Undergraduate Project

David Valdes - Biochar

One possible carbon capture solution comes in the form of biochar that’s created through pyrolysis, the process that uses an input of biomass and/or organic matter that’s thermally decomposed in the presence of little or no oxygen. This biomass then passes through a combustion chamber (temp range: 300-900 C) where two byproducts are then created: biofuels and biochar. Biochar, in the stable form of solid black carbon, serves as a semi-permanent method of carbon sequestration and can be used to revitalize soil fertility. The biochar can sequester the carbon anywhere from 100 years to approximately 1000 years, depending on the stability of the biochar and the coproducts yielded in this process .1

The pyrolysis process in itself can vary widely; changing the reaction parameters can help you achieve certain chemical and physical characteristics of the biochar. There are two types of pyrolysis: ‘fast pyrolysis’ and ‘slow pyrolysis’. The fast pyrolysis process achieves the same temperature that the slow pyrolysis reaction occurs at, but at a much faster rate. Fast pyrolysis can help you achieve higher biofuel content and less biochar yield with increased stability, producing approximately 90% biofuel product and 10% biochar product. Slow pyrolysis can help you achieve higher quantities of biochar with less stability and less biofuel byproduct, producing approximately 65% biofuel product and 35% biochar product . It’s difficult to sequester 2 more carbon through biochar without depleting its stability and therefore its ability to sequester carbon for longer periods of time. More research needs to be conducted in order to optimize the pyrolysis process and, specifically, improve biochar efficiency by altering its chemical and physical characteristics.

A study calculated that the maximum amount of global carbon removal that biochar production can produce is anywhere between 0.7-1.3 GtC per year . Biochar has the possibility to compete versus other carbon 3 captures solutions, such as DAC, that have higher energy demands and are more expensive. The current limiting factors for widespread implementation of biochar come from underdeveloped biofuel processing infrastructure and the lack of a complete understanding of how beneficial biochar is as a soil additive. Both BECCS and biochar are lacking the necessary carbon and fuel processing and transportation infrastructure required to make this process more economically lucrative.

1 Lee, J. (2010) The Capacity of Smokeless Biomass Pyrolysis for Energy Production, Global Carbon Capture and Sequestration, Earth and Environmental Science 2 Mohan, D. (2014) Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent, Bioresource Technology 3 Smith, P. (2016) Soil carbon sequestration and biochar as negative emission technologies, Global Change Biology

Elizabeth Menten - Advancements In Solar Cell Conversion Efficiencies: The Urgent Need For Good Scientific Writing

This semester in the Chemical Engineering and Applied Chemistry course, we studied a coupled solar cell and hydrogen fuel cell system in an effort to characterize its individual component and coupling efficiencies. We then evaluated the ability of this system to supply a specified energy load over a two-year period, given these performance specifications. This investigation informed our understanding of the need for optimized and well-characterized renewable energy technology-- especially in light of the ongoing global climate crisis.

Through our investigation, we determined the efficiency of the photovoltaic (PV) cell to be 6.6%, the efficiency of the electrolyzer to be 82.8%, and the efficiency of the fuel cell to be 36.4%. The coupling efficiency of the PV-electrolyzer system was determined to be 90.4%. We were then able to conclude that the coupled PV-fuel cell system would not be able to supply the necessary power load over the course of two years. To compensate for this energy deficit, 2,642 m³ of hydrogen must be supplied, accounting for the efficiencies of hydrogen storage and the fuel cell.

It was clear, through this analysis, that the unsatisfactory efficiency of the PV cell is the rate-limiting step, as it were, of effective deployment of this system for sustainable energy production: only a small fraction of the incident solar radiation was effectively converted to usable energy. This understanding motivates investigation of the ongoing research into PV cell design optimization.

Following the move of classes to an online format, Professors Aghavni Bedrossian and Jim Russo have worked to keep us abreast of recent breakthroughs in fields relevant to the experiments we have conducted this semester. One such update referenced a paper published by the III-V Multijunctions Group at the National Renewable Energy Laboratory (NREL) which detailed the design of a solar cell with record-breaking solar conversion efficiency.^[1]

