Search

Abstract: With a large number of oil deposits in Canada, Alberta oil sands industries are currently conducting bitumen extraction processes using hot water. In oil sands process water (OSPW) from these oil sands operations, naphthenic acids (NAs) are identified as one of the primary sources of acute toxicity and were assessed for their endocrine-disrupting potentials. Hence, the monitoring of NAs in aqueous environmental matrices is crucial for oil sands-related industries. Commonly used analytical methods for NAs, such as Fourier transform infrared spectroscopy and high-performance liquid chromatography, are time-consuming, expensive, and samples must be sent to an analytical lab for analysis. Therefore, this study aims to develop a microbial electrochemical biosensor (MXC) for the detection of NAs in water samples. First, experiments were conducted to develop an optimal calibration method for the MXC biosensor by comparing different approaches (closed-circuit operation vs. charging-discharging operation) using a single model NA compound (cyclohexane carboxylic acid). The charging-discharging operation significantly increased the peak currents by 90-124 folds higher than that observed for closed-circuit operation. Besides, a strong linear relationship between model NA concentrations and the peak currents (R2 = 0.96) was observed. Second, experiments were conducted to evaluate the impact of different environmental parameters on biosensor performance. The results revealed that this MXC biosensor would be sensitive to salinity levels and temperature changes; however, once calibrated, it can be used for measurement of NA concentrations. The method was further validated with a complex model NA compound (mixtures of alkylated cyclopentane carboxylic acid, CNA). Interestingly, enriching the anode biofilm with salt content (1500 mg/L) significantly reduced the performance of the MXC biosensor applied for CNA detection. Furthermore, the presence of other organics, such as polycyclic aromatic hydrocarbons (e.g., 2-methylnaphalene and pyrene) in OSPW, can greatly interfere with the current output produced by CNA. However, still a linear relationship has been observed between CNA concentrations and current from the MXC biosensor. Overall, the results of this study demonstrated that with further development, MXC biosensors could be used as a simple bioanalytical tool for monitoring NA concentrations in OSPW.

Wastewater treatment has developed as a mature technology over time. However, conventional wastewater treatment is a very energy-intensive process. Bioelectrochemical system (BES) is an emerging technology that can treat wastewater and also recover resources such as energy in the form of electricity/hydrogen gas and nutrients such as nitrogen and phosphorus compounds. Microbial electrolysis cell (MEC) is a type of BES that, in the presence of an additional voltage, can treat wastewater and generate hydrogen gas. This is a promising approach for wastewater treatment and value-added product generation, though it may not be sustainable in the long run, as it relies on fossil fuels to provide that additional energy. Thus, it is important to explore alternative renewable resources that can provide energy to power MEC. Waste heat is one such resource that has not been researched extensively, particularly at the low-temperature spectrum. This was utilized as a renewable resource by converting waste heat to electricity using a device called thermoelectric generator (TEG). TEG converted simulated waste heat from an anaerobic digester to power an MEC. The feasibility of TEG to act as a power source for an MEC was investigated and its performance compared to the external power source. Various cold sources were analyzed to characterize TEG performance. To explore this integrated TEG-MEC system further, a hydraulic connection was added between the two systems. Wastewater was used as a cold source for TEG and it was recirculated to the anode of the MEC. This system showed improved performance with both systems mutually benefitting each other. The operational parameters were analyzed for the optimization of the system. The integrated system could generate hydrogen at a rate of 0.36 ± 0.05 m3 m-3 d-1 for synthetic domestic wastewater treatment. For the practical application, it is necessary to estimate the cost and narrow the focus on the functions of the system. Techno-economic analysis was performed for MEC with cost estimation and net present value model to understand the economic viability of the technology. The application niche of the BES was described and directions for addressing the challenges towards a full-scale operation were discussed. The present system provides a sustainable method for wastewater treatment and resource recovery which can play an important role in human health, social and economic development and a strong ecosystem.

Effective wastewater treatment is needed to reduce the water pollution problem. However, massive energy is consumed in wastewater treatment, required to design an innovative system to reduce the energy consumption to solve the energy crisis. Integrated photobioelectrochemical system (IPB) is a powerful system to combine microbial fuel cells (MFCs) and algal bioreactor together. This system has good performance on the organic degradation, removal of nitrogen and phosphorus, and recover the bioenergy via electricity generation and algal harvesting. This dissertation is divided to twelve chapters, about various aspects of the working mechanisms and actual application of IPB. Chapter 1 generally introduces the working mechanisms of MFCs, algal bioreactor, and modeling. Chapter 2 demonstrates the improvement of cathode material to improve the structure and catalytic performance to improve the MFC performance. Chapter 3 describes the process to use microbial electrolysis cell (MEC) to generate biohythane for the energy recovery. Chapters 4 and 5 demonstrate the application of stable isotope probing to study Shewanella oneidensis MR-1 in the MFCs. Chapters 6 to 8 describe the application of models to optimize MFC and IPB system performance. Chapter 9 describes the strategy improvement for the algal harvesting in IPB. Chapter 10 describes the application of scale-up bioelectrochemical systems on the long-term wastewater treatment. Chapter 11 finally concludes the perspectives of IPBs in the wastewater treatment and energy recovery. This dissertation comprehensively introduces IPB systems in the energy recovery and sustainable wastewater treatment in the future.

