Browsing by Author "Morton A. Barlaz, Committee Member"

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Adsorption of Methyl Tertiary-Butyl Ether on High-Silica Zeolites: Effects of Adsorbent Characteristics and Natural Organic Matter on Adsorption Isotherms
(2004-08-06) Rossner Campos, Alfred Armin; Detlef R.U. Knappe, Committee Chair; Joel J. Ducoste, Committee Member; Morton A. Barlaz, Committee Member
Methyl tertiary-butyl ether (MTBE) is frequently detected in surface and ground water. Because of its hydrophilicity, MTBE is difficult to remove from aqueous solution by activated carbon adsorption processes. In drinking water treatment applications, natural organic matter (NOM) also adsorbs on activated carbons, which further decreases the MTBE adsorption capacity. Unlike activated carbons, high-silica zeolites are adsorbents with well-defined pore sizes. From a drinking water treatment perspective, it may be possible to select high-silica zeolites with pore sizes that are suitable for the adsorption of smaller organic contaminants while preventing the adsorption of competing NOM components of larger molecular size. Therefore, the objectives of this research were to evaluate the effects of zeolite pore structure and hydrophobicity on the adsorption of MTBE in the presence of NOM. MTBE adsorption isotherm data were collected for a matrix of high-silica zeolites with different pore sizes (ZSM-5/silicalite, Mordenite, Beta, Y), exchangeable cations (H+, Na+, NH4+), and hydrophobicities (SiO2/Al2O3 ratios). MTBE adsorption capacities of high-silica zeolites were compared to those of three GACs (one coconut-shell-based, two coal-based) and a carbonaceous resin (Ambersorb 563). Single-solute isotherm tests were conducted in ultrapure water buffered at pH 7.2. Additional isotherm studies were conducted to determine the effects of co-adsorbing and preloaded NOM on MTBE adsorption from Tar River water (Greenville, NC). Single-solute MTBE adsorption isotherm data showed that high-silica zeolites with smaller pores (ZSM-5/silicalite, Mordenite) were more effective adsorbents for MTBE than zeolites with somewhat larger pores (Beta, Y). Over a range of 90-700, the SiO2/Al2O3 ratio of the tested ZSM-5 zeolites had no effect on MTBE adsorption capacity. Similarly, the exchangeable cation (H+, Na+, NH4+) of high-silica ZSM-5 zeolites had little effect on MTBE adsorption at the tested conditions, and no zeolite-catalyzed MTBE hydrolysis was apparent for ZSM-5 zeolites in the H+ form. For high-silica zeolites, co-adsorbing and preloaded NOM lowered the single-solute MTBE adsorption capacity at a liquid-phase MTBE concentration of 10 μg/L (q10) by 0-23%. Similar decreases in MTBE adsorption capacity as a result of NOM adsorption were measured for the coconut-shell-based activated carbon CC-602; however, its MTBE adsorption capacity (q10) was only about 25% of that obtained for ZSM-5 zeolites. In the presence of preloaded NOM, the MTBE adsorption capacity of the carbonaceous resin (q10) decreased by about 47% relative to the single-solute value while that of one coal-based activated carbon decreased by almost 60%. Overall, the coal-based activated carbons exhibited the smallest MTBE adsorption capacities (q10), which were approximately one order of magnitude lower than those of the ZSM-5 zeolites. Using an equilibrium model, adsorbent usage rates (AURs) and costs associated with adsorbent usage were calculated to evaluate the feasibility of zeolite-based adsorption systems. The latter analysis showed that the lowest treatment cost ($0.7/1000 gal) was associated with the usage of HiSiv3000 zeolite (cost: ~$7/lb) and CC-602 GAC (cost: ~1.50/lb). Despite the similar cost for these two adsorbents, the zeolite-based adsorption system may be more advantageous because (1) the AUR calculated for the HiSiv3000 zeolite was less than 25% of that calculated for the CC-602 GAC and (2) the calculated bed life for a packed bed adsorber containing HiSiv3000 zeolite was more than 6 times longer than that for an equally sized packed bed adsorber containing CC-602 GAC, a result that was affected by the lower packed bed density of the latter adsorbent. Thus, adsorbent replacement/ regeneration would have to occur on a less frequent basis when zeolites are used. Finally, it may be possible to regenerate spent high-silica zeolite with steam or microwave methods rather than with more energy-intensive thermal methods. This opportunity could further lower the cost of zeolite-based adsorption systems for MTBE removal from water.
