Continuous and scalable applications of microbial fuel cells: a critical review

The depletion of conventional energy sources has motivated countries to shift towards renewable and eco-friendly sources of energy. One of the major global energy consumers is wastewater treatment facilities, particularly biological processes. The microbial fuel cell (MFC) is an emerging biotechnology that has been proven to be able to treat a wide range of wastewaters while generating electricity. However, after two decades of extensive research, the MFC technology remains mostly trapped in laboratory experimentations studying its performance and potential improvements. Moving towards the commercialization of MFC technology, multiple studies have focused on its actual performance under realistic conditions, i.e., large-scale continuous operation. Scaling up MFCs has been tested by increasing the unit size, stacking individual cells, and/or using multiple electrodes. As more research had been carried out in this area, the aim of the present article is to review the various designs and configurations of continuous scaled-up experiments from treatment, power generation, and applicability perspectives. This review compiles more than one hundred research studies on continuous scalable MFCs. The key operation parameters, including the hydraulic retention time and organic loading rate, are thoroughly discussed to obtain practical optimum ranges in comparison to conventional treatment processes. The various scaled-up cell materials and configurations are analyzed and correlated to their reported performance. Design guidelines for process variables and system components/configurations are suggested, and relevant research gaps and challenges are identified.