Brian K. Gullett

The effect of metal catalysts on the formation of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran precursors

The catalytic effects of copper and iron compounds were examined for their behavior in promoting formation of chlorine (Cl2), the major chlorinating agent of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), in an environment simulating that of municipal waste fly ash. Formation of Cl2 occurred as a result of a metal-catalyzed reaction of HCl with O2. Catalytic activity was greatest at a temperature of approximately 400 °C, supporting a theory of de novo synthesis of PCDDs and PCDFs on fly ash particles downstream of waste combustion.

Variables Affecting Emissions of PCDD/Fs from Uncontrolled Combustion of Household Waste in Barrels

Abstract The uncontrolled burning of household waste in barrels has recently been implicated as a major source of airborne emissions of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). A detailed, systematic study to understand the variables affecting emissions of PCDD/Fs from burn barrels was performed. The waste composition, fullness of the barrel, and the combustion conditions within the barrel all contribute significantly to determining the emissions of PCDD/Fs from burn barrels. The study found no statistically significant effect on emissions from the Cl content of waste except at high levels, which are not representative of typical household waste. At these elevated Cl concentrations, the impact of Cl on PCDD/F emissions was found to be independent of the form of the Cl (inorganic or organic). For typical burn conditions, most of the PCDD/F emissions appear to be associated with the later stages of the burn when the waste is smoldering. Polychlorinated biphenyls (PCBs) were also measured for a subset of the tests. For the nominal waste composition, the average emissions were 76.8 ng toxic equivalency units (TEQ)WHO98 /kg of waste com busted, which suggests that uncontrolled burning of household waste could be a major source of airborne PCDD/Fs in the United States.

Observations on the effect of process parameters on dioxin/furan yield in municipal waste and coal systems

Effects of fly ash loading; ash-borne, extractable organics; sulfur dioxide (SO2) and hydrogen chloride (HCl) concentration; and combustion quality on the formation of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran (PCDD/F) were evaluated in pilot scale tests simulating municipal waste combustion and coal/waste co-combustion testing. Similar PCDD/F yields from reinjection of as-received and extracted fly ash injection along with testing under “poor combustion” conditions show the importance of combustion quality on minimizing precursors. Co-firing coal and municipal solid waste ash leads to increased formation from that of firing coal alone, indicating that the municipal solid waste ash provides additional reactants and/or catalytic sites for formation. Finally, tests with elevated SO2 levels found that, at sufficiently high sulfur/chlorine levels, formation of PCDD/F is prevented in both simulated municipal waste combustion and coal/waste co-firing.

Entrained-flow adsorption of mercury using activated carbon.

ABSTRACT Bench-scale experiments were conducted in a flow reactor to simulate entrained-flow capture of elemental mercury (Hg0) by activated carbon. Adsorption of Hg0 by several commercial activated carbons was examined at different C:Hg ratios (by weight) (350:1-29,000:1), particle sizes (4-44 um), Hg0 concentrations (44, 86, and 124 ppb), and temperatures (23-250 °C). Increasing the C:Hg ratio from 2100:1 to 11,000:1 resulted in an increase in removal from 11 to 30% for particle sizes of 4-8 um and a residence time of 6.5 sec. Mercury capture increased with a decrease in particle size. At 100 °C and an Hg0 concentration of 86 ppb, a 20% Hg0 reduction was obtained with 4- to 8-um particles, compared with only a 7% reduction for 24- to 44-um particles. Mercury uptake decreased with an increase in temperature over a range of 21-150 °C. Only a small amount of the Hg0 uptake capacity is being utilized (less than 1%) at such short residence times. Increasing the residence time over a range of 3.8-13 sec did not increase adsorption for a lignite-based carbon; however, increasing the time from 3.6 to 12 sec resulted in higher Hg0 removal for a bituminous-based carbon.

Mono- to tri-chlorinated dibenzodioxin (CDD) and dibenzofuran (CDF) congeners/homologues as indicators of CDD and CDF emissions from municipal waste and waste/coal combustion

Total homologue concentrations and select congener concentrations from amongst the mono- to tri-chlorinated dibenzodioxins (CDDs) and dibenzofurans (CDFs) are used to model both Total (mono- to octa-) CDD + CDF emissions and the toxicity equivalent (TEQ) of the 2,3,7,8-chlorine-substituted emissions. Analysis of emission data from two facilities indicates that use of total homologue concentrations shows limited, facility-specific correlations with Total CDDs/CDFs and TEQ. Concentrations of select mono- to tri-CDD/CDF congeners show promising correlation with CDD/CDF TEQ across facilities, suggesting that these compounds can act as TEQ indicators.

NOx Removal with Combined Selective Catalytic Reduction and Selective Noncatalytic Reduction: Pilot-Scale Test Results

Pilot-scale tests were conducted to develop a combined nitrogen oxide (NOx) reduction technology using both selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR). A commercially available vanadium- and titanium-based composite honeycomb catalyst and enhanced urea (NH2CONH2) were used with a natural-gas-fired furnace at a NOx concentration of 110 ppm. Changes in SNCR chemical injection temperature and stoichiometry led to varying levels of post-furnace ammonia (NH3), which acts as the reductant feed to the downstream SCR catalyst. The urea-based chemical could routinely achieve SNCR plus SCR total NOx reductions of 85 percent with less than 3 ppm NH3 slip at reductant/NOx stoichiometries ranging from about 1.5 to 2.5 and SCR space velocities of 18,000 to 32,000 h−1. This pilot-scale research has shown that SNCR and SCR can be integrated to achieve high NOx removal. SNCR provides high temperature reduction of NOx followed by further removal of NOx and minimization of NH3 slip by a ...

Design and characterization of a 1200 °C entrained flow, gas/solid reactor

The design and characterization of a 1200 °C flow reactor for studying noncatalytic, gas/solid reactions are presented. The reactor system is designed for high‐temperature, isothermal operation in a developing, laminar flow regime. The process gas is raised to the reaction temperature by flowing through a tubular preheat furnace fitted with sequential alumina honeycombs for increased convective and radiative surface area. The preheat furnace eliminates typical use of a flame burner to reach these high temperatures, thereby preventing the existence of combustion gases that may affect the reaction of interest. The reactive solid is introduced into the flow reactor by a water‐cooled injection probe. Reacted solids are collected by a stainless‐steel, water‐cooled probe capable of axial movement. Solids residence times can be varied between ∼50 and 250 ms, dependent upon process gas flow rate and collection probe height in the reactor. Sample results are presented for the calcium oxide/sulfur dioxide (CaO/SO2)...

Design of a graphite element drop‐tube reactor system for study of SO2 removal by injected limestone sorbents

The design and operation of a graphite element drop‐tube reactor system for a study of the fundamental mechanisms and reaction rates of sulfur dioxide (SO2) removal by high‐temperature injection of limestone‐based sorbents is described. The reactor system is designed for laminar flow in an environment that allows for control of reaction temperature, sorbent particle residence time, and atmosphere composition. The sorbent injection system allows variable feed rates to as low as 1 mg/min for particles as small as 1 μm in diameter. The water‐cooled sorbent collection system arrests the high‐temperature reaction upon capture and allows analysis of the sorbent’s efficiency of SO2 capture and in situ particle‐size distribution. The results presented show the reactivity of different types of sorbents at varying conditions of system operation.

Particulate matter and black carbon optical properties and emission factors from prescribed fires in the southeastern United States

Aerosol optical properties of biomass burning emissions are critical parameters determining how these emissions impact the Earths climate. Despite their importance, field measurements of aerosol optical properties from fires remain scarce. Aerosol emissions from prescribed fires of forested and grass plots in the southeastern United States were measured and compared to emissions from laboratory simulations. Fine particulate matter (PM2.5), black carbon (BC), and aerosol light scattering and absorption were characterized for all fires. Refractory BC emission factors (EFs) measured at ground level (~2 m) were 0.76 ± 0.15 g/kg, comparable to the 0.93 ± 0.32 g/kg measured aloft (~100–600 m). However, PM EFs measured by aircraft were only 18% (5.4 ± 2.0 g/kg) of those measured on the ground (28.8 ± 9.8 g/kg). Such large differences in PM EFs for the same fire have not been previously reported and may plausibly be due to the differing particle measurement methodologies being applied but also likely related to partitioning of organic compounds to the gas phase as the plume dilutes aloft. Higher PM EFs on the ground may also be related to a higher contribution from smoldering combustion. The absorption Angstrom exponents (αa) for the high intensity South Carolina fires were 3.92 ± 0.6, which was larger than prescribed forest fire in Florida (2.84) and the grass fire in Florida (2.71), implying a larger absorption contribution from brown carbon from higher-intensity fires. Aerosol optical properties from laboratory simulations did not represent field measurements.

Detection of androgenic activity in emissions from diesel fuel and biomass combustion

The present study evaluated both diesel fuel exhaust and biomass (wood) burn extracts for androgen receptor-mediated activity using MDA-kb2 cells, which contain an androgen-responsive promoter-luciferase reporter gene construct. This assay and analytical fractionization of the samples were used as tools to separate active from inactive fractions, with the goal of identifying the specific compounds responsible for the activity. A significant androgenic response was detected from the diesel emission. High-performance liquid chromatographic fractionation of the sample indicated that significant androgenic activity was retained in three fractions. 4-Hydroxybiphenyl was identified from the most active fraction using gas chromatography/mass spectroscopy. This purified compound was then tested at doses from 1 nM to 100 microM. 4-Hydroxybiphenol exhibited antagonist activity at low concentrations and agonist activity at high concentrations. A competitive-binding assay confirmed binding to the androgen receptor, with a median inhibitory concentration for radioligand binding of approximately 370 nM. Significant androgenic activity also was detected in the wood burn samples, but we were unable to identify the specific chemicals responsible for this endocrine activity. The present study demonstrates that in vitro bioassays can serve as sensitive bioanalytical tools to aid in characterization of complex environmental mixtures.