Rotary Kiln Incineration II. Laboratory-Scale Desorption and Kiln-Simulator Studies—Solids

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.     

Exceedances of the National Ambient Air Quality Standard for Ozone Occurring at a “Pristine” Area Site

Abstract

This paper presents a comparative study of the biodegradation of three aromatic volatile compounds in a compost-based biofilter: toluene, xylene, and 1,2,4-trimethyl-benzene, used in the course of this work for the first time in the field of biofiltration. Hence, three identical biofiltration units have been operated at the laboratory scale. During the experiments, nitrogen (as urea) was supplied at various concentrations to each reactor, via irrigated nutrient solutions. A comparative analysis of the results showed that the biodegradability scale followed the degree of substitution around the aromatic ring: toluene > xylene > trimethylbenzene, with 95, 80, and 70% maximum conversions, respectively. In addition, and despite the different removal levels achieved in the three biore-actors, it was established that from a reaction viewpoint, the degradation of the three compounds seemed to follow similar metabolic pathways involving methylcatechol isomers. Finally, by varying the nitrogen input concentrations in the three reactors, three degradation regimes have been highlighted: an N-limitation regime and an N-optimum regime, common to the three solvents, and an N-excess regime, favorable to the colonization of the filter beds by nitrifying species, which particularly affected the xylene and trimethylbenzene biodegradation.     

An Evaluation of the Effects of Ozone Injury on Radial Growth of Ponderosa Pine (Pinus ponderosa) in the Southern Sierra Nevada

Growth of ponderosa pines with visible symptoms of ozone injury was compared with that of asymptomatic trees in the southern Sierra Nevada, California. Time series analysis indicated that there was no significant reduction in annual radial increment of symptomatic trees during recent years compared to past growth and growth of asymptomatic trees. First order autocorrelation and climatic variables accounted for a large proportion of the variance in growth index, and winter precipitation was positively correlated with growth for all size and age classes. Although ozone concentrations are high enough to cause chlorosis and premature needle senescence in ponderosa pine, there has been no significant change in growth associated with ozone injury.     

The Effects of Infiltration and Insulation on the Source Strengths and Indoor Air Pollution from Combustion Space Heating Appliances

Many energy conservation strategies for residences involve reducing house air exchange rates. Reducing the air exchange rate of a house can cause an increase in pollutant levels if there is an indoor pollution source and if the indoor pollutant source strength remains constant. However, if the indoor pollutant source strength can also be reduced, then it is possible to maintain or even improve indoor air quality. Increasing the insulation level of a house is a means of achieving energy conservation goals and, in addition, can reduce the need for space heating and thereby reduce the pollutant source strengths of combustion space heaters such as unvented kerosene space heaters, unvented gas space heaters, and wood stoves. In this paper, the indoor air quality trade-off between reduced infiltration and increased insulation in residences is investigated for combustion space heaters. Two similar residences were used for the experiment. One residence was used as a control and the other residence had infiltration and insulation levels modified. An unvented propane space heater was used as the source in this study. A model was developed to describe the dependence of both indoor air pollution levels and the appliance source strengths on house air exchange rates and house insulation levels. Model parameters were estimated by applying regression techniques to the data. Results show that indoor air pollution levels in houses with indoor combustion space heating pollution sources can be held constant (or lowered) by reducing the thermal conductance by an amount proportional to (or greater than) the reduction of the air exchange rate.     

Effectiveness of Smokeless Ashtrays

Abstract

Most environmental tobacco smoke (ETS) issues from the tips of smoldering cigarettes between puffs. Smokeless ashtrays are designed to reduce ETS exposure by removing particulate and/or gas-phase contaminants from this plume. This paper describes an experimental investigation of the effectiveness of four smokeless ashtrays: two commercial devices and two prototypes constructed by the authors. In the basic experimental protocol, one or more cigarettes was permitted to smolder in a room. Particulate or gas-phase pollutant concentrations were measured in the room air over time. Device effectiveness was determined by comparing pollutant concentrations with the device in use to those obtained with no control device. A lung deposition model was applied to further interpret device effectiveness for particle removal. The commercial ashtrays were found to be substantially ineffective in removing ETS particles because of the use of low-quality filter media and/or the failure to draw the smoke through the filter. A prototype ashtray using HEPA filter material achieved better than 90% particle removal efficiency. Gasphase pollutant removal was tested for only one prototype smokeless ashtray, which employed filters containing activated carbon and activated alumina. Removal efficiencies for the 18 gas-phase compounds measured (above the detection limit) were in the range of 70 to 95%.     

