Controlling Nitrous Oxide Emissions in Single-Stage Partial Nitritation and Anammox Reactors Under Hypersaline Conditions

Monitoring and controlling nitrous oxide (N2O) emissions from partial nitritation - anammox (PN/A) processes has become an important objective as the technology has become more widespread. Here, N2O emissions from completely mixed single-stage partial nitritation and anammox reactors for nitrogen removal under hypersaline conditions (4%) were investigated. Results show that N2O emissions in fixed bed and suspended PN/A reactors ranged from 0.08% to 1.0% and 0.09% to 1.5% of ammonium removed, respectively. Bulk ammonium and nitrite concentration were shown to be the main controlling factors for N2O emissions. The addition of acetate to both fixed bed and suspended reactors reduced N2O emissions by 52.5% and 72.4%, respectively. Quantitative PCR results showed an increase in the functional genes related to denitrification (nirS, nirK and nosZ) with the addition of acetate, however deammoniafication was not significantly affected. The ammonia oxidizing bacteria and anammox bacteria identified in both PN/A reactor systems were from the genus Nitrosomonas and genus Candidatus Scalindua, respectively.