Environmental and Water Resources Decision-Making Under Uncertainty
(2002-12-05) Harrison, Kenneth Watson; H. Christopher Frey, Committee Member; E. Downey Brill, Committee Member; Kenneth Reckhow, Committee Member; Morton A. Barlaz, Committee Member; S. Ranji Ranjithan, Committee Chair
"Decision-making under uncertainty" is an important area of study in numerous disciplines. The variety of quantitative methods that have been proposed to address environmental and water resources problems reflects the importance of this subject. In a review of the literature, methods were compared and contrasted and promising areas for future research were identified. Conclusions drawn from the review were that 1) large gains may be realized from cross-disciplinary research, 2) significant benefits may be realized from considering uncertainty, 3) advanced algorithms—probabilistic search methods and efficient methods for Bayesian analysis—and increased computing power should greatly extend the applicability of existing methods, and 4) in particular, decision-theoretic methods that have wide application for sequential decision-making. A new decision-theoretic method, Bayesian programming (BP), was developed that takes advantage of the increased computing power and improvements in Bayesian analysis methods. The method has wide applicability, suitable for problems in which there is 1) uncertainty in the modeling, 2) stochastic behavior in the systems that are modeled, 3) the possibility to reduce uncertainty through data collection, and 4) the opportunity for a recourse decision after a period of data collection. The approach combines systematic search methods (mathematical programming) and Bayesian statistical analysis techniques (Markov chain Monte Carlo) in a decision analysis framework. The BP method is tested with application to a hypothetical, but realistic river basin management problem, using real data from the much-studied Athabasca River in Alberta, Canada. The management problem involves balancing the objectives of pulp mill development and water quality protection (dissolved oxygen). Results from application of the BP method were compared with those applying other methodologies. Examination of the results indicated that the BP method is a practical method worthy of additional research. Ultimately, it is hoped, this research will lead to computer-based tools that will improve environmental and water resources decision-making.
Factors Controlling Desorption Rates of Hydrophobic Organic Contaminants from Municipal Solid Waste
(2005-05-31) Mitchell, Lisa A.; Detlef R. U. Knappe, Committee Chair; Morton A. Barlaz, Committee Member; Joel J. Ducoste, Committee Member
The overall goal of this research was to determine desorption rates of hydrophobic organic contaminants (HOCs) from municipal solid waste (MSW). Toluene and o-xylene, two alkylbenzenes that frequently occur in landfill leachates, served as model HOCs. HOC desorption rates were measured for individual MSW components expected to contribute to HOC sorption [high density polyethylene (HDPE), and poly(vinyl chloride) (PVC), newsprint, office paper, and degraded rabbit food as a model food and yard waste]. To quantify effects of MSW decomposition on HOC desorption rates, newsprint and office paper were tested in both fresh and anaerobically degraded forms. Effects of aqueous phase composition were evaluated by comparing HOC desorption rates in both acidogenic and methanogenic leachates to those obtained in ultrapure water. To determine the effects of aging (i.e., contaminant-sorbent contact time), desorption tests in ultrapure water were performed after aging times of 1 day, 1 week, 1 month, 6 months, and 9 months. Toluene desorption rates in acidogenic and methanogenic leachates and o-xylene desorption rates in ultrapure water were measured after aging times of 1 week and 6 months. To compare HOC desorption rates in a quantitative manner, experimental data were described by polymer diffusion models. A single-parameter polymer diffusion model was used to describe HOC desorption rates from PVC and HDPE, while a three-parameter biphasic polymer diffusion model was implemented to describe HOC desorption rates from biopolymer composites. Desorption tests showed that HOC desorption rates varied greatly with sorbent characteristics. HOC desorption rates from plastics were rapid for rubbery polymers such as HDPE and slow for glassy polymers such as PVC. For biopolymer composites, an initial phase of rapid HOC desorption was followed by an extended period of slow HOC desorption. In general, HOC desorption rates in acidogenic or methanogenic leachates were similar to those observed in ultrapure water. Exceptions were experiments conducted with PVC and fresh office paper in acidogenic leachate, in which cases enhanced HOC desorption rates were obtained. Volatile fatty acids such as propionic or butyric acids, which are important constituents of acidogenic leachate organic matter, may have plasticized PVC and thus enhanced HOC desorption rates. For fresh office paper, prior work by Wu (2002) showed that the lower pH of acidogenic leachate was primarily responsible for enhanced HOC desorption rates. Regarding sorbate characteristics, desorption rates for toluene were generally faster than those of o-xylene, a larger more hydrophobic molecule. For biopolymer composites, the HOC fraction associated with the slowly releasing sorbent organic matter fraction increased with increasing aging time, and, compared to toluene, this trend was more pronounced for o-xylene. Model predictions for simulated MSW mixtures showed that both waste composition and HOC characteristics greatly affect HOC desorption rates. Predicted half-lives for toluene and o-xylene were <1 and ~7 days, respectively, for a MSW mixture typical of the year 1960 and ~600 and 1525 days, respectively, for a MSW mixture typical of the year 2000. The principal changes in MSW composition that occurred between 1960 and 2000 was a decrease in food and yard waste and an increase in plastics. In particular, the greater presence of glassy polymers, such as PVC, in the newer MSW mixture led to slower alkylbenzene desorption rates. These predictions suggest that the mineralization rate of alkylbenzenes in old landfills may be controlled by biological processes while desorption processes may control alkylbenzene biodegradation rates in newer landfills.
