Flow Injection Analysis of MWC Fly Ash Leaching Characteristics

Abstract

A completely mixed batch reactor leaching method utilizing flow injection analysis (the CMBR-FIA method) was developed to study the lead leaching characteristics of municipal waste combustor fly ash. Flow injection analysis (FIA) coupled with atomic absorption spectrophotometry enabled the determination of lead concentrations at one minute intervals. The pH and oxidation-reduction potential of the solution were continuously monitored to characterize the leaching conditions. Automatic titration was used to alter the solution pH to defined endpoints. The CMBR-FIA method offers the ability to immediately observe alterations to the leaching solution, and grants the freedom to study a number of parameters concurrently. The CMBR-FIA method is a rapid and reliable means to investigate leaching characteristics. This paper describes the method and demonstrates its use to monitor the leaching of lead from municipal solid waste combustor fly ash as a function of pH. Soluble lead concentrations are shown to increase quickly with decreasing pH.

A maximum of 50% of the total lead concentration was available in solution at pH 2. This value gradually decreased with time to over 35% of the total.     

Airborne Particulate Emissions from a Chromic Acid Anodizing Process Tank

Particulate mass concentration, particle size distribution, and particle chemical composition measurements have been conducted on the gases exhausting from a chromic acid anodizing process tank. Particle mass concentrations in the 200 to 20,000 μg/m³ range were measured using open-faced filters (47 mm diameter) adjacent to the process tank liquid and with closed filters (90 mm diameter) in the exhaust duct. Particle size distributions, measured using University of Washington Mark 3 and Mark 20 Cascade Impactors, showed the particle aerodynamic mass median diameter was about 3 microns. Chemical analysis of the particle samples obtained by the Modified EPA Method 5 sampling train, the Mark 20 UW Cascade Impactors, and by the 47 mm and 90 mm diameter filters showed Cr⁺⁶ concentrations in the 20 to 1,500 μg/m³ range with over 99 percent of the chromium in particles larger than 1.0 microns diameter. An integrating nephelometer was used to measure the light scattering coefficient of the exhaust gases upstream of the wet scrubber. The light scattering coefficient increased by a factor of about 2–3 over the background level during the 40 minute time period while a part was being anodized. The bscat values ranged from 3 × 10^?5 to 3 × 10^?4 meters^?1 for the aerosol particles less than about 6 microns aerodynamic diameter.     

Reactivity-Based Hydrocarbon Controls: Scientific Issues and Potential Regulatory Applications

The California Air Resources Board and the South Coast Air Quality Management District hosted a conference on April 8-9, 1991 to examine the scientific issues associated with reactivity-based hydrocarbon controls, and to identify the obstacles to potential regulatory applications. Owing to residual uncertainties in the underlying science, and the complex emission measurement capabilities required for enforcement, a general consensus emerged on the need for further research before application of reactivity-based controls. A number of recommendations were made for research on the remaining scientific, enforcement, and policy issues, many of which have led to cooperative efforts initiated since the conference.     

Rotary Kiln Incineration of Dichloromethane and Xylene: A Comparison of Incinerability Characteristics Under Various Operating Conditions

Comparisons are made, for the first time, between the combustion characteristics of dichloromethane and xylene in an industrial rotary kiln incinerator. The comparisons are made under different operating conditions, including variable kiln rotation rate and operation both with and without turbulence air. Continuous gas composition and temperature measurements and batch gas composition measurements were obtained from two vertical locations hear the exit region of the rotary kiln. The measurements show that there is significant vertical stratification at the exit of the kiln. Addition of turbulence air enhanced combustion conditions throughout the kiln during xylene processing. During dichloromethane processing, however, the addition of turbulence air had minimal effect and only promoted greater bulk mixing; chlorinated compounds transported from the lower kiln during operation with turbulence air were not efficiently processed in the upper kiln. Evolution of test liquids from the bed was not constant but rather was characterized by intermittent peaks. The field-scale data of this work suggest that the evolution rate of the test liquid was increased as kiln rotation rate increased. Many of the differences between xylene and dichloromethane processing during these experiments are explained by a simple stoichiometric analysis.     

Effect of Moisture on the Pollutant Concentration Measurement

The effects of removing moisture from gaseous samples on the measurement of pollutant concentration were studied. Simple mathematical analysis was conducted to derive the formula for correcting the measured results. It was found that the error increases with increase in relative humidity or increase in temperature. The error may become significant under extreme conditions.     

