Increasing aridity in already water scarce regions in the United States and around the world is being exacerbated with increased population combined with climate change. With dwindling freshwater resources in these areas, we are forced to turn to non-traditional water sources, such as reclaimed wastewater. Current wastewater reuse strategies involve the use of expensive and energy intensive membrane technology. These membrane systems, however, are cost prohibitive and require large amounts of energy thereby leading to carbon dioxide emissions which can further exacerbate climate change. There may be other, less energy intensive options that can be used in combination with, or in lieu of, these technologies.
This project aims to have a profound impact on the sustainability of wastewater treatment through the incorporation of nanotechnology. By using a fixed electrogenic biofilm on an electrically conductive substrate, organic contaminants in wastewater can be anaerobically degraded. The proposed work considers the use of an activated carbon nanofiber nonwoven (ACNFN) as a novel biofilm substrate as it will facilitate the transfer of electrons from the biofilm during anaerobic degradation, increasing treatment efficiency. A typical platform for evaluating this method of wastewater treatment is the microbial fuel cell (MFC). This project, however, is not intended to maximize power production of the MFC system but instead focuses on elucidating the influence of biofilm substrate architecture, surface area, conductivity, and surface functionality on wastewater treatment efficiency during anaerobic biological treatment, here measured as a reduction in chemical oxygen demand (COD). These novel materials, constructed from thermal treatment of polymeric nanofiber precursors offer many advantages over existing conductive biofilm substrates.
This project uniquely combines a novel nanomaterial into a wastewater treatment platform. Combining materials science, nanotechnology, biotechnology, and chemical engineering, the collaborative research team will use a multidisciplinary approach to integrating these disparate technologies. Carbon-based substrates for MFC treatment systems are common, but never before has a nanofibrous nonwoven carbon material been considered as a biofilm substrate. By using this extraordinary material with excellent electrical properties and an exceptionally high specific surface area, wastewater treatment efficiency of this emerging technology could vastly improve.
The societal impacts of energy neutral (or possibly net energy positive) wastewater treatment would be significant given the significant energy allocation currently given to the practice (3% of total energy use in the U.S.). By greatly reducing, or even eliminating this energy requirement, we would improve the sustainability of wastewater treatment while simultaneously reducing carbon dioxide emissions which exacerbate climate change. This technology may also provide a low energy treatment option for the developing world, where electricity is not always available in remote areas.
For direct potable reuse ever to be accepted, educating the public about various reuse technologies is essential. Both the PI and co-PI are full affiliates of the Center for Environmental Sciences and Engineering, a research center which promotes multidisciplinary research, education, and outreach in environmental science, engineering, policy, and sustainability. Through this entity, The PI and co-PI will conduct a series of education programs, including Engineering 2000 and the da Vinci Project. Both programs specifically target high school students and teachers, respectively, from the Greater Hartford Area and give the PI and co-PI an opportunity to disseminate information about current and emerging water treatment technologies. Underrepresented groups will be specifically encouraged to take advantage of sustainable engineering education and research opportunities through university programs like the Science Engineering & Health Professions Collaborative Symposium at the University of Connecticut and an Environmental Issues Seminar at a local community college
Jeffrey McCutcheon and Baikun Li This work has successfully demonstrated that a new material, called activated carbon nanofiber nonwoven (ACNFN) serves as a superior anode material in a microbial fuel cell (MFC). The MFC platform presents a unique opportunity to treat wastewater while simultaneously generating a small, albeit non-negligible, amount of electricity. We have demonstrated that the MFC platform, at a lab scale, can be effective means at reducing the contaminant loading of wastewater using only the bacteria that are present in that wastewater. During the digestion of these organic contaminants, electrons are produced. In the absence of oxygen, these electrons are free to move into a circuit where they become electrical current that can operate equipment and instrumentation. The bacteria act as the catalyst that degrades the organic material and generates the electric current. This bacteria must reside directly on the anode of the fuel cell in the form of a biofilm. The anode must be capable of holding a large amount of bacteria in order to promote the reaction. However, many anode materials not only cannot hold a large amount of bacteria, they also cannot easily accept the electrons that are produced by the bacteria. ACNFN is a material based off of electrospun fibers that fulfill the needs of the MFC anode by offering a high surface area for electron transfer and a high porosity to support a large quantity of biofilm. Electrospun nanofibers were originally developed as scaffolds for tissue engineering and thus they serve as an appropriate platform for holding a biofilm in a MFC. We made these fibers by electrospinning a polymer known as polyacrylonitrile. This polymer is a known precursor to carbon and, through a series of thermal treatments, can be changed into the carbon nanofiber nonwoven. Subsequent steam exposure at high temperature activates the carbon, giving it a high surface area similar to the granular activated carbon that might be used for water filtration. We tested these materials as anodes in MFCs and found that the organic degradation performance exceeded that of conventional anode materials like carbon cloth and granular activated carbon. The power production capability substantially exceeded these anodes as well, with our anodes showing a 6 fold increase in current density over the best performing anodes in the literature thus far. This result is largely a result of the anodes being able to hold a substantial amount of biofilm because of their high porosity and surface area. Figures 1 shows a scanning electron microscope image of the biofilm forming on the ACNFN. The next steps would be to make enough of this material to place into a sizeable MFC system that is beyond the bench scale. We believe that through scaleup of the ACNFN fabrication process, we would be able to make a substantial amount of anode material to clean raw wastewater and generate enough power to run simple instrumentation. Further applications of MFC technology to beyond wastewater, such as benthic microbial fuel cells (that can generate power from sediments) may also be enabled by this material.
