An analysis of UV disinfection of municipal wastewater following natural treatment systems

Author

Jonathan Andrew KirchubelFollow

Graduation Date

Summer 2025

Document Type

Thesis

Program

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

Committee Chair Name

Josephine Archibald

Committee Chair Affiliation

Cal Poly Humboldt Faculty or Staff

Second Committee Member Name

Tesfayohanes Yacob

Second Committee Member Affiliation

Cal Poly Humboldt Faculty or Staff

Third Committee Member Name

Christa Meingast

Third Committee Member Affiliation

Cal Poly Humboldt Faculty or Staff

Keywords

Wastewater disinfection, Natural treatment systems, UV ultra-violet, Municipal

Subject Categories

Environmental Resources Engineering

Abstract

On January 30, 2024, the City of Arcata replaced chlorine with ultraviolet (UV) irradiation as its disinfection method for treating its wastewater prior to discharging to Humboldt Bay. The Arcata wastewater treatment facility (AWTF) utilizes natural treatment systems for treating its secondary effluent, which can provide issues for UV disinfection through variance in turbidity, total suspended solids (TSS), pH, humic acids, and color. This project aimed to identify whether the water quality characteristics of natural treatment systems in the AWTF would impact UV disinfection of municipal wastewater.

Thirty-one sampling periods occurred between June 8, 2024, and March 1, 2025, recording temperature, pH, turbidity, total solids, total dissolved solids (TDS), TSS, total and fecal coliform reduction, phosphorus as orthophosphate, nitrogen as ammonia, UV transmittance (UVT), flows, and precipitation. Through using ANOVA Regression Analysis for 95% confidence intervals, this study showed a strong negative exponential relationship between UVT and turbidity (R² > 0.98, p-value = 2.21 x 10-¹²) and a moderate negative relationship between UVT and total solids and TSS, (R² > 0.60, p-value = 1.5 x 10^-6) and (R² > 0.51, p-value = 1.3 x 10^-4) respectively. Turbidity, total solids, TSS, and flows were not shown to significantly impact log reduction in total and fecal coliforms as average daily dosage remained consistently above the design dosage of 50 mJ/cm², and this was most likely due to compensation through increased power input during times of increased turbidity, solids, and flows.

Citation Style

ASCE

Recommended Citation

Kirchubel, Jonathan Andrew, "An analysis of UV disinfection of municipal wastewater following natural treatment systems" (2025). Cal Poly Humboldt theses and projects. 2331.
https://digitalcommons.humboldt.edu/etd/2331