Graduation Date

Spring 2023

Document Type



Master of Science degree with a major in Environmental Systems, option Environmental Resources Engineering

Committee Chair Name

Eileen Cashman (Co-Chair)

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Catalina Cuellar-Gempeler (Co-Chair)

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Robert Gearheart

Third Committee Member Affiliation

Community Member or Outside Professional

Subject Categories

Environmental Resources Engineering


This thesis addressed two challenging aspects of microplastic research, including the quantification of microplastics in organic-rich water, and the investigation of how microplastics impact microorganisms and related nutrient-cycling. Two projects were designed and executed to address specific research objectives relating to these broad topics. The first objective was to develop and implement methods to determine the effectiveness of microplastic removal across the natural treatment systems at the Arcata Wastewater Treatment Facility (AWTF). The second objective was to observe how microplastics found in domestic wastewater impact the bacterial communities and nitrogen cycling in freshwater treatment wetland sediment through a bench-scale experiment, modelled after Seeley et al. (2020). The objectives for both parts of this study were successfully met. Methods were developed to sample large volumes of AWTF water and determine microplastic concentrations. Compared to the Primary Clarifier effluent, there is a greater than 99% reduction of microplastics in the Oxidation Ponds, with no further net removal in the Treatment Wetlands or Enhancement Wetlands. From the bench-scale experiment, it was determined that polyamide microplastics, commonly found in domestic wastewater, significantly impact freshwater marsh sedimentary bacterial communities and related nitrogen cycling. Overall, results indicate that a high load of microplastics is accumulating in the Oxidation Ponds and that those microplastics have the potential to impact nitrogen cycling and ammonia treatment.

Citation Style



Thesis/Project Location


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