Anaerobic digestion and bioeletrochemical systems combination for energy and nitrogen recovery optimisation
- Autores: Míriam Cerrillo Moreno
- Directores de la Tesis: August Bonmatí Blasi (dir. tes.), Marc Viñas Canals (codir. tes.), Xavier Flotats Ripoll (tut. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2016
- Idioma: español
- Tribunal Calificador de la Tesis: Abraham Esteve Núñez (presid.), Sebastià Puig Broch (secret.), Albert Guisasola Canudas (voc.)
- Programa de doctorado: Programa de Doctorado en Ingeniería Ambiental por la Universidad Politécnica de Catalunya
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Anaerobic digestion (AD) is a widespread technology for treating high strength waste streams, such as livestock manure. AD has some limitations: i) high nutrient concentrations in effluents (especially nitrogen and phosphorus); ii) process instability against organic or nitrogen overloads; and iii) the need for increasing biogas methane content for using it as renewable energy for certain uses. Therefore, it is necessary to implement strategies to keep the DA process and effluent quality under control, and increase the amount of energy recovered in the system.
In this Thesis the combination of AD-BES technology has been studied with the aim of increasing energy recovery and recover nitrogen from a complex waste stream such as pig slurry. Two-chambered cells with cation exchange membrane operated both in microbial fuel cell (MFC) and microbial electrolysis cell mode (MEC) have been used.
In the first part of the Thesis integration of BES technology with AD was studied to improve system stability, the quality of the effluent and recovery of nitrogen. Firstly, batch tests were performed using an MFC and a MEC to compare the operation with fresh and digested pig slurry in both systems regarding the reduction of organic load and ammonium recovery for its reuse. Subsequently, both cells were operated continuously with digestate and their ability to absorb specific organic overloads was checked by simulating a malfunction of the AD by performing volatile fatty acids pulses in the anode chambers. Next, a lab-scale AD was connected in series with both cells and was subjected to an organic and nitrogen overload, which caused inhibition process. The MEC and MFC functioned as suitable systems for maintaining the quality of the effluent, reducing the residual organic load of the digestate and recovering ammonium. In addition, a recirculation loop between the AD and the MEC allowed stabilising the inhibited AD. Afterwards, the effectiveness of the recirculation loop for maintaining the operation of the AD was checked by its temporary interruption and subsequent reconnection. Total and active microbial populations of the reactors were analysed during the different phases to study their evolution during periods of inhibition and recirculation.
In the second part of the Thesis the implementation of the MEC technology for the enrichment of the biogas produced in the AD, through the establishment of a biofilm on the cathode of the MEC capable of converting CO2 to methane, was studied to increase energy recovery of the system. First, an up-flow anaerobic sludge blanket reactor (UASB) was operated with the objective of obtaining biomass enriched in methanogenic archaea to be inoculated into the cathode of a MEC. Two MECs were set up to compare their operation with two different inocula (biomass enriched in the UASB and anaerobic granular biomass) and the evolution of the microbial population. Finally, AD-MEC-biocathode technology was integrated into a system where the digestate was refined in the anode chamber of the MEC and recirculated to control AD inhibition by organic and nitrogen overload; ammonia was recovered from the digestate thanks to its transfer to the cathode chamber; and CO2 introduced into the cathode chamber was transformed into methane to increase the calorific value of biogas.
The work developed in this Thesis has revealed at lab-scale that BES systems have the versatility to be combined with the AD and improve its operation, the effluent quality and energy recovery and nitrogen.
