Extracting the Excess, Fueling the Future

August 25, 2014
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The Internship Program at the National Socio-Environmental Synthesis Center (SESYNC) provides undergraduate students with opportunities to deepen their understanding of socio-environmental issues. Interns spend the majority of their time working with mentors at their offices or labs on research projects and participate in weekly Internship Program events, including field trips and seminars. Below, we highlight the summer research experience of one of our interns.

by TAMARA WALSKY
SESYNC intern
University of Maryland student

What do you think smells worse: a power plant, spewing noxious greenhouse gases and heavy particulates into the atmosphere; a landfill, full of used, unwanted trash and the scraps of society and civilization; or a heap of degrading cow manure, festering of flies and oozing liquid just as rancid as its solid mother form? It’s something we don’t often think about, thanks to effective waste removal and storage systems. But that doesn’t mean our current level of consumption and waste output doesn’t pose a problematic habit to kick if we want to get serious about climate change and environmental degradation.

As traditional non-renewable energy sources deplete, there is great need for alternative energies on both industrial and small scales. Anaerobic digesters (AD) create an ideal environment for anaerobic (i.e., non-oxygen using) bacteria to break organic wastes down to simpler organic hydrocarbon products used for fuel, such as methane, by a process called methanogenesis. Microbial fuel cells (MFC) utilize the sulfate reducing anaerobic bacteria present in the organic waste, which reduce hydrogen sulfate to hydrogen sulfide gas, to harness energy via a chemical electric current. Coupled together, the resulting system presents a sustainable, renewable energy source. Digesters provide energy independence by decreasing reliance on fossil fuels and producing heat usable for space heating. Multiple successful digesters operate on a commercial level, but prove too expensive on a small scale, creating a demand for the optimization of digesters for cost effective use, in particular for use by small farmers.

For the study I worked on during my internship, a series of different substrates, including iron additives and bactericides, have been added to the AD in hopes of finding an additive that optimizes the amount of methane and electricity extracted from the organic wastes. In addition, this study evaluates the production of hydrogen sulfide gas (a source of corrosion for the AD) for each substrate.

While operating the digesters and treatments themselves seems like the nitty gritty, my work with the digestate truly digs to the core of the process. By quantifying the microbial community behind each sample, we determine the amount of bacteria for each sample and relate it to the amount of methane and hydrogen sulfide gas produced by the AD—and how that might affect the optimization of conditions for methogen production, decreasing hydrogen sulfide production, and optimally powering a MFC after methanogenesis.

To determine the microbial community composition and quantity, we extract the microbial DNA from the samples and quantify it using a process called qPCR (qualitative polymerase chain reaction.) Much molecular biological work uses kits manufactured by biotech companies and involve adding a series of solutions and filtering your original sample to isolate out the particular substance you want—and from the brown, murky digestate soup emerges a clean, indiscriminate sample, as clear as if it were pure water. Then, the samples were diluted to a concentration of 1.25 ng/uL and a final volume of 25 uL: a tiny sample, but jam packed with genetic material!

The next step: amplify the DNA with qPCR. qPCR uses a fluorescent dye to measure the actual amount of DNA amplified in each cycle. Since we focus on particular types of bacteria, we amplify the DNA with respect to the gene unique to that community—mcrA, a methanogenesis gene; dsrA, a sulfate reducing gene; and 16S, a gene only found in bacteria and archaea (to quantify the entire bacterial and archaeal community in each sample). qPCR plates for the 16S gene run as I type this, and plates for dsrA will follow.

Looking over the graphs of the preliminary data shows the trend that iron additives result in a decreased gene copy number compared to treatments without iron additives. This correlates with the decreased methane production trends from the iron additive treatments. But since some additives reduce H₂S production, the decreased methane production might be worth it!

Top photo: Intern Tamara Walsky pipetting in the Yarwood Lab
Bottom photo: Doctoral candidate Annie Yarberry and the treatment samples in the Lansing Lab

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