The Effects of Biofilms on the Settling and Transport of Microplastic Particles
Open Access
- Author:
- Fazio, Annalie
- Graduate Program:
- Mechanical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 24, 2022
- Committee Members:
- Daniel Haworth, Professor in Charge/Director of Graduate Studies
Margaret Louise Byron, Thesis Advisor/Co-Advisor
Jay Regan, Committee Member
Matthew J Rau, Committee Member - Keywords:
- Microplastics
Biofilms
Spatial distribution
Rise velocity
Lateral motion
Tumbling rate
Biofilm coverage - Abstract:
- Microplastic (MP) particles-- small pieces of plastic ranging from nanometers to several millimeters in length-- are becoming more and more common in aquatic ecosystems all over the world, and are a major source of pollution within the environment. They enter the environment from many channels and in a variety of forms, including microfibers shed from clothing, microbeads from cosmetics, and a number of byproducts from industrial processes. Upon their introduction into the environment, plastic particles may be inert, but they quickly become active participants within ecosystems due to the growth of biofilms upon their surfaces. These biofilms include microbial communities of bacteria, algae, fungi, protozoa, and other microorganisms, which adhere to virtually all surfaces. The biofilms formed upon the surfaces of MPs affect important physical parameters, such as settling velocity and aggregation potential; however, very little research focuses on how the presence and/or spatial distribution of biofilms over the microplastics’ surface can affect their overall transport. Particle-scale physical properties like shape, mass distribution, and surface properties may play a major role in how MPs are transported throughout the environment; biofilm development (and its uniformity or non-uniformity over a surface) affect these properties. Here, we investigate how the presence and the spatial distribution of biofilm affects the settling and rising of MPs. As a starting point, we compare the rising behavior of positively buoyant virgin plastic pellets (nurdles) subjected to two different biofilm colonization regimes. In the first of the two colonization regimes, nurdles float undisturbed at the water surface and biofilm develops only on one side of the plastic. In the second, nurdles are regularly mixed into the water, allowing the biofilm to develop on all sides. The nurdles were then recorded while rising through water, using a macro lens and a high-speed videography. From the videos, we extracted the rising kinematics and calculated the rising velocity; we then compared the rising velocity and overall rising behavior between the differently colonized MPs. We find that the presence of biofilm reduces rising velocity relative to the un-biofilmed case, and that the non-uniformly biofilmed nurdles rise more slowly than the uniformly biofilmed nurdles despite similar biofilm coverage (in the regions of the nurdles that do have biofilm present). This leads to the conclusion that the spatial distribution of biofilm affects rising velocity, and may be a key factor in the overall environmental transport of MPs