Nitrous oxide (N2O), a potent greenhouse gas and ozone-depleting compound, can be emitted from biological nitrogen removal (BNR) processes. Emissions have been reported to range from <1% - 25% of the influent nitrogen. Nitrous oxide reductase (nosZ), a key enzyme of the denitrification pathway, is the only known biological sink of N2O. Denitrification is a modular pathway resulting in distinct denitrifying guilds: complete denitrifiers, incomplete denitrifiers and nitrous oxide sinks. The high variability in reported N2O emissions may result from variation in the denitrifying microbial populations between studies.
This study presents a meta-genomic survey of three New Zealand WWTP denitrifying microbial populations. Data was mined for 16s rDNA and the functional denitrifying genes nirK, nirS, nosZ Clade I and nosZ CladeII. 16s analysis shows WWTPs to have a phyla profile typical of WWTPs and that they differ from one another at the genus level. Functional marker analysis shows a similar distribution of denitrifying genes across the WWTPs surveyed, with high nirK:nirS and low nosZ CladeII:nosZ Clade I ratios, indicative of a genetic potential for N2O production.