By Shawn Muslim
This Superfund REU experience was by far the most fun I’ve had learning in a long time. The environment in Dr. Mark Weisner’s lab is “user-friendly” and quite encouraging, post-doc Alexis Carpenter was extremely patient throughout my learning experience and quite knowledgeable. Everyone in the neighboring Gunsch and Hsu-Kim labs were equally engaging and always ready to lend a hand. This positive influence has solidified my future master’s thesis research goals in nanoparticles and water remediation.
As you may remember from some of our other posts, Project 4 is experimenting with how to clean up environmental contaminants using nanoparticles like nano-scale zero valent iron (NZVI). But, due to some of its properties, using NZVI in the environment can be tricky – they’re pretty sensitive and, thus, how they react with themselves and with other compounds is depends on the environment. In most cases, the particles tend to clump together (aggregate) instead of binding with the contaminants they’re supposed to be cleaning up…not very useful for remediating a contaminated site!
I spent my summer working on one possible solution to this problem. The main purpose of my project was to evaluate whether bacteria in the environment are able to break down carboxymethyl cellulose (CMC) that has bound to the surface of NZVI. CMC has long been used to stabilize polymers, and in this experiment we used it to prevent NZVI from clumping and to slow its rate of oxidation. While the presence of CMC on the surface of NZVI helps prevent aggregation, it also blocks contact between the NZVI and the target compounds (again, not useful for remediation). But, if there were a slow biotic degradation of CMC on the particle surface of NZVI then there would be reason to believe that maybe CMC would eventually be degraded by cellulolytic microbes present in the sediment and thereby expose the NZVI to degrade contaminants (remediation!).
By the end of my project I was able to
- isolate cellulose-degrading bacteria,
- synthesize the nanoparticles with a CMC polymer stabilizer, and
- evaluate the biotic degradation of a cellulose-based polymer stabilizer on NZVI.
We modified a colorimetric assay for assessing the rate of the CMC degradation as a function of both time and concentration as developed and presented in a published article on: Quantitative colorimetric measurements of cellulose degradation under microbial culture conditions by Haft, Gardner, and Keating by using CMC instead of cellobiose.
Coming into this project, I had limited chemical engineering experience. However, by the end of my time at Duke, I had gained valuable hands-on experience using a: Nanoseries Zetasizer, sonicator, ALV/LSE J004 Light Scattering Electron and Multiple Digital Correlator, nitrogen glove box, Spectra Max UV-Vis, anaerobic glove box, autoclave, pH conductivity meter, and the DR 4000 UV Spectrophotometer. I had also gained a better understanding of how CMC degrades when bound to a particle surface and when freely dissolved in a solution. Part of the reason I had such a rewarding experience is because I was able to participate in a second project from Dr. Hsu-Kim’s Lab. I helped to synthesize NZVI nanoparticles stabilized with Nitrilotri (methyl phosphoric acid) (ATMP). In this project, the ability of the ATMP-stabilized NZVI to reduce a target compound was compared to unstabilized commercially available NZVI to understand the role of stabilizer and particle size on NZVI’s reductive capacity.
All in all, what a full summer! Better than the classroom. Better than a textbook. This is a story all about how…
Now this is a story all about how,
We’re trying to clean water all around town.
And I’d like to take a minute just sit right tight,
I’ll tell you how you can remediate a Superfund site.
On West Duke’s campus, born and hazed.
Hudson Basement is where I spent most of my days.
Weighing out, assays, pipets all cool
And all, learning real techniques outside grad school.
When a couple of sites, they were really no good,
Started getting toxic in the neighborhood.
Nano-zero valent iron freely donates e’s
We use its reactivity properties to get rid of these.
If we can coat each nano particle with a CMC,
Then we can slow down aggregation of the nano- Z.
If anything I could say this project was rare,
Coating NZVI with a stable polymer.
We used Congo Red Dye for assessing the rates
Of the CMC which we hope will degrade.
Looked at my project, I was half the way there.
Superfund here I come, nano- tech engineer.