Avaluació, modelització y mitigació de les emissions de gasos d'efecte hivernacle en estacions de recuperació de recursos de l'aigua

Resumen

In the face of ever-growing demand for water for different uses, wastewater has gained momentum as an alternative and reliable source of water, shifting the paradigm of wastewater management from treatment and disposal to reuse, recycle and resource recovery. In this sense, wastewater treatment plants (WWTPs) are being transformed into water resource recovery facilities (WRRFs). The main objective of WRRF is not only to achieve a good effluent quality, but also to recover resources, water and energy in a sustainable way. In addition, over the past years, concerns regarding the sustainability of current WWTPs have increased, with a particular focus on the C footprint due to the impact of greenhouse gases (GHG) emissions on climate change. Therefore, many water utilities have become aware of the potential GHG emissions and there is a growing need to reduce these emissions and to identify the factors that control GHG emissions from WWTPs. N2O is produced and emitted during the biological nitrogen removal (BNR) in WWTPs. Due to their high global warming potential, the C footprint of WWTPs is highly sensitive to N2O emissions. Mathematical modelling of BNR processes has gained increased attention in view of a better understanding of N2O production, accumulation and emission. This thesis aimed to advance the development, knowledge and application of novel operational and control strategies to mitigate N2O emissions during wastewater treatment. In the first part, the ASM2d-N2O kinetic model, which accounts for the N2O production in C/N/P removal WWTPs, was used to study the associated emissions from a full-scale WWTP with two independent lines. The ASM2d-N2O model was calibrated using experimental data obtained under dynamic conditions. A good model fit was obtained during the dynamic calibration, giving a good description of nutrients and N2O emissions. In the second part of the thesis, the performance and N2O and CH4 emissions during long-term operation of a novel WRRF configuration, the mainstream SCEPPHAR, were monitored and assessed. The long-term N2O and CH4 emission factors calculated were in the low range of the literature. Different aeration strategies were implemented to study the impact on N2O emissions in the nitrifying reactor. The intermittent aeration was the aeration strategy that most mitigated the N2O emissions in the nitrifying reactor. Finally, a plant-wide model describing the fate of chemical oxygen demand (COD), C, N and P compounds, upgraded to account for GHG emissions, was implemented within the Benchmarking Simulation Model No. 2 (BSM2). The proposed approach included the main biological N2O production pathways and describes mechanistically the CO2 emissions in the activated sludge reactors as well as the biogas production from the anaerobic digester. Novel control strategies were proposed to obtain high plant performance as well as nutrient recovery and mitigation of GHG emissions in a plant-wide context. The implemented control strategies led to an overall more sustainable and efficient plant performance in terms of better effluent quality, reduced operational cost and lower GHG emissions.