Chemical Engineering

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This is the collection for the University of Waterloo's Department of Chemical Engineering.

Research outputs are organized by type (eg. Master Thesis, Article, Conference Paper).

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Now showing 1 - 8 of 8

Antibacterial and Mercury Detection Abilities of Triangular Silver Nanoparticles
(University of Waterloo, 2016-08-30) An, Ran; Anderson, William
Silver nanoparticles (AgNPs) have been studied for a long time, because of their significant application in photonics, drug delivery, biological medicine, wastewater treatment, antimicrobials, catalysis and sensors. This is due to their inherent electronic, physicochemical, biological, and visual properties, which are determined by their size, shape, composition, crystallinity, and structure. This study focuses on the synthesis of triangular silver nanoparticles, and functionalization by the biopolymer Poly-L-lysine (PLL). NaBH4 reduced triangular AgNPs were successfully synthesized, and attached by Poly-L-lysine (PLL). The morphology of AgNPs and AgNP-PLL was measured by transmission electron microscopy (TEM). The results of UV/Vis-spectroscopy, zeta-potential and dynamic light scattering (DLS) indicate that the AgNP-PLL have the property of broad-spectrum activity for both Gram-negative bacteria and Gram-positive bacteria. The bacteria tests show good results, such that when AgNP-PLL was applied to the tested bacterial strains, E. coli decreased 97.27 %, P. aeroginosa decreased 99.2%, B. subtilis decreased 99.14%, and S. aureus decreased 94.6% in 4 hours. Toxic heavy metals have been considered to be one of the contaminants of concern in certain aqueous solutions. Polyvinylpyrrolidone (PVP) stabilized triangular AgNPs were developed for the detection of mercury (II) (Hg2+). AgNPs were characterized via TEM, DLS, and UV-Vis spectrophotometry, proving that the shape of the AgNPs are triangular with an intense surface plasmon resonance, and the zeta potential results indicate that the negative surface charge of the AgNPs (-27.6 mV) can attract Hg2+. In a selectivity study, four kinds of heavy metals ions (Cr3+, Pb2+, Cd2+, and Hg2+) were applied in de-ionized (DI) water. It was shown by TEM and UV-Vis spectrophotometry that the AgNPs were specific for Hg2+, which acted as a bridge to induce AgNPs aggregation. The minimum effective concentration (MEC) that could be detected by the aggregation of these AgNPs was 0.938 M, ( 188.2 ng Hg2+/mL water). The optimal working pH range of the AgNPs for Hg2+ detection was pH 7.5 to 10. From a study with tap water spiked with Hg2+ ions, AgNPs were slightly disturbed by ions in the tap water, but the sensitivity towards Hg2+ was exceptional (minimum effective concentration (MEC) is 1.25 M).
Antimicrobial activity of polyethyleneimine/polyurethane (PEI/PU) colloidal films
(University of Waterloo, 2021-08-27) Liu, Minghui; Zhao, Boxin; Anderson, William
With the occurrence of healthcare associated infections (HAIs), the development of novel antimicrobial materials has drawn significant research attention. However, developing an antimicrobial material that can be long-term effective and environmentally friendly without cytotoxicity is still a technical challenge and normally results in large production costs. In this thesis research, we fabricated, characterized and evaluated a polyethyleneimine/polyurethane (PEI/PU) colloidal film for antimicrobial coating applications. Following the previous work in our group, the colloidal film was obtained by introducing polyethyleneimine into a waterborne polyurethane. This colloidal film was found having excellent mechanical properties. From tensile tests it was found that the PU/PEI composites displayed superior mechanical properties compared to pure PU with an ultimate tensile strength of 23 MPa compared to 18 MPa for pure PU. In addition to tensile tests, scratch tests were performed on the coatings. It was found that at 5 wt% PEI the coatings displayed the best abrasion resistance at 2000 g of applied force on the tip compared to 1200 g for pure PU. The antimicrobial activities were investigated in this work with the hypothesis of PU/PEI colloidal films being a dual-functional antibacterial material. The ion-releasing activity and contact-killing efficiency of PU/PEI colloidal films were tested separately. Though there have not been conclusive results showing the existence of ion-releasing antibacterial working principle, a high killing rate of contact-active antibacterial activity was observed. Furthermore, explorative evaluations were performed to check possible virucidal effect against baculovirus.
