Madjid Mohseni

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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Advanced oxidation processes (AOPs) are promising treatment options for the degradation of micropollutants in water. Vacuum-UV (VUV), as one such AOPs with UV photons under 200 nm, can directly photolyze water to produce •OH without extra oxidant or catalyst. However, a potential challenge in treating micropollutants by VUV, is the formation of nitrite in nitrate-containing water. Nitrate absorbs 185 nm photons, leading to the potential formation of nitrite. Given the greater toxicity and more stringent regulatory limits of nitrite on its concentration in drinking water, it is essential to examine the mechanisms of nitrite formation during VUV AOP. This research focused on understanding the effect of common solutes present in water, including dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), chloride, and sulfate on the formation of nitrite in nitrate-containing water during VUV photolysis. Experimental work involved kinetic studies using a custom-made benchtop UV/VUV collimated beam setup. Water samples containing solutes of interests at different concentrations were irradiated and collected for analysis at set intervals, corresponding to UV254 fluences of up to 1200 mJ/cm2. The results indicated that the formation of nitrite follows a very complex mechanism and is not simply dependent upon the concentration of nitrate. Among the solutes evaluated, DOC and chloride had the greatest impact on nitrite formation. The presence of DOC, through its scavenging of •OH, resulted in increased formation of nitrite. Chloride, on the other hand, led to a significant reduction in nitrite formation due to its competition with nitrate for absorbing VUV photons. Unlike chloride and DOC, sulfate and DIC, at concentrations commonly present in water, had little impact on nitrite formation. Their impact was only evident at extremely high concentrations to slightly reduce nitrite formation. When all the solutes, i.e., DOC, DIC, sulfate, and chloride, were present simultaneously, the effect of DOC was more dominant and eventually increased nitrite formation. Finally, dissolved oxygen was determined to decrease nitrite formation through the scavenging of ∙H and hydrate electrons. The details of the experimental and mechanistic studies can provide scientific guidance towards more effective and optimized application of VUV technology for drinking water treatment.

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The stability and electrochemical regeneration of activated carbon electrodes used for Capacitive Deionization have been investigated. To assess the electrode state, electrochemical properties such as capacitance and potential at the point of zero charge (EPZC) were monitored and complemented by elemental composition, wettability and bulk porosity analysis.Long-term cycling was performed with electrolytes containing dissolved organic matter (DOM) and iron (II) under anaerobic and aerobic conditions. It was found that DOM, at concentrations of up to 40 mg L-¹, had a marginal impact on capacitance loss and relocation of the EPZC. On the other hand, the scaling nature of iron was apparent from early cycling stages, in waters containing as little as 0.2 mg Fe²⁺ L-¹. In all cases performed, elemental composition analysis demonstrated that incorporation of oxygen to the surface occurred predominantly during the first 15 to 20 cycles. Specifically, the oxygen content increased by a factor of four. Over this time frame, the contact angle decreased from approx. 130˚ to 34˚, on average; which indicated an increase in electrode wettability. In addition, cycling experiments with simple electrolytes revealed improved electrode stability as cycling time increased and as pH decreased. Degradation tests conducted using a two-electrode cell demonstrated the effect of reaction coupling between the processes of carbon corrosion and oxygen reduction. As a result, electrode decay occurred at an accelerated rate.Electrochemical regeneration was proven successful at recovering the electrode capacitance but not at regressing the EPZC. Their corresponding response surfaces were mapped through a 32-factorial design of experiments and revealed a significant potential dependence. Further tests revealed a point of maximum recovery near a potential of -1.68 V vs RHE and 50 s of holding time. Furthermore, the contribution of a regenerative step to the long-term electrode stability was assessed. In general, an improved retention of capacitance was observed during the first 25 cycles. However, it was noted that most of the capacitance recovered was lost in the subsequent degradation cycles. Consequently, the apparent initial improvement did not translate to an extension of the electrode lifetime, deeming this approach inadequate to mitigate the effect of carbon corrosion.

