The Effect of Salinity on N₂O Emissions during Domestic Wastewater Partial Nitrification Treatment in a Sequencing Batch Reactor

Previous studies have highlighted the salinization caused by the use of seawater to flush toilets and industrial wastewater entering the urban wastewater systems in coastal areas. Thus, in this study, the effect of salinity on N₂O emissions during the partial nitrification process, as well as the emission mechanism, was investigated using a partial nitrification system of wastewater as the research object. The results showed that (1) the increase in salinity decreased the oxidation rate of NH₄⁺ and the formation rate of NO₂⁻ during partial nitrification; (2) the increase in salinity increased the N₂O emissions during NH₄⁺ oxidation and NH₂OH oxidation and decreased the formation rate of NO₂⁻-N during hydroxylamine oxidation; (3) the total N₂O emissions during hydroxylamine oxidation were less than those during ammonia nitrogen oxidation, and a greater amount of NO₂⁻ was reduced to N₂ instead of N₂O during hydroxylamine oxidation; and (4) a novel finding was that, during partial nitrification with the available organic matter, the N₂O emissions via heterotrophic denitrification by heterotrophic bacteria should not be ignored, and the increase in salinity can increase the N₂O emissions generated via heterotrophic denitrification. These results would provide a theoretical basis for reducing the N₂O emissions in the wastewater treatment process.