Characterization and Improvement of Oxygen Mass Transfer in a Rocking Disposable Bioreactor
(University of Waterloo, 2020-06-04) Bai, Yun; Anderson, William; Moo-Young, Murray
Rocking disposable bioreactors use a cyclic rocking motion to induce mixing and oxygen transfer from the headspace gas into the liquid and are a novel type of bioreactor currently suitable for smaller-scale cell growth. At present they are used primarily for mammalian cell cultures. There are still unresolved knowledge gaps which render the broader applications of rocking disposable bioreactors challenging. These include adequate understanding of the gas-liquid mass transfer mechanism and the lack of quantitative correlations between the mass transfer capacity (to satisfy oxygen demand of a culture) and critical operational parameters, notably for scale-up applications in industry. This knowledge gap creates barriers for rational scale-up and application of these bioreactor systems in industrial biotechnologies. Industry is also interested about the applicability of these bioreactors to aerobic microbial fermentation processes which are faster than mammalian cultures for production of certain biological products. In this work, the oxygen transfer pathways in a rocking disposable bioreactor were analyzed and a semi-empirical correlation for mass transfer coefficient based on a prediction (kLa) model was developed that account for two types of aeration mechanisms, namely surface aeration and aeration via a breaking wave with air entrainment. Experimental kLa data across a range of possible operating conditions (rocking speed, angle, and liquid volume) supported the modelling approach, with most predictions falling within ±20% of experimental data. At low speeds (up to 20 rpm) the surface aeration mechanism was shown to be dominant with a kLa value of around 3.5 h-1, while at high speeds (40 rpm) and angles the breaking wave mechanism contributed up to 91% of the overall kLa (65 h-1). This model provides an improved mechanistic understanding of gas-liquid mass transfer for the operation, scale-up and potential design improvements for rocking bioreactors for aerobic fermentation processes. Secondly, an electrical method was applied for measuring the specific power input into the liquid of the disposable rocking bioreactor at benchtop scales of 10 and 20 L volume capacities. Although power input varied periodically with the rocking motion, the peak power input was shown to be suitable for characterizing the impact of various operational parameters including rocking frequency, rocking angle and liquid volumes. The average power inputs measured in this work ranged from 66.5 W/m^3 to 680.1 W/m^3 which were comparable with power inputs reported in the literature for stirred-tank and orbitally-shaken disposable bioreactors. The kLa was shown to correlate with the peak power input in a power law model, which confirmed that the gas-liquid mass transfer capacity rapidly improved as the power input increased, especially for power inputs of 600 W/m^3 and greater. The correlation between mixing time and power input indicated that a power input greater than 400 W/m^3 was more than enough to induce rapid mixing in the bioreactor. Two potential improvements in the bioreactor design were tested for their capability to enhance the mass transfer capacity of rocking disposable bioreactors. First, an external rod baffle was installed diagonally on the rocking tray aiming to divert the dominant limited unidimensional liquid flow into both longitudinal and horizontal directions. This imposed diversion was shown to be very effective in reducing the mixing time of the bioreactor especially for liquid loadings at 50% of the total bag volume. The kLa however was reduced, especially when the rocking frequency was intensified to 30 and 40 rpm and the rocking angle was increased to 12 degrees This reduction was due to a diminished strength of the waves generated in the bioreactor which impacted the dominant mechanism contributing to the kLa. Secondly, a submerged sintered polyethylene tube sparger was installed into the bioreactor to improve its oxygen gas-liquid mass transfer capacity. The gas flow condition and sparger surface wettability were changed to study the impact of these variables on the sparger performance. The results showed that the sparger could effectively increase the kLa of the bioreactor up to 8-fold when the rocking intensity was low with larger liquid volumes, but the improvements were diminished as the rocking intensity increased. The kLa of the modified bioreactor was observed to depend on the air flow but was not strongly affected by the sparger surface wettability unless the superficial gas velocity was decreased. Based on the progress in this study, future research is recommended for testing the applicability of the derived mass-transfer mechanistic models at larger scales, examining the proposed improvements on various types of cell cultures, especially aerobic microbial fermentations, and combining the modified bioreactor design with other process intensification techniques such as with perfusion and with microcarrier systems.