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Safe drinking water is essential to humans, thus natural raw water requires necessary treatment, especially removing pathogenic microorganisms for disinfection. In addition to conventional chemical disinfectant, ultraviolet (UV) radiation has been increasingly used for water disinfection. Recently a new UV source - UV light-emitting diodes (UV-LEDs) - has emerged with many special features, which is believed to be a promising alternative to conventional UV lamps for water disinfection. This research focused on two special features of UV-LEDs, multiple wavelengths and pulsed irradiation, to explore the effect and potential on water disinfection.UV-LEDs in different UV wavelength ranges were combined in various manners to investigate the effect of multiple wavelengths on microorganisms inactivation in water. The results showed the effect of UV-LEDs multiple wavelengths depends on the wavelength combinations among UVA (315 – 400 nm), UVB (280 – 315 nm) and UVC (200 – 280 nm), the manner to apply different wavelengths (e.g. simultaneous, sequential), as well as different types of microorganisms (e.g. bacteria, virus). Combinations of UVC/UVB always achieved additive effect on microorganisms inactivation due to the same photochemical reactivation induced by UVC/UVB on DNA that follows the Second Law of Photochemistry. However, combining UVA with UVC/UVB simultaneously or applying UVA after UVC/UVB reduced the inactivation of bacterium E. coli due to DNA repair and photoreactivation effect of UVA. A special wavelength combination was developed by applying UVA as pretreatment followed by UVC inactivation, which achieved dramatic inactivation improvement and significant reactivation reduction on E. coli. The effects and mechanisms of this special combination were thoroughly investigated and revealed in this research.The effect of UV-LEDs pulsed irradiation was examined by applying pulsed irradiation with various pulsed patterns (frequency and duty rate) on different microorganisms in pure water and wastewater. Comparable inactivation were obtained by UV-LEDs continuous irradiation and various pulsed irradiation on all the four microorganisms examined, which clarified the role of pulsation on UV disinfection.The findings in this research promote a better understanding on UV disinfection and are of considerable significance to take full advantage of UV-LEDs for water disinfection.

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Application of ultraviolet (UV) radiation for water treatment has been increasing steadily in the past two decades. Further, significant improvements in semiconductor technology have made ultraviolet light emitting diodes (UV-LEDs) a viable alternative to conventional UV sources for water treatment. However, utilizing UV-LEDs for water disinfection comes with challenges related to their radiation measurements due to their specific structure, operation, and radiation pattern. Without a standardized measurement method, the efficacy of this new radiation source on the inactivation of waterborne microorganisms could not be determined accurately. In this study, in order to determine the fluence delivered to a microorganism’s solution, first, a method was developed to properly operate, control, and measure the output of the UV-LEDs. It was found that, not only the operational conditions affect the UV-LEDs output, but also the measurement techniques were critical in obtaining accurate results. Then, the radiation distribution was simulated. The radiation model was validated by two common measurement techniques, chemical actinometry and radiometry. Using the validated model, common radiation modeling presumptions such as the point source assumption and symmetry assumption for radiation profile of UV-LEDs were evaluated. Subsequently the radiation model and the operational method were implemented to develop a protocol for fluence determination of UV-LED systems. In this protocol, the average fluence was estimated by measuring the irradiance at a few points for a collimated and uniform radiation on a petri dish surface containing microorganism solution. Finally, the developed fluence determination protocol was tested in different setups to evaluate the radiation distribution and its effect on microbial inactivation kinetics measurements. A novel setup was presented for UV-LED kinetics studies; further, the inactivation kinetics of a common waterborne microorganism, E. coli, was measured. This study includes a fundamental holistic insight for fluence determination of UV-LED systems. The developed protocols for UV-LED operation and fluence determination studies help researchers to perform reliable UV-LED inactivation studies and obtain precise kinetics data.

