Constructed wetland microbial fuel cells: electricity generation, treatment efficiency improvement, cod bioindication and clogging assessment
- Autores: Clara Corbella Vidal
- Directores de la Tesis: Jaume Puigagut (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Juan Antonio Baeza Labat (presid.), Sebastià Puig Broch (secret.), Yaqin Zhao (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
Horizontal Subsurface Flow Constructed Wetlands (HSSF CWs) are natural wastewater treatment systems showing a marked redox gradient between the surface of the system and the bottom zone of the treatment bed. Therefore, they constitute a suitable environment for Microbial Fuel Cells (MFCs) implementation. MFCs are bioelectrochemical systems in which the electrons resulting from the oxidation of the organic matter are transferred, by means of exoelectrogenic bacteria, to an external circuit thus generating an electric current. The implementation of MFC into HSSF CWs (CW-MFCs) allows the removal of organic matter and the production of electricity simultaneously. Besides electricity generation, MFCs implemented in HSSF CWs could encompass other beneficial aspects of special relevance within the constructed wetlands domain such as the semi-continuous monitoring of the organic matter entering the system, the improvement of CWs¿ treatment efficiency and the assessment of the clogging state of the treatment bed. However, CW-MFC is a novel research field that lacks from specific knowledge on both HSSF CWs and MFC design and operational aspects to optimize the technology. Therefore, the objective of this thesis was to determine, quantify and maximize the benefits resulting from the synergy between HSSF CW and MFCs.
To address the objectives of this study two different experimental designs were considered: pilot-scale and lab-scale CW-MFCs. Results showed that continuous flow regime and planted wetlands generate higher redox gradients through the bed gravel than unplanted wetlands operated under discontinuous flow regime. CW-MFCs performed to a better extent under the presence of a HUSB reactor as primary treatment when compared to conventional settling. More precisely, the presence of HUSB reactor stimulated the presence of exoelectrogenic bacteria in anodic biofilms. Optimal cathode to anode surface ratio was that of 4:1. In order to maximize CW-MFCs performance, the cathode shall be placed semi-submerged within the water and kept at a distance of ca. 10 cm from the anode. Overall, even under these optimal wetlands and MFC operational and design conditions the energy produced by CW-MFCs would only cover between the 3 and the 14% of the total energy requirements of a CW treatment plant. Therefore, energy surplus provided by CW-MFCs, yet interesting, is not its most advantageous feature.
In terms of CW-MFCs environmental applications, MFCs showed the capacity to improve CWs treatment efficiency. Organic matter effluent concentration for connected CW-MFCs was significantly lower either in terms of total or soluble COD than unconnected CW-MFCs. Furthermore, CW-MFCs showed potential for COD assessment. Although results indicate that linear relationships can be established between both parameters, several factors can affect the precision, repeatability and operational stability of the sensor. Therefore, other alternatives such as its utilization as qualitative response tools should be considered for biosensor CW-MFCs. Finally, CW-MFCs also showed potential as a tool for indirect, continuous clogging assessment.
In terms of the environmental impacts associated to the implementation of MFCs, CW system coupled with graphite-based anode MFC appeared as the most environmentally friendly solution which could reduce CW both surface requirements and system footprint (by around 20%). Also CW systems coupled with high performance MFCs would be competitive with conventional CWs in terms of costs.
In conclusion, though to be at its infancy, CW-MFCs represent a novel technology able produce energy while wastewater is treated. Although it might not be a very attractive technology if the electrical gain is considered exclusively, CW-MFCs is a very promising technology when it comes down to environmental applications such as the improvement of HSSF CWs removal efficiency, or the utilization of CW-MFCs as both organic matter and clogging assessment tool.