Development of Alternative Protocols for Antimicrobial Efficacy Testing of Antimicrobial Surfaces
(University of Waterloo, 2020-12-17) Nwaiwu, Joseph; Anderson, William
Self-disinfecting surfaces have been studied for a long time for use in reducing the occurrence of infections. Several industries are focused on manufacturing antimicrobial products with high toxicity to microbes for contact killing. However, when these products are manufactured, they need to be tested to determine their antimicrobial efficacy before they can be sold for public use. This study focuses on developing fast and accurate protocols to determine the antimicrobial efficacy of antimicrobial products and can be useful for irregular or larger surfaces where some regulatory protocols based on small coupons cannot be applied. Three different protocols were developed and their results for testing antimicrobial products using industrially manufactured samples against E. coli and P. aeruginosa were compared to results obtained from a coupon-based method which is similar to the EPA protocol. Protocol 1 (modified EPA protocol) was used as the control, for comparison with other protocols and this protocol involved applying bacteria solution on a test surface coupon for 1-hour contact time, the test surface was then placed in a beaker containing phosphate buffered saline (20 µl), sonicated for 5 minutes, then bacteria solution was plated on agar plates and incubated. Protocol 2 involved applying bacteria solution on a test surface for 1 hour, then the bacteria solution was retrieved using a pipette, dilutions were made, plated and incubated. Protocol 3 involved applying bacteria onto the test surface, then the test surface was inverted onto an agar plate surface, left for 1-hour contact time, then surface was removed, and plate incubated. Protocol 4 involved applying bacteria onto test surface and left in contact for 1 hour, then stamped onto an agar surface for 30 seconds, removed and incubated. The results from comparing the log reductions and killing percentages from these protocols show that protocol 4 show the best comparison for both microorganisms, compared to results from protocol 1 and possesses less coefficient of variation calculations in all cases. Protocol 2 shows good comparison with results from the Protocol 1 however, there is higher coefficient of variation while protocol 3 did not correlate with results from the Protocol 1 when bacteria is applied on a pure copper surface. Plate counting techniques are the widely used for enumeration of live bacteria. It involves plating microorganisms on an agar plate, incubation for 24 – 48 hours then counting of colonies formed. Obtaining results using this technique takes time and can be inaccurate sometimes depending on the concentration of plated microorganism. An accurate flow cytometry FCM technique was developed to determine the antimicrobial efficacy of test samples. Microbial solution (E. coli, P. aeruginosa and Saccharomyces cerevisiae) stained with calcein am dye was analysed with a flow cytometer. FCM results showed correlation with plate count results when the microbial solution was diluted to 104 CFU/ml without application on a copper surface but failed to correlate with plate count results when bacterial solution was exposed to copper, due to the interaction between calcein AM and copper. So, another technique involving staining 106 CFU/ml yeast solution with propidium iodide after exposure to copper surface and comparing with plate count results was studied. This technique was used to accurately predict the log reduction of yeast applied on some industrially manufactured antimicrobial samples with a maximum underestimation and overestimation range of -0.33 and 0.48.
Examination of binding elements and conditions of Cryptosporidium parvum oocysts to assess its detection potential in water
(University of Waterloo, 2022-09-29) Rodriguez Ruiz-Andino, Irene; Anderson, William; Aucoin, Marc
Cryptosporidium parvum is an intestinal parasite that can be spread through environmental and recreational waters, most often in the form of oocysts. As an oocyst, this parasite is resistant to chlorine disinfection, and it is the known cause of the diarrheal disease Cryptosporidiosis. In this thesis, binding elements like antibodies and aptamers are studied and compared with the purpose of assessing their binding under different conditions and therefore their potential as biorecognition elements to detect C. parvum in water. Several methods have been used to fulfill this purpose. Flow cytometry and imaging flow cytometry was used to compare and assess the binding of commercial fluorescently labelled antibodies, and aptamers reported in literature, under different conditions such as pH, inactivation procedures or heat-inactivation contact time. Horseradish peroxidase (HRP)-labelled antibodies was used to assess the colorimetric potential for Cryptosporidium detection both as a part of an in-filter detecting scheme and to assess the binding differences between live and inactivated Cryptosporidium. It was found that antibodies had better binding affinity than aptamers for Cryptosporidium that was inactivated under different methods such as desiccation, heat-treatment, freeze-treatment, and formalin-treatment. Furthermore, aptamers show an increase of non-specific binding under low pH conditions. An in-filter detection method involving the preincubation of HRP-labelled antibodies with the target and passing this solution through a syringe filter followed by the addition of 3,3',5,5'-Tetramethylbenzidine (TMB), which could allow visual observation of a color change, was also explored. This biosensor was developed as part of a detection scheme to avoid any detection sensitivity loss due to poor recovery from filters and was meant to help make detection simpler for the public. The limit of detection of this approach was found out to be 105 oocysts/mL . While this limit of detection is rather high, improvements could be made by changing the labelling of the antibodies or by changing the type of antibodies.
