Josh Simpson
Temple University, MS
DCA Scholar 2022
Electromethanogenesis in Anaerobic Digestion for Increased Methane Content, Energy Efficiency, and Economic Benefit Project Description:
In 2018 alone, the EPA estimated that 63 million tons of wasted food were produced in commercial, institutional, and residential sectors in the US – of this waste, a whopping 55.9% went to landfills, 12% to controlled combustion, and only 8.3% to anaerobic digestion (AD). There is a growing interest in applying AD to food waste management, but it is hindered by low methane (CH4) content, slow biogas production, and poor system stability. Electromethanogenesis (EM) is a newly discovered methanogenic mechanism that can achieve a high CH4 content (over 98%) with outstanding energy efficiency and economic benefit. During electromethanogenesis, methanogens capable of extracellular electron uptake receive electrons from a cathode electrode to reduce CO2 to CH4.
Josh’s primary research project involves studying the use of electrical enrichment, via applied potential with polarity reversal, for improved electromethanogenesis (EM) in Bioelectrochemical Systems. Josh has deemed this process “electro–syntrophy”. Despite many experiments with applied voltage since the discovery of EM in 2009, very few researchers have toyed with the concept of polarity reversal, with even fewer attempting it. Thus, this relatively novel proposal involves the characterization of EM and Direct Interspecies Electron Transfer (DIET) for improving the anaerobic digestion (AD) of solid and liquid waste. As an alternate pathway in anaerobic digestion, DIET presents several advantages over the predominant hydrogen/formate–-mediated electron pathway, namely: 1) greater system stability through improved resistance to pH shock and high organic loading conditions, 2} a greater biogas production rate, and 3} it is faster, as it does not rely on the diffusion of small electron carriers like hydrogen or formate. Additionally, DIET has a thermodynamic advantage over interspecies hydrogen/formate transfer (~0.7 KJ/mol).
Similarly, EM is a recently discovered method that captures energy from wastewater COD, in the form of methane-rich biogas, by applying a low potential to an electrode immersed in an AD bioreactor. Herein, the electrode itself serves as the direct electron donor for the reduction of CO2 to CH4. While biogas collected from landfills (also known as Landfill Gas or LFG) typically has a methane content of 50–60%, corresponding to an upper calorific value of 6.0 KWh/m3 at STP, EM can achieve a CH4 concentration greater than 98%, with outstanding energy efficiency and economic benefit. Thus, Josh’s current experiment has two main goals: 1) The first goal is to ascertain whether applying potential with polarity reversal (i.e., switching from –0.6 V versus Ag/ AgCI to +0.6V versus Ag/ AgCI after every hydraulic retention time) to reactors supplemented with conductive materials (GAC} will select for both electrotrophic (electron accepting) methanogens and electrogenic (electron donating) bacteria. This will be accomplished through routine 16S rRNA and metagenomic analyses of the biofilm every 9 days. Moreover, Josh hypothesizes that biogas production rate and CH4 content will be greater than both the control reactor (no applied potential, just conductive materials) and the treatment (R1) reactor, which has a constant -0.4V of applied potential. 2} Since both EM and DIET share the characteristic of extracellular electron uptake (EEU} on the electron-receiving side, the second goal of this experiment is to ascertain the mechanistic differences in EEU between DIET and EM, once an electroactive community is achieved. This goal is rooted in the fact that some species, such as M. harundinacea and M. horonobensis, have been shown to be capable of accepting electrons from G. metallireducens via DIET, but NOT capable of performing electromethanogenesis. Thus, it logically follows that the mechanism of EEU is different in DIET versus EM. Elucidating these differences will be accomplished through transcriptomic analyses before and after the applied potential is turned off. In other words, once the applied potential is turned off, electrotrophic methanogens will have to turn to electrogenic bacteria (i.e., Geobacter spp) as an electron donor. Thus, DIET will occur. By comparing what genes are up/down-regulated before and after the potential is removed, Josh hopes to get a better idea at the proteins and genes involved in the two respective processes. In the long run, Josh hopes to develop a dynamic model for anaerobic digestion, using artificial neural networks (ANN}, bioinformatics, and detailed economic analyses.
Biography:
Josh received his undergraduate degree in Environmental Science from Temple University in 2020 where he became fascinated by sustainability challenges within the food-water-energy nexus. While the focus of Josh’s research is on the mechanisms of extracellular electron transfer, Josh is an adamant believer in environmental justice and hopes to incorporate at–risk youth from the surrounding under-served neighborhoods of North Philadelphia to stimulate minority engagement in STEM. Over the summer of 2022, he mentored two local high school students who interned in the lab, teaching them how to work with microbial desalination/electrolysis cells, vacuum membrane distillation, and forward osmosis membranes.
Josh is currently an Environmental Engineering M.S. student at Temple, with an anticipated graduation date of May 2024. He hopes to contribute to the field of waste treatment during this period by providing insights into direct interspecies electron transfer and electromethanogenesis for energy recovery via biomethane. Additionally, he hopes to mentor more local high school students in the lab and get involved with Temple’s Jumpstart program.
