Storing of exoelectrogenic anolyte for efficient microbial fuel cell recovery

Abstract

Starting up a microbial fuel cell (MFC) requires often a long-term culture enrichment period, which is a challenge after process upsets. The purpose of this study was to develop low cost storage for microbial fuel cell enrichment culture to enable prompt process recovery after upsets. Anolyte of an operating xylose-fed MFC was stored at different temperatures and for different time periods. Storing the anolyte for one week or one month at +4 °C did not significantly affect power production, but lag time for power production was increased from 2 days to 3 or 5 days, respectively. One month storing at -20 °C increased the lag time to 7 days. The average power density in these MFCs varied between 1.2 and 1.7 W/m3. The share of dead cells (measured by live/dead staining) increased with storing time. After six-month storage the power production was insignificant. However, xylose removal remained similar in all cultures (99-100%) whilst volatile fatty acids production varied. The results indicate that fermentative organisms tolerated the long storage better than the exoelectrogens. As storing at +4 °C is less energy intensive compared to freezing, anolyte storage at +4 °C for maximum of one month is recommended as start-up seed for MFC after process failure to enable efficient process recovery.