Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7581. Adviser: Mark J. Rood. Includes bibliographical references (leaves 168-179) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7585. Adviser: Benito J. Marinas. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thèse (M.Sc.A.)--Université de Sherbrooke (Canada), 2007. / Titre de l'écran-titre (visionné le 1 février 2007). In ProQuest dissertations and theses. Publié aussi en version papier.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6648. Adviser: Barbara S. Minsker. Includes bibliographical references (leaves 139-161). Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6652. Adviser: Benito J. Marinas. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Bench-scale systems, if properly designed, can become a valuable tool to evaluate fouling in dead-end ultrafiltration systems. The purpose of this study was to design and build a bench-scale hollow fiber ultrafiltration system to examine the effect of operational parameters and chemical pretreatment on membrane performance. For this research, a bench-scale hollow fiber ultrafiltration system that operates at constant flux and includes a backwash cycle was designed and built. The system was also designed to be used as a tool in the evaluation of critical flux for source waters. The study demonstrated that shorter operating time between backwash cycles resulted in reduced membrane fouling, improved backwash efficiency and natural organic matter rejection. The study also indicated that fouling rate increased with increase flux while backwash efficiency decreased with increasing operating flux. Chemically pretreated ORW showed superb reduction in normalized specific flux decline when compared with uncoagulated ORW.

Photooxidation of isoprene has a large influence on the oxidation capacity of the atmosphere and is a significant source of secondary organic material (SOM) of atmospheric particles. A quantitative understanding of isoprene photooxidation mechanism, in particular in the clean atmosphere, is important but challenging. This thesis presents laboratory and field studies of isoprene photooxidation via the hydroperoxyl (HO2) pathway, believed to be the most important reaction pathway of isoprene-derived peroxy radicals under clean conditions, by using a switchable-reagent-ion (NO+; H3O+) time-of-flight mass spectrometer (SRI-TOF-MS). Isoprene photooxidation via the HO2 pathway was investigated in a continuous-flow chamber. Production yields of methyl vinyl ketone (MVK) and methacrolein (MACR) pathway were determined as (3.8 ± 1.3)% and (2.5 ± 0.9)%, respectively, at <2% RH at 25 oC. Production of MVK and MACR via the HO2 pathway implies concomitant production of hydroxyl ((6.3± 2.1)%) and hydroperoxyl ((6.3± 2.1)%) radicals. The experiments also revealed an unexpected instrument bias that isoprene-derived hydroperoxides (ISOPOOH), the major isoprene oxidation products via the HO2 pathway, were detected as the same product ions as the MVK and MACR. This finding implies that scientific conclusions based on previous ambient measurements of MVK and MACR under clean conditions using similar techniques need to be revisited. As a follow-up study, preliminary analysis of the ambient measurements in the Amazon Basin showed that ISOPOOH isomers contributed to (36±15)% of the total concentration of MVK, MACR, and ISOPOOH isomers under clean conditions. The value is useful for re-evaluation of previous measurements and also defines range of possible anthropogenic influence on isoprene chemistry in the region. SOM production from isoprene photooxidation via the HO2 pathway was also investigated. Isoprene photooxidation was separated from SOM production by using two continuous-flow reactors connected in series and operated at steady state. Relative importance of various intermediates was directly compared from the drop of their gas-phase signals. Isoprene epoxydiols (IEPOX) had a much larger contribution to SOM production than other previously suggested isoprene SOM precursor, ISOPOOH isomers and isoprene, for a wide range of aciddity The IEPOX contribution to isoprene SOM production was further quantified. IEPOX isomers lost from the gas phase accounted for (46 ±11)% of the produced SOM mass concentration. The IEPOX isomers comprised (59±21)% (molecular count) of the loss of monitored gas-phase species. The implication is that for the investigated reaction conditions IEPOX pathway accounted for half of the SOM mass concentration.

