Microbial Fuel Cell–Aided Processing of Kitchen Wastewater Using High-Performance Nanocomposite Membrane

Microbial fuel cell (MFC) is an eco-friendly energy source that generates electricity by degrading natural wastes through bacterial activity. The electrolyte that is sandwiched between the electrodes for the separation and transportation of protons is a critical component of the MFC system. Currently available membranes used as electrolytes to transport protons are expensive and exhibit high oxygen crossover with low mechanical and chemical stability, which make the commercialization of MFC difficult. Therefore, in this study, we synthesized a cost-effective ionically-crosslinked nanocomposite membrane made up of cationic aniline-treated polysulfone (APSf) doped with anionic sulfonated multiwalled carbon nanotube (SMWCNT) to lower the oxygen crossover and enhance the chemical, tensile, and thermal stabilities. The impact of the incorporation of SMWCNT on oxygen diffusivity of the synthesized membrane was evaluated by molecular dynamics (MD) simulation. Polysulfone is a material that conducts protons but has low ion exchange power and electrons are produced to a marginally lesser extent than in case other membranes. However, when aniline is used as a crosslinking agent in the polysulfone polymer solution to produce APSf membrane, the material becomes electron driven, which results in a functional bearing unit that can engage in hydrogen bonding interactions. The APSf/SMWCNT membrane containing 1% by weight of carbon nanotubes provided a maximum power density of $304.2\mathrm{mW}/{\mathrm{m}}^2$ with substantially high columbic efficiency (17%) and considerable removal of chemical oxygen demand (COD) (82%) as compared to Nafion 117 or APSf incorporated with 0.5% by weight nanotubes. The APSf/SMWCNT (1% by weight) membrane also exhibited high ion exchange capacity ($1.6\mathrm{meq.}{\mathrm{g}}^{-1}$) as well as proton conductivity ($0.19{\mathrm{Scm}}^{-1}$). The low oxygen diffusivity of APSf/SMWCNT membrane ($8.3\times {10}^{-8}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$) obtained from MD simulation compared to plain APSf ($8.16\times {10}^{-7}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$) and Nafion 117 ($6.5\times {10}^{-7}{\mathrm{cm}}^2{\mathrm{s}}^{-1}$) are good indications of its potential in MFC application. These results indicate that the membranes synthesized in this study play a crucial role in the performance of MFCs and could be inexpensive alternatives to existing commercial membranes for MFC-based treatment of domestic and industrial wastewater.