Date of Award

2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Civil and Environmental Engineering

Specialization

Environmental Engineering

Department

Civil and Environmental Engineering

First Advisor

Vinka Oyanedel Craver

Abstract

This thesis addresses three challenges related to the microplastic contamination in water and wastewater treatment plants. The first challenge is the multiple methodologies used to collect, quantify, and characterize microplastics in both wastewater and drinking water. Our study shows a lack of consensus regarding the techniques used at all of the stages (from collection to characterization) required for the quantification of microplastics in urban water systems. This represents a barrier to accurately determine the loads of microplastic contamination and to the comparison of the results obtained among different studies. Our results indicate large discrepancies in the concentrations reported in both wastewater effluents and drinking water, microplastic characteristics (i.e. size, color, shape, and composition), and quality control and assurance procedures. Finally, we propose the use of a ranking system that can stimulate researchers to reduce the deficit of studies using the results obtained in the high-ranked papers.

The second challenge is the large contribution of wastewater treatment plants in discharging microplastic into natural bodies of water. This study evaluated the use of electrocoagulation for the removal of microplastics from both synthetic wastewater solutions and real wastewater effluents. The experiments were performed in batch reactors using commercial polyester microplastic glitter. The results indicate removal efficiencies in synthetic wastewater ranging between 98% and 99% using initial pH between 4 and 7 and applying current densities of 2.88 mA/cm2 and 8.07 mA/cm2, respectively. When real wastewater effluent was used, electrocoagulation removed 96.5% of MPs, 92.2% of COD, and 88.8% of fecal coliform colonies using the best conditions found for synthetic wastewater.

The third challenge is the use of model particles to study the microplastic contamination in aquatic environments. Our study used glitter as a model for microplastic laboratory testing due to their diversity in sizes, shapes and composite composition. This study characterized the physical and chemical properties of different size classes and colors of commercial microplastic glitters; and tests the weathering effects on them by simulating their degradability in synthetic wastewater performed in batch reactors. The results indicate that size, composition and structure of the particles lead to different behavior during weathering tests. Delamination, cracks and breaking off were observed in the large particles, while no physical changes were observed for the small particles. However, titanium oxide was released onto the small particles’ surface, indicating that this metal oxide became more reactive during the weathering process. The addition of titanium oxide to those particles.

In conclusion, this study provides an overview of the MP contamination in water and wastewater and presents some challenges in the research field while providing possible solutions and suggests recommendations for further research.

Available for download on Monday, May 16, 2022

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