The Torres Lab focuses mainly on fundamental and applied research related to microbial electrochemistry. This young field of research bloomed about a decade ago when we learned that microbes can electrically connect to an electrode, producing an electrical current. The electrical current produced is actually part of their metabolic respiration, as the anode serves as their local electron acceptor (thus, we call them anode-respiring bacteria, ARB). Today, there are still many unknowns regarding the mechanism that allows ARB to transport electrons from thick biofilms, sometimes over 100 micrometers, to the electrode. Despite these unknowns, many technologies have been proposed using ARB in microbial electrochemical cells (MXCs). MXCs can be used to convert complex organic compounds, such as wastes, into electrical power or valuable products. Our group tackles both the fundamental understanding of ARB biofilms, focusing on transport processes, and the development and optimization of MXC technologies. Currently, we have four major research efforts:
Characterization of Novel Anode-respiring Bacteria
Most of the research in microbial electrochemistry so far has focused on two main microorganisms: Geobacter sulfurreducens and Shewanella oneidensis. While these are excellent model microorganisms to study anode respiration, there is a need to study other ARB. Our group has focused on identifying and characterizing new ARB, including thermophiles (~ 60 deg C)Thermincola ferriacetica and Thermoanaerobacter spp., alkalophileGeoalkalibacter ferrihydriticus, and halophile Geoalkalibacter subterraneus. But the search for ARB continues! Our goal is to focus on those ARB that bring novel metabolic capabilities that can be used in MXC applications.
Fundamental Studies on Electron and Proton Transport in Anode Bioilms
The unique phenomenon of extracellular respiration in biofilm-forming ARB requires efficient transport of electrons and protons out of the biofilm. We apply advanced electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy to study these transport processes in detail. We especially focus on how accumulation of electrons and protons inside biofilms affects the energy metabolism of ARB. We also use, in our studies, novel electrode geometries wherein electron and proton gradients can be influenced. We combine the use of electrochemical techniques with powerful microscopic techniques to understand these gradients. We use the information obtained through such studies to develop mathematical models that accurately describe and predict the current generated by ARB biofilms under a range of conditions.
Optimizing the Microbial Ecology of MXC Anodes
ARB participate in syntrophic interactions with various microbial trophic groups in an anaerobic microbial food web in order to achieve high efficiencies of electron capture from complex organics. Competing microbial processes such as methanogenesis, sulfate reduction, and denitrification can drive electrons away from anode respiration. Source of inoculum, pH, degree of substrate complexity are some of the key variables that influence the microbial ecology of anodes. We focus on unearthing the microbial ecology of complex organic substrates from globally diverse environmental inocula under different environmental conditions. Suppression of undesirable microbial sinks such as methanogenesis and promotion of desirable microbial partners such as homoacetogenesis is another central research theme. Molecular microbial ecology tools from the Krajmalnik-Brown lab aid in the characterization along with microscopic techniques. We strive to employ beneficial ecological management in microbial electrochemical cells through sound engineering and microbiological practices.
Optimization of MXC Processes Towards Scale-up
The electrical current produce by ARB can be used for many applications, such as power production (microbial fuel cell), hydrogen production, and other chemicals. Our research focuses on optimizing processes that can have near-term impacts in society, while envisioning new processes that can be developed based on new discoveries. For example, through the study of thermophilic ARB, we are optimizing a process to produce H2 from cellulosic biomass taking advantage of efficient cellulosic degrading microbes at this temperature. We are also optimizing a process to produce hydrogen peroxide at the cathode of a microbial fuel cell fed with wastewater. The hydrogen peroxide can then be used to further treat and disinfect the wastewater stream. Through the fundamental knowledge obtained in other research efforts discussed above, we develop mathematical models that allow us to predict and optimize these new processes to achieve economic feasibility.