Semester of Graduation

Summer 2025

Degree

Master of Science (MS)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

The edaphic characteristics of Louisiana particularly in Tangipahoa parish make the suitability of onsite wastewater treatment systems a challenge. Sewage runoff through ditches from failed aerobic treatment units (ATUs) during intense rainfall impacting nearby water bodies. The Yellow Water and the Natalbany Rivers in the Tangipahoa parish are such rivers that have been impacted by fecal contamination posing potential risks to humans and the aquatic biota. Germicidal ultraviolet (UVC) light-emitting diodes (LEDs) technology offers exciting advancements for water and wastewater disinfection. Although UV disinfection of ATU effluent is a promising solution, cellular repair is triggered which includes dark, or photo-repair post-UVC exposure. A novel disinfection technology for onsite treatment systems has been assembled. The reactor was tested for UVC doses achieved using chemical actinometry (potassium ferrioxalate) and with over 5-log reduction using a fluence of 15.2 mJ/cm2 and rate constant of 0.299 ±0.037 cm2/mJ. Disinfection experiments were performed under varied turbid conditions to test the effects of full and pulsed illumination (50% and 25% duty cycle) and a flow-through process using Escherichia coli ATCC 15597. Particle size and type influenced UV disinfection efficiency. The results indicated a decline in disinfection efficiency, as turbidity (amount of silica particles) increased with respect to the particle sizes. Further, photo-repair experiments were performed obtaining the highest survival fraction of 2.159 ± 0.67 % and SUVA at 3.6 NTU suggesting high humic or aromatic hydrophobic matter which absorbs photons and aggregates out of solution providing a shield and source of attachment for microorganisms. Micro-toxicity and residual chlorine experiments were performed obtaining minimal toxic levels (peak level: 3.61%) and residual chlorine levels of ~0.5 mg/L. Additionally, the novel UV/Cl technology addresses the drawbacks of traditional ATU designs with a decrease in thermotolerant coliform count to ~ 2 log when the retention time and water depth within the reactor were optimized. Absorption coefficient at 278 nm obtained a 13.3% higher fluence per unit power. Also, the UV-LED reactor made up of 101.6 cm long polypropylene plastic (ADR-002) was the most energy efficient. Smart reactor design with optimum water depth might suppress turbidity impact on UV disinfection efficiency.

Date

7-30-2025

Committee Chair

Snow, Samuel D.

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