The ubiquitous use of antibiotics has led to an increasing number of antibioticresistant bacterial strains, including strains that are multidrug resistant, pathogenic, or both. Numerous studies have been conducted showing the presence of antibioticresistance genes (ARGs) and antibiotic-resistant and multidrug resistant bacteria in wastewater and drinking water treatment plants. There is also evidence to suggest that ARGs spread to the environment, and to humans and animals, through wastewater effluents. The overall objective of this study was to investigate the effect of UV light disinfection on ARGs and antibiotic resistant bacteria. Wastewater effluent samples from a wastewater treatment plant (WWTP) in Texas were evaluated for differences in abundance and diversity of tetracycline resistant bacteria before and after UV treatment. The effects of photoreactivation or dark repair on the reactivation of bacteria present in WWTP effluent after UV disinfection were also examined. Culture based methods were used to characterize viable heterotrophic, tetracycline resistant heterotrophic, E. coli, and tetracycline resistant E. coli bacteria present before and after UV treatment. Molecular methods were used to characterize the diversity of organisms present and to test for the presence of tet(Q), a tetracycline resistance gene associated with human origins. UV disinfection was found to be as effective at reducing concentrations of resistant heterotrophs and E. coli as it was at reducing total bacterial concentrations. The lowest survival ratio following UV disinfection was observed in tetracycline-resistant E. coli, showing it to be particularly susceptible to UV treatment. Photoreactivation and dark repair rates were found to be comparable to each other for all bacterial populations. UV disinfection was found to significantly alter the community composition of tetracycline-resistant bacteria, though it did not have the same effect on the total bacterial community.

Wastewater microbial flocs can protect microorganisms from inactivation by UV light. This effect is detected as tailing at high UV doses in the UV dose response curve. A double-layer structure composed of an inner compact core surrounded by a loose outer layer was proposed by earlier studies to describe UV resistance of microbial flocs. Due to limited oxygen diffusion into the compact cores, the UV inactivation of compact cores and microbial flocs under anaerobic conditions needed to be addressed. The UV disinfection kinetics under anaerobic culturing condition was nearly identical to that of the aerobic study. Moreover, the role of iron concentration on the differences in the UV inactivation kinetics of flocs and cores was assessed. The increase in UV absorbance of floc material due to iron addition could dominate the UV disinfection kinetics of flocs and cores such that they exhibited similar UV disinfection kinetics.

Wastewater microbial flocs can protect microorganisms from inactivation by UV light. This effect is detected as tailing at high UV doses in the UV dose response curve. A double-layer structure composed of an inner compact core surrounded by a loose outer layer was proposed by earlier studies to describe UV resistance of microbial flocs. Due to limited oxygen diffusion into the compact cores, the UV inactivation of compact cores and microbial flocs under anaerobic conditions needed to be addressed. The UV disinfection kinetics under anaerobic culturing condition was nearly identical to that of the aerobic study. Moreover, the role of iron concentration on the differences in the UV inactivation kinetics of flocs and cores was assessed. The increase in UV absorbance of floc material due to iron addition could dominate the UV disinfection kinetics of flocs and cores such that they exhibited similar UV disinfection kinetics.

<p>Rapid growth of energy consumption and greenhouse gas emissions from fossil fuels have promoted extensive research on biofuels. <a>Algal biofuels have been considered as a promising and environmentally friendly renewable energy source</a>. However, several limitations have inhibited the development of cost-effective biofuel production, which includes unstable cultivation caused by invading organisms and high cost of lipid extraction. This dissertation aims to investigate photochemical approaches to prevent culture collapse caused by invading organisms and biological approaches for the development of cost-effective lipid extraction methods.</p><p> </p><p>As a chemical-free water treatment technology, ultraviolet (UV) irradiation has been widely applied to inactivate pathogens but has not been used in algal cultivation to control invading organisms. To evaluate the potential of using UV irradiation to control invading algal species and minimize virus predation, <i>Tetraselmis sp. </i>and <i>Paramecium bursaria Chlorella virus 1</i> (PBCV-1) were examined as challenge organisms to evaluate effectiveness of UV disinfection. The concentration of viable (reproductively/infectively active) cells and viruses were quantified by a most probable number (MPN) assay and a plaque assay. A low-pressure collimated-beam reactor was used to investigate UV₂₅₄ dose-response behavior of both challenge organisms. A medium-pressure collimated-beam reactor equipped with a series of narrow bandpass optical filters was used to investigate the action spectra of both challenge organisms. Both challenge organisms showed roughly five log₁₀ units of inactivation for UV₂₅₄ doses over 120 mJ/cm². the most effective wavelengths for inactivation of <i>Tetraselmis</i> were from 254 nm to 280 nm, in which the inactivation was mainly attributed to UV-induced DNA damage. On the contrary, the most effective wavelength for inactivation of PBCV-1 was observed at 214 nm, where the loss of infectivity was mainly attributed to protein damage. These results provide important information for design of UV reactors to minimize the impact of invading organisms in algal cultivation systems.</p><p> </p><p>Additionally, a virus-assisted cell disruption method was developed for cost-effective lipid extraction from algal biomass. Detailed mechanistic studies were conducted to evaluate infection behavior of <i>Chlorovirus </i>PBCV-1 on <i>Chlorella sp.</i>, impact of infection on mechanical strength of algal cell wall, lipid yield, and lipid distribution. Viral disruption with multiplicity of infection (MOI) of 10^-8 completely disrupted concentrated algal biomass in six days. Viral disruption significantly reduced the mechanical strength of algal cells for lipid extraction. Lipid yield with viral disruption increased more than three times compared with no disruption control and was similar to that of ultrasonic disruption. Moreover, lipid composition analysis showed that the quality of extracted lipids was not affected by viral infection. The results showed that viral infection is a cost-effective process for lipid extraction from algal cells as extensive energy input and chemicals required by existing disruption methods are no longer needed.</p><p> </p><p>Overall, this dissertation provides innovative approaches for the development of cost-efficient algal biofuels. Application of UV disinfection and viral disruption significantly reduces chemical consumption and improves sustainability of algal biofuel production.<br></p>