Water treatment is a critical global challenge requires innovated effective solution. Conventional treatment methods includes membrane filtration, adsorption and electrochemical oxidation of organics. This dissertation proposed a new hybrid of the three conventional technologies and investigated the mechanism and application potential for water treatment using carbon nanotube (CNT) based anodic filter. A qualitative reactive transport model consisting of mass transport, adsorption/desorption, electron transfer was developed to understand reaction mechanism and compare the filtration with the batch electrochemical system. The mass transport step is found to be the key advantage (>6-fold) of the electrochemical filtration over the batch system due to convective mass transport through the filter pores. This indicate synergy between the filtration and the electrochemisty. A quantitative model coupling the above three steps was also build to quantitatively simulate the reaction kinetics and probe information about reactive sites. The model simulation was successfully validated by experimental methyl orange oxidation data and was further used to identify kinetics from reactive sites. It was found that two types of reactive sites–the sidewall sites and oxy-defect sits are both reactive for ferrocyanide oxidation with a slightly different overpotential. Also, microscopic flux and steamline plot again verify the convective mass transport enhance reaction kinetics–synergy of the filtration and electrochemistry. To improve potential for organic oxidation applications, the CNT filter was coated with 3.9±1.5 nm bismuth-doped tin oxide (BTO) nanoparticles. In the oxalate oxidation experiments, the current efficiency increased by 1.5–3.5 times and TOC removal increased by 2–8 times after coating. The BTO-CNT anode energy consumption was 25.7 kWh kgCOD-1 at ~93% TOC removal and 8.6 kWh kgCOD-1 at ~50% TOC removal, comparable to state-of-the-art oxalate oxidation processes (22.5–81.7 kWh kgCOD-1). The anode stability also improved by extending the working potential range from 1.4 V of pure CNT to 2.2 V of BTO coated CNT. For inorganic ion removal applications, the CNT filter was coated by a 5.5 ± 2.7 nm layer of TiO2 for arsenic removal. Compared with the conventional adsorption column using granular adsorbents, the TiO2-CNT filter is a highly dispersed nano-system allows forced convective transport through the pores whereas diffusive mass transport dominates and limits kinetics for granular adsorbents. As a result, adsorption kinetics of the TiO2-CNT filter increased by two orders of magnitude due to structure improved site accessibility (20–30 fold), internal convection (4–6 fold) and electrosorption (0.15–2 fold). Groundwater samples containing 44 ppb As were treated by single-pass filtration, and 12500 bed volumes (residence time of 4.5 s; 127 L m-2 h-1; 5.8 mg m-2 h-1). TiO2 filter was successfully regenerated by 5 mM NaOH for both As(III) and As(V). / Engineering and Applied Sciences - Engineering Sciences

Organic and microbial fouling are the initial steps for biofilm formation, resulting in severe fouling problems in many environmental and engineered applications including membrane water filtration. Electro-active methods are proposed to mitigate microbial as well as organic fouling via electrokinetic and/or electrochemical mechanisms. In the first part of this thesis, a parallel-electrode configuration was adopted and the cathode antifouling was evaluated. A carbon nanotube-polyvinylidene fluoride (CNT-PVDF) porous non-Faradaic cathode was first fabricated on top of an ultrafiltration (UF) membrane to produce negative surface charges via capacitive charging at 2 V, which reduced energy requirements (up to 2-fold) in comparison to the unmodified control. A semi-quantitative study was then completed on cathode coatings of different nanomaterials (CNM) to reduce microbial fouling. The bacterial attachment and inactivation were correlated to the electric potential and cathodic H2O2 generation, respectively. Next, a CNT and carbon black (CB) composite cathode was made on a forward osmosis (FO) membrane surface and challenged with synthetic and actual wastewater, which reduced fouling in regard to initial flux loss (~60%) for the actual wastewater and fouling rate (~50%) for both solutions at 2 V in 84 h. In the other part of the thesis, the electrode configuration was improved by fabricating interlaced surface electrodes on a substrate or membrane surface instead of only using a cathode. Insulated interlaced Ag electrodes resulted in optimal bacterial inactivation (84%) and detachment (94% after 15 h biofilm growth) with 2 min treatment at 50 V AC (10 kHz). Interlaced CNT electrodes on a microfiltration (MF) membrane altered the bacterial density and morphology at 2 V DC and reduced the fouling rate by up to 75% under the optimal filtration conditions at 2 V AC. / Engineering and Applied Sciences - Engineering Sciences

The main objectives of this dissertation were to refine electrochemical GAC reactivation technology, a promising alternative technology, and to investigate its technical feasibility. The specific objectives of the study were: (1) to evaluate alternative reactor designs; (2) to assess the effect of contaminant and GAC types on the regeneration efficiency; (3) to study the electrolyte post-treatment; and (4) to investigate reactivation mechanisms and model them. To achieve these objectives many interrelated topics were investigated using phenol, 2-nitrophenol (2NP) and naturally occurring background organic matter (NOM) as adsorbates and Filtrasorb 400 (F-400), Westvaco Carbon (WV-B), Darco Norit, and Filtrasorb 300 (F-300) as adsorbents. The impact of reactor operation conditions (reactivation time, current density, pH) on the reactivation efficiency showed that the reactivation efficiency (RE%) could be increased to a maximum by increasing the current and/or time. It was concluded that electrochemical reactivation of GAC is contaminant-type dependent. The reactivation efficiencies of F-400 loaded with 2NP and phenol at different reactivation currents and times showed similar patterns. A comparison of the percent reactivation of GACs showed that F-400 and WV-B performed essentially the same for the tested conditions. Total destruction of desorbed contaminants and their by-products were possible. Desorbed phenol and 2NP from loaded GAC react to form a number of reaction by-products that are eventually oxidized to CO2 and H 2O. The main mechanism responsible for electrochemical reactivation is high-pH induced desorption at the cathode. It accounts for approximately 50--60% of the total reactivation of a single layer of GAC. It is recommended that the GAC electrochemical reactivation should be a three step process. First, the GAC is reactivated with a relatively low current to minimize potential alterations of the GAC surface. Second, the GAC is drained and rinsed with a buffered solution. Finally, the electrolyte is treated electrochemically for an extended time at a much higher current (and possibly a different electrode) to reduce the electrolyte's TOC so that it may be reused or discharged. (Abstract shortened by UMI.)