Initial Investigations of Aerobic Granulation in an Annular Gap Bioreactor
(2005-04-19) Williams, Jon Christopher; Morton A. Barlaz, Committee Member; Joel J. Ducoste, Committee Member; Detlef R. Knappe, Committee Member; Francis L. de los Reyes III, Committee Chair
This research describes the design, construction, and characterization of a novel annular gap bioreactor. The bioreactor was conceived as a tool for the shear-based control of activated sludge floc particle size in batch and continuous-run experiments. Initial experiments on the feasibility of cultivating aerobic granular sludge in the bioreactor are described. The bioreactor was found to experience turbulent Taylor vortex flow, rather than laminar Couette flow, at all rotational speeds tested. This flow regime is the result of inner cylinder rotation. Despite turbulent flow conditions, the bioreactor was found to behave approximately as a plug-flow device when not aerated, and as a complete-mix reactor when aerated. Floc size control was found to depend on bioreactor rotational speed for two sludges tested, with higher rotational speed leading to smaller particle size. Three experimental attempts at aerobic granular sludge cultivation in the annular gap bioreactor are described in this study. Although none of the three attempts was successful at producing aerobic granules, the experiments allowed critical control issues related to bioreactor operation and influent composition to be identified and addressed. The Bacterial and Eukaryal population dynamics during each run were tracked with denaturing gradient gel electrophoresis and rDNA sequence analysis, using methods developed or streamlined in the course of this research. The foundational work described in this study culminated in the development of a series of protocols and recommendations for the next phase of aerobic granular sludge investigation with this novel annular gap bioreactor.
Laboratory Studies in Chlorinated Solvents and Hydrocarbon Bioremediation
(2008-04-24) Tillotson, Jason Matthew; Robert C. Borden, Committee Chair; Morton A. Barlaz, Committee Member; Francis de los Reyes, Committee Member
Quantifying Activated Sludge Bulking-Causative Filamentous Bacteria Using Molecular Methods
(2003-04-22) Liao, Jiangying; Francis de los Reyes III, Committee Chair; Morton A. Barlaz, Committee Member; Detlef R. Knappe, Committee Member
Filamentous bulking is a widespread problem in activated sludge wastewater treatment plants. In North Carolina, 63% of wastewater treatment plants (WWTPs) surveyed have experienced bulking. Determining the dominant bulking-causative bacteria and their level of proliferation is a necessary step in bulking control. This study used molecular techniques, i.e. quantitative Fluorescent in situ Hybridization (FISH) and membrane hybridization to identify and quantify the specific filamentous microorganisms and their threshold values for causing bulking in both lab scale reactors and full scale treatment plants. Filament length of a specific filamentous organism, Eikelboom Type 1851, correlated strongly with the sludge volume index (SVI) and was identified to be the major bulking-causative microorganism in lab scale reactors and a full scale activated sludge plant. The full scale plant is a biological nutrient removal (BNR) plant, a common operational mode in North Carolina, suggesting that this organism may be prevalent in North Carolina WWTPs. The threshold value for Eikelboom Type 1851-caused-bulking was determined. This threshold value will allow the monitoring of incremental improvements in control methods and the delineation of the niche of Eikelboom Type 1851 in activated sludge. Furthermore, the lab scale experiments verified the kinetic selection theory and the filamentous backbone theory for Type 1851.