Browsing by Subject "Drinking water treatment"
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Item Adhesion of silver nanoparticle amendments to ceramic water filters(2015-08) Mikelonis, Anne Marie; Lawler, Desmond F.; Katz, Lynn E; Kirisits, Mary Jo; Kovar, Desiderio; Willets, Katherine A.Silver nanoparticles (Ag NPs) are frequently added as a disinfectant to ceramic filters used for household drinking water treatment. To provide suspension phase particle stability, Ag NPs can be synthesized using a number of different molecules to cap the metal core. The goal of this doctoral work was to advance the fundamental understanding of how stabilizing agents influence the attachment and detachment of Ag NPs from ceramic water filters. To achieve this goal, deposition experiments onto Al₂O₃ membranes and clay-based ceramic filters were performed using Ag NPs stabilized by three different agents: citrate, polyvinylpyrrolidone (PVP), and branched polyethylenimine (BPEI). Laboratory and field- scale filtration experiments were also conducted to evaluate the removal of Ag NPs from ceramics under different water conditions -- the presence of hardness and natural organic matter (NOM). Citrate-stabilized Ag NPs were found to have the highest attachment densities, regardless of filter material. Differing attachment densities for the three types of Ag NPs were extensively explained using a combination of classic Derjaguin, Landau, Verwey and Overbeek (DLVO) theory, steric forces, and particle-particle interaction energy calculations. A multilevel statistical model was built to describe the removal of Ag NPs from ceramic water filters under different water conditions. The type of Ag NP was found to affect the initial release of Ag from the filters, while the interaction of the type of Ag NP and water were found to affect the rate of removal. Hardness and NOM prolonged the release of Ag from ceramic water filters.Item Catalytic nitrate reduction in drinking water using a trickle bed reactor(2016-05) Bertoch, Madison; Werth, Charles J.; Lawler, DesmondPalladium-based bimetallic catalysts hold promise as an alternative water treatment technology for nitrate (NO3-), but practical application requires development of a flow-through reactor that efficiently delivers hydrogen (H2) from the gas phase into water, where it serves as the electron donor for NO3- reduction. In this work, a trickle bed reactor (TBR) was fabricated and evaluated to address this challenge. A series of batch experiments with Pd-In/γ-Al2O3 catalysts were conducted in excess H2 to identify a highly active catalyst for the TBR. A 0.1wt%Pd-0.01wt%In on 1 mm γ-Al2O3 catalyst was selected due to its high activity and support size that promotes a uniform liquid distribution in a packed bed. The TBR was packed with the same catalyst, and various liquid and gas flow rates were tested to evaluate apparent catalyst activity. Influent and effluent NO3- concentrations were used to calculate apparent zero-order rate constants, and they generally increased with H2 flow rate. Above 900 mL/min, a change in flow regime from pulse to bubble flow was observed, and the calculated zero-order rate constants decreased. An optimal catalyst activity in the TBR of 19.5 mg NO3-/min∙g Pd was obtained at a liquid flow rate of 900 mL/min and H2 flow rate of 320 sccm, which is ~22% of the activity obtained in the batch reactor by the same catalyst, indicating H2 mass transfer limitations. A reactive transport model was developed and used to quantify H2 mass transfer rate coefficients from the liquid to gas phase. Mass transfer coefficients initially decrease and then stabilize as the H2 flow rate increases. At elevated H2 flow rates, the highest mass transfer coefficients were obtained at the 900 mL/min liquid flow rate, in agreement with activity trends. Evaluation of a larger range of liquid and gas flow rates is warranted to determine if H2 mass transfer in the TBR can be further enhanced.Item Chemical usage and savings at the Austin Water Utility drinking water treatment plants(2012-05) Dobbertien, Matthew Francis, 1988-; Lawler, Desmond F.; Katz, LynnThe goal of this research was to maintain excellent water quality at reduced chemical operations cost. Chemical usage data at the Austin water treatment plants were examined by identifying trends and investigating suspected inefficiencies. The investigation consisted in jar test experiments, plant-scale experiments, and equilibrium modeling. Lime and ferric sulfate were suspected to be added inefficiently with respect to cost while the other treatment chemicals were assessed to be added efficiently. Lime was investigated in greater depth than ferric sulfate because ferric sulfate was better characterized in its effect on finished water quality within the range of interest. The goal of lime addition is to remove hardness from the water by a process called lime softening. Hardness removal decreases corrosion in transmission lines and prevents deposition of unwanted solids in household appliances. Additionally, lime softening aids in particle removal and disinfection-by-product precursor reduction. The efficiency of lime addition was evaluated