speed and stability class) for stacks with buoyant plumes in urban or rural areas. Site-specific meteorological data are not required, as the computed concentrations are maximized against all credible combinations of wind speed, stability class, and mixing height. The analysis is based on the dispersion relations of Pasquill-Gifford and Briggs for rural and urban settings, respectively, the buoyancy induced dispersion correlation of Pasquill, the wind profile exponent values suggested by Irwin, the buoyant plume rise relations of Briggs, as well as the Benkley and Schulman's model for the minimum mixing heights. The model is particularly suited for air pollution management studies, as it allows fast screening of the maximum impact on any selected receptor and evaluation of the ways to have this impact reduced. It is also suited for regulatory purposes, as it can be used to define the minimum stack size requirements for a given source as a function of the exit gas volume and temperature, the pollutant emission rates and their hourly concentration standards, as well as the source location relative to sensitive receptors.     

Consultant Guide/1989

The European Economic Community (EEC) has proposed strict limits on emissions of dioxins and furans from hazardous waste incinerators. The proposed limit is 0.1 ng/Nm³, expressed as the 2,3,7,8 TCDD toxic equivalent of 17 specific dioxin and furan congeners. These limits will potentially redefine technology selection and design for combustion, energy recovery, and air pollution control. The EPA has a different approach for controlling emissions of products of incomplete combustion (PICs) and reformation products such as dioxins and furans. Rather than limiting these contaminants individually and quantitatively, EPA proposes controlling them by assuring good combustion as measured by stack emissions of carbon monoxide (CO) and total hydrocarbons (THC).

Dioxins and furans are combustion by-products and emission control relies mainly on control of the combustion process. These compounds can also be reformed from certain precursor compounds and elements in lower temperature regions of the system downstream of the combustion process. Air pollution control technologies have demonstrated the ability to remove dioxins and furans as contaminants on fine particulate.

This paper will discuss the two regulatory approaches, the mechanisms for the formation and reformation of dioxins and furans, and the technologies available to control emissions.     

危险废物回转式流化冷渣多段焚烧系统焚烧特性研究

危险废物的处理和处置是摆在我国各级市政府面前的紧迫任务。然而我国已经运行的危险废物焚烧装置普遍存在回转窑挂壁结渣、热灼减率偏高和污染排放超标等问题,作者通过将回转窑和流化床特点相结合的方法提出了一种新型危险废物回转式流化冷渣多段焚烧处置装置。该装置采用回转窑(一燃室)、二燃室和流化床结合的热解-流化焚烧工艺,特别是采用控制窑头温度避免了回转窑挂壁结渣;采用流化冷渣装置延长未燃烬渣的焚烧时间,解决了热灼减率偏高问题;水冷式烟气急冷装置可以将烟气温度从1 100℃降到200℃,防止了二恶英的尾部低温再生成。该系统运行稳定可靠,可以处理医疗垃圾和大多数的固态和液态危险废物,实现了烟气污染物尤其是二恶英排放达到国家标准的目标。同时对该系统运行时窑头温度分布、二燃室炉膛出口氧量变化、回转窑和炉膛升温特性、燃烧室外壁温度分布等几方面运行数据都进行了详细的介绍,为危险废物焚烧炉的运行提供了宝贵的经验数据。     

A novel one-step synthesis for carbon-based nanomaterials from polyethylene terephthalate (PET) bottles waste

Nowadays our planet suffers from an accumulation of plastic products that have the potential to cause great harm to the environment in the form of air, water, and land pollution. Plastic water bottles have become a great problem in the environment because of the large numbers consumed throughout the world. Certain types of plastic bottles can be recycled but most of them are not. This paper describes an economical solvent-free process that converts polyethylene terephthalate (PET) bottles waste into carbon nanostructure materials via thermal dissociation in a closed system under autogenic pressure together with additives and/or catalyst, which can act as cluster nuclei for carbon nanostructure materials such as fullerenes and carbon nanotubes. This research succeeded in producing and controlling the microstructure of various forms of carbon nanoparticles from the PET waste by optimizing the preparation parameters in terms of time, additives, and amounts of catalyst.

Implications: Plastic water bottles are becoming a growing segment of the municipal solid waste stream in the world; some are recycled but many are left in landfill sites. Recycling PET bottles waste can positively impact the environment in several ways: for instance, reduced waste, resource conservation, energy conservation, reduced greenhouse gas emissions, and decreasing the amount of pollution in air and water sources. The main novelty of the present work is based on the acquisition of high-value carbon-based nanomaterials from PET waste by a simple solvent-free chemical technique. Thus, the prepared materials are considered to be promising, cheap, eco-friendly materials that may find use in different applications.     

Effective pollutant emission heights for atmospheric transport modelling based on real-world information

Emission data needed as input for the operation of atmospheric models should not only be spatially and temporally resolved. Another important feature is the effective emission height which significantly influences modelled concentration values. Unfortunately this information, which is especially relevant for large point sources, is usually not available and simple assumptions are often used in atmospheric models. As a contribution to improve knowledge on emission heights this paper provides typical default values for the driving parameters stack height and flue gas temperature, velocity and flow rate for different industrial sources. The results were derived from an analysis of the probably most comprehensive database of real-world stack information existing in Europe based on German industrial data. A bottom-up calculation of effective emission heights applying equations used for Gaussian dispersion models shows significant differences depending on source and air pollutant and compared to approaches currently used for atmospheric transport modelling.     

A pore-scale investigation of mass transport from dissolving DNAPL droplets

Spheres and pendular rings of trichloroethylene and tetrachloroethylene are observed dissolving in an artificial porous medium consisting of a single layer of glass beads. Given the simple geometry of the droplets, pore-scale mass transfer coefficients are calculated. For dissolving spheres, mass transfer coefficients are found to be constant over time. However, coefficients for pendular rings are found to decrease as the rings shrink in size. This is consistent with the concept of diffusion-controlled mass transfer in low-flow zones. Sherwood numbers measured at Reynolds numbers between 0.0033 and 8.33 show a similar trend to empirical relationships established by previous researchers using other techniques. As in previous experiments, considerable scatter in mass transfer rates is observed at a given mean flux. It is hypothesized that this variation in local mass transfer rates is caused by variations in local pore velocity.