Experimental Utilization of Urine to Recharge Soil Microbial Fuel Cell for Constant Power Generation

Abstract

The simplicity of the soil-based microbial fuel cells (MFCs) makes them very attractive, as perhaps the only natural components they need to run are nutrient-rich soil combined with water to form mud. However, the MFC will cease to produce electricity when the soil runs out of its nutrient-rich characteristics and bacteria. It is against this background that this study was designed to investigate the possible utilization of urine to recharge soil MFCs that have run out of their nutrient-rich characteristics. The mud-watt MFC was utilized for this study. It was run continuously for forty days until the power output was nearly zero. Fresh urine was then introduced into the soil, and the power output was determined. The initial (24 hours after set-up) open circuit voltage (OCV) was 219 mV. A maximum OCV of 731 mV was obtained on day 14 of the study. The OCV of the MFC was 7.31 mV on day 40 before the injection of urine into the soil. Twenty-four hours after the ejection of urine, the OCV was 360 mV and rose to 407 mV forty-eight hours later. The OCV remained constant at this value for fifteen days, after which urine was reinjected. The voltage drop across seven external loads also showed a similar trend. This study has demonstrated that fresh urine can be successfully utilized to recharge a soil-based MFC that has run out of its nutrient-rich characteristics.