On 4 October at 14:15 Ergo Rikmann will defend his doctoral thesis „Autotrophic nitrogen removal and relevant equilibrial processes”.
Professor Emeritus Toomas Tenno, Institute of Chemistry, University of Tartu
Research Fellow Anne Menert, Institute of Molecular and Cell Biology, University of Tartu
Professor William Hogland (Linnaeus University, Sweden)
In recent decades, a couple of discoveries have been made that greatly improve the knowledge of the natural nitrogen cycle. In wastewater treatment, the anammox-process is implemented, where ammonium nitrogen is oxidized under anoxic conditions using bacterial phylum Planctomycetes. In this process, nitrite is used as an electron acceptor. In present work, nitrogen removal by the bacterial consortia containing anammox bacteria under anoxic conditions using sulphate as an electron acceptor was studied. Nitrogen removal involving different groups of bacteria and different metabolic pathways took place, but only in a modest extent, (about ¼ of nitrogen was removed) and the process as a whole was unstable. As part of the work within the scope of the current thesis, the start-up of autotrophic nitrogen removal pilot plant was performed and operated in three different configurations (separated biosludge-based nitritation reactor and biofilm-based anammox reactor; intermittently aerated biofilm reactor; and biosludge-based sequence batch reactor). It was concluded that autotrophic nitrogen removal while treating reject water can be started up independently of applied technological concept, but the best results (nitrogen removal rate up to 1 kg-N m–3 d–1) were achieved in an intermittently aerated biofilm reactor. The critical factors for start-up of a deammonification process are pH control (pH <7.5), free ammonia concentration in reject water (< 10 mg-N L–1), time and concentration-based aeration control (dissolved oxygen 0.3-0.8 mg-O2 L–1) and the control of suspended solids of influent (< 1000 NTU). Reject water is a complex multi-component system. The concentrations of its components are determined by multiple pH-dependent equilibrial processes which are interconnected over protons. In order to ensure efficient and stable treatment of reject water, it is important to know the accurate concentrations of its components. In the present thesis, theoretical mathematical models for three heterogeneous equilibrium systems were derived: for open and closed systems CO2-–HCO3––CO32––CaCO3 and for closed system H2O–CO2–CaCO3–NH4Cl. All three models were experimentally validated. Mathematical models allow to calculate the concentrations of all components in the observed systems and to evaluate the impact of anthropogenic processes on the environment.