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This dissertation uses molecular dynamics (MD) simulations to mainly focus on the study of the interaction between neutral surfactants-water and anionic surfactant-anionic polyelectrolyte on the water surface. Besides, this study devotes to finding the possible routes of improving the design of a drug candidate, polyethylene-glycol-linked cationic binding groups (PEG)n-HBG, to inhibit polyphosphate (polyP) thrombotic activities. It is found that the behavior of the nonionic polyoxyethylene glycol alkyl ether on the water surface is more anionic-like, even though the surfactant is overall neutral. The non-ionic surfactant increases the depth of the surface anisotropic layer and the average number of hydrogen bonds per water molecule. MD simulation showed that the negatively-charged O atoms have the most impact on the orientation of water as most water molecules arrange with their H atoms pointing toward the surface. In contrast, the behavior of the zwitterionic surfactant, N-dodecyl-N, N-dimethyl-3-ammonio-1-propanesulfonate, on the water surface is more cationic-like as the positively charged group is more capable of orienting interfacial water. The zwitterionic surfactant orients water molecules with their OHs mostly pointing toward the liquid water. While the complex formation between highly-charged surfactants and polyelectrolytes of the same charge is generally expected to be prohibited by the electrostatic repulsion, my study shows it is possible to form thermodynamically stable complexes in the presence of excess ions. With excess Na⁺ ions, the charge screening effect allows anionic polyelectrolyte to weakly interact with anionic surfactant via hydrogen bonds. In the presence of divalent Ca²⁺ ions, the surfactant and the polymer is strongly coupled by forming Ca²⁺ ion bridges and hydrogen bonds.The mechanism of complex formation between (PEG)n-HBG and polyP are studied using metadynamics simulations with the all-atom and coarse-grained force fields. It is shown that the PEG length does not have any impact on the interaction between the (PEG)n-HBG and polyP. However, it mostly improves the drug’s hemocompatibility by preventing the cationic drug from binding to other negatively- charged biomolecules. Increasing the number of the positive charges on the headgroup strengthens drug binding to polyP. It is found that the binding of (PEG)n-HBG remains intact against various lengths of polyP.

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Photocatalytic oxidation process has been demonstrated as an effective technology for the removal of micropollutants in water. This process, however, is greatly affected by the presence of natural organic matter (NOM) in natural water, which interferes with treatment process by absorbing UV radiation and scavenging oxidant species. This research focused on investigating the effect of NOM on the photocatalytic oxidation of 2,4-dichlorophenoxy acetic acid (2,4-D), as target contaminant at different pH. Experiments were performed in fluidized photocatalytic reactor using template free photocatalyst spheres.Changes in solution pH were used to decouple the effects of NOM on adsorption and major oxidative mechanisms, e.g., reactions on the surface of the photocatalytic spheres via positive hole mediation and in the solution via hydroxyl radicals (●OH) reaction. At pH 3, due to electrostatic attraction between solutes (2,4-D and NOM) and photocatalyst surface, photocatalytic oxidation mostly occurred via charge transfer on the surface of the photocatalyst. At pH 7, on the other hand, electrostatic repulsion between solutes and photocatalyst surface reduced adsorption and the process was primarily driven by hydroxyl radical reactions. The removal of 2,4-D reduced from 49% in the absence of NOM to 7% in the presence of 5 mgL-1 TOC NOM in neutral pH. At pH 3, this reduction was from 88% to 58%. It was observed that at neutral pH, due to higher aromatic moieties concentration and lower NOM adsorption, the effect of NOM on scavenging ●OH was considerable. This effect substantially decreased at low pH due to high adsorption of NOM.Higher 2,4-D removal at low pH was also due to the effect of pH on the kinetic of photocatalytic oxidation. Photocatalytic oxidation at pH 7 followed first order kinetic model. At pH 3, on the other hand, the rate of oxidation was a combination of first order and L-H models. Furthermore, the dependence of rate constants on UV intensity changed with pH; the rate constant was directly proportional to UV intensity at pH 3; whereas it is proportional to the square root of intensity at pH 7.

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Natural organic matter (NOM), a constituent in surface drinking water sources, requires removal to minimize its negative impacts on water quality and water treatment processes. Ion exchange (IEX) has been considered as an effective technology for the removal of NOM. However, despite many studies on the IEX removal of NOM, the removal mechanism and the molecular interactions involved in the IEX process are quite unknown due to the complexity of the NOM molecular structure. This research aimed to investigate the NOM removal with a focus on fundamentals underpinning the IEX process and the molecular interactions/forces that drive the retention of NOM onto the IEX resins. Different isolates of NOM along with some pure organic acids were studied. Hydrophobicity was found to play a key role in the removal process. The changes that the hydrophobic moieties impose to the structure of water molecules (i.e., entropy reduction) were found very influential in determining the selectivity of the IEX process. Moreover, the removal of UV-absorbing compounds (more hydrophobic fraction of NOM) was enhanced in the presence of sodium sulphate, as the electrostatic interactions are screened by added salt and consequently the entropic contribution to the removal is promoted. Nonetheless, the entropic contribution from the resin phase (i.e., hydrophobic resin backbone) was shown to negatively impact the removal of UV-absorbing compounds. Overall, combining the findings, it is concluded that the difference in the hydrophobicity (entropy) of the water and the resin phase is the main driving force in transferring NOM molecules from water to the resin. The contribution of the electrostatic and hydrophobic effects to the removal of NOM by IEX resins was further evaluated by quantitative characterization of the thermodynamic properties using isothermal titration calorimetry technique. The results confirmed the significance of entropic contribution to the removal of components with higher hydrophobic characteristics.Findings of this research provide a quantitative framework for the interpretation of the experimental results and facilitate the proper design of the IEX process for different water sources and under various conditions.