As discussed in this paper published by Geisz et al., multiple junctions and concentrated light have revolutionized the solar-to-electricity conversion efficiencies of solar cells. Whereas single-junction flat-plate terrestrial solar cells are fundamentally limited to conversion efficiencies of about 30%, the III-V Multijunctions Group demonstrated that by implementing multi-junction and light concentration innovations in their design, they were able to achieve efficiencies of up to 47.1%. That is, by incorporating multiple layers of semiconductor materials-- each with a distinct bandgap that facilitates maximal absorption at a specific photon wavelength-- this solar cell design more effectively harnesses a larger portion of the broad solar spectrum, thereby improving the conversion efficiency of the incident solar energy. While the six-junction design proposed in this paper achieved a conversion efficiency of 47.1%, the group anticipated that up to 85% efficiency could theoretically be achieved through  implementation of an infinite number of junctions at maximum concentration. They specifically reference the seminal paper published by Martí and Araújo in 1996, which explores the thermodynamic limiting efficiency of multigap systems through balance theory.^[2] Similarly, by concentrating the incident light-- a technique which is achieved using systems of lenses or curved and flat mirrors^[3]-- the group was able to significantly improve the measured current density in their engineered device, consequently increasing the conversion efficiency. Through these innovations, the NREL group achieved an improvement in solar conversion efficiency (relative to single-junction flat-plate terrestrial solar cells) of almost 60%.

With such gains in efficiency, the PV-fuel cell system we studied in our coupling experiment would not only meet the specified energy demand, but significantly exceed it. The resulting excess energy could then be leveraged to enable hydrogen production for efficient energy storage: over the course of two years, the PV-fuel cell system would produce 5,768 m³ of surplus hydrogen under the determined performance specifications. As demonstrated by these calculations, this work to optimize solar cell efficiencies-- carried out by research groups like the one at NREL-- translates to significant steps towards a revolution in our energy dependence and salient progress in our efforts to combat global warming.

Discussion of these advances in engineered technologies-- especially within the field of renewable energy-- is critical. The need for clear, approachable, and topical scientific literature for the public sphere could not be greater than in this moment. Misinformation and misunderstanding, propagated by pseudoscience and manipulated data, is both widespread and dangerous. Over the course of my four years at Columbia, I have been a part of a community that has redefined the frontiers of what was thought possible. If there is one thing I have learned as a CU engineer, it is that we cannot constrain possibility-- the limits on our ability to innovate are further away than we can resolve. After all, at one point, we thought it impossible to get to the moon.

Chang M. Yun - Covid-19 Antibody Testing and ELISAs (Enzyme-Linked Immunosorbent assays)

With the Covid-19 pandemic beginning to show signs of slowing down, the world is now trying to figure out how to bring things back the way they were. One solution that has been gaining spotlight is antibody testing. Antibody testing is a medical test that checks the presence of specific antibodies in an individual’s blood stream. By testing for antibodies that target the Covid-19 virus, we can verify if the individual has been previously infected by the virus, and thus will likely have immunity against the virus going forward. Many countries, such as Germany, China, and the US, are looking towards antibody tests as the road to reopening the economy.

How do antibody tests work? While there are several serological antibody testing methods, including agglutination, fluorescent/chemiluminescent antigens, precipitation etc., one technology has been providing accurate and effective detection of small concentrations of macromolecules: ELISA, or Enzyme-Linked Immunosorbent assays.

ELISAs work by attaching specific indicator enzymes to the immunoassay reagent, such as horseradish peroxidase (HRP) or alkaline phosphatase (AP). The reagent (in the case of antibody testing, the corresponding antigen) binds to the target antibody ‘analyte’. The antibody-antigen pair can then be identified via the attached enzyme, with the addition of certain reagents (e.g. peroxide or phosphate)

Lactase Enzyme Inhibition and ELISA Enzymes and antibodies operate under similar mechanisms. For enzymes, the ‘enzyme’ is the selective protein molecule and the ‘substrate’ is the target, while for antibodies, the ‘antibody’ is the selective protein and the ‘antigen’ is the target. The two differ only by function: enzymes function as biocatalysts that accelerate a reaction; antibodies function as an immune system response to neutralize pathogenic threats.

Like our studies of lactase inhibition, we could expand the experiment to study activity of 1) the antibody, and 2) the linked enzyme (HRP or AP) under different conditions. 1) Antibody-antigen sensitivity is key to precise measurement of analyte concentrations. Analytic modeling of antibody activity can provide insight into the accuracy of ELISA tests. 2) ELISA requires good understanding of the linked enzyme’s activity, in order to use the enzyme to detect and calculate analyte concentration. Inhibition of the linked enzyme can seriously disrupt ELISA test accuracy.

While ELISA may not prove to be the solution to the Covid-19 problem, it could be the answer for other future infections.

References
‘How does a coronavirus antibody home test kit work, and how do I get one?’ The Telegraph, 04/30/2020
‘What You Need to Know About the Covid-19 Antibody Test’ The New York Times, 04/30/2020
Raso, V., Stollar, B. D., Antibody-enzyme analogy. Comparison of enzymes and antibodies specific for phosphopyridoxyltyrosine. Biochemistry 1975, 14, 3, 591-599
Adams, R. E. et al. Evaluation of antibody testing for SARS-Cov-2 using ELISA and lateral flow immunoassays. medRxiv 2020.04.15.20066407