Design and operation of plant microbial fuel cells using municipal sludge

Plant microbial fuel cells (PMFC) can simultaneously treat wastewater and generate bioelectricity. In the context of municipal wastewater, most PMFC studies have focused on settled sewage instead of the sludge produced in the treatment process. This research focused on designing and operating a PMFC that used thickened waste activated sludge (WAS) and soil as a substrate. Granular activated carbon (GAC) was used as the anode because of its large surface area, bio-compatibility, ability to conduct electricity and relatively low price. Carbon paper coated with 0.4 mg/cm(2) Pt was used as the cathode. The PMFC systems were operated using two indigenous South African plant species, namely, Wachendorfia thyrsiflora and Cyperus papyrus nanus. During the operation, the importance of ensuring the cathode stayed attached to the cell, having a wet cell and the right selection of the resistor connected was noted. When comparing the power output of the plant species, the W. thyrsiflora produced the highest, 1036 +/- 59 mW/m(3) followed by C. papyrus with 510 +/- 92 mW/m(3) and the lowest was measured in the control (no plant), 392 +/- 67 mW/m(3). However, the W. thyrsiflora did not survive the duration of the experiment and died. The most likely reason for plant death was high nutrient load. The C. papyrus survived the duration of the experiment and hence this plant species is recommended for future PMFC applications that use WAS as a substrate. This work provides a novel treatment method for WAS that is also capable of producing power.