Photocatalytic Oxidation of Anesthetic Gases
(University of Waterloo, 2020-08-27) Srinivasan, Shruthi; Anderson, William
Inhaled anesthetics used in surgeries are typically volatile halogenated hydrocarbons. In a typical situation only 5% of the administered anesthetic is metabolized by the human body, while the remaining 95% is exhaled through the ventilation systems eventually into the environment as it is. The anesthetics contribute to global warming and stratospheric ozone depletion. This research focuses on using advanced oxidation processes as a treatment system for the common anesthetic gases namely Halothane, Sevoflurane and Isoflurane. The first step was to determine an appropriate reactor setup which could contain the light source and the catalyst medium with an accessible sampling port. The loss of anesthetic gas due to leaks and wall effects were measured and considered to be a baseline for further tests. In developing a treatment system, UV-photolysis, UV-ozonation, and UV-photocatalysis were tested in different batch experiments using Halothane, and UV-photocatalysis was found to be the most effectiveadvanced oxidation process among the ones tested. Since UV-photocatalysis was efficient in degrading ~ 99.9 % of the anesthetic gas in 20 min, the influence of several parameters such as the type of catalyst, the type of catalyst support surface, the catalyst loading, the incident light wavelength, the power of the incident light, catalyst surface area illuminated, inlet reactant concentration and the moisture content on the degradation efficiency of UV-photocatalysis was tested. Based on the results obtained UV-photocatalysis with the appropriate conditions was used to test the degradation of Isoflurane and Sevoflurane. The post oxidation contents of the reactor with Isoflurane and Sevoflurane were measured using Ion Chromatography for their anion concentration and a possible degradation mechanism was suggested for their photocatalytic degradation in the presence of TiO2.
Reducing Environmental Impacts of The Petroleum Refining Operations: Studies Related to Water Treatment and Carbon Dioxide Emissions Management
(University of Waterloo, 2018-12-21) AL-SHEIKH, FAROOQ; Elkamel, Ali; Anderson, William
Petroleum refining is one of the most important chemical processing industries, converting crude oil into many usable and useful products, but it can cause adverse environmental impacts. Two environmental issues were addressed: i) reducing ammonia concentrations in wastewater and ii) reducing selected carbon dioxide emissions using carbon capture technology. Ammonia removal during waste water treatment is important because of its potential toxic effects in aqueous environments. Although biological treatment is generally favourable, its application in cold climates is ineffective due to slow kinetics. An adsorption process is one viable alternative process that can be used to reduce ammonia concentrations, and accordingly 10 commercial ion exchange resins and 6 zeolites were tested to assess their effectiveness for the removal of ammonia from real polluted water samples (3.8 to 8 mg/L NH3−N) containing other cations. In subsequent tests, the performance of six selected adsorbents was further characterized using Langmuir, and Freundlich isotherm and pseudo-1st, and pseudo-2nd order kinetic models. The results showed that the Dowex resin was best characterized by the Langmuir isotherm while LEWATIT resin, AZLB-Na and NV-Na zeolites were by the Freundlich one. Also, each adsorbent was best characterized by pseudo-2nd order kinetics. Adsorbent equilibrium capacities in the range of 0.2 to 0.4 mg/g were determined for ammonia concentrations of approximately 1 mg/L. Because of its high selectivity towards ammonia, a LEWATIT S 108 H resin was tested to assess its effectiveness in the batch and continuous adsorption of ammonia from the real wastewater. Batch adsorption tests were conducted using different masses of LEWATIT for 22.7 mg/L (NH3−N) wastewater and the equilibrium data so obtained were characterized using Langmuir and Freundlich isotherms to obtain model constants. Continuous adsorption tests were then carried out in two different sized fixed-bed-glass columns to obtain breakthrough curves. Also, ammonia desorption from LEWATIT was achieved using (5:100 w/v) HCl with an efficiency of approximately 50%. The Bohart-Adams and Thomas models were used to fit the experimental breakthrough curves for finding model parameters. The results show that the LEWATIT performance can be well-characterized by both the Bohart-Adams and Thomas models in the fixed-bed column. For comparison, a column was loaded with the AZLB-Na