Term of Award

Fall 2017

Degree Name

Master of Science in Applied Engineering (M.S.A.E.)

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Copyright Statement / License for Reuse

Digital Commons@Georgia Southern License

Committee Chair

Francisco Cubas

Committee Member 1

Arpita Saha

Committee Member 2

Peter Rogers

Abstract

Ammonia accumulation in surface waters is of great concern because it exacerbates eutrophication, is toxic, and it is a disinfection byproduct precursor. In surface waters, ammonia may be rapidly oxidized, consumed by aquatic biota, or it may directly sorb into the sediment surface. Although, the mechanisms controlling ammonia production and oxidation are well understood, little is known about the mechanisms governing sediment ammonia sorption and desorption. The study aims at illuminating the effect of ORP and different environmental conditions on sediment ammonia desorption as well as the sediment ammonia release. In certain cases, field testing of surface waters exhibits, the concentration of ammonia as high as 5 mg-N/L in the absence of oxygen. Lab results showed that, sediment ammonia release occurs in both aerobic and anaerobic environments at comparable rates, suggesting ammonia release is not affected by the level of oxidation of the system. However, experimental analyses revealed that, ammonia desorption from the sediments increases as the oxidation-reduction potential (ORP) of the system decreases. Furthermore, nitrate can decrease sediment ammonia desorption, eventually the sediment ammonia release, by elevating oxidation reduction potential. In microcosm set ups, the ammonia concentration in increased to values as high as 1.8 mg/L-N which reflected the total sediment ammonia release in the anaerobic or reduced environment (ORP-100 mV). Furthermore, cation exchange analyses performed on the sediments showed that, extracted ammonia concentration may reach values as high as 23mg-N/L, demonstrating the high capacity for sediments to continuously produce and sorb ammonia. Additionally, in reduced environments (-100 mV), sediment ammonia desorption was approximately 25% more than that in an oxidized environment (380mV). These results suggest that, under reduced or low ORP environments, sediments lose their ammonia sorption capacity. The understanding helps to manage sediment ammonia release as well as contributes to the overall nitrogen cycle.

Research Data and Supplementary Material

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