Wastewater Treatment with Concomitant Bioenergy Production Using Microbial Fuel Cells

Abstract

Billions of dollars are spent on wastewater treatment each year, and the worldwide energy crisis makes green technologies increasingly more attractive. Microbial fuel cells (MFCs) can potentially be used to digest organic matter in wastewaters and reduce its solids by up to 90%. MFCs generate electricity by harvesting the electrons donated to the anode from organic carbon oxidation in an anaerobic anodic chamber mediated by bacteria in biofilms. The electrons flow through an external circuit to reach the cathode where they are used to react with oxygen and protons to form water in the cathodic chamber. Instead of using oxygen in the cathodic chamber, which requires expensive catalytic cathodes, alternate oxidants such as nitrate and nitrite in wastewaters can also be used as electron acceptors with a biocathode. It was claimed that MFCs have the potential to reduce power consumption in wastewaters by as much as 50%. By operating MFCs in electrolysis mode, known as microbial electrolysis cells (MECs), biohydrogen can be produced by applying a much lower external voltage than that for the direct water electrolysis. In laboratory investigations, MECs have been used to treat many kinds of hazardous wastes and wastewaters. Recently, there is a growing interest in producing value-added bioproducts from MFCs or MECs, as well as microbial desalination cells. Significant technical hurdles need to be overcome before large-scale MFCs become practical. Recent advances such as genetically engineered, dispersion-deficient microbes that bind tenaciously to an electrode, electrogenic hyperpilated bacteria, new anodic materials, more efficient mediators, and membrane-less MFCs make the feasibility of MFCs for wastewater treatment more promising than ever. This review discusses new advances in MFC operation, design, and optimization for wastewater treatment with concomitant bioenergy production.