In this study, the effects of neutral particles addition on the breakage of wastewater flocs toimprove the efficiency of sonication pretreatment for UV disinfection process have been studied.Kaolin particles as a potentially useful material that is neutral, natural and cheap were added towastewater samples prior to sonication. Results obtained in this study indicated that hard andsmall kaolin particles do not have any significant effect on the particle breakage efficiency byultrasound. The addition of kaolin particles did not significantly increase the cavitation activity(as characterized by potassium iodide actinometry) either. These findings contradict earlierreports that neutral particles can act as nucleation sites and hence enhance cavitation intensity. Inthis work, sonication of wastewater samples for 60s in the absence of kaolin particles resulted inan approximately one log decrease in the number of surviving bacteria colonies at the tailinglevel and 1.4 log units increase at the initial slope of coliform removal in UV dose responsecurve, however addition of kaolin particles prior sonication did not significantly affect the UVdose response curve .The results presented in this study should be treated as preliminary andfurther detailed investigations are needed to better evaluate this issue.

This study showed that hydrodynamic particle breakage had potential as a method to help improve the disinfection of wastewater effluents. The physicochemical properties of flocs from four distinct effluents sources (combined sewer overflow, settled combined sewer overflow, primary effluent, and final effluent) were compared before and after hydrodynamic treatment. The use of hydrodynamic force to cause floc breakage was shown to be effective, though variable, across all source types. This variation in floc breakage did not have a significant impact on the UV disinfection achieved, as the UV dose kinetics were similar across samples from the same source type. The results of this study demonstrate how the physicochemical properties of floc are affected when exposed to shear force. These observations further the understanding of floc composition and behaviour when shear forces are applied while also providing evidence to indicate this process improves the performance of UV disinfection technology.

In the present work, the breakage of wastewater particles in orifice flow is investigated through numerical simulations. Using maximum strain rate along particle paths as the breakage criterion, breakage is predicted using computational fluid dynamics. The numerical simulations confirm that nominal orifice strain rate cannot explain the higher particle breakage in single-orifice systems compared to that of multi-orifice systems, instead particle breakage was found to correlate well with the maximum strain rates in the system. On the issue of effect of initial particle location on breakage, numerical modeling shows that particles travelling along the centerline are suspected to break less than those travelling near the wall. However, experiments designed to study the breakage of particles injected at various radial locations proved inconclusive. Finally, results suggest that while single orifice systems are ideal for strong particles, multi-orifice systems may be more effective in breaking weak particles.

In the present work, the breakage of wastewater particles in orifice flow is investigated through numerical simulations. Using maximum strain rate along particle paths as the breakage criterion, breakage is predicted using computational fluid dynamics. The numerical simulations confirm that nominal orifice strain rate cannot explain the higher particle breakage in single-orifice systems compared to that of multi-orifice systems, instead particle breakage was found to correlate well with the maximum strain rates in the system. On the issue of effect of initial particle location on breakage, numerical modeling shows that particles travelling along the centerline are suspected to break less than those travelling near the wall. However, experiments designed to study the breakage of particles injected at various radial locations proved inconclusive. Finally, results suggest that while single orifice systems are ideal for strong particles, multi-orifice systems may be more effective in breaking weak particles.

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