Semester

Spring

Date of Graduation

2026

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Lian-Shin Lin

Committee Co-Chair

Emily Garner

Committee Member

Sean Collins

Abstract

Aerobic microbial reactions have commonly been utilized in treatment processes to oxidize and remove organics and nitrogen through aeration, using processes such as nitrification that converts ammonium (NH4+) into nitrite (NO2-) and nitrate (NO3-). Anoxic microbial reactions like denitrification often require organic compounds as an external source to chemically reduce the oxidized nitrogen (NO3- and NO2-) to nitrogen gas (N2) for nitrogen removal from the liquid phase. These mainstream processes have a high chemical cost and energy footprint which results in an increased release of greenhouse gas (GHG) emissions. The introduction of iron (Fe) as ferric iron (Fe3+) under iron reducing conditions has shown promotion of both organics and ammonium oxidation without aeration, complete nitrogen removal without additional organic dosing, and decreased sludge production due to the lower bacterial yields. Dosing Fe within an upflow anaerobic sludge-blanket (UASB) bioreactor can further reduce the environmental footprint and associated GHG emissions, while allowing for resource recovery of generated byproducts like vivianite (Fe3(PO4)2·8H2O). Internal cycling of Fe in the bioreactor through iron redox reactions that facilitate continuous removal of organics, nitrogen, and phosphate results in a significantly lower Fe demand compared to stoichiometric estimations.

Bench-scale testing of a 5L UASB bioreactor was conducted in this study to evaluate the feasibility of the treatment concept. Dosed with 0.1 g/L Fe to treat a medium to high strength synthetic municipal wastewater (200 mg/L carbon, 35 mg/L ammonium, 9.5 mg/L phosphate), the bioreactor was operated in three phases over a 10-month period under a hydraulic retention time (HRT) of 8 hours (flow rate: 0.64 L/hr and a upward velocity: 0.12 m/hr). The theoretical molar concentration required for this wastewater was calculated to be 1.8 mol/L ferric iron while the actual dose was only 0.0019 mol/L (i.e., 0.1% of the stoichiometric estimation). Performance showed that Phase One had the highest percent removal for phosphate (62%), organics (81%), nitrate (60%), and nitrite (68%), with a high iron retention (93%) whereas Phase Three had the highest ammonium removal (66%). Performance variability was a result of sludge removal techniques that were tested during Phase Two. Microbial community characterization was also completed to elucidate the microbial functions that facilitated the pollutant removal. Differences in bacterial diversity across the column of the bioreactor were observed, suggesting specialized colonies forming at different heights of the UASB bioreactor. The results show that there is nutrient cycling occurring within the bioreactor and that there is potential for concurrent organics and ammonium removal in a singular bioreactor, with an increased Fe dose likely to improve the removal performance.

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