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Microscopic algae have been investigated extensively by researchers for decades for their ability to bioremediate wastewater and flue gas while producing valuable biomass for use as feed, fuel, fertilizer, nutraceutical, and other specialty products. Reports of the exciting commercial potential of this diverse group of organisms started appearing in

Microscopic algae have been investigated extensively by researchers for decades for their ability to bioremediate wastewater and flue gas while producing valuable biomass for use as feed, fuel, fertilizer, nutraceutical, and other specialty products. Reports of the exciting commercial potential of this diverse group of organisms started appearing in the literature as early as the 1940’s. However, nearly 80 years later, relatively few successful commercial microalgae installations exist and algae have not yet reached agricultural commodity status. This dissertation examines three major bottlenecks to commercial microalgae production including lack of an efficient and economical cultivation strategy, poor management of volatile waste nutrients, and costly harvesting and post processing strategies. A chapter is devoted to each of these three areas to gain a better understanding of each bottleneck as well as strategies for overcoming them.

The first chapter demonstrates the capability of two strains of Scenedesmus acutus to grow in ultra-high-density (>10 g L-1 dry weight biomass) cultures in flat panel photobioreactors for year-round production in the desert Southwest with record volumetric biomass productivity. The advantages and efficiency of high-density cultivation are discussed. The second chapter focuses on uptake and utilization of the volatile components of wastewater: ammonia and carbon dioxide. Scenedesmus acutus was cultured on wastewater from both municipal and agricultural origin and was shown to perform significantly better on flue gas as compared to commercial grade CO2 and just as well on waste nutrients as the commonly used BG-11 laboratory culture media, all while producing up to 50% lipids of the dry weight biomass suitable for use in biodiesel. The third chapter evaluates the feasibility of using gravity sedimentation for the harvesting of the difficult-to-separate Scenedesmus acutus green algae biomass followed by microfluidization to disrupt the cells. Lipid-extracted biomass was then studied as a fertilizer for plants and shown to have similar performance to a commercially available 4-6-6 fertilizer. Based on the work from these three chapters, a summary of modifications are suggested to help current and future microalgae companies be more competitive in the marketplace with traditional agricultural commodities.
ContributorsWray, Joshua (Author) / Dempster, Thomas (Thesis advisor) / Roberson, Robert (Thesis advisor) / Bingham, Scott (Committee member) / Neuer, Susanne (Committee member) / Arizona State University (Publisher)
Created2019
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Description
Microbial fuel cells (MFCs) promote the sustainable conversion of organic matter in black water to electrical current, enabling the production of hydrogen peroxide (H2O2) while making waste water treatment energy neutral or positive. H2O2 is useful in remote locations such as U.S. military forward operating bases (FOBs) for on-site tertiary

Microbial fuel cells (MFCs) promote the sustainable conversion of organic matter in black water to electrical current, enabling the production of hydrogen peroxide (H2O2) while making waste water treatment energy neutral or positive. H2O2 is useful in remote locations such as U.S. military forward operating bases (FOBs) for on-site tertiary water treatment or as a medical disinfectant, among many other uses. Various carbon-based catalysts and binders for use at the cathode of a an MFC for H2O2 production are explored using linear sweep voltammetry (LSV) and rotating ring-disk electrode (RRDE) techniques. The oxygen reduction reaction (ORR) at the cathode has slow kinetics at conditions present in the MFC, making it important to find a catalyst type and loading which promote a 2e- (rather than 4e-) reaction to maximize H2O2 formation. Using LSV methods, I compared the cathodic overpotentials associated with graphite and Vulcan carbon catalysts as well as Nafion and AS-4 binders. Vulcan carbon catalyst with Nafion binder produced the lowest overpotentials of any binder/catalyst combinations. Additionally, I determined that pH control may be required at the cathode due to large potential losses caused by hydroxide (OH-) concentration gradients. Furthermore, RRDE tests indicate that Vulcan carbon catalyst with a Nafion binder has a higher H2O2 production efficiency at lower catalyst loadings, but the trade-off is a greater potential loss due to higher activation energy. Therefore, an intermediate catalyst loading of 0.5 mg/cm2 Vulcan carbon with Nafion binder is recommended for the final MFC design. The chosen catalyst, binder, and loading will maximize H2O2 production, optimize MFC performance, and minimize the need for additional energy input into the system.
ContributorsStadie, Mikaela Johanna (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Barrett, The Honors College (Contributor) / Chemical Engineering Program (Contributor)
Created2015-05
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Description
In our modern world the source of for many chemicals is to acquire and refine oil. This process is becoming an expensive to the environment and to human health. Alternative processes for acquiring the final product have been developed but still need work. One product that is valuable is butanol.

