Importance of substrate type and its constituents on overall performance of microbial fuel cells

Microbial Fuel Cells (MFC) have emerged as a potential wastewater treatment technology that utilizes metabolic processes of microorganisms present in the wastewater to disintegrate organic substrates and harness direct electricity. This paper reviews the potential of different wastewater types as a suitable substrate for microbial activities in MFCs. Substrate composition (carbon source, nutrient content and inhibitory compounds) directly affects the microbial growth, wastewater treatment potential, electron transfer rate and power harvested. Readily biodegradable substrates such as acetate and glucose promote microbial metabolism and electron transport, thus resulting in enhanced power generation. Substrates such as municipal or agricultural wastewater that constitute both simple and complex organic matter require longer breakdown durations but can provide MFCs with long term operational stability. On the other hand, substrates such as leachate from landfills, mining wastewater etc. are generally unsuitable for regular operations. The paper discusses the challenges such as suitability of various wastewaters, unpredictability of composition, presence of inhibitory chemicals like heavy metals or toxic organics that can subdue the microbial activity and reduce efficiency of a MFC reactor. It aims to identify the relationship between the substrate characteristics and MFC performance in order to select the substrate for achieving optimal output from MFC technology. The suitable substrates that exhibit optimal performance in terms of current and power output, coulombic efficiency, and reduction in chemical oxygen demand are identified.