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- Creators: Ravel, Maurice, 1875-1937
Description
Microbial electrochemical cells (MXCs) serve as an alternative anaerobic technology to anaerobic digestion for efficient energy recovery from high-strength organic wastes such as primary sludge (PS). The overarching goal of my research was to address energy conversion from PS to useful resources (e.g. hydrogen or hydrogen peroxide) through bio- and electro-chemical anaerobic conversion processes in MXCs.
First, a new flat-pate microbial electrolysis cell (MEC) was designed with high surface area anodes using carbon fibers, but without creating a large distance between the anode and the cathode (<0.5 cm) to reduce Ohmic overpotential. Through the improved design, operation, and electrochemical characterization, the applied voltages were reduced from 1.1 to ~0.85 V, at 10 A m-2. Second, PS conversion was examined through hydrolysis, fermentation, methanogenesis, and/or anode respiration. Since pretreatment often is required to accelerate hydrolysis of organic solids, I evaluated pulsed electric field technology on PS showing a modest improvement of energy conversion through methanogenesis and fermentation, as compared to the conversion from waste activated sludge (WAS) or WAS+PS. Then, a two-stage system (prefermented PS-fed MEC) yielded successful performance in terms of Coulombic efficiency (95%), Coulombic recovery (CR, 80%), and COD-removal efficiency (85%). However, overall PS conversion to electrical current (or CR) through pre-fermentation and MEC, was just ~16%. Next, a single-stage system (direct PS-fed MEC) with semi-continuous operation showed 34% CR at a 9-day hydraulic retention time. The PS-fed MEC also showed an important pH dependency, in which high pH (> 8) in the anode chamber improved anode respiration along with methanogen inhibition. Finally, H2O2 was produced in a PS-fed microbial electrochemical cell with a low energy requirement (~0.87 kWh per kg H2O2). These research developments will provide groundbreaking knowledge for MXC design, commercial application, and anaerobic energy conversion from other high-strength organic wastes to resources.
First, a new flat-pate microbial electrolysis cell (MEC) was designed with high surface area anodes using carbon fibers, but without creating a large distance between the anode and the cathode (<0.5 cm) to reduce Ohmic overpotential. Through the improved design, operation, and electrochemical characterization, the applied voltages were reduced from 1.1 to ~0.85 V, at 10 A m-2. Second, PS conversion was examined through hydrolysis, fermentation, methanogenesis, and/or anode respiration. Since pretreatment often is required to accelerate hydrolysis of organic solids, I evaluated pulsed electric field technology on PS showing a modest improvement of energy conversion through methanogenesis and fermentation, as compared to the conversion from waste activated sludge (WAS) or WAS+PS. Then, a two-stage system (prefermented PS-fed MEC) yielded successful performance in terms of Coulombic efficiency (95%), Coulombic recovery (CR, 80%), and COD-removal efficiency (85%). However, overall PS conversion to electrical current (or CR) through pre-fermentation and MEC, was just ~16%. Next, a single-stage system (direct PS-fed MEC) with semi-continuous operation showed 34% CR at a 9-day hydraulic retention time. The PS-fed MEC also showed an important pH dependency, in which high pH (> 8) in the anode chamber improved anode respiration along with methanogen inhibition. Finally, H2O2 was produced in a PS-fed microbial electrochemical cell with a low energy requirement (~0.87 kWh per kg H2O2). These research developments will provide groundbreaking knowledge for MXC design, commercial application, and anaerobic energy conversion from other high-strength organic wastes to resources.
ContributorsKi, Dong Won (Author) / Torres, César I (Thesis advisor) / Rittmann, Bruce E. (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Parameswaran, Prathap (Committee member) / Popat, Sudeep C (Committee member) / Arizona State University (Publisher)
Created2016
Description
The microbial electrochemical cell (MXC) is a novel environmental-biotechnology platform for renewable energy production from waste streams. The two main goals of MXCs are recovery of renewable energy and production of clean water. Up to now, energy recovery, Coulombic efficiency (CE), and treatment efficiency of MXCs fed with real wastewater have been low. Therefore, the overarching goal of my research was to address the main causes for these low efficiencies; this knowledge will advance MXCs technology toward commercialization.
