Enhanced and sustainable high-level nitrate reduction in a membrane-less microbial fuel cell by watermelon rind fermentation broth

This study developed a strategy for enhanced and sustainable high-level nitrate reduction in a membrane-less microbial fuel cell (MLMFC). We first optimized the fermentation procedure using response surface methodology and then made watermelon rind into fermentation broth (WRFB) in an anaerobic bioreactor. The major component in WRFB was lactic acid that was as high as 13.2 g/L. As electron donors for the nitrogen removal, WRFB was comparable to some traditional carbon sources. During the long-term operation of the MLMFC fueled by WRFB to reduce high levels of nitrate, the average removal efficiency for both COD and TN was higher than 95 %, and the greatest voltage attained 363 mV. Microbial diversity analysis demonstrated that apart from special microorganisms enriched on the anode (e.g. Methanosaeta) and cathode (e.g. Comamonas), some functional bacteria (Thauera and Desulfovibrio) predominated on both bioelectrodes, all of which contributed to an excellent performance of MLMFC. The strategy proposed in this work may considerably promote sustainable development of integrated watermelon rind recycling, high-level nitrate removal and electricity generation.