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The treatment of water via 185 nm radiation allows for the oxidative degradation of trace organic contaminants without the need for chemical addition.Critical information required for the practical application of such a processhas been lacking. Carbamazepine was determined to be an ideal probe compound for study of the 185 nm regime due to negligible direct photolysis at254 nm. An increase in probe degradation rate due to 185 nm is observedwith increasing temperature when water is the only significant absorber ofphotons. A comparison with the temperature dependence of the 254 nm -H₂O₂ process is made and a fundamental explanation proposed. Experimental evidence reveals that probe degradation rate is strongly influencedby anionic composition at environmentally relevant concentrations, particularly chloride. Evidence for the role of the chlorine radical is obtained bykinetic studies involving select probes, radical scavengers, and ionic strength.Interactions between the major organic and inorganic solutes indicate thatresulting degradation kinetics are highly sensitive to the composition of thewater matrix, a fact that has been neglected from the literature. A methodto quantify molar absorption coefficients is developed that is not prone toerrors due to stray radiant energy or wavelength inaccuracies. A method toquantify the 185:254 nm output of a low pressure mercury lamp is presentedwith results in agreement with values reported in the literature. In additionto the hydroxyl radical (*OH), other radical species such as chlorine (C1*) and sulphate (SO₄*¯) are proposed to be involved in oxidative degradationof trace organics in the 185 nm regime. This suggests that the degradation rate of a given target contaminant depends on the composition of the water matrix, the second-order rate constants with the relevant radicals, and the relative reaction rate constants of the target and the matrix.

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Water authorities are increasingly worried about the occurrence of organic micropollutants (e.g., algal toxins, endocrine disrupting compounds, pesticides, industrial chemicals, taste and odor compounds) in water supplies. Removal of organic micropollutants (OMPs) from water is cost-prohibitive, particularly for small and remote communities. Vacuum-UV/UV process, an incipient catalyst/chemical-free advanced oxidation process (AOP), is potentially a cost-effective solution for removal of harmful micropollutants from water. The main objective of this thesis was to investigate the feasibility of VUV/UV process for the removal of OMPs using a comprehensive computational fluid dynamics (CFD) analyzes. The developed model involved simultaneous resolution of the local transfer equations of momentum, mass, and radiative energy (for UV and VUV radiations), along with a complex kinetic scheme with more than 50 reactions. Given the importance of 185 nm and 254 nm emissions for the accurate modeling of the VUV/UV process, a new experimental method for measuring VUV and UV emissions of the mercury lamps was proposed. To assess the CFD model, VUV-induced degradation of model pollutants (atrazine, p-CBA) in ultrapure water samples was investigated under laminar flow conditions utilizing an axisymmetric laboratory-scale reactor. Afterwards, using an asymmetrical pilot-scale VUV/UV reactor, experimental validation of the CFD model was conducted for simulating the degradation of model pollutants (atrazine, 1,4-dioxane) in synthetic and natural contaminated waters under turbulent flow regime. Comparison of the modeling and experimental data indicated that the developed CFD model was able to predict successfully the degradation rate of target pollutants in the analyzed reactors. In addition, the proposed model showed to predict well the impact of the flow rates, and water matrix (NOM and alkalinity) on target pollutants degradation with less than 3 % average absolute relative deviation (AARD%). Relying on the insights gained by CFD analysis (e.g., knowing the critical role of pollutant mass transfer on the AOP performance of VUV systems), an improved VUV/UV process was developed through retrofitting baffles within the reactor. When compared the pollutant degradation and energy consumption of VUV/UV and H₂O₂/UV processes, superior performance of the improved VUV/UV process was observed.

