Effect Of Volatile Fatty Acids On Methane Production İn Ozone Pre-Treated Anaerobic Digesters

Date

2018-09-07

Author

Tuncay, Sera
İçgen, Bülent

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Anaerobic digestion (AD) is a biological wastewater sludge treatment process which transforms organic matter into methane-rich biogas. AD involves four key steps as hydrolysis, acidogenesis, acetogenesis and methanogenesis, respectively. In hydrolysis, a rate-limiting step, large organic polymers are broken down into simpler monomers. AD with ozone pre-treatment is used for the acceleration of this rate limiting step by converting solids into more easily biodegradable matter. As a result, sludge biodegradability and biogas production can be enhanced. In acidogenesis, volatile fatty acids (VFAs) are formed while in acetogenesis, those VFAs are further catabolised for methanogenesis to produce methane. Accumulation of those VFAs in the system leads to pH drop and this inhibits the activity of methanogens in the digester. Therefore, one of the most important parameters to be considered in the operation of anaerobic digesters is VFA analysis. Hence, in this study, the relationship between total VFAs and methane production in anaerobic digesters pre-treated with different ozone dosages was examined. In the study, three anaerobic reactors pre-treated with different ozone dosages (0.03, 0.06 and 0.09 g O3/g TSS) and a control without pre-treatment were operated. Seed sludge for the reactors was obtained from ASKI Tatlar Central Wastewater Treatment Plant and the feed sludge was obtained from METU Vacuum Rotating Membrane. During the operation, methane production was daily measured daily by using graduated cylinder and gas chromatography. The total VFA concentration were measured for every other day by using titration method. While no significant increase in methane production was observed in the reactors pre-treated with 0.03 and 0.09 g O3/g TSS ozone dosages and control reactor, the highest methane production was obtained in the reactor pre-treated with 0.06 g O3/g TSS between the second and tenth days of operation. Similarly, the total VFA concentration increased in 0.03, 0.09 g O3/g TSS ozone dosed and control reactors and decreased in 0.06 g O3/g TSS ozone dosed reactor in the same time interval. In conclusion, there was a direct relationship between VFAs and methane production in practice too. In ozone pre-treated anaerobic digesters, low (0.03 g O3/g TSS) and high (0.09 g O3/g TSS) ozone dosages led to an increase in VFAs and so, a decrease in methane production. However, 0.06 g O3/g TSS ozone dosage indicated a meaningful reduction in VFAs by providing the highest methane production.

URI

https://hdl.handle.net/11511/85038
http://mess-earth.org/files/WMESS2018_Book.pdf

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Department of Environmental Engineering, Conference / Seminar