Zum Einfluß von Sauerstoffkonzentration und pH-Wert bei der heterotrophen Denitrifikation Heterotrophic Denitrification: The Influence of Oxygen and pH Value

Zur Aufbereitung von nitratbelastetem Grundwasser zu Trinkwasser wird seit 1989 in Coswig bei Dresden eine Grosversuchsanlage zur biologisch-heterotrophen Denitrifikation betrieben. Das NEBIO-Rohrreaktor-Verfahren sieht die Denitrifikation im Wirbelbett mit kontinuierlicher Regeneration der Aufwuchstrager vor. Es wurde der Einflus veranderter Rohwasserbedingungen (Sauerstoffkonzentration, pH-Wert) auf die Leistungsfahigkeit des Verfahrens untersucht. Aus den Ergebnissen konnten weitergehende Aussagen zur Stochiometrie der heterotrophen Denitrifikation gewonnen werden. Eine Modellierung der Abbauvorgange im Reaktor auf der Basis enzymkinetischer Ansatze kann die Auslegung eines Reaktors an einem neuen Standort mit speziellen Rohwasserverhaltnissen unterstutzen. A demonstration plant for biological heterotrophic water treatment of nitrate polluted groundwater has been operated in Coswig near Dresden since 1989. In this NEBIO tube reactor process the denitrification is achieved in a downstream fluidized bed with continuous regeneration of sintered polystyrene particles as inert carrier material. A nutrient consisting of ethanol and phosphate is dosed in the reactor influent. In the subsequent treatment stages the denitrified water is aerated, filtered through a multilayer and GAC filter, and is finally disinfected with chlorine gas. The influence of changing raw water quality (oxygen content, pH value) on the process performance was examined. Increasing oxygen concentration lowers the nitrate reduction potential and rises the consumptive ratio ΔC/ΔNO3. The technology shows a high removal performance of 270 g NO3 m−3 h−1 in the range of pH 6.2 to pH 7.3 which is typical for natural groundwaters. The degradation of nitrate is increasingly inhibited for pH values beyond 7.6. Nitrite production occurs significantly in high pH ranges. The results lead to further insight in the stoichiometry of heterotrophic denitrification. By expressing the stoichiometric equations for nitrate and oxygen respiration as functions of oxygen and pH value it could be shown that the influent water quality has strong effects on the consumption of ethanol. A kinetic model was developed to predict the reactor performance under changing raw water conditions. A two stage kinetic model was designed, regarding two main effects: biochemical degradation of oxygen, nitrate and ethanol and distribution of active biomass due to hydraulic properties of the tube reactor. This model may be helpful for reactor design for sites of various ground water qualities.