Research

Converting nitrogen gas into fertilizer and food

Ammonia is a critical resource for farming and industrial activities. The majority of ammonia is generated through the industrial scale Haber-Bosch process. While highly efficient, this process consumes 1-2% of global energy and generates 2.5% of all carbon dioxide emissions annually. It is critically important to discover sustainable and low-cost alternatives to the Haber-Bosch process. Naturally occurring microorganisms can convert atmospheric nitrogen gas into ammonium and can do so at ambient temperature and pressure. We are exploring the use of electricity to drive the microbial conversion of nitrogen gas into ammonium. This technique uses low voltages (~0.5 volts) and can result in microbial fixation rates of nitrogen gas that rival those of model aerobic diazotrophs. Additionally, we are studying the ability of mixed or "open" cultures to accumulate sufficient biomass to provide natural "microbial fertilizers" that can support the growth of crops.

Collaborators

Amy Grunden (Plant and Microbial Biology, NC State), Mike Hyman (Plant and Microbial Biology, NC State), Rodolophe Barrangou (Food Science, NC State)

Waste = Resource

We look at waste as a resource that contains valuable energy, water, and nutrients. Domestic, industrial, and animal wastewaters are rich in these resources. The challenge is to extract them in a cost and energy effective manner. We are currently focusing on anaerobic digestion, which is a commercially-available process for degrading organic waste into a variety of products such as biogas. We seek a basic understanding of how microbial communities in these systems work together to degrade complex wastes. We study the use of electrically conductive materials to accelerate electron transfer within these communities and increase rates of waste degradation. Currently we are examining process controls that can shut down electron flow towards methanogenesis in order to recover more valuable products such as volatile fatty acids. We also collaborate with materials scientists to understand fundamental mechanisms of phosphate (an important nutrient present in wastewater) removal using metal-based sorbents.

Collaborators

Francis de Los Reyes (Environmental Engineering, NC State); Mort Barlaz (Environmental Engineering, NC State); Orlando Coronell (Environmental Sciences and Engineering, UNC-CH); Jeffrey Dick (Chemistry, UNC-CH).

Contaminant transformations mediated by hybrid microbe-material reactions

Pollution from past releases of toxic organic contaminants continue to plague the Nation's water, soil, and sediment. While various technologies and approaches have been developed to remediate these legacy pollutants, they continue to present challenges for communities around the country. Our overall goal is to study fundamental mechanisms of how microbial-driven electron transfer into redox-active materials transforms organic contaminants. Conventional methods for the biological treatment of organic contaminants like chlorinated solvents rely on the activity of specific bacteria. These bacteria are often low in abundance and sparsely distributed in the subsurface. Amending materials that can harness the activity of more widely abundant bacteria may improve our ability to enhance and sustain contaminant removal. Geobacter, a group of bacteria that are present in water, soil, and sediment are extremely metabolically versatile in their ability to utilize insoluble electron acceptors such as pyrogenic carbonaceous materials (PCMs). Geobacter use PCMs such as activated carbon and biochar to shuttle electrons through the material and abiotically degrade contaminants on the material surface. We are combining electrochemistry, spectroscopy, and molecular biology to address knowledge gaps at microbial-material-contaminant interfaces. The fundamental insight gained will permit the informed design and optimization of materials that can degrade specific pollutants. These materials can then be applied to engineered systems such as water and wastewater treatment plants.

Electrically-Driven Separations

Two grand challenges facing the water treatment community are (1) the need for new sources of freshwater and (2) the presence of challenging legacy and emerging contaminants. Electrochemical separations are a particularly attractive option to address these challenges because they require lower energy demands relative to conventional pressurized membrane processes, and they can be easily cycled for in-situ regeneration. Our group studies capacitive deionization (CDI), wherein ions (e.g., Na+ and Cl-) are "pushed" into charged electrode microstructures. Reversing the charge releases the ions and regenerates the electrodes. We are studying new electrode materials and configurations to maximize salt adsorption capacities during desalination and are exploring ionic contaminant removals in the presence of charged sorbents. Our goal is to provide the fundamental knowledge needed to inform CDI designs for both decentralized and centralized applications.

Collaborators

Detlef Knappe (Environmental Engineering, NC State)