The use of methane as a sole carbon source for wastewater denitrification

This paper presents the results obtained in wastewater denitrification studies using methane as sole carbon source under two different conditions—i.e. in the presence of oxygen and under strict anoxic conditions. In the latter case, no significant denitrification was observed. However, in the presence of oxygen, a successful denitrification was obtained in batch reactors with a denitrification rate reaching 0.6 kg N-NO3− kg−1 VSS per day. It was shown that nitrate consumption could not be solely attributed to nitrogen assimilation and from 5 to 75% of the initial N-NO3− was escaping from the reactors in gaseous form. An important wasteful methane oxidation (indirectly related to denitrification) was also observed reaching in some experiment 90% of the total methane oxidation. The system obtained appeared to consist of an association of methanotrophic bacteria, oxidising methane and producing one or several intermediate organic compounds, still unidentified, which are later consumed by the denitrifying bacteria. No evidence was found for the involvement of methanol or acetate as intermediates, as suggested by the literature.