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This research has investigated the factors influencing the kinetics and efficacy of natural organic matter (NOM) removal during the anionic ion exchange process (IEX). A holistic approach was undertaken to evaluate various IEX resins in terms of their NOM removal kinetics and regeneration efficiency under batch and consecutive multiple loading cycles. Initial screenings indicated the strongly basic resin as a better candidate for NOM removal, and hence it was employed for subsequent experiments.Different treatment parameters (resin dose, contact time, NOM source) were tested and detailed kinetic evaluations were conducted to determine the affinity and removal rate of NOM as well as nitrate, and sulfate that are generally present in natural waters. Results obtained showed a substantial removal of NOM (up to 80 %) and nitrate (up to 80 %), and a superior removal for sulfate (up to 98 %). Charge density and molecular weight were found to play a major role in the removal process. Different mathematical and physical models were employed to predict the experimental data and the rate-limiting step was found to be pore diffusion which was affected by the resin dose/solute concentrations ratio. Moreover, the impact of IEX resins on NOM fractions and subsequent water quality parameters was investigated in this study. Humic (-like) substances were mainly targeted by IEX, and more hydrophilic and/or non-ionic fractions were slightly removed. Application of IEX reduced the formation potential of carbonaceous and nitrogenous disinfection by-products by 13-20 % and 3-50 %, respectively. Also, the practice of IEX treatment reduced the assimilable organic carbon levels by 30-40 %. Additionally, a positive effect of IEX, as a pretreatment to UV/H₂O₂, at reducing the ⦁OH scavenging characteristics of the water was observed. Electrical energy per order for removing a probe compound (i.e., pCBA) showed 20-40 % reduction indicating the improvement in the efficacy of UV/H₂O₂ treatment.Findings of this study display the robustness of IEX process for drinking water applications and lay down a quantitative approach for evaluating the kinetics of this process under various treatment conditions.

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UV-based advanced oxidation processes (UV-AOPs) have been demonstrated as effective technologiesfor the removal of micropollutants in water. One promising UV-AOP is Vacuum UV (VUV), which relies on the formation of hydroxyl radicals (HO•) by the photolysis of water induced by VUV photons. TiO₂/UV photocatalysis is another promising AOP. Both VUV and UV photocatalysis are greatly affected by the water matrix, inorganic ions and natural organic matter (NOM). Water constituents can absorb the UV and VUV radiations, they can act as HO• radicals scavengers, and can produce radicals when photolyzed.The main objective of this research was to study the effects of water matrix on the efficiencyof VUV for the degradation of micropollutants (with atrazine as a model contaminant). First, theabsorbance of radiation at 254 nm and 185 nm was measured in the presence of different ionsand NOM. All the inorganic ions showed a molar absorption coefficient equal to zero at 254 nmexcept nitrate with a ɛ= 3.51 M−¹ cm−¹. On the other hand, at 185 nm all the ions absorbed185 nm radiation, with chloride showing the highest absorption coefficient ɛ=2791 M−¹ cm−¹.NOM showed a high absorption coefficient at both 254 and 185 nm ranging from 116 to 638 M−¹cm−¹ at 254 and from 1137 to 1537 M−¹ cm−¹ at 185 nm). Second, the HO• scavenging effectsof different components were evaluated; nitrate showed a detrimental effect both with UV/H₂O₂and with VUV. The presence of 50 ppm of bicarbonate reduced the degradation rate of atrazineconsiderably. Sulfate seemed to photolyze at 185 nm to form HO•. NOM was found to be a strongHO• scavenger : in the presence of 9 ppm (DOC) NOM, less than 1% of the HO radicals were available to react with atrazine. The next component of this work involved developing a method for the measurement of quantum yield of atrazine at 185 nm. This allowed to measure the degradation of atrazine due to photolysis only. Finally, this research investigated the combination of VUV with TiO₂/UV. The results showed that incorporating photocatalysis cannot improve significantly theefficacy of VUV.

