Modeling nitrogen removal for a denitrification biofilter

Nitrous oxide (N₂O) is a major greenhouse gas, heavily contributing to global warming. N₂O is emitted from various sources such as wastewater treatment plants, during the nitrification and denitrification steps. ASM models, which are commonly used in wastewater treatment, usually consider denitrification as a one-step process (NO₃ ⁻ directly reduced to N₂) and are as such unable to provide values for intermediate products of the reaction like N₂O. In this study, a slightly modified ASM1 model was implemented in the GPS-X™ software to simulate the concentration of such intermediate products (NO₂ ⁻, NO and N₂O) and to estimate the amounts of gaseous N₂O emitted by the denitrification stage (12 biofilters) of the Seine-Centre WWTP (SIAAP, Paris). Simulations running on a 1-year period have shown good agreements with measured effluent data for nitrate and nitrite. The calculated mean value for emitted N₂O is 4.95 kgN–N₂O/day, which stands in the typical range of estimated experimental values of 4–31 kgN–N₂O/day. Nitrous oxide emissions are usually not measured on WWTPs and so, as obtained results show, there is a certain potential for using models that quantify those emissions using traditionally measured influent data.