Diploma Thesis Defense by Mrs Sofia Kyritsi
Thesis Title: « Optimization of LDPE pellets biodegradation rates »
Thursday February 11 2021, at: 11:00, Venue: : Link Zoom Meeting
https://tuc-gr.zoom.us/j/82900634959?pwd=ZDZqRTAvV2wrV3czUUd0N1FiRUNoUT09
Examination Committee
- Professor Nicolas Kalogerakis (advisor)
- Associate Professor Danae Venieri
- Dr. Siranidou Evdokia
Abstract
Plastic has been fully integrated into everyday life and is now an integral part of modern life. However, despite its advantages, it is responsible for a large number of environmental problems such as marine and land pollution that negatively affect organisms and human health while at the same time causing a variety of direct and indirect ecological, social and economic problems. Marine plastic waste varies greatly in shape, type and size. Plastic microspheres (pellets) are a typical example. The exposure of plastic particles to various environmental conditions such as sunlight (UV) and high temperatures in combination with mechanical stress (waves, wind) results in their aging. This process contributes significantly to the biodegradation of plastics as it enhances the action of microbial populations on their surface.
The purpose of this dissertation is to study the ability of marine microorganisms, collected from the Souda bay, to biodegrade aged low-density polyethylene (LDPE) pellets in a simulated marine microcosm. The experiment was divided into two parts with variable the carbon source availability. More specifically, in the first part the LDPE microspheres were the only carbon source for the microbial community, while in the second part glucose was periodically added to the treatments. The duration of the simulations was 4 and 2 months, respectively. By comparing the two treatments, it was investigated whether and to what extent the addition of nutrients accelerates the biodegradation of microspheres. The following measurements were performed concerning the polymer and the biofilm developed on the surface of the pellets: weight, microplastic size distribution, infrared spectroscopy with total reflectance technique (FTIR_ATR), dissolved organic carbon (DOC) and quantification of microbial growth, extracellular EPS (proteins, carbohydrates) and measurement of cells within the biofilm.
Overall, marine microorganisms managed to survive and grow successfully in the simulated marine microcosms with or without the addition of nutrients. However, when glucose was added, we observed the growth of a more stable biofilm formation in a shorter period. Spectroscopy showed that the microorganisms caused common and different changes on the surface of the microspheres. Also, the distribution of microparticles in the liquid phase showed that the action of microorganisms resulted in the fragmentation of microplastics in both experiments.