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Pharmaceuticals, personal care products (PPCPs), endocrine disrupting compounds (EDCs), and disinfectant by-products (DBPs) in drinking water are all associated with potential health implications that warrant their removal and formation prevention during drinking water treatment. This work presents the results of several pilot scale studies carried out using; a) dual train conventional treatment processes of coagulation, flocculation, sedimentation, filtration (conventional); and b) (multistage) slow sand filtration (SSF); both coupled with ozone and advanced oxidation processes (AOPs) such as ozone/H₂O₂ and UV/H₂O₂ using natural water from three different sources. Removal of selected PPCPs and EDCs (as a group) was limited (on average 30%) by conventional treatment. On the contrary, ozone/H₂O₂ plus conventional was the most effective process (average of about 97%) to remove the selected PPCPs and EDCs, followed closely by ozone along with conventional treatment which was also very effective; however, at a slightly lower percent (average 95%) removal. Overall, ozone/H₂O₂ or ozone followed by conventional was very effective, irrespective of the raw water quality. However, the effectiveness of conventional treatment plus UV/H₂O₂ AOP was varied by raw water quality, resulting in reduced efficiency for lower raw water quality containing higher organics, bicarbonates, carbonates and particles. The average removal of PPCPs and EDCs with conventional plus UV/H₂O₂ treatment was about 86%. Experiments involving ozone or ozone/H₂O₂ followed by SSF also showed relatively high removals of target contaminants. On average, the removal rates of PPCPs and EDCs were around 95-100% for the combined processes. In comparison, stand-alone ozone or ozone/H₂O₂ showed removals of around 77% of PPCPs and EDCs. Reduction of disinfection by-products formations, measured as THM-FP (trihalomethanes formation potential), was also investigated over the course of all pilot studies and for each of the treatment scenarios. In most experiments, application of ozone/H₂O₂ and ozone alone upstream of the conventional led to additional reductions in THM-FPs as compared to that of the standalone conventional treatment. However, in most experiments, UV/H₂O₂, when applied downstream of the conventional process, increased THM-FPs of the conventionally treated water. SSF process showed to be effective and reduced 71% of THM-FPs.

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Passive air-breathing microbial fuel cells (MFC) are a promising technology for energy recovery from wastewater. The performance of the passive air breathing MFCs is dependent on the separator characteristics, isolating the anaerobic anode from the air-breathing cathode. The separator plays a more important role when the electrodes are placed in close proximity, to reduce the Ohmic resistance.The goal of the present work was to study the separator characteristics and its effect on the performance of passive air-breathing flat-plate MFCs (FPMFCs), through a combination of experimental and theoretical approaches. This was performed through characterization of 8 separators to investigate the ionic resistivity, oxygen and ethanol crossover, and proton transport number. The separators were then examined in three passive air-breathing FPMFCs with different electrode spacing, using three-dimensional graphite felt anodes and platinum-based cathodes. A numerical model was developed based on the mixed potential theory to investigate the sensitivity of the electrode potentials and the power output to the separator characteristics.The separator characterization indicated a greater susceptibility to oxygen and ethanol crossover in diaphragms, compared to the ion-exchange membranes (IEMs). Increasing the electrode spacing was also shown to be desirable for the application of diaphragms, as the anodic mixed potentials were reduced.The peak power density decreased by increasing the mass transfer coefficients of oxygen and ethanol in the separator. The model indicated that this was due to the increased mixed potentials at the anode, caused by the oxygen crossover. The mixed potentials at the cathode did not vary as the ethanol crossover increased, due to the slow kinetics of ethanol oxidation over Pt. The model also indicated that the peak power was affected by the proton transport number of the separator, which affected the cathode pH. The peak power was not sensitive to the resistivity of the separator due to the overshadowing effect of the oxygen crossover.The passive air-breathing FPMFC, using a 6 mm thick graphite felt anode, Pt-based cathode, and Nafion®117 membrane, showed the highest peak power density of ca. 0.52 W/m², which was higher than those reported for the active air flow FPMFCs in the literature.

