(18b) An Energy Efficient Nitrogen Removal Process Via Simultaneous Nitrification and Denitrification in Wastewater

Bacteria capable of simultaneous nitrification and denitrification (SND) and phosphate removal could eliminate the need for separate reactors to remove nutrients from wastewater and alleviate competition for carbon sources between different heterotrophs in wastewater treatment plants (WWTPs). Here we report a newly isolated Thauera sp. strain SND5, that removes nitrogen and phosphorus from wastewater via SND and denitrifying-phosphate accumulation, respectively, without accumulation of metabolic intermediates. Strain SND5 simultaneously removes ammonium, nitrite, and nitrate at an average rate of 2.85, 1.98, and 2.42 mg-N/L/h, respectively. Batch testing, detection of functional genes, nitrogenous gas detection and thermodynamic analysis suggested that nitrogen gas, with hydroxylamine produced as an intermediate, was the most likely end products of heterotrophic ammonium oxidation by strain SND5. The generated end products and intermediates suggest a novel nitrogen removal mechanism for heterotrophic ammonium oxidation in strain SND5 (). The heterotrophic ammonium oxidation to nitrogen gas without emission of N₂O by strain SND5 is a particular advantage from the perspective of greenhouse gas emissions in WWTPs. As a greenhouse gas, N₂O shows 298 times the atmospheric heat-trapping capacity of CO₂, and its emission from WWTPs is associated with denitrification of nitrate and nitrite during biological nutrients removal. Since the majority of NO₂^-and NO₃^-in WWTPs is derived from ammonium oxidation, bypassing this pathway could have a major impact on overall N₂O production. Since strain SND5 generates neither NO₂^- or N₂O during heterotrophic ammonium oxidation, its metabolic activity could help to limit greenhouse emissions from WWTPs while at the same time leads to energy saving.