ANAEROBIC AMMONIUM REMOVAL BY FEAMMOX BACTERIA IN ELECTRODE BASED SYSTEMS & MICROBIAL PERFORMANCE IN A NITRIC OXIDE DENITRIFICATION BIOREACTOR.

Abstract

The coupling of natural nitrogen removal pathways into engineered systems helps minimize the detrimental effects of excessive nitrogen releases. The dominant anthropogenic nitrogen form is ammonium, which accumulates in soils and water, and undergoes nitrification and denitrification forming NO, N2O and N2 which are released to the atmosphere. The demand for clean resources requires the removal of N pollution, thus, we need to improve the existing technologies and development new ones with lower energy demand. Therefore, a core step is to understand the nitrogen cycle, the organisms involved, and their needs and interactions in different environments.

The motivation of this work is to contribute to: 1) the understanding of anaerobic ammonium oxidation by the Feammox bacterium Acidimicrobiaceae sp. A6 (A6), and its ability to use electrodes as terminal electron acceptor in lieu of iron oxides, its natural electron acceptor; and 2) the understanding of the denitrifying microbial community response to different nitrate and nitric-oxide loadings in a hollow fiber membrane (HFM) bioreactor.

Electrodes deployed in a forested riparian wetland soil where A6 thrives showed that A6 is capable of colonizing electrodes. Electrodes in soil columns in the laboratory showed that A6 preferably colonizes the anode over the cathode. Microbial electrolysis cells (MECs) showed that A6 is an electrode-reducing bacterium since current was produced, with the anode as the sole electron acceptor and ammonium as the sole electron donor. Taken together, this study expands our knowledge on electrogenic bacteria and opens the possibility to develop Feammox-based technologies coupled to bioelectric systems for the treatment of ammonium and other contaminants in anoxic systems.

By tracking the relevant genes responsible for each denitrification step during different nitrate and nitric-oxide loading regimes in a HFM bioreactor, results showed that the denitrifying microbial community can adjust rapidly to changes in nitrogen loading. This rapid adjustment means that the nitrifying bacteria formed a vigorous microbial community which resulted in a robust performance of this type of nitric-oxide removal bioreactors.

The results presented in this dissertation provide information to build upon for the development of technologies based on microbial pathways for the removal of the above-mentioned nitrogen compounds.