Autotrophic nitrogen removal and relevant equilibrial processes
Date
2019-09-10
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Abstract
Viimastel aastakümnetel on tehtud ridamisi avastusi, mis on oluliselt täiendanud teadmisi loodusliku lämmastikuringe kohta. Üks olulisemaid neist on reoveepuhastuses kasutatav anammoks-protsess, mis toimub Planctomycetes hõimkonda kuuluvate autotroofsete bakterite vahendusel ja mille käigus ammooniumlämmastik oksüdeeritakse anoksilistes tingimustes, kasutades elektronaktseptorina nitritit. On teada, et teatud osa anammoks-bakterid võivad kasutada peale ammooniumi ka teisi substraate. Käesolevas töös uuriti lämmastikuärastust, kasutades elektronaktseptorina sulfaati. Uuritud tingimustes jäi ärastuse efektiivsus madalaks (ca ¼ lämmastikust) ning protsess oli ebastabiilne.
Töö ühe osana teostati autotroofse lämmastikuärastusega pilootseadme käivitamine kolmes erinevas konfiguratsioonis (eraldatud biomudaga nitritatsiooni- ja biokilepõhine anammoks reaktor, vahelduvaeratsiooniga biokilereaktor ja biomudapõhine annuspuhasti). Protsessi aluseks oli ammooniumlämmastiku osalise nitriteerimise kombineerimine konventsionaalse anammoks protsessiga. Protsessi sissevooluna kasutati munitsipaalreoveepuhasti liigmuda anaeroobsel stabiliseerimisel tekkivat eeltöötlemata vädu. Autotroofne lämmastikuärastus käivitus kõikides uuritud reaktorites, parimad tulemused (ärastuskiirus kuni 1 kg-N m–3 d–1) saavutati vahelduvaeratsiooniga biokilereaktoris. Edukas protsessi käivitamine nõuab pH kontrolli (pH<7,5), vaba ammoniaagi kontsentratsiooni jälgimist (< 10 mg-N L–1), aeratsiooni aja- ja hapniku kontsentratsiooni (0,3-0,8 mg-O2 L–1) ning sissevoolu heljumi kontrolli (heljumit < 1000 NTU).
Vädu on keerulise koostisega süsteem, mille üksikute komponentide kontsentratsioonid on määratud mitmete pH-st sõltuvate tasakaaluliste protsessidega. Vädu efektiivseks käitluseks on oluline teada selle koostises olevate komponentide kontsentratsioone. Käesolevas töös tuletati matemaatilised mudelid kolmele heterogeensele tasakaalulisele süsteemile: avatud ja suletud süsteemidele CO2–HCO3––CO32––CaCO3 ning suletud süsteemile H2O–CO2–CaCO3–NH4Cl. Kõigile kolmele mudelile teostati eksperimentaalne valideerimine. Mudelite kasutamine võimaldab hinnata konjugeeritud tasakaalulisi protsesse keskkonnas ning leida nendes protsessides osalevate osakeste kontsentratsioone.
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.
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.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Keywords
lämmastikuärastus, reoveepuhastus