The role of complex and undefined microbiomes in contemporary environment, health, and energy applications is increasingly found to be important. Bioelectrochemical systems (BESs) possess the ability to play a critical role in these applications by interacting with microbiology electrochemically. While most efforts have been aimed at environmental, energy, and chemical production aspects, BESs have demonstrated value as tools for the study of complex microbiomes. Here, I performed work with the goal of developing a BES reactor that could be employed to study hydrogen-gas producing syntrophs to understand their role in critical environments, and further to enrich and isolate syntrophs in pure culture from their microbiome. I first studied poly(3,4-ethylenedioxythiophene) (PEDOT) as a coating for electrodes to increased BES performance in both large-scale systems and BESs aimed for sensing applications. I then modeled and performed experiments to support the model to understand the complex synergistic interactions of microbes using redox-active mediators to interact with BES electrodes. Finally, I modeled and developed a novel BES architecture to enrich and isolate syntrophs from their microbiome so that they can be studied in pure-culture to understand their role in the environment. My results indicate that the BES architecture, which I built and tested based on modeling, was successful at enriching syntrophs, and indicated further steps that can lead to syntroph isolation.

Organic waste streams, like domestic wastewater and municipal solid waste, have the potential to be used as feedstocks for biotechnology processes to produce high value products and energy. This thesis investigated the technological, economical, and environmental potential for integrated anaerobic digestion (AD) and bioelectrochemical system (BES) platforms as they were theoretically and physically evaluated for energy recovery from domestic wastewater. The first chapter of this thesis compared the theoretical energy efficiencies of converting waste directly into electricity, using AD and BES alone and in various combinations. This chapter reviewed the experimentally demonstrated energy efficiencies reported in the literature with comparisons to the maximum theoretical efficiencies, considering thermodynamic limits. Acetate was used as an ideal substrate for theoretical calculations, whereas complex wastes were used for extended analyses of practical efficiencies. In addition, to address the potential economic and environmental benefits of this technology, a brief case study was investigated using the Oak Ridge National Laboratory (ORNL) water resource recovery facility (WRRF). This work identified a combined Anaerobic Digestion/Microbial Electrolysis Cell (ADMEC) platform as the most viable treatment process for further study. In the second chapter, the abovementioned ADMEC system was tested using real domestic wastewater from the ORNL WRRF. The system was modified to include two pretreatment methods, alkaline and thermal hydrolysis, to observe potential effects of pretreatment on energy recovery. The systems in chapter two were operated so that hydrogen recovery was maximized, at the expense of biogas recovery. The results from this chapter indicated that thermal hydrolysis pretreatment had the greatest positive effect on methane composition and hydrogen production, while also reducing overall biogas production. Alkaline pretreatment had a net-negative impact on energy recovery compared to the control. This thesis concludes with my personal reflection on these technologies and where I think they may play a role in the future.

Bioelectrochemical systems (BES) is a platform technology that is able to realize versatile engineering functions and recover valuable resources in an energy-efficient manner. One of the potential applications of BES is to remove and recover nutrients simultaneously from nutrient-rich wastewater, such as digested manure from livestock. A four-chamber BES was developed and used in this study to explore the potential to remove and recover hexavalent Chromium from synthetic wastewater, and ammonia and phosphate from digested manure. The BES was able to achieve 99.6% removal of Chromium by membrane adsorption in 5 days but failed to recover in the concentration chamber. Nutrients were removed from the waste stream and recovered in the recirculated catholyte by the electrical field generated from the waste. The BES was demonstrated to achieve substantial COD removal, nutrients removal and recovery. On average, the removal efficiencies were about 50% for COD, 85% for NH4-N and 40% for PO4-P, and the concentration of NH4-N recovered in the catholyte was 670 mg/L after 5 cycles under an applied voltage of 0.8 V. PO4-P was not recovered in solution, probably because it has precipitated under the alkaline condition together with Mg2+ and Ca2+ concentrated in the catholyte. It was also demonstrated that nutrients removal and recovery depended on the current generation and were mostly completed at high current. To sum up, the BES was proven to be an effective and sustainable approach to remove and recover nutrients from digested manure.