An Analysis of Biomedical Waste Incineration

The California Air Resources Board (ARB) completed a series of source tests of eight operating biomedical waste incinerators (BMWI) under conditions of typical operation. The emissions of certain metals, and chlorinated dioxins and furans in the flue gases of BMWI are relatively high in comparison to emissions from other combustion sources, such as hazardous waste or municipal waste incinerators of modern design. This study reports on an analysis of the status of the existing regulatory framework and the California data base. Clarification of definitional issues at the federal level is needed to effectively treat BMWI management issues. Although few relationships among combustion parameters and emissions were uncovered, patterns of emissions were evident, suggesting commonality and relationships among the waste stream constituents and emissions. Potential implications for future research, operation of BMWI, controls and source reduction and waste segregation strategies are also discussed.     

Wind Tunnel Modelling of Roadways: Comparison with Mathematical Models

The assessment of air quality impacts from roadways is a major concern to urban planners. In order to assess future road and building configurations, a number of techniques have been developed, including mathematical models, which simulate traffic emissions and atmospheric dispersion through a series of mathematical relationships and physical models. The latter models simulate emissions and dispersion through scaling of these processes in a wind tunnel. Two roadway mathematical models, HIWAY-2 and CALINE-4, were applied to a proposed development in a large urban area. Physical modelling procedures developed by Rowan Williams Davies & Irwin Inc. (RWDI) in the form of line source simulators were also applied, and the resulting carbon monoxide concentrations were compared. The results indicated a factor of two agreement between the mathematical and physical models. The physical model, however, reacted to changes in building massing and configuration. The mathematical models did not, since no provision for such changes was included in the mathematical models. In general, the RWDI model resulted in higher concentrations than either HIWAY-2 or CALINE-4. Where there was underprediction, it was often due to shielding of the receptor by surrounding buildings. Comparison of these three models with the CALTRANS Tracer Dispersion Experiment showed good results although concentrations were consistently underpredicted.     

Seasonal Variations in Aerosol Composition and Acidity at Shenandoah and Great Smoky Mountains National Parks

The concentration of elements Na through Pb, select ions, and organic carbon from fine (<2.5 µm) particles has been monitored at Shenandoah and Great Smoky Mountains National Parks from 1988 through 1995. The data obtained from 1988 through 1994 show that significant changes in the concentrations of many aerosol constituents occur on a seasonal basis. Particulate sulfate and organic carbon are shown to exhibit substantially higher concentrations during the summer, while sulfur dioxide and nitrate concentrations are highest during the winter.

A method for estimating the degree of neutralization of particulate sulfate is given. This method uses routinely measured aerosol elemental compositions because ammonium ion, the primary neutralizing species for sulfate, is not measured on a routine basis. Application of this method to the selected data set shows that sulfate aerosol is most acidic during summer with an average molar H_s (moles of hydrogen associated with sulfur) to S (moles of sulfur) ratio of approximately 4. This suggests the average sulfate particle during the summer has a molar coon slightly more acidic than ammonium bisulfate (NH₄HSO₄) which has a molar hydrogen to sulfur ratio of 5. Winter H_s to S ratios, however, are approximately 8, suggesting the aerosol is on average fully neutralized ammonium sulfate [(NH₄)₂SO₄].     

Application of a Three-Layer Photochemical Box Model in an Athens Street Canyon

ABSTRACT

The aim of this paper is to show that a photochemical box model could describe the air pollution diurnal profiles within a typical street canyon in the city of Athens. As sophisticated three-dimensional dispersion models are computationally expensive and they cannot serve to simulate pollution levels in the scale of an urban street canyon, a suitably modified three-layer photochemical box model was applied. A street canyon of Athens with heavy traffic was chosen to apply the aforementioned model. The model was used to calculate pollutant concentrations during two days with meteorological conditions favoring pollutant accumulation. Road traffic emissions were calculated based on existing traffic load measurements. Meteorological data, as well as various pollutant concentrations, in order to compare with the model results, were provided by available measurements. The calculated concentrations were found to be in good agreement with measured concentration levels and show that, when traffic load and traffic composition data are available, this model can be used to predict pollution episodes. It is noteworthy that high concentrations persisted, even after additional traffic restriction measures were taken on the second day because of the high pollution levels.