Douglas Call

This fundamental research is motivated by three major global challenges that directly involve the transformation of gas molecules: carbon dioxide (CO2) capture for greenhouse gas mitigation, CO2 conversion to fuels and chemicals, and nitrogen (N2) gas conversion to biologically available ammonia to meet growing fertilizer demand. The research focuses on creating and investigating multi-functional interfaces that durably immobilize enzymes near their gaseous substrates while simultaneously delivering essential chemical and electrical reducing equivalents and removing reaction products to achieve maximum catalytic rates. Biocatalytic systems to be explored are: conversion of CO2 to bicarbonate catalyzed by carbonic anhydrase, reduction of CO2 to formate catalyzed by formate dehydrogenase, and reduction of N2 to ammonia catalyzed by nitrogenase. We envision that minimization of reaction barriers near immobilized biocatalyst interfaces involving gas molecule conversions will lead to transformative innovations that help overcome global sustainability challenges.

The Science and Technologies for Phosphorus Sustainability (STEPS) Center is a convergence research hub for addressing the fundamental challenges associated with phosphorus sustainability. The vision of STEPS is to develop new scientific and technological solutions to regulating, recovering and reusing phosphorus that can readily be adopted by society through fundamental research conducted by a broad, highly interdisciplinary team. Key outcomes include new atomic-level knowledge of phosphorus interactions with engineered and natural materials, new understanding of phosphorus mobility at industrial, farm, and landscape scales, and prioritization of best management practices and strategies drawn from diverse stakeholder perspectives. Ultimately, STEPS will provide new scientific understanding, enabling new technologies, and transformative improvements in phosphorus sustainability.

There is an urgent need to develop solutions to treat legacy and emerging organic contaminants in water. The objective of this proposal is to investigate the ability of a new class of electrically conductive, biocompatible materials that can quickly and selectively mediate the degradation of mixtures of organic contaminants. The results will lay the foundation for strategies to remediate contaminated environments and degrade contaminants in water/wastewater.

Enabling the next generation of sustainable farms requires a paradigm shift in resource management of the two most critical agricultural inputs for food production: water and nitrogen (N) - based fertilizer. Inefficient management of these resources increases food production costs, decreases productivity, and impacts the environment. An integrated approach is needed to improve the sustainability and efficiency throughout the production chain. Emerging (bio)electrochemical (BEC) technologies offer alternatives to conventional, fossil-fuel intensive N fertilizer production. Recently our team has demonstrated two game-changing BEC technologies: 1) microbial conversion of nitrogen gas into ammonium, and 2) plasma generation of N species (e.g., nitrate, nitrite) and other reactive species in water for fertilization and anti-pathogen benefits. We will integrate these technologies to produce BEC, N-based fertilizer, and with advanced sensor and delivery systems, we will precisely supply fertilizers for sustainable precision agriculture. Our proposed approach focuses on the development of a novel “BEC fertigation on demand system” by using sensor-driven data and molecular analyses to investigate BEC fertigation impact on the plants’ growth, adaptation, and microbiome; its impact on food safety and quality, and its economic feasibility for on-farm deployment.

Around 10 million tons of post-consumer textile waste (PCTW) are disposed of in U.S. landfills annually, 8% of all municipal solid waste. PCTW is landfilled because it contains complex blends of natural and synthetic fibers that are not easy to recycle as well as dyes and other chemicals that interfere with reuse. Microbial communities in anaerobic digesters (AD) have the potential to convert natural fibers in PCTW to a useful biofuel, biomethane, as well as degrade associated dyes and chemicals. By gently deconstructing and separating PCTW into less complex material streams, it will be possible to recover valuable non-degraded fibers, generate co-products and efficiently treat residuals to divert PCTW from landfills. The goal of this project is to use mild enzymatic methods to convert PCTW from large heavy solids to pumpable slurries with compositions that are compatible with microbial growth in AD, while recovering non-degraded fractions for recycling.

Re-engineering the anaerobic co-digestion (AD) of municipal solids waste (MSW) to yield high-value chemical products could dramatically change the economics of this solid waste management strategy. Shutting down the biological pathways to CH4 production in AD (via inhibition of methanogenesis) can result in the production of volatile fatty acids (VFAs) without compromising solids destruction goals. VFAs are highly valued because they can serve as precursors to a wide-spectrum of chemicals, including fuels, paints, adhesives, cosmetics, and food additives. While the knowledge of how to operate AD to generate these VFAs exists, the primary challenge facing implementation of this approach is the lack of effective methods to separate and recover VFAs from AD. The objective of the proposed research is to investigate the potential of an electrically-driven, membrane-based technology to separate and recover VFAs during AD of MSW. The results will provide fundamental insight into VFA transport through membranes and apply the knowledge to the recovery of VFAs from representative MSW mixtures.