zeolite to generate a breakthrough curve, and the desorption process was achieved using sodium hydroxide. Bohart-Adams and Thomas models were employed to find model parameters that would describe the breakthrough curve of the adsorption process. These were then compared with experimental results, showing good agreement. With respect to carbon dioxide emissions, the Fluid Catalytic Cracking (FCC) unit was the focus because it causes the bulk of the CO2 emissions in a refinery (around 30%). Simplified mathematical models were derived using static and dynamic heat balances of both the reactor and regenerator. The main purpose of studying dynamic responses was to find the most influencing flow rates and their lower/upper limits to ensure that reactors/regenerator temperatures work within normal operating conditions, which are used as side constraints in the optimization technique. In the regenerator where combustion takes place, two systems were examined: post-combustion and oxy-combustion since percentages of the CO2 content differ. In an oxy-combustion system, the CO2 captured will not only be sequestered but also will be used as a side stream to the FCC unit since the operation will be continuous.
The Role of Germicidal Ultraviolet Light in the Formation of Secondary Organic Aerosols
(University of Waterloo, 2017-09-26) Choi, Eureka; Anderson, William; Tan, Zhongchao
Ultraviolet (UV) light with a wavelength of 254 nm has proven to be effective at inactivating microorganisms, and thus has been increasingly employed as a method of disinfection of indoor environments. UV light with wavelengths of over 300 nm is known to promote the formation of secondary organic aerosol (SOA) particles. The portion of UV light produced by the sun that penetrates into the Earth’s atmosphere has wavelengths of over 300 nm, and is observed to promote SOA formation within the Earth’s atmosphere. The majority of SOA particles can be classified as fine particulate matter, or particles with diameters of 2.5 μm or smaller. The particles of fine particulate matter are of particular concern for human health, as they are associated with enhancing infectious diseases, causing allergic effects, and promoting respiratory and cardiovascular conditions. Germicidal UV treatment, using UV light with a wavelength of 254 nm, is commonly used for the purpose of improving air quality and reducing the transmission of infectious microorganisms. Thus, it is often used in environments such as hospitals, where there are individuals with weaker or compromised immune systems, and thus more susceptible to a variety of negative health effects. As such, these individuals would also be at higher risk for the health effects associated with exposure to fine particulate matter. Therefore, it is of importance to determine if the use of germicidal UV treatment in indoor environments will promote significant SOA formation. SOA particles are formed as a result of gas phase oxidation of volatile organic compounds (VOCs), and various types of VOCs are commonly found in almost all indoor environments. In this work, toluene was selected as the representative VOC to be tested. In the experiments, mixtures of air and toluene were exposed to 254 nm UV light, varying the conditions of the air, the amounts of toluene added, the duration of UV exposure, and the duration of post-UV recirculation. The amount of particles formed in the fine particulate matter size range were measured for each experiment. Significant levels of particle formation were observed for UV exposure periods of as short as 5 minutes. The particle formation levels ranged from 2.383 particles/cm3 for 5 minutes of UV exposure, to 1449.76 particles/cm3 for 15 minutes of UV exposure. Particle formation was found to increase with increasing concentrations of gas phase toluene, as well as increasing durations of UV irradiation. Higher levels of relative humidity also resulted in increased particle formation and growth. However, the amount of recirculation time after UV exposure did not appear to have a significant effect on the level of particle formation. The initial amount of ambient particles present prior to UV exposure varied from 3.781 particles/cm3 to 27.082 particles/cm3, and was found to correlate positively with the relative humidity of the air. Variations in the initial amount of particles present over this range did not have an effect on the amount of particle formation. Overall, in this work, it was determined that exposure of toluene to 254 nm germicidal UV light does result in SOA particle formation.

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Browsing Chemical Engineering by Author "Anderson, William"