Evaluation of electrode separators and the external resistance in electrochemically assisted constructed wetlands

Abstract

A proton exchange membrane increases the electrical performance of a microbial fuel cell (MFC). New inexpensive materials should be sought, especially in a constructed wetland microbial fuel cell (CW-MFC). Here, in a laboratory-scale system of five CW-MFCs, wet clay, wet earth or mud, and non-woven cloth were used as inexpensive separators with long-term stability. The five CW-MFCs were planted with Typha latifolia, fed with synthetic wastewater, and packed with natural porous material. Graphite felt was used as electrodes and the experimental system had a hydraulic residence time of 3 days, operating under shade and natural conditions of temperature and light. Electrodes were connected to current collectors (copper wire) and to an external resistance, with a change every 20 days, starting in open-circuit and following with 20000, 18000, 15000, 10000, 5600, 1000, 560, and 10 Ω. These laboratory-scale CW-MFCs reduced concentrations of nitrates, ammonium ion, and sulfates without inhibiting electricity production. Microbiological analyses indicated that anaerobic, facultative, aerobic, and denitrifying bacteria may have caused these reductions. The reactor with the live plant and with the wet earth or mud separator achieved the highest production of electricity (22.6 mW/m²), and may be worth further attention.

Keywords:

• Electrochemically assisted constructed wetlands
• NWC non-woven cloth
• PEM proton exchange membrane or half-reaction separators
• wet clay
• wet earth or mud

Acknowledgments

The second author acknowledges the scholarship granted by the Mexican Council for Humanities, Sciences, and Technologies (Consejo Nacional de Humanidades, Ciencias y Tecnologías) for the graduate studies. She also acknowledges the financial support granted by the National Autonomous University of Mexico Engineering Graduate Studies Program (Universidad Nacional Autónoma de México, Programa de Maestría y Doctorado en Ingeniería, UNAM-PMyDI) for the academic three-month residency in the Helmholtz Zentrum für Umweltforschung UFZ, Leipzig. Helpful discussions with Dr. Uwe Kappelmeyer from UFZ are also deeply appreciated. Research was financed by the UNAM DGAPA PAPIME Projects EN103704, PE101709, PE100514, and PE101822, and the PAIP Program 50009067 belonging to the UNAM Facultad de Química. The first author also acknowledges to UNAM DGAPA PAPIIT Project IA107020 for financial support for these experiments. Finally, the authors appreciate the valuable revision and improvement of the English grammar by Ann Grant.

Additional information

Funding

This study was supported by Consejo Nacional de Humanidades, Ciencias y Tecnologías (Mexico).