Effects of CH4 and O2 Concentrations on Methane-dependent Denitrification

概要

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Methane is utilizable as a carbon source for nitrogen removal from wastewater that lacks organic carbon sources. In this study, we confirmed that methane-dependent denitrification by biomass from the biogas scrubber of a swine wastewater treatment plant occurs in the presence of CH4 and O2, but not in the presence of CH4 alone. We further found that the CH4/O2 ratio in supplied gas needs to be more than 1.0 for high nitrate removal activity using methane. In this condition, methane oxidation activity was maximized, and DO concentration decreased to less than 0.3 mg/l. It was supposed that the O2 consumption rate owing to methane oxidation was higher than the O2 transfer rate from the gas phase to the liquid phase, and consequently DO concentration declined to a low level suitable for denitrification. Moreover, when the CH4/O2 ratio exceeded 1.0, high nitrate removal activity occurred under incubation with high O2 partial pressure. Heightening the O2 supply rate while maintaining a CH4/O2 ratio greater than 1.0 would improve the NO3- removal activity. Sustaining a biomass with high concentration and controlling DO concentration would be required to avoid excess O2 supply relative to the O2 consumption rate by microorganisms.
日本水処理生物学会の論文