First, I found that fermentation, not anode respiration, was the rate-limiting step for achieving complete organics removal, along with high current densities and CE. The best performance was achieved by doing most of the fermentation in an independent reactor that preceded the MXC. I also outlined how the efficiency of fermentation inside MXCs can be enhanced in order to make MXCs-based technologies cost-competitive with other anaerobic environmental biotechnologies. I revealed that the carbohydrate and protein contents and the BOD5/COD ratio governed the efficiency of organic-matter fermentation: high protein content and low BOD5/COD ratio were the main causes for low fermentation efficiency.
Next, I showed how a high ammonium concentration can provide kinetic and metabolic advantages or disadvantages for anode-respiring bacteria (ARB) over their competitors, particularly methanogens. When exposed to a relatively high ammonium concentration (i.e., > 2.2 g total ammonia-nitrogen (TAN)/L), the ARB were forced to divert a greater electron flow toward current generation and, consequently, had lower net biomass yield. However, the ARB were relatively more resistant to high free ammonia-nitrogen (FAN) concentrations, up to 200 mg FAN/L. I used FAN to manage ecological interactions among ARB and non-ARB in an MXC fed with fermentable substrate (glucose). Utilizing a combination of chemical, electrochemical, and genomic tools, I found that increased FAN led to higher CE and lower methane (CH4) production by suppressing methanogens. Thus, managing FAN offers a practical means to suppress methanogenesis, instead of using expensive and unrealistic inhibitors. My research findings open up new opportunities for more efficient operation of MXCs; this will enhance MXC scale-up and commercial applications, particularly for energy-positive treatment of waste streams containing recalcitrant organics.
First, I found that fermentation, not anode respiration, was the rate-limiting step for achieving complete organics removal, along with high current densities and CE. The best performance was achieved by doing most of the fermentation in an independent reactor that preceded the MXC. I also outlined how the efficiency of fermentation inside MXCs can be enhanced in order to make MXCs-based technologies cost-competitive with other anaerobic environmental biotechnologies. I revealed that the carbohydrate and protein contents and the BOD5/COD ratio governed the efficiency of organic-matter fermentation: high protein content and low BOD5/COD ratio were the main causes for low fermentation efficiency.
Next, I showed how a high ammonium concentration can provide kinetic and metabolic advantages or disadvantages for anode-respiring bacteria (ARB) over their competitors, particularly methanogens. When exposed to a relatively high ammonium concentration (i.e., > 2.2 g total ammonia-nitrogen (TAN)/L), the ARB were forced to divert a greater electron flow toward current generation and, consequently, had lower net biomass yield. However, the ARB were relatively more resistant to high free ammonia-nitrogen (FAN) concentrations, up to 200 mg FAN/L. I used FAN to manage ecological interactions among ARB and non-ARB in an MXC fed with fermentable substrate (glucose). Utilizing a combination of chemical, electrochemical, and genomic tools, I found that increased FAN led to higher CE and lower methane (CH4) production by suppressing methanogens. Thus, managing FAN offers a practical means to suppress methanogenesis, instead of using expensive and unrealistic inhibitors. My research findings open up new opportunities for more efficient operation of MXCs; this will enhance MXC scale-up and commercial applications, particularly for energy-positive treatment of waste streams containing recalcitrant organics.
ContributorsMohamed, Mohamed Mahmoud Ali (Author) / Rittmann, Bruce E. (Thesis advisor) / Torres, Cesar I. (Thesis advisor) / Westerhoff, Paul (Committee member) / Parameswaran, Prathap (Committee member) / Arizona State University (Publisher)
Created2016
ContributorsRavel, Maurice, 1875-1937 (Composer) / Goulart, Renato (Arranger)
ContributorsRavel, Maurice, 1875-1937 (Composer)
ContributorsRavel, Maurice, 1875-1937 (Composer)
ContributorsRavel, Maurice, 1875-1937 (Composer)
ContributorsRavel, Maurice, 1875-1937 (Composer)
ContributorsRavel, Maurice, 1875-1937 (Composer)
ContributorsRavel, Maurice, 1875-1937 (Composer)
ContributorsRavel, Maurice, 1875-1937 (Composer)