Hydrocarbon Measurements During the 1992 Southern Oxidants Study Atlanta Intensive: Protocol and Quality Assurance

Abstract

A major component of the Southern Oxidants Study (SOS) 1992 Atlanta Intensive was the measurement of atmospheric nonmethane hydrocarbons. Ambient air samples were collected and analyzed by a network of strategically located automated gas chromatography (GC) systems (field systems). In addition, an extensive canister sampling network was deployed. Combined, more than 3000 chromatograms were recorded. The SOS science team targeted for quantitative analysis 56 compounds which may be substantial contributors to ozone formation or used as air mass tracers. A quality assurance program was instituted to ensure that good measurements were being made throughout the network for each target compound. Common, high-quality standards were used throughout the network. The performance of individual field systems was evaluated during the intensive through the analysis of challenge mixtures. This methodology helped to identify and correct analytical problems as they arose.     

The OTC Challenge: Adding VOC Controls in the Northeast

The 1990 Clean Air Act Amendments create an ozone transport region made up of the northeastern and mid-Atlantic states. These new provisions call for VOC and NOx controls even in clean areas of the region in order to reduce ozone transport to downwind areas. The stationary and mobile source requirements will subject many air pollution sources to controls for the first time.

The provisions also create an Ozone Transport Commission, which can recommend that additional control measures be adopted in all or part of the region. So far, the commission has focused primarily on region-wide mobile source controls, such as California low emission vehicle standards and reformulated gasoline. But lately it has been paying increasing attention to stationary source measures, including NOx controls.     

Controlled Exposures of Volunteers to Respirable Carbon and Sulf uric Acid Aerosols

Respirable carbon or fly ash particles are suspected to increase the respiratory toxicity of coexisting acidic air pollutants, by concentrating acid on their surfaces and so delivering it efficiently to the lower respiratory tract. To investigate this issue, we exposed 15 healthy and 15 asthmatic volunteers in a controlled- environment chamber (21°C, 50 percent relative humidity) to four test atmospheres: (i) clean air; (ii) 0.5-μm H2SO4 aerosol at =100 μg/m³, generated from water solution; (iii) 0,5-μm carbon aerosol at =250 μg/m³, generated from highly pure carbon black with specific surface area comparable to ambient pollution particles; and (iv) carbon as in (iii) plus =100 μg/m³ of ultrafine H2SO4 aerosol generated from fuming sulfuric acid. Electron microscopy showed that nearly all acid in (iv) became attached to carbon particle surfaces, and that most particles remained in the sub-μm size range. Exposures were performed double-blind, 1 week apart. They lasted 1 hr each, with alternate 10-min periods of heavy exercise (ventilation =50 L/min) and rest. Subjects gargled citrus juice before exposure to suppress airway ammonia. Lung function and symptoms were measured pre-exposure, after initial exercise, and at endexposure. Bronchial reactivity to methacholine was measured after exposure. Statistical analyses tested for effects of H₂SO₄ or carbon, separate or interactive, on health measures. Group data showed no more than small equivocal effects of any exposure on any health measure. One individual's responses were consistent with a clinically significant excess airway constriction from H₂SO₄ plus carbon, and 2-3 others showed slight excess responses to the combined pollutants, but all these observations might have reflected chance variations. We conclude that coexisting carbon aerosol did not increase respiratory irritancy of H₂SO₄, in most healthy and asthmatic subjects exposed for 1 hr under simulated "worst-case" ambient conditions.     

Measurement of Volatile Organics at Part per Billion Concentrations Using a Cold Trap Inlet and High Speed Gas Chromatography

Direct inlet gas chromatography (GC) is becoming one of the most frequently used techniques for measurement of volatile organics in air. Although GC is an effective tool, its usefulness as a field method can be limited by retention times of several minutes or more, and by the limits of detection. In order to address these issues, a high speed GC system featuring a capillary cold trap inlet and variable speed electrometeramplifier was developed and tested.

The gas cooled inlet was used to collect and focus organic vapors from injection volumes of up to 1 ml. Resistance heating of the metal cold trap produced a narrow injection band that allowed simple separations to be completed in 5 to 20 seconds. Use of a variable speed electrometer-amplifier allowed the response time and noise suppression characteristics to be adjusted to the needs of the specific analysis.

Simple mixtures of organics including aromatics, alkanes and chlorinated hydrocarbons were separated in 20 seconds or less. The limits of detection for 13 test compounds ranged from less than 1 part per billion by volume (ppbv) to about 50 ppbv. Data presented here indicate that high speed GC using a cold trap inlet may be a feasible approach for near real-time measurement of volatile organics in ambient air.