Hydroxylamine Driven Nitrous Oxide Formation During Wastewater Chlorination

Author

• Madelyn Y. Hathcock, Louisiana State University and Agricultural and Mechanical CollegeFollow

Semester of Graduation

Spring 2026

Degree

Master of Science in Civil Engineering (MSCE)

Department

Department of Civil and Environmental Engineering

Document Type

Thesis

Abstract

Despite significant efforts to understand nitrous oxide (N₂O) formation in biological wastewater treatment, a significant downstream source of N₂O formation has been entirely overlooked. One seemingly unknown pathway of N₂O production occurs within the chlorine contact basins of wastewater treatment plants. Free chlorine reacts readily with hydroxylamine (NH₂OH), yielding N₂O gas on a stoichiometric basis. Yet few, if any, reports have documented the amount of NH₂OH that enters wastewater disinfection contactors. Here, this overlooked source of N₂O formation potential (NH₂OH chlorination) is quantified and analyzed in several wastewater systems. Wastewater samples were collected and brought back to the laboratory where N₂O generation was observed during the chlorination of NH₂OH-containing samples using a N₂O probe. Additionally, NH₂OH concentrations in clarifier effluent samples (disinfection contactor influent) were quantified via high performance liquid chromatography with a UV detector (HPLC-UV). The developed method entails the reaction of NH₂OH with a reagent, 8-hydroxyquinoline, to form a larger compound, indooxine, that absorbs strongly in the visible range at 705 nm and at 261 nm in the UV window. This chromatographic method was tested for sensitivity and performance in wastewater and river water matrices, in addition to pure water cases, achieving reliable results in each solution. The protocol achieved accurate measurements of NH₂OH concentrations as low as 0.05 µM, vastly improving previous detection limits. Sampling procedures that ensure preservation of NH₂OH were also established; samples acidified below a pH of 2.0 remained stable under room temperature conditions for up to two months. NH₂OH concentrations were measured in multiple different wastewater systems in southeastern Louisiana for one year. This method revealed that wastewater samples had NH₂OH concentrations ranging between < 0.05 and 19.56 µM. Effective, stoichiometric conversion of NH₂OH to N₂O was confirmed within wastewater during chlorination by using a combination of NH₂OH-quantified N₂O formation and the developed method. According to the findings here, wastewater chlorination contributes an additional 3.4 to 13.7% of N₂O emissions from the discharge of treated wastewater annually than previously estimated. Chemical wastewater disinfection is an important, overlooked source of N₂O gas formation; current estimations of global N₂O wastewater emissions estimates likely need upwards revision.

Date

4-7-2026

Recommended Citation

Hathcock, Madelyn Y., "Hydroxylamine Driven Nitrous Oxide Formation During Wastewater Chlorination" (2026). LSU Master's Theses. 6331.
https://repository.lsu.edu/gradschool_theses/6331

Committee Chair

Snow, Samuel D.

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1