Document Type

Thesis - Open Access

Award Date

2026

Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

First Advisor

Christopher Schmit

Abstract

This study evaluates the fate and removal efficiency of Escherichia coli (E. coli) across both liquid and sludge treatment processes at a full-scale activated sludge water resource recovery facility (WRRF) in Brookings, South Dakota. Understanding pathogen reduction within wastewater treatment systems is critical for protecting public health and ensuring regulatory compliance, particularly in facilities practicing water reuse and biosolids management. Liquid and sludge samples were collected from multiple treatment stages between January and July 2025 and analyzed using the IDEXX Colilert Quanti-Tray 2000 method. This study quantifies E. coli concentrations throughout the treatment train to assess removal performance and identify key unit processes contributing to microbial reduction. Results demonstrate a progressive decrease in E. coli concentrations across the treatment system. In the liquid stream, concentrations decreased from 2.34 × 10⁶ most probable number (MPN)/100 mL in the influent to 1.11 × 10² MPN/100 mL in the final effluent following ultraviolet disinfection, corresponding to a 4.32-log reduction. In the sludge line, concentrations declined from 7.07 × 10⁶ MPN/g to 2.48 × 10⁴ MPN/g after anaerobic digestion and dewatering, representing a 2.45-log reduction. Among the treatment processes evaluated, biological treatment and secondary clarification were identified as primary contributors to E. coli reduction in the liquid stream, while ultraviolet disinfection provided an additional final barrier, significantly improving effluent quality. In the sludge treatment train, mesophilic anaerobic digestion played a major role in microbial inactivation prior to dewatering. The findings emphasize the importance of integrated monitoring of both wastewater and biosolids streams to fully understand pathogen fate and to ensure effective protection of environmental and public health.

Publisher

South Dakota State University

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Rights Statement

In Copyright