07/10/2025
By Danielle Fretwell

The Francis College of Engineering, Department of Civil and Environmental Engineering, invites you to attend a Doctoral Dissertation defense by Mythreyi Sivaraman on: "Environmental assessment and recycling methods for two types of contemporary solid waste."

Candidate Name: Mythreyi Sivaraman
Degree: Doctoral
Defense Date: Tuesday, July 22, 2025
Time: 1 - 4 p.m.
Location: Perry Hall, Room 215

Committee:
Advisor: Weile Yan, Associate Professor, Civil and Environmental Engineering, UMass Lowell

Committee Members*
1. Robert Whitehouse, Ph.D., Adjust Faculty, Plastics Engineering, UMass Lowell
2. Clifford Bruell, Ph.D., Professor Emeritus, Civil and Environmental Engineering, UMass Lowell
3. Xiaoqi Zhang, Ph.D., Professor(Chair), Civil and Environmental Engineering, UMass Lowell

Abstract:
Microplastics, defined as plastic debris smaller than 5 mm, are emerging environmental contaminants found widely in both terrestrial and aquatic systems due to extensive plastic use and inadequate waste management. Their small size, low abundance, and the complexity of environmental matrices make detection and quantification challenging. While previous studies show that appropriate pretreatment combined with thermal analysis by pyrolysis can enable quantification, existing protocols still need optimization to improve accuracy and sensitivity. Moreover, data on the size- and depth-dependent distribution of microplastics remain limited and inconsistent, highlighting the need for further research to address this gap. In this dissertation, the author investigated plastic debris distribution patterns across four New England states using the Marine Debris Tracker, a citizen science–based tool, and complemented this with the application of a thermal degradation method, pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS), to identify and quantify microplastics in both coastal and riverine environments. Beach sand samples were collected by the author from two public beach parks along the northeastern U.S. coast (Salisbury Beach, MA and Hampton Beach, NH), with the motivation to understand size and depth dependent distribution of microplastics. The river sediments were obtained from the Indian Head River and the Merrimack River to further refine the pretreatment method established in the beach study, tailoring it for river sediments and enabling comparison of size-dependent distributions between coastal and riverine environments. At both Salisbury and Hampton beaches, polyethylene terephthalate (PET) and polystyrene (PS) were identified primarily in the surface layer (0–5 cm), with notable differences in abundance between surface and subsurface (5–10 cm) samples. Finer microplastics (1.2–100 µm) tended to accumulate near the surface, while no clear depth-dependent trend was observed for
intermediate-sized particles (100 µm–1.2 mm). The two rivers also differed significantly in microplastic abundance, with the Indian Head River exhibiting higher overall levels than the Merrimack River, likely due to differences in location and hydrodynamic conditions. In contrast to PET and PS, polyethylene (PE) and polypropylene (PP) were not detected at either beach site or in the Merrimack River. However, intermediate-sized PE particles were identified in the Indian Head River samples using attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR). The plastic debris trends identified using the citizen science tool, together with the abundance and size and depth-dependent distribution of microplastics quantified in this dissertation, could provide critical insight for shaping policies to mitigate plastic pollution in coastal and freshwater systems. In the final part of this dissertation, the author addressed sustainable resource recovery to meet critical material demands in a world transitioning toward carbon neutrality. This was investigated through the selective separation of lithium (Li), nickel (Ni), and cobalt (Co) from spent lithium-ion battery black mass using electrodialysis (ED). Commercial cation exchange membranes were surface-modified to enhance lithium selectivity. The modified membranes demonstrated approximately
200-fold and 12-fold greater selectivity for Li⁺ over Co²⁺ compared to unmodified and monovalent-selective membranes, respectively. Systematic studies were conducted to evaluate the effects of polyelectrolyte molecular weight, concentration, applied voltage, and feed composition on lithium flux, current efficiency, and specific energy consumption.