Salinity effects on polyvinyl alcohol separators and the use of spray-on separators in air-cathode microbial fuel cells

Open Access
Author:
Hoskins, Daniel Lee
Graduate Program:
Environmental Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 02, 2014
Committee Members:
  • Bruce Ernest Logan, Thesis Advisor
  • Michael Anthony Hickner, Thesis Advisor
  • John Michael Regan, Thesis Advisor
Keywords:
  • Bioelectricity; bioelectrochemical; microbial fuel cell; separat
Abstract:
Separators in microbial fuel cells (MFCs) can be used to increase coulombic efficiencies (CEs), but they can also adversely affect power production. A new spray method of PVA separator preparation was compared to the traditional cast preparation method. Anode solution conductivities were varied to span values typical of domestic wastewater (~1 mS/cm) and laboratory solutions (7 and 13 mS/cm). Power densities were unaffected by the addition of a PVA separator onto the Pt catalyst cathode in the low conductivity solution relative to MFCs lacking a separator. However, power densities were reduced by 28% in a 7 mS/cm solution, and by 50% in a 13 mS/cm solution. The use of a separator enabled close placement of the electrodes, which resulted in power production 33% higher than control MFCs with widely spaced, separatorless electrodes in the 1 mS/cm. This low-conductivity condition was the only instance of where the power density was higher than that of the control. The reduced impact on power production in the low ionic conductivity solution was attributed to swelling of the PVA polymer, and the smaller contribution of solution resistance to total resistance in lower conductivity solutions. Addition of PVA onto activated carbon cathodes produced results similar to those obtained with the Pt catalyst, with a 26% reduction in the maximum power density (from 702 ± 29 mW/m2 to 519 ± 6 mW/m2) in the 7 mS/cm solution. The reduction in power was reduced to <10% (636 ± 64 mW/m2) when switching to closely spaced electrodes compared to MFCs lacking a separator with widely spaced electrodes in the 7 mS/cm solution. Cast separators on both AC and Pt catalyst cathodes produced power densities 7-8% greater than the spray-on separators in a 7 mS/cm conductivity solution. These results show that spray on separators can be an effective method for insultating closely spaced electrodes in low conductivity solutions and that PVA can be used as a separator in low conductivity solutions to increase CE with minimal effect on power production.