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Linda Posada: I Used Sewage Water to Biodegrade Single-Use Plastic Cups!

Did you know that sewage water can be used to test the environmental impact of your single-use plastic cups? I know this may sound strange, but I can explain! This summer, I had the opportunity to work in my first undergraduate research position under Dr. Nathalie Lavoine, who works in the Department of Forest Biomaterials at the College of Natural Resources. My research focused on how different types of plastic degraded over time in a freshwater environment (don’t let the word “freshwater” trick you!). I can’t stand how tons of plastics end up in our oceans, resulting in the deaths of thousands of marine animals and contributing to the microplastic problem. I’ve been trying to find my place in fighting this crisis, so I decided to make research my starting point!

A typical day in the lab wearing fashionable PPE

My first three weeks of work were not what I expected them to be. I was tasked with reading as many research papers on topics like the degradation of plastics in different conditions, different types of plastics, plastic waste in a circular economy, and more! As I accumulated information related to plastics, Dr. Lavoine introduced me to the topic of bioplastics. This was when I shifted my focus to learning more about a specific kind of plastic, polylactic acid better known as PLA. I quickly found that PLA was marketed to be an environmentally friendly product because of its capability of being composted and made from corn. While compostable and biodegradable plastic seems like a great idea, the problems with its disposal are just too big to ignore. The majority of PLA can only be industrially composted and if thrown into the landfill, it can last just as long as other petroleum-based plastics. These inconsistencies made me want to focus and learn more about the issues with PLA so I decided to start my research by conducting a literature review.

I was given the option to present my findings about PLA at the NC State 22nd Annual Summer Undergraduate Research & Creativity Symposium. Compiling the information for my literature review was the easy part but trying to make the actual poster was harder than I expected! To make my poster presentation more impactful, I used the PLA-lined cups from Talley as an example. I wanted to point out the negatives of PLA, one example being its ability to create microplastics faster than other plastics. I also wanted to highlight the lack of industrial composting facilities available to people who live in Wake County. Once presentation day came around, I was happy to share what I had learned with everyone. This was a huge accomplishment for me as I

tend to avoid public speaking but there’s no better way of improving my skills by stepping out of my comfort zone!

Me at the summer symposium (a little nervous)

With my newly acquired knowledge of PLA, I was able to finally start my experiment! First, I had to drive twenty-five minutes to reach the Neuse River Wastewater Treatment Plant in Raleigh, NC, to pick up (free!) sewage water or more scientifically named, return-activated sludge (RAS). Why didn’t I just use regular tap water instead? Well, tap water doesn’t contain an abundance of active and hungry bacteria and other microorganisms -thankfully- to help speed up the so-called biodegradation process. Since I was focusing on testing plastic materials, RAS would allow me to get data faster! I chose to study seven different materials which included store-bought PLA cups, PLA coffee cups from a cafe located in Jordan Hall (I peeled off the PLA lining from the paper and used both as separate samples), paperboard, microcrystalline cellulose, polypropylene, and polystyrene. The microorganisms in the sludge are aerobic, meaning that they need oxygen to survive and eat the plastic samples. This is very important since they were sealed shut into glass bottles with the RAS. I had to be in the lab every other day to check and record the dissolved oxygen levels inside these bottles. If the dissolved oxygen levels ever reached zero, it meant all the microbes had died which would ruin the experiment. Fortunately, this never happened! If the dissolved oxygen levels were low, I would use an air pump to inject enough oxygen into the bottles, measure the dissolved oxygen again to confirm a stable value, screw the bottles shut, and place them into a shaker set at room temperature. I’ve learned how to understand my biodegradation data and am now trying to translate it into words to write a report -which I’m currently doing!

Injecting air into 24 glass bottles took a very long time.
I used this incubator shaker to incubate and shake my samples!

My favorite part of this internship was the flexibility in choosing which topics I wanted to research. I didn’t have to focus on PLA, but I found that the topic was something I could create an impact with. This experience has piqued my interest in pursuing a career in research where I could develop different sustainable and environmentally friendly materials. I’m still keeping my career path options open but I know it will be related to combating our global plastic pollution problem!

I’m very appreciative of Dr. Lavoine’s support throughout this internship. She has helped me learn the basics of research and has helped me grow my knowledge as a whole. I’m grateful to my wonderful mentors, Dr. Mani, Erfan Kimiaei, and Chisom Umeileka for their willingness to help me achieve my goals. I also want to thank the Faculty Research and Professional Development program in the College of Natural Resources for funding my experience. I couldn’t have asked for a better summer research experience!