based on settled water pH and causticity goals, which serve as the operating parameters for the water treatment plants. The most efficient lime softening occurs when multiple softening goals are simultaneously achieved. First, the dissolved calcium concentration must achieve a minimum. Second, the dissolved magnesium concentration must be reduced by at least 10 mg/L as CaCO₃. Third, total alkalinity must be preserved at its maximum concentration while also achieving excellent hardness removal. Fourth, natural organic matter (NOM), which serves as a precursor for disinfection-by-products, must be removed sufficiently to achieve DBP reduction goals. Finally, the turbidity in the effluent from the settling basin must be below 2.0 NTU. Through the chemical investigation of lime based on existing scientific literature, computer modeling, jar test experiments, and full-scale testing, it was determined that the optimal condition operating condition for lime softening was a settled water pH range from 10.0 - 10.1.Item Significance of trihalomethanes in preventing distribution system nitrification(2007-08) Bayer, Benjamin Morrey; Speitel, Gerald E.Chloramination is popular in drinking water treatment because it can provide microbial control, but unlike chlorination it results in much less formation of disinfection by-products (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs). Unfortunately, nitrification in drinking water distribution systems is a widespread issue when chloramination is employed as a residual disinfection process. Nitrification is undesirable because the disinfectant residual can be lost and re-growth of bacteria may occur. Nitrification is a well understood process where ammonia-oxidizing bacteria (AOB) oxidize ammonia into nitrite (NO2-), which is then converted to nitrate (NO3-) by nitrite-oxidizing bacteria (NOB). Recent research has shown that AOB are able to biodegrade THMs through an enzymatic process known as cometabolism. The cometabolism by-products are highly reactive substances thought to be capable of either damaging or killing AOB. These observations led to a working hypothesis that under certain conditions and THM concentrations, THMs play a significant role in preventing distribution system nitrification. This research was composed of two distinct tasks aimed at determining how background concentrations of THMs, in the absence of residual disinfectant, impact nitrifying biofilms in a mock distribution system under ideal conditions for microbial growth. For the first task, nitrifying biofilms were developed in annular reactors and were challenged by increasing concentrations of THMs until nitrification was halted. In the next task, THMs were continuously fed to the reactors to determine the concentration of THMs necessary to prevent the initial onset of nitrification. The results from these experiments will be used to design future experiments to investigate the coupled effects of monochloramine and THMs in preventing the onset of nitrification. The goal of this research is to advance our understanding of distribution system nitrification by examining the role that THMs play. This improved understanding will allow utilities to more accurately assess the potential for nitrification in their distribution systems and to anticipate nitrification problems that may arise as a result of treatment process modifications.Item Synthesis of palladium-gold alloy nanoparticle catalysts for the reduction of nitrite in water(2016-05-06) Seraj, Sarah; Werth, Charles J.; Humphrey, Simon M.Hydrogenation using palladium-based (Pd-based) catalysts has emerged as a promising treatment method for nitrate in drinking water. However, low catalytic activity and longevity can be a barrier to widespread adoption over conventional treatment methods. Controlling catalyst structure at the molecular scale is one approach to improving catalytic activity and longevity. Intermetallic palladium-gold nanoparticle (PdAu NP) alloy catalysts of varying composition were synthesized for nitrite reduction using a polyol reduction method and microwave-assisted heating. The average size of PdAu NPs was 4.1 ± 2.2 nm. Enhanced nitrite reduction has been previously observed for Pd combined with Au in a core-shell NP structure, but has not been studied for intermetallic PdAu alloy NPs. Moreover, the mechanism by which Au enhances Pd-catalyzed nitrite reduction is not well understood. The PdAu NPs were loaded into an amorphous silica support and evaluated for nitrite reduction in a batch reactor. Reaction followed pseudo first-order kinetics for greater than 80% of conversion. Catalyst activity showed volcano-like behavior with varying composition .... All PdAu alloys were significantly more active for nitrite reduction compared to pure Pd NPs, despite Au being catalytically inactive for hydrogenation. Sulfide fouling and catalyst longevity studies were conducted. The presence of Au in the catalyst structure did not appear to enhance resistance to sulfide fouling. Moreover, catalyst activity was reduced upon repeated cycles of nitrite reduction. Further investigation is required to understand the mechanism for catalyst deactivation.