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Monitoring and modelling of N2O emissions from innovative nitrogen removal processes
Book - Dissertation
Subtitle:Meten en modelleren van N2O emissies bij innovatieve stikstofverwijderingsprocessen
The emissions of greenhouse gases (such as N2O) from wastewater treatment is a matter of growing concern. The current atmospheric concentration of N2O, a potent greenhouse gas, is the highest in history. Conventional biological nitrogen removal is based on nitrification, i.e. conversion of ammonium to nitrate, followed by denitrification, i.e. conversion of nitrate to N2. Over the last 20 years, innovative nitrogen removal processes have been developed as an alternative, such as those based on the combined partial nitritation-anammox conversions which result in savings in aeration energy, no external carbon source, less CO2 emissions and sludge production. The overall goal of this PhD thesis was to elucidate the formation mechanisms of N2O from innovative nitrogen removal processes. To reach this goal, models were developed and applied in simulation studies. One of the first mechanistic models describing N2O formation by ammonia oxidizing bacteria was developed and formed the basis for later adaptations and extensions reflecting additional insights gathered. Monitoring campaigns were conducted on full-scale reactors for innovative nitrogen removal, including the development and application of a novel monitoring method and rigorous assessment of the gathered experimental data. The carbon footprint of the monitored full-scale partial nitritation reactor consisted almost entirely (92%) of N2O emissions. A novel method to measure dissolved N2O concentration on a minutely time scale was theoretically developed and applied on the full-scale reactor. The reactor off-gas N2O profile showed large variations during an operating cycle. This transient behaviour was exploited, enabling monitoring of the interphase transfer rate kLa and average N2O formation rates under different conditions, the latter was validated with the dissolved N2O measurements. By combining simulation and experimental results, it was found that the majority of N2O emissions was related to AOB, both under aerobic and anoxic conditions.