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Novel BES

Bioelectrochemical Systems, or BESs, are biologically-mediated systems that allow the decoupling of oxidation and reduction reactions via the use of a membrane-based electrochemical cell.
Microbial Fuel Cells (MFCs)
Microbial fuel cells (MFCs) have been heralded as a low-temperature waste-to-energy technology that produces electricity from carbon-rich liquid waste streams. MFCs are biologically-mediated systems that allow the decoupling of oxidation and reduction reactions via the use of an electrochemical cell such as a polymer electrolyte membrane (PEM) cell. In an MFC, the oxidative reactions at the working electrode (i.e., anode) are decoupled from the reductive reactions at the counter electrode (i.e., cathode) by the PEM, with the difference in half-cell potentials resulting in a in an electromotive force that drives current flow. Generally, anoxic conditions are maintained in the anodic chamber in order to facilitate acidogenic fermentative pathways that produce fermentation products that can act as substrate to anodophiles and maximize reducing equivalent yield; fermentative pathways other than acidogenic pathways reuse reducing equivalents to produce reduced products such as alcohols. While in the cathodic chamber, generally oxidative conditions are maintained with the selection of a terminal electron acceptor such as oxygen, whose reduction, in the presence of protons permeating across the PEM, provides the highest thermodynamic driving force between the two half-cells. The oxygen reduction reaction suffers from kinetic limitations, necessitating the presence of catalyst at the counter electrode.
Cellulosic and Other Novel MFCs
To date, MFCs have demonstrated limited power generation, typically in the range of unit kWh/d, from municipal wastewater and soluble sugar substrates in laboratory systems. A joint project between Professor Farrukh Ahmad of the Masdar Institute and Professor Greg Stephanopoulos at the Massachusetts Institute of Technology (MIT) marks a departure from conventional MFC research by shifting from low-strength soluble substrates to high-strength wastes (e.g., biopolymers such as cellulose) in order to enhance total energetic output by allowing sustained operation of the MFC in batch mode. This could potentially allow MFC to be used in remote locations where carbon substrate replenishment might be infrequent.

Cellulose, a renewable material found in abundance across the plant taxa, makes up a large portion of municipal solid waste in the form of paper/packaging materials. The overall aim of the joint project is to utilize cellulosic waste materials as substrate in model microbial fuel cells (MFCs) in order to produce an effective bioreduction system that can (i) generate electricity and (ii) treat recalcitrant pollutants in industrial wastewater and contaminated groundwater. Other areas of exploration in BES research at the Masdar Institute include the development of integrated processes that can yield commercially valuable chemicals. As mentioned earlier, BESs allow the decoupling of oxidation and reduction reactions, thereby allowing a variety of applications. 

The use of pure cellulolytic cultures in MFCs, instead of the commonly used mixed cultures, adds another level of novelty to the joint project. Pure cultures facilitate the utilization of metabolic flux analysis (MFA) tools, pioneered by Professor Stephanopoulos for the biopharmaceutical industry. The application of MFA tools can create highly controlled model systems in which the metabolism of the organism is optimized for maximum efficiency. Once an optimization strategy has been devised using MFA, other kinetic factors limiting electrical power output, such as rates of cellulose hydrolysis and electron transfer between the bacteria and the anode, can be further evaluated. Hence, the project could lead to new approaches to optimize BESs for maximum efficiency with respect to its thermodynamic potential.

Biocathode Development and BES Modeling

BES can potentially be modeled using biofilm models involving extracellular electron transfer. Although anode-side-biofilm models for MFCs have recently become available in literature, a mathematical description of a functioning "biocathode", i.e., a cathode acting as an electron donor to a electrochemically enriched microbial biofilm that catalyzes the reduction of targeted compounds, remains the missing piece in describing integrated water treatment processes. Integrated water treatment processes that fulfill the dual role of municipal wastewater treatment and industrial wastewater, promise significant energy and space saving to the future sustainable cities.

The proposed project aims to develop a validated mathematical model of an energy-efficient BES that simultaneously oxidizes organic matter in municipal wastewater (anodic compartment) while reducing perchlorate as a model pollutant in industrial wastewater (cathodic compartment). The project represents the first attempt to develop a comprehensive mathematical model for an integrated BES process.  This project is run collaboratively with Dr. Rodriguez.