Bio-energy Production and Biological Wastewater Treatment using Microbial Fuel Cells (MFCs)

Abstract

Monumental efforts have been made to find a convincing solution to energy tension by considering renewable energies as the most important and least damaging. Microbial Fuel Cell (MFC) is an attractive green technology to deal with the current and forthcoming energy crisis and environmental issues. This technology employs microbial communities as biocatalysts to convert chemical energy from organic substrates to electrical energy. A variety of feedstock such as acetate, glucose, municipal wastewater, agricultural wastewater, etc. can be utilized in this reactor system. MFCs show marvelous performance in the treatment of wastewater. In this consideration, the investigation of MFCs incorporated with anaerobic mixed cultures is of certain interest for this research due to its competency to generate renewable biological energy along with wastewater treatment. To enhance the performance of the reactor, a systematic optimization of crucial operational process parameters such as temperature, pH, and mediator concentration was carried out. The reactor optimization was carried out via the Design of Experiments (DOE) approach using MiniTab software to perform Taguchi Analysis and ANOVA. The performance of the batch reactor was optimal with the operating conditions of temperature 300C, pH 7, and mediator concentration 400μM. The transfer of electrons from microorganisms to the anode electrode is a prominent constraint for the elevation of the voltage output from MFCs. In this concern, the introduction of an electron mediator in the MFC reactor to facilitate electron transfer was a must for encouraging the efficiency of the reactor. Methylene blue was used as an effective redox mediator in this study. The data obtained on the energy generation and pollution removal were at par with the statistical predictions of Taguchi Design of Experiments. It was introspected that a fraction of the mediator concentration was degraded resulting in mediator color removal. MFC fed with 400μM methylene blue concentration generated a maximum voltage of 319mV and the highest % removal of COD of 92.3%. In addition to operating process parameters and redox mediators, the performance of MFC has also been affected by electrode materials. The electrode should possess high stability, low toxicity, conductivity, low over potential, and high surface area to volume ratio. So, different materials like graphite, copper, and stainless steel were employed in these reactors to further get a comparative analysis on reactor performance. The results showed that batch MFC reactor employed with stainless steel electrode represented the highest performance in terms of bio-electricity production and % removal of COD i.e. 371mV and 93.7%.