Shewanella oneidensis MR-1 is a model microbe for use in bioelectrochemical systems (BESs) for several reasons, including its ability to produce electric current in the presence of oxygen and its use of endogenous electron shuttles for electron transfer. I performed in-depth studies on the growth and physiology of S. oneidensis to gain insight into BES performance with this microbe. In the first study, I analyzed changes in current production when oxygen was added to batch- and continuously-fed BESs with S. oneidensis. These experiments revealed that oxygen is more beneficial under continuously-fed conditions because it allows S. oneidensis to grow and produce flavins at a faster rate, and therefore decreases flavin washout. In the second study I optimized poised electrode potentials, because previous research suggested that electrodes poised at oxidizing potentials may cause a stress response in S. oneidensis. I grew S. oneidensis in continuously-fed BESs with potentiostatically poised electrodes at 5 different redox potentials and concluded that oxidizing electrode potentials do not cause a general stress response, but decrease current production by direct damage of biofilm cells at the electrode surface. In the third study, I compared the transcriptomes of S. oneidensis grown in a wide variety of conditions and used machine learning to discover genes important to anode- and iron-respiration in this organism. This meta-analysis revealed that some putative members of the electron transport chain, including an NADH dehydrogenase and a cytochrome oxidase, were important under anode- or Fe(III)-respiring conditions. Knockouts strains with these genes deleted confirmed their role in the anaerobic electron transport chain of S. oneidensis. Future work is needed to better characterize the efficiency of the anaerobic electron transport chain in S. oneidensis. The overall finding of this work is that S. oneidensis is not appropriate for use in BES applications that require strict anaerobic conditions or quick exchange of medium (e.g., wastewater treatment), because it performs better when mediators and planktonic cells are not washed out of the system.

Bioelectrochemical systems, such as microbial fuel cells (MFCs), are a specialized branch of biotechnology which aims to use the diversity of microbial metabolism for industrial applications including: the treatment of wastewater coupled with the production of electricity; the production of high value compounds (e.g. hydrogen); and biosensing applications. MFC technologies use exoelectrogenic bacteria such as Geobacter sp. These bacteria possess a particular metabolism that allows them to exchange electrons with solid surfaces like electrodes. One major parameter that can limit efficient electron transfer from biofilms to the electrode is the metabolic capability and microbial composition of the biofilm. Consequently, a main focus of this research was to determine if it is possible to select and maintain stable electrode biofilm communities that have efficient electron transfer properties and are suitable for specific functions such as biological oxygen demand (BOD) biosensing and electricity production. To achieve this objective, the influence of four parameters including the anode potential, the inoculum source, the substrate and the electrode surface properties, was tested on the selection of exoelectrogenic biofilms. The differences in community structures and electrochemical properties of the different biofilms selected were investigated using population profiling (e.g. SSCP, ARISA, RFLP), cloning and electrochemical analysis (e.g. cyclic voltammetry, power curves). Here, I present evidence that these four parameters altered the dominant community of the selected biofilms, with the anode potential and the substrate having the most effects. These results enrich an ongoing controversy in the literature as to whether electrode potential can influence the composition of anode-respiring biofilms or if they physiologically adapt to different potentials. In this study, I proved that the anode potential affects the composition of Geobacter-dominated biofilms at a strain level. My results imply that it is possible to select for high current-producing biofilms using specific anode potentials. In addition to microbial composition, operational stability of anode-respiring biofilm communities is also of importance for electricity production and the development of biosensors. In this study, I explored the use of a biosensor based on an exoelectrogenic biofilm for the real-time monitoring of BOD, as a fast alternative to the conventional 5-day BOD assay. A Geobacter-dominated biofilm was selected at an anode potential of -0.36 V vs Ag/AgCl with ethanol as the sole carbon source. The biofilm had a broad metabolic capability and accurately quantified the BOD of complex media, opening the way to a new generation of biosensors. Although MFCs are mainly limited by the efficiency of electron transfer at the anode, processes such as the reduction of oxygen at the cathode can also alter the current output of these systems. In this work, I demonstrated that photosynthetic cathodic biofilms enhance the power output of microbial fuel cells by saturating the catholyte in oxygen under illumination. This project contributes significant knowledge to the parameters affecting the formation of anode- respiring biofilms, especially those dominated by Geobacter sp., the dynamics of their community structures, their operational stability and their potential use as BOD biosensors. It also provides evidence of the utility of photosynthetic biofilms to overcome cathodic limitations caused by low rates of the oxygen reduction reaction. The combination of my key research findings provides substantial opportunities to enhance the reliable use and implementation of MFC technologies for environmental monitoring and energy production applications.