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Electrocoagulation (EC), a disruptive “green” technology, was investigated for the removal of natural organic matter (NOM) from drinking water sources. Three anode materials (aluminum, zinc, and iron) and three NOM sources (Suwannee, Nordic, and a local source) were investigated. After one minute of process time, dissolved organic carbon (DOC) reduction was approximately 70-80%. High performance size exclusion chromatography (HPSEC) fractionation showed reductions mostly in the larger apparent molecular weight (AMW) fraction of NOM, from 76% of NOM > 1450 Da initially to approximately 40% after EC. For iron EC, significant EC design variables were investigated, including: current density (i) (2.43-26.8 mA/cm²), and charge loading rate (CLR) (100 to 1000 C/L/min). Optimum NOM removal was found at i ~10 mA/cm² and lower CLR. In-situ identification of iron speciation in EC investigated the impact of i and CLR on speciation and NOM removal from a local natural source. Low i and intermediate CLR increased bulk pH and reduced bulk dissolved oxygen (DO), where green rust (GR) was identified in-situ for the first time in EC by Raman spectroscopy. Further oxidation at higher i and CLR led to magnetite (Fe₃O₄) formation, while all other conditions led to increased DO and/or increased pH, with subsequent identification of only orange lepidocrocite (γ-FeOOH). GR showed the marginally higher NOM DOC and AMW fraction reductions. In synthetic water, differing operating parameters led to differences in φ and iron speciation, characterized by in-situ Raman spectroscopy, aqueous XRD, SEM, and cryo-TEM. High i in the presence of pitting promoters led to φ near unity where a GR intermediate was seen, and an end product of Fe₃O₄. A mechanism scheme summarizing EC speciation is proposed. A general model relating cell potential and current was developed for parallel plate continuous EC, relying only on geometric and tabulated variable inputs. For the model, the anode and cathode were vertically divided into n equipotential segments. Potential and energy balances were simultaneously solved for each vertical segment iteratively. Model results were in good agreement with experimental data, mean relative deviation was 9% for a low flow rate, narrow electrode gap, and polished electrodes.

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A computational fluid dynamics (CFD) model for the simulation of immobilized photocatalytic reactors for water treatment was developed and evaluated experimentally. The model integrated hydrodynamics, species mass transport, chemical reaction kinetics, and irradiance distribution within the reactor. For the development of this integrated CFD model, each of the above phenomena was individually evaluated against experimental data and proper models were identified. The experimental evaluation was performed using various configurations of annular reactors and UV lamp sizes, over a wide range of hydrodynamic conditions (350
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This thesis focused on the physical and chemical transformations undergone by natural organic matter (NOM) in two natural waters (from British Columbia, Canada) during ultraviolet plus hydrogen peroxide (UV/H₂O₂) advanced oxidation treatment as a function of UV fluence (up to 2000 mJ cm⁻­­­­­²­) and initial H₂O₂ concentration (up to 20 mg L⁻­­­­­­¹­). Under these conditions NOM was not mineralized but the hydroxyl radical (•OH) partially oxidized NOM leading to reductions in the chromophoric natural organic matter (CNOM) (i.e., NOM absorbing at 254 nm). NOM was degraded into more readily biodegradable compounds, such as aldehydes. An appreciable reduction in the very hydrophobic acid (VHA) fraction of NOM was observed. Considerable reductions in the formation potentials of trihalomethanes (THMs) or haloacetic acids (HAAs) were not observed. An increase in alkalinity slowed down the rate of degradation of CNOM during UV/H₂O₂. A dynamic kinetic model was developed to predict the degradation of CNOM. Model parameters were developed using isolated aquatic NOM from Suwannee River. For the two natural waters, the model adequately predicted the degradation of CNOM as a function of initial H₂O₂ concentration, irradiation time (i.e., UV fluence). Including the reduction in CNOM improved the modeling of H₂O₂ degradation, but H₂O₂ degradation was still slightly under predicted. For water that had undergone ultrafiltration (UF), NOM was readily mineralized during UV/H₂O₂ treatment due to the absence of high molecular size NOM. For water from which the VHA fraction of NOM was removed, UV/H₂O₂ treatment led to mineralisation of NOM suggesting that, when coupled with a pre-treatment capable of removing a large portion of the VHA fraction, UV/H₂O₂ can achieve reductions in TOC.Combining UV/H₂O₂ with downstream biological activated carbon (BAC) filtration led to reductions in NOM and formation potentials of THMs and HAAs. Formaldehyde and H₂O₂ were effectively removed by BAC.Development of a method for the determination of assimilable organic carbon (AOC) in UV/H₂O₂ treated water concluded that manganese dioxide was a suitable agent for the removal of H₂O₂ prior to AOC analysis. The method was applied to observe an increase in AOC as fluence increased during UV/H₂O₂ treatment of raw water.

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