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Gewählte Master / Diploma Thesis:

Xiao Juan Zhou (2008): Prozesse im Kanal. Entstehung von flüchtigen Fettsäuren und Distickstoffmonoxid.
Master / Diploma Thesis, BOKU-Universität für Bodenkultur, pp 95. UB BOKU obvsg

Data Source: ZID Abstracts
Degradation processes in sewers can cause corrosion and lead to the formation of odorous substances and environmental relevant gases. Volatile fatty acids are important for the formation of odors in wastewater sewers. Nitrous oxide (N2O) is an intermediate during nitrate reduction, which contributes to the greenhouse effect. In this work the mechanisms of formation and influencing factors of both products were determined. The experiments were conducted in a 5.5 litre reactor, which contained 2.8 litre liquid and was inoculated with 1- 1.5 mg/L dry matter of sludge (digested or activated sludge). In order to investigate the fate of volatile fatty acids and N2O, batch and flow through experiments were operated under low oxidative and reductive potentials (ORP) (with N2- aid gas in the headspace 0.25 Nm3/L) and high ORP (with aeration). The ORP was a good response factor for the formation of volatile fatty acids; the acids were always formed below ORP –300 mV but not if higher than 0 mV. Under anaerobic conditions the formation of volatile fatty acids in digested sludge is higher than in activated sludge and the acetic acid had the highest formation rate, the volatile fatty acids production was 3 % as acetic acid related to COD (chemical oxygen demands). After nitrate addition the generated volatile fatty acids were used as carbon source and quickly consumed. Acetic acid and propionic acid had the highest consumption rates. Normally under anaerobic conditions N2O was generated slowly due to its high reduction rate. When nitrate was added to systems under low ORP- conditions, the conversion rate of N2O was 2.25 % based an nitrate consumption. An addition of nitrite showed also similar N2O production (3.9%). High concentrations of N2O were observed during nitrate reduction when inhibitors such as H2S were present (conversion was 12 %), therefore nitrate should not be added when high H2S concentration are present.

Beurteilende(r): Fürhacker Maria

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