Using watermelon rind and nitrite-containing wastewater for electricity production in a membraneless biocathode microbial fