Author ORCID Identifier

https://orcid.org/0009-0009-7675-1824

Semester

Spring

Date of Graduation

2026

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Emily Garner

Committee Co-Chair

Lance Lin

Committee Member

John Hando

Committee Member

Kevin Orner

Committee Member

Bradley Schmitz

Abstract

Ensuring reliable access to safe drinking water is a growing global challenge as water utilities face variable source water quality driven by population growth, land‑use change, and climate change impacts. To address these challenges, utilities are implementing advanced treatment technologies designed to improve reliability under variable source water conditions. Ozone-biofiltration has emerged as a treatment approach that can reduce a wide range of natural and anthropogenic contaminants. However, despite its increased use, there is limited insight into the biological processes shaping filter function or how they respond to operational and environmental changes. Advances in molecular microbiology and high-throughput sequencing now provide opportunities to resolve these knowledge gaps and link microbial dynamics to treatment outcomes. The overall goal of this research was to develop a comprehensive and mechanistic understanding of ozone-biofiltration performance by integrating long-term monitoring with microbial community profiling and functional predictions at a full-scale drinking water treatment facility.

The specific objectives of this research were to: 1) assess the impacts of intermittent ozonation, variable hydraulic loading, and seasonal fluctuations on treatment performance and identify performance indicators and operational benchmarks for an ozone-biofiltration system, 2) characterize microbial communities in granular activated carbon biofilters over an 18‑month period and determine how operational and environmental factors influence community structure, and 3) examine relationships between microbial community structure and water quality parameters and to identify potential metabolic functions of the microbial community. A comprehensive evaluation of 30 water quality, operational, and biological parameters at 11 locations throughout the full-scale treatment train over one year showed that seasonal and environmental variability had a greater influence on treatment performance than operational changes such as intermittent ozonation or hydraulic re‑rating (obj. 1). However, media adenosine triphosphate (ATP), an indicator of active biomass, decreased significantly following increased hydraulic loading, likely due to increased exposure to chlorine from more frequent backwashing of the biofilters.

Long-term microbial monitoring revealed that the biofilter communities were generally resilient but exhibited measurable shifts in response to seasonal conditions, source water characteristics, and operational variations (obj. 2). For example, ozone application appeared to influence which microbes were present but did not reduce overall microbial diversity. In contrast, the period of increased hydraulic loading, which corresponded to more frequent exposure to chlorine backwash water, resulted in a decrease in microbial diversity. PERMANOVA analyses demonstrated that microbial community structure was strongly associated with specific water quality parameters, with biofilter influent total organic carbon concentrations emerging as the primary correlation during ozone operation and warmer months while nitrate became more influential when ozone was off or during colder periods. Shifts in biofilter community composition also corresponded with higher UV254 transmittance in the effluent during ozone application, which is consistent with the increased biodegradability of organic matter produced through ozonation. Together, these relationships highlight how influent conditions may shape biofilter microbial ecology and how microbial activity influences effluent water quality. Functional predictions using PICRUSt2 identified putative metabolic pathways linked to the taxa in the biofilters which enabled going beyond identifying the microbes present to predicting the degradation pathways those organisms may support within the biofilters (obj. 3). Functional predictions also indicated that intermittent ozone application and seasonal fluctuations produced greater differences in metabolic pathways than the periods of increased hydraulic loading.

This dissertation provides one of the most extensive datasets linking water quality, treatment operations, microbial ecology, and predicted functional potential in a full-scale drinking water ozone-biofiltration system. The findings offer new tools and indicators for water utilities and advance understanding of how operational decisions influence biofilter biology. Collectively, this work supports more informed monitoring and long‑term management of ozone‑biofiltration systems by giving utilities clearer insight into how biological and operational factors interact under increasingly variable environmental conditions.

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