Application of urine as fuel in a soil-based membrane-less single chamber microbial fuel cell

Abstract

Microbial fuel cell (MFC) technology is a promising bio-technology that utilizes the microorganisms in organic wastes to generate electricity. Although human urine has been identified as a suitable substrate in MFCs, its possible utilization in a soil-based membrane-less single chamber microbial fuel cell (MSCMFC) for constant power generation has, hitherto, not been reported. In this study, an MFC was set up with mud as inoculum in a plastic cylindrical vessel using carbon felt electrodes. It was operated for 19 days (456 hours) without extra substrate. Then, the MFC was treated with human urine (as substrate) four times (Days 19, 24, 32, and 36), each time the MFC output stabilized across external loads. A control MFC (MFCcontrol) was made the same way and operated under the same conditions, but without the addition of urine. Both MFCs were operated for 40 days. The initial open circuit voltage (OCV) of the MFC treated with urine (MFCurine) was 227 mV, and that of the MFC control was 219 mV. Both MFCs produced overlapping OCVs to the point of adding urine. The maximum OCVs of MFC control and MFCurine prior to treatment were 729 mV and 740 mV, respectively. The OCV of MFCurine increased to a maximum value of 755 mV, four days after the initial treatment (day 23). At the final stage (Day 40), the OCV of MFCurine was 474.64 mV; whereas the corresponding value for MFCcontrol was 7.31 mV. A microchip was used to amplify the output of the MFCs to power a light-emitting diode. In addition, MFCurine was used to power a digital clock/thermometer. This study showed that human urine can be successfully utilized as fuel in a soil-based MSCMFC for the production of electrical energy, which can be boosted to power low-energy utility devices in farms or homes.