Mathematical Modeling of Nitrous Oxide (N<sub>2</sub>O) Emissions from Full-Scale Wastewater Treatment Plants
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Abstract
Mathematical
modeling of N<sub>2</sub>O emissions is of great importance
toward understanding the whole environmental impact of wastewater
treatment systems. However, information on modeling of N<sub>2</sub>O emissions from full-scale wastewater treatment plants (WWTP) is
still sparse. In this work, a mathematical model based on currently
known or hypothesized metabolic pathways for N<sub>2</sub>O productions
by heterotrophic denitrifiers and ammonia-oxidizing bacteria (AOB)
is developed and calibrated to describe the N<sub>2</sub>O emissions
from full-scale WWTPs. The model described well the dynamic ammonium,
nitrite, nitrate, dissolved oxygen (DO) and N<sub>2</sub>O data collected
from both an open oxidation ditch (OD) system with surface aerators
and a sequencing batch reactor (SBR) system with bubbling aeration.
The obtained kinetic parameters for N<sub>2</sub>O production are
found to be reasonable as the 95% confidence regions of the estimates
are all small with mean values approximately at the center. The model
is further validated with independent data sets collected from the
same two WWTPs. This is the first time that mathematical modeling
of N<sub>2</sub>O emissions is conducted successfully for full-scale
WWTPs. While clearly showing that the NH<sub>2</sub>OH related pathways
could well explain N<sub>2</sub>O production and emission in the two
full-scale plants studied, the modeling results do not prove the dominance
of the NH<sub>2</sub>OH pathways in these plants, nor rule out the
possibility of AOB denitrification being a potentially dominating
pathway in other WWTPs that are designed or operated differently