Eliminació autotròfica de nitrogen en depuradores urbanes mitjançant el procés anammox
- Autores: Xènia Juan Diaz
- Directores de la Tesis: Julian Carrera Muyo (dir. tes.), Julio Pérez Cañestro (codir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2021
- Idioma: catalán
- Tribunal Calificador de la Tesis: David Gabriel Buguña (presid.), Maite Serrano Vilalta (secret.), Jesús Colprim Galcerán (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología Ambientales por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Wastewater needs to be correctly treated to avoid the associated public health risks and pollution of natural ecosystems. Nowadays, wastewater treatment plants (WWTPs) remove nitrogen through nitrification/denitrification. Despite current facilities are robust and provide a successful effluent quality, they require for a high energy consumption and operating costs. Research efforts have been focused on achieving energy sustainable and self-sufficient facilities. The implementation of anammox bacteria in the main water line of an urban WWTP allows the uncoupling of the organic carbon (COD) and nitrogen removal. Firstly, COD is concentrated and redirected to anaerobic digestion to maximize biogas production. The effluent is then treated autotrophically through the partial nitritation (PN) and anammox (AMX) reactions. However, its implementation is limited by the cold, diluted and variable concentrations of the main water line, by the strict discharge limits and by the need to be competitive with conventional treatments.
As a first approach, the PN/AMX process was tested in one-stage reactor configurations, although destabilization occurred at low temperatures. Two-stage systems were recognized for a better optimization of both processes. Thus, the aim of this thesis was to assess and understand the feasibility of a two-stage PN/AMX process at mainstream conditions.
The first objective was to investigate the feasibility of an up-flow anammox sludge bed (UAnSB) reactor during a summer-to-winter temperature transition, from 20 to 10 ºC, plus a three months period at 10 ºC by treating a real mainstream wastewater for ca. 350 days. The UAnSB reactor was able to damp a 10 ºC drop while maintaining high and stable nitrogen removal rates throughout the operation. The successful reactor performance was attributed to the heterogenous substrate distribution along the sludge bed that allowed for an intra bed overcapacity.
The optimization of nitrogen removal efficiency and effluent quality is still a challenge of the PN/AMX process. The second objective was to design a reactor configuration for coupling anammox to heterotrophic denitrification in a single reaction unit (i.e. the CANDLE reactor, Coupling Anammox and Denitrification in a singLE unit). The CANDLE reactor treated a real mainstream wastewater and was fed with acetate as a C-source over a temperature range from 20 to 14 ºC for ca. 200 days. The enhancement of heterotrophic denitrifying activity allowed to reduce the nitrate produced by anammox bacteria, without compromising the anammox performance and, thus, to improve effluent quality while maintaining high and constant nitrogen removal rates. The study of substrate distribution along the sludge bed and of the microbial community showed that the coexistence of both populations in a single unit was possible as anammox and heterotrophic denitrifiers occupied differentiated niche compartments. Finally, the enhancement of heterotrophic denitrifying activity allowed for mitigation of nitrous oxide (N2O) emissions.
The potential nitrate production in the PN step is currently limiting the application of mainstream PN/AMX process, although successful long-term operations have been achieved in granular reactors at low temperatures. The last aim was to investigate the influence of different operational parameters in the development of an autotrophic granular sludge performing a stable nitritation using conventional activated sludge as inoculum in an air lift reactor. The enhancement of the ammonium oxidation activity and of the air-flow rate showed to be effective in the development of an autotrophic granular sludge performing a stable nitritation.
Overall, this thesis demonstrated that there seems to be no obstacles for the application of the anammox process at mainstream conditions and that a successful start up of a granular PN reactor can be attained under optimal conditions. Future research should be focused on gaining insight for the implementation of the PN/AMX process at full-scale conditions.
