Emissions of Trace Products of Incomplete Combustion from a Pilot-Scale Incinerator Secondary Combustion Chamber

Abstract

Experiments were performed on a 73 kW rotary kiln incinerator simulator equipped with a 73 kW secondary combustion chamber (SCC) to examine emissions of products of incomplete combustion (PICs) resulting from incineration of carbon tetrachloride (CC14) and dichloromethane (CH2C12). Species were measured using an on-line gas chromatograph (GC) system capable of measuring concentrations of eight species of volatile organic compounds (VOCs) in a near-realtime fashion. Samples were taken at several points within the SCC, to generate species profiles with respect to system residence time. For the experiments, the afterburner on the SCC was operated at conditions ranging from fuel-rich to fuellean, while the kiln was operated at a constant set of conditions. Results indicate that combustion of CH2C12 produces higher levels of measured PICs than combustion of CC14, particularly 1, 2 dichlorobenzene, and to a lesser extent, monochlorobenzene. Benzene emissions were predominantly affected by the afterburner air/fuel ratio regardless of whether or not a surrogate waste was being fed.     

The Use of Ambient Measurements To Identify which Precursor Species Limit Aerosol Nitrate Formation

ABSTRACT

A thermodynamic equilibrium model was used to investigate the response of aerosol NO₃ to changes in concentrations of HNO₃, NH₃, and H₂SO₄. Over a range of temperatures and relative humidities (RHs), two parameters provided sufficient information for indicating the qualitative response of aerosol NO₃. The first was the excess of aerosol NH₄ ⁺ plus gas-phase NH₃ over the sum of HNO₃, particulate NO₃, and particulate SO₄ ^2- concentrations. The second was the ratio of particulate to total NO₃ concentrations. Computation of these quantities from ambient measurements provides a means to rapidly analyze large numbers of samples and identify cases in which inorganic aerosol NO₃ formation is limited by the availability of NH₃. Example calculations are presented using data from three field studies. The predictions of the indicator variables and the equilibrium model are compared.     

Air Emission Inventories in North America: A Critical Assessment

Abstract

Although emission inventories are the foundation of air quality management and have supported substantial improvements in North American air quality, they have a number of shortcomings that can potentially lead to ineffective air quality management strategies. Major reductions in the largest emissions sources have made accurate inventories of previously minor sources much more important to the understanding and improvement of local air quality. Changes in manufacturing processes, industry types, vehicle technologies, and metropolitan infrastructure are occurring at an increasingly rapid pace, emphasizing the importance of inventories that reflect current conditions. New technologies for measuring source emissions and ambient pollutant concentrations, both at the point of emissions and from remote platforms, are providing novel approaches to collecting data for inventory developers. Advances in information technologies are allowing data to be shared more quickly, more easily, and processed and compared in novel ways that can speed the development of emission inventories. Approaches to improving quantitative measures of inventory uncertainty allow air quality management decisions to take into account the uncertainties associated with emissions estimates, providing more accurate projections of how well alternative strategies may work. This paper discusses applications of these technologies and techniques to improve the accuracy, timeliness, and completeness of emission inventories across North America and outlines a series of eight recommendations aimed at inventory developers and air quality management decision-makers to improve emission inventories and enable them to support effective air quality management decisions for the foreseeable future.     

Development of Artificial Neural Network Based Metamodels for Inactivation of Anthrax Spores in Ventilated Spaces Using Computational Fluid Dynamics

ABSTRACT

Linear, quadratic, and artificial neural network (ANN)-based metamodels were developed for predicting the extent of anthrax spore inactivation by chlorine dioxide in a ventilated three-dimensional space over time from computational fluid dynamics model (CFD) simulation data. Dimensionless groups were developed to define the design space of the problem scenario. The Hammersley sequence sampling (HSS) method was used to determine the sampling points for the numerical experiments within the design space. A CFD model, comprised of multiple submodels, was applied to conduct the numerical experiments. Large eddy simulation (LES) with the Smagorinsky subgrid-scale model was applied to compute the airflow. Anthrax spores were modeled as a dispersed solid phase using the Lagrangian treatment. The disinfectant transport was calculated by solving a mass transport equation. Kinetic decay constants were included for spontaneous decay of the disinfectant and for the reaction of the disinfectant with the surfaces of the three-dimensional space. To enhance the mixing of the disinfectant with the room air, a momentum source was included in the simulation. An inactivation rate equation accounted for the reaction between the spores and the disinfectant. The ANN-based metamodels were most successful in predicting the number of viable bioaerosols remaining in an arbitrary enclosed space. Sensitivity analysis showed that the mass fraction of the disinfectant, inactivation rate constant, and contact time had the most influence on the inactivation of the spores.

IMPLICATIONS This investigation presents a framework for the development of user-friendly models; metamodels for the prediction of the number of viable spores remaining in an indoor room during disinfection from accurate but time-consuming CFD studies. During any decontamination event, to know when to stop pumping in the disinfectant and to know what level of log reduction of the spores have been achieved before even starting decontamination would provide valuable guidance. The neural network based metamodels can be applied to obtain quick and relatively accurate answers. This would be necessary when immediate information is required during emergencies.     

Simultaneous Control of Hg0, SO2, and NOx by Novel Oxidized Calcium-Based Sorbents

Abstract

Efforts to develop multipollutant control strategies have demonstrated that adding certain oxidants to different classes of Ca-based sorbents leads to a significant improvement in elemental Hg vapor (Hg⁰), SO₂, and NO_x removal from simulated flue gases. In the study presented here, two classes of Ca-based sorbents (hydrated limes and silicate compounds) were investigated. A number of oxidizing additives at different concentrations were used in the Ca-based sorbent production process. The Hg⁰, SO₂, and NO_x capture capacities of these oxidant-enriched sorbents were evaluated and compared to those of a commercially available activated carbon in bench-scale, fixed-bed, and fluid-bed systems. Calcium-based sorbents prepared with two oxidants, designated C and M, exhibited Hg⁰ sorp-tion capacities (~100 μg/g) comparable to that of the activated carbon; they showed far superior SO₂ and NO_x sorption capacities. Preliminary cost estimates for the process utilizing these novel sorbents indicate potential for substantial lowering of control costs, as compared with other processes currently used or considered for control of Hg⁰, SO₂, and NO_x emissions from coal-fired boilers. The implications of these findings toward development of multipollutant control technologies and planned pilot and field evaluations of more promising multipollutant sorbents are summarily discussed.     

Toxicity of Chemical Components of Fine Particles Inhaled by Aged Rats: Effects of Concentration

Abstract

This study tested the hypothesis that exposure to mixtures containing fine particles and ozone (O₃) would cause pulmonary injury and decrements in functions of immunological cells in exposed rats (22–24 months old) in a dose-dependent manner. Rats were exposed to high and low concentrations of ammonium bisulfate and elemental carbon and to 0.2 ppm O₃. Control groups were exposed to purified air or O₃ alone. The biological end points measured included histopathological markers of lung injury, bronchoalveolar lung fluid proteins, and measures of the function of the lung’s innate immuno-logical defenses (macrophage antigen-directed phagocytosis and respiratory burst activity). Exposure to O₃ alone at 0.2 ppm did not result in significant changes in any of the measured end points. Exposures to the particle mixtures plus O₃ produced statistically significant changes consistent with adverse effects. The low-concentration mixture produced effects that were statistically significant compared to purified air but, with the exception of macrophage Fc receptor binding, exposure to the high-concentration mixture did not. The effects of the low- and high-concentration mixtures were not significantly different. The study supports previous work that indicated that particle + O₃ mixtures were more toxic than O₃ alone.     

Full-Scale Evaluation of Mercury Control with Sorbent Injection and COHPAC at Alabama Power E.C. Gaston

Abstract

The overall objective of this project was to determine the cost and impacts of Hg control using sorbent injection into a Compact Hybrid Particulate Collector (COHPAC) at Alabama Power’s Gaston Unit 3. This test is part of a program funded by the U.S. Department of Energy’s National Energy Technology Laboratory (NETL) to obtain the necessary information to assess the costs of controlling Hg from coal-fired utility plants that do not have scrubbers for SO₂ control. The economics will be developed based on various levels of Hg control.

Gaston Unit 3 was chosen for testing because COHPAC represents a cost-effective retrofit option for utilities with existing electrostatic precipitators (ESPs). COHPAC is an EPRI-patented concept that places a high air-to-cloth ratio baghouse downstream of an existing ESP to improve overall particulate collection efficiency. Activated carbons were injected upstream of COHPAC and downstream of the ESP to obtain performance and operational data.

Results were very encouraging, with up to 90% removal of Hg for short operating periods using powdered activated carbon (PAC). During the long-term tests, an average Hg removal efficiency of 78% was measured. The PAC injection rate for the long-term tests was chosen to maintain COHPAC cleaning frequency at less than 1.5 pulses/bag/hr.     

Matrix Diffusion Modeling Applied to Long‐Term Pump‐and‐Treat Data: 1. Method Development

Despite the installation in the 1980s and 1990s of hydraulic containment systems around known source zones (four slurry walls and ten pump‐and‐treat systems), trichloroethene (TCE) plumes persist in the three uppermost groundwater‐bearing units at the Middlefield‐Ellis‐Whisman (MEW) Superfund Study Area in Mountain View, California. In analyzing TCE data from 15 recovery wells, the observed TCE mass discharge decreased less than an order of magnitude over a 10‐year period despite the removal of an average of 11 pore volumes of affected groundwater. Two groundwater models were applied to long‐term groundwater pump‐and‐treat data from 15 recovery wells to determine if matrix diffusion could explain the long‐term persistence of a TCE plume. The first model assumed that TCE concentrations in the plume are controlled only by advection, dispersion, and retardation (ADR model). The second model used a one‐dimensional diffusion equation in contact with two low‐permeability zones (i.e., upper and lower aquitard) to estimate the potential effects of matrix diffusion of TCE into and out of low‐permeability media in the plume. In all 15 wells, the matrix diffusion model fit the data much better than the ADR model (normalized root mean square error of 0.17 vs. 0.29; r² of 0.99 vs. 0.19), indicating that matrix diffusion is a likely contributing factor to the persistence of the TCE plume in the non‐source‐capture zones of the MEW Study Area's groundwater‐extraction wells. © 2013 Wiley Periodicals, Inc.     

Enantiomer fractions of polychlorinated biphenyls in three selected Standard Reference Materials

The enantiomer composition of six chiral polychlorinated biphenyls (PCBs) were measured in three different certified Standard Reference Materials (SRMs) from the US National Institute of Standards and Technology (NIST): SRM 1946 (Lake Superior fish tissue), SRM 1939a (PCB Congeners in Hudson River Sediment), and SRM 2978 (organic contaminants in mussel tissue--Raritan Bay, New Jersey) to aid in quality assurance/quality control methodologies in the study of chiral pollutants in sediments and biota. Enantiomer fractions (EFs) of PCBs 91, 95, 136, 149, 174, and 183 were measured using a suite of chiral columns by gas chromatography/mass spectrometry. Concentrations of target analytes were in agreement with certified values. Target analyte EFs in reference materials were measured precisely (<2% relative standard deviation), indicating the utility of SRM in quality assurance/control methodologies for analyses of chiral compounds in environmental samples. Measured EFs were also in agreement with previously published analyses of similar samples, indicating that similar enantioselective processes were taking place in these environmental matrices.     

Contamination status of arsenic and other trace elements in drinking water and residents from Tarkwa, a historic mining township in Ghana

This study was conducted to assess the contamination status of 22 trace elements, especially As in water and residents in Tarkwa, a historic mining town in Ghana. Drinking water and human urine samples were collected from Tarkwa in addition to control samples taken from Accra, the capital of Ghana in March, 2004. Concentrations of As and Mn in some drinking water samples from Tarkwa were found above the WHO drinking water guidelines posing a potential health risk for the people. A potential health risk of As and Mn is a concern for the people consuming the contaminated water in this area. No significant difference of As concentrations in human urine between mining town (Tarkwa) and control site (Accra) was observed. Although As concentrations in drinking water in Tarkwa were low, urinary As levels were comparable to those reported in highly As-affected areas in the world. These results suggest the presence of other sources of As contamination in Ghana. This is the first study on multi-elemental contamination in drinking water and human from a mining town in Ghana.