Emerging contaminants are widely present in raw and treated drinking water and present an ongoing threat to human health, prosperity, and the planet. Per- and polyfluoroalkyl substances (PFAS), a broad class of fluorinated chemicals compounds used in a variety of industrial products, such as food packages, and household products, have been detected in drinking water across the country, including locally in Wilmington, North Carolina. Many PFAS are known or suspected carcinogens and pose a risk to humans even at trace levels (ng/L to ug/L). Moreover, they present a risk to the planet because they poorly degrade in the environment. The profound health risk of PFAS has therefore created an urgent need to develop viable methods and technologies to remove PFAS from water resources. The proposed technology in this project directly addresses the three aspects of sustainability because it will result in a cost- and energy-efficient PFAS removal method that can be readily adopted in households across the US. Furthermore, this project will provide an excellent opportunity for educating the public, especially school students in the regional community, many of which have been exposed to PFAS-contaminated waters. To broaden our dissemination of our project and the concepts of sustainability, we will attend and present our results in regional science fairs, such as at the NC Science Festival.

The removal of per- and polyfluoroalkly substances (PFASs) from contaminated groundwater is required to minimize human exposure to these compounds. Activated carbon is a widely used sorbent to remove PFASs, but it suffers from two limitations: 1) the inability to remove short-chain PFASs, and 2) the lack of cost-effective regeneration methods. The overall objective of this proposal is to electrically enhance adsorption of high priority PFASs onto activated carbon and electrically discharge them as an innovative, chemical-free regeneration technique.

Nitrogenous fertilizers are critical for sustaining small to large farms in the US. The Haber-Bosch process generates the majority of fixed nitrogen, but it comes at a high cost, both in terms of dollars and environmental impact. Requiring temperatures between 400-500oC and pressures of 150-250 bar, this process consumes 1-2% of global energy. Reliance on fossil fuels to power this process translates into unstable fertilizer prices and a significant release of greenhouse gases. Low-cost and carbon-neutral ammonia fertilizer production is therefore needed to improve the sustainability of our food production systems. Biological nitrogen (N2) fixation, as practiced in the farming of legumes, is attractive because of its low-energy demand, operation under ambient conditions, and point-of-use production; however, slow fixation rates and, in the case of non-legume crops, a lack of abundant N2 fixing symbiotic diazotrophs in the soil, limit the large-scale feasibility of this approach. Moreover, options to accelerate symbiotic N2 fixation rates to the industrial levels needed to compete with the Haber-Bosch process are lacking. As an alternative, we propose investigating a hybrid microbial electrochemical system to electrically enhance microbial N2 fixation rates. Bacteria in these systems consume organic matter (such as waste biomass) and generate electrical current when they respire (breathe) on anode electrodes. By exploiting their physiology, we hypothesize that we can electrically “boost” N2 fixation rates in these organisms. The overall objective of this proposal is to determine the influence of the electrical driving force on the rates, mechanisms, and pathways of microbial N2 fixation. The rationale is that with this knowledge, we can improve N2 fixation rates in these communities and optimize a scalable technological platform to produce fixed nitrogen from small-scale farms to industrial-scale applications.

North Carolina has a tremendous need for efficiently treating high-strength waste streams. These include agricultural residuals, food wastes, and wastewater-derived biosolids. Anaerobic digestion is one promising treatment and energy recovery method, but several limitations prevent widespread adoption. One of which is the instability that can arise from disruptions between key groups of microorganisms and another is the incomplete conversion of organics to methane gas (CH4). To overcome these limitations, we propose augmenting anaerobic digesters with electrically conductive micro-scale particles. These particles have proven effective as conduits for microbe-to-microbe direct electron transfer, resulting in improved rates of CH4 generation using pure strains in the lab. We hypothesize that supplementing anaerobic digesters with these particles will improve stability and CH4 recovery by strengthening interspecies electron transfer between the two central microbial communities: syntrophic bacteria and the methane-generating methanogens. Our objectives are to (1) determine the impact of various particle properties (type, conductivity, size) on organics removal and CH4 generation, (2) determine optimal particle loading densities for two distinct waste streams, and (3) assess the settleability of particle-augmented waste. To do this, we will operate lab-scale anaerobic digesters with and without conductive particles (activated carbon, magnetite, biochar). These findings will be especially beneficial for wastewater treatment facilities and farmers around the state looking for strategies to tip the economics in favor of anaerobic digestion technology while ensuring the health of our water resources.