In our modern world the source of for many chemicals is to acquire and refine oil. This process is becoming an expensive to the environment and to human health. Alternative processes for acquiring the final product have been developed but still need work. One product that is valuable is butanol. The normal process for butanol production is very intensive but there is a method to produce butanol from bacteria. This process is better because it is more environmentally safe than using oil. One problem however is that when the bacteria produce too much butanol it reaches the toxicity limit and stops the production of butanol. In order to keep butanol from reaching the toxicity limit an adsorbent is used to remove the butanol without harming the bacteria. The adsorbent is a mesoporous carbon powder that allows the butanol to be adsorbed on it. This thesis explores different designs for a magnetic separation process to extract the carbon powder from the culture.
ContributorsChabra, Rohin (Author) / Nielsen, David (Thesis director) / Torres, Cesar (Committee member) / Barrett, The Honors College (Contributor) / Chemical Engineering Program (Contributor)
Created2015-05
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Description
Microbial fuel cells (MFCs) facilitate the conversion of organic matter to electrical current to make the total energy in black water treatment neutral or positive and produce hydrogen peroxide to assist the reuse of gray water. This research focuses on wastewater treatment at the U.S. military forward operating bases (FOBs).

Microbial fuel cells (MFCs) facilitate the conversion of organic matter to electrical current to make the total energy in black water treatment neutral or positive and produce hydrogen peroxide to assist the reuse of gray water. This research focuses on wastewater treatment at the U.S. military forward operating bases (FOBs). FOBs experience significant challenges with their wastewater treatment due to their isolation and dangers in transporting waste water and fresh water to and from the bases. Even though it is theoretically favorable to produce power in a MFC while treating black water, producing H2O2 is more useful and practical because it is a powerful cleaning agent that can reduce odor, disinfect, and aid in the treatment of gray water. Various acid forms of buffers were tested in the anode and cathode chamber to determine if the pH would lower in the cathode chamber while maintaining H2O2 efficiency, as well as to determine ion diffusion from the anode to the cathode via the membrane. For the catholyte experiments, phosphate and bicarbonate were tested as buffers while sodium chloride was the control. These experiments determined that the two buffers did not lower the pH. It was seen that the phosphate buffer reduced the H2O2 efficiency significantly while still staying at a high pH, while the bicarbonate buffer had the same efficiency as the NaCl control. For the anolyte experiments, it was shown that there was no diffusion of the buffers or MFC media across the membrane that would cause a decrease in the H2O2 production efficiency.
ContributorsThompson, Julia (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
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Description
Alternative ion exchange membranes for implementation in a peroxide production microbial electrochemical cel (PP-MEC) are explored through membrane stability tests with NaCl electrolyte and stabilizer EDTA at varying operational pHs. PP-MEC performance parameters \u2014 H2O2 concentration, current density, coulombic efficiency and power input required \u2014 are optimized over a 7

Alternative ion exchange membranes for implementation in a peroxide production microbial electrochemical cel (PP-MEC) are explored through membrane stability tests with NaCl electrolyte and stabilizer EDTA at varying operational pHs. PP-MEC performance parameters \u2014 H2O2 concentration, current density, coulombic efficiency and power input required \u2014 are optimized over a 7 month continuous operation period based on their response to changes in HRT, EDTA concentration, air flow rate and electrolyte. I found that EDTA was compatible for use with the membranes. I also determined that AMI membranes were preferable to CMI and FAA because it was consistently stable and maintained its structural integrity. Still, I suggest testing more membranes because the AMI degraded in continuous operation. The PP-MEC produced up to 0.38 wt% H2O2, enough to perform water treatment through the Fenton process and significantly greater than the 0.13 wt% batch PP-MEC tests by previous researchers. It ran at > 0.20 W-hr/g H2O2 power input, ~ three orders of magnitude less than what is required for the anthraquinone process. I recommend high HRT and EDTA concentration while running the PP- MEC to increase H2O2 concentration, but low HRT and low EDTA concentration to decrease power input required. I recommend NaCl electrolyte but suggest testing new electrolytes that may control pH without degrading H2O2. I determined that air flow rate has no effect on PP-MEC operation. These recommendations should optimize PP-MEC operation based on its application.
ContributorsChowdhury, Nadratun Naeem (Author) / Torres, Cesar (Thesis director) / Popat, Sudeep (Committee member) / Chemical Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
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Description

Optimizing cathodes for microbial fuel cells is important to maximize energy harvested from wastewater. Cathodes were made by modifying a recipe from previous literature and testing the current of the cathode using linear sweep voltammetry. The cathodes contained an Fe-N-C catalyst combined with a Polytetrafluoroethylene binder. Optimizing the power resulting

Optimizing cathodes for microbial fuel cells is important to maximize energy harvested from wastewater. Cathodes were made by modifying a recipe from previous literature and testing the current of the cathode using linear sweep voltammetry. The cathodes contained an Fe-N-C catalyst combined with a Polytetrafluoroethylene binder. Optimizing the power resulting from the microbial fuel cells will help MFCs be an alternative energy source to fossil fuels. The new cathodes did improve in current production from −16 𝐴/𝑚 to −37 𝐴/𝑚 at -0.4 V. When fitted using a Butler-Volmer model, the cathode linear-sweep voltammograms did not follow the expected exponential trend. These results show a need for more research on the cathodes and the Butler-Volmer model, and they also show that the cathode is ready for further and longer application in a microbial fuel cell.

ContributorsRussell, Andrea Christine (Author) / Torres, Cesar (Thesis director) / Young, Michelle (Committee member) / School of Sustainable Engineering & Built Envirnmt (Contributor) / School of Sustainability (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
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Description
Energy can be harvested from wastewater using microbial fuel cells (MFC). In order to increase power generation, MFCs can be scaled-up. The MFCs are designed with two air cathodes and two anode electrodes. The limiting electrode for power generation is the cathode and in order to maximize power, the cathodes

Energy can be harvested from wastewater using microbial fuel cells (MFC). In order to increase power generation, MFCs can be scaled-up. The MFCs are designed with two air cathodes and two anode electrodes. The limiting electrode for power generation is the cathode and in order to maximize power, the cathodes were made out of a C-N-Fe catalyst and a polytetrafluoroethylene binder which had a higher current production at -3.2 mA/cm2 than previous carbon felt cathodes at -0.15 mA/cm2 at a potential of -0.29 V. Commercial microbial fuel cells from Aquacycl were tested for their power production while operating with simulated blackwater achieved an average of 5.67 mW per cell. The small MFC with the C-N-Fe catalyst and one cathode was able to generate 8.7 mW. Imitating the Aquacycl cells, the new MFC was a scaled-up version of the small MFC where the cathode surface area increased from 81 cm2 to 200 cm2. While the MFC was operating with simulated blackwater, the peak power produced was 14.8 mW, more than the smaller MFC, but only increasing in the scaled-up MFC by 1.7 when the surface area of the cathode increased by 2.46. Further long-term application can be done, as well as operating multiple MFCs in series to generate more power and improve the design.
ContributorsRussell, Andrea (Author) / Torres, Cesar (Thesis advisor) / Garcia Segura, Sergio (Committee member) / Fraser, Matthew (Committee member) / Arizona State University (Publisher)
Created2022
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Description
Plastic pollution has become a global threat to ecosystems worldwide, with microplastics now representing contaminants reported to occur in ambient air, fresh water, seawater, soils, fauna and people. Over time, larger macro-plastics are subject to weathering and fragmentation, resulting in smaller particles, termed ‘microplastics’ (measuring < 5 mm in diameter),

Plastic pollution has become a global threat to ecosystems worldwide, with microplastics now representing contaminants reported to occur in ambient air, fresh water, seawater, soils, fauna and people. Over time, larger macro-plastics are subject to weathering and fragmentation, resulting in smaller particles, termed ‘microplastics’ (measuring < 5 mm in diameter), which have been found to pollute virtually every marine and terrestrial ecosystem on the planet. This thesis explored the transfer of plastic pollutants from consumer products into the built water environment and ultimately into global aquatic and terrestrial ecosystems.

A literature review demonstrated that municipal sewage sludge produced by wastewater treatment plants around the world contains detectable quantities of microplastics. Application of sewage sludge on land was shown to represent a mechanism for transfer of microplastics from wastewater into terrestrial environments, with some countries reporting as high as 113 ± 57 microplastic particles per gram of dry sludge.

To address the notable shortcoming of inconsistent reporting practices for microplastic pollution, this thesis introduced a novel, online calculator that converts the number of plastic particles into the unambiguous metric of mass, thereby making global studies on microplastic pollution directly comparable.

This thesis concludes with an investigation of a previously unexplored and more personal source of plastic pollution, namely the disposal of single-use contact lenses and an assessment of the magnitude of this emerging source of environmental pollution. Using an online survey aimed at quantifying trends with the disposal of lenses in the US, it was discovered that 20 ± 0.8% of contact lens wearers flushed their used lenses down the drain, amounting to 44,000 ± 1,700 kg y-1 of lens dry mass discharged into US wastewater.

From the results it is concluded that conventional and medical microplastics represent a significant global source of pollution and a long-term threat to ecosystems around the world. Recommendations are provided on how to limit the entry of medical microplastics into the built water environment to limit damage to ecosystems worldwide.
ContributorsRolsky, Charles (Author) / Halden, Rolf (Thesis advisor) / Green, Matthew (Committee member) / Neuer, Susanne (Committee member) / Polidoro, Beth (Committee member) / Smith, Andrew (Committee member) / Arizona State University (Publisher)
Created2020