Browsing by Subject "Volatile organic compounds--Environmental aspects"
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Item Biodegradation of paint VOC mixtures in biofilters(2004) Park, Jung Su; Kinney, Kerry A.The surface coating industry is facing increasingly stringent environmental regulations that require the control of volatile organic compounds (VOCs) and hazardous air pollutants. Biofiltration is an attractive alternative for paint spray booth applications but these facilities pose several challenges to biofiltration technology . Specifically, offgas streams from painting operations are characterized by complex VOC mixtures, frequent shutdown and restart events, high volumetric flow rates, and relatively low contaminant concentrations. The objectives of this research were to investigate the feasibility of biofiltration for paint spray booth applications and to delineate how key operating parameters and biofilter history affect the degradation of VOC mixtures and the microbial population in biofilters. The results indicate that biofilters are a feasible option for treating the emissions from paint spray booth facilities. Removal efficiencies as high as 95% or greater were achieved even under intermittent feed conditions. Biofilter performance was found to strongly depend on nitrogen supply, particularly during the start up period. Overall VOC removal was limited by the toluene and xylene components of the waste gas stream. When the inoculating culture was developed so as to maintain the degradation capacity of the culture for each VOC component of the paint mixture, a sequential feeding strategy did not provide any initial advantage with respect to VOC removal; however, the system ultimately achieved higher removals of the toluene. Biofilm samples analyzed using the DGGE technique indicate that the fungal population in the bioreactors was relatively uniform across the biofilters and stable over extended periods of operation. The DGGE banding pattern for the bacterial population, on the other hand, indicates that the bacterial community was spatially distinct and became less diverse after 200 days of operation. While this research focused on biofilters treating paint VOC mixtures, it is anticipated that many of the phenomena observed will be applicable to other bioreactor systems and contaminant mixtures.Item Biofiltration of volatile organic compounds using fungal-based bioreactors(2002-08) Woertz, Jennifer Renee; Kinney, Kerry A.Stricter regulations for volatile organic compounds have increased the demand for efficient abatement technologies. Biofiltration, a process in which contaminated air is passed through a biologically active bed, can be used to remove these pollutants from air streams. In this study, the black fungi Exophiala lecanii-corni and Cladophialophora sp. were evaluated for use in vapor-phase bioreactors. Batch tests indicated that E. lecanii-corni can tolerate low pH and minimal nutrient conditions and degrade a wide variety of contaminants including toluene and methyl propyl ketone. A series of bench-scale bioreactor studies were then conducted to determine how nitrogen supply, mite predation and surfactant washing affected pollutant removal in fungal biofilters. In experiments to evaluate the influence of nitrogen supply on bioreactor performance, it was determined that a nitrogen mass loading of approximately 2% of the carbon mass loading was needed to achieve near-complete removal of the pollutant. When the nitrogen supply was discontinued, the bioreactors continued to degrade pollutant; however, clogging of the bioreactor occurred due to more extensive filamentation and conidiophore formation by the fungi in the biofilm. Additional bench-scale studies using Cladophialophora sp. indicated that clogging can be controlled using the fungal-grazing mite, Tyrophagus putrescentiae. Clogging also was minimized by packing the bioreactors with an open-structured foam medium, which was found to favor hyphal growth in the internal pores of the packing. To reduce the 7- to 10-day start-up period typically observed in fungal bioreactors, surfactants were evaluated as fungal spore activators. Results showed that Tween 20, a nonionic surfactant, enhanced inoculum development by shortening the lag period prior to spore germination. However, when bioreactors were presoaked in medium containing Tween 20, washout of the cells occurred during inoculation. Finally, results from the bench-scale experiments were used to evaluate Ottengraf’s bioreactor model developed for bacterial biofilters in an attempt to predict toluene removal profiles in fungal systems. The model reasonably predicted toluene removal profiles for inlet concentrations of less than 250 ppm , but it did not account for nutrient limitations nor the complex morphology of fungal biofilms. Overall, the fungal biofilters evaluated in this study efficiently removed gas-phase pollutants and tolerated harsh environmental conditions, indicating that they are a viable alternative to physical-chemical treatment options.Item Refueling and evaporative emissions of volatile organic compounds from gasoline powered motor vehicles(2007-12) Quigley, Christopher John, 1962-; Corsi, Richard L.The United States Environmental Protection Agency has estimated that over 111 million people reside in areas that exceed the National Ambient Air Quality Standards for ozone. One major source of the chemical precursors (nitrogen dioxides and volatile organic compounds (VOCs)) for ozone are motor vehicles. The overall goal of this research is to improve the knowledge base related to VOC refueling and evaporative emissions from motor vehicles. Refueling, running loss, hot soak, and diurnal loss total and speciated VOC emissions were investigated. A total of 12 uncontrolled refueling events were completed and involved the determination of volumetric flow rates of gasoline vapor during refueling, as well as total and speciated VOC concentrations. Total VOC emissions were compared with two commonly used algorithms. Speciated VOC vapor profiles were compared with two published gasoline vapor profiles and theoretical predictions based on knowledge of liquid composition and environmental conditions. An evaluation of refueling emissions impacts on ozone formation potentials using MIR was completed and results were compared against speciated emissions and MOBILE-based total VOC emissions estimates coupled with a default speciation profile. Refueling VOC emissions and resultant ozone formation potential may be underestimated in existing emission inventories, particularly during the summer ozone season, A model was developed to predict the speciation of VOCs associated with evaporative emissions from motor vehicles. Model-predicted speciation profiles were evaluated using SHED studies. Running loss, hot soak and diurnal emissions were included in each test. Total VOC emissions measured during each test were compared against MOBILE6 predicted emissions. An evaluation of evaporative emissions impacts on ozone formation potentials using MIR was completed, comparing measured and predicted emissions. The measured:predicted speciation results ranged between 0.93 and 1.11 and had an average value of 1.02. For the conditions tested, MOBILE6 underestimated evaporative emissions in 20 of 24 comparisons. MOBILE6-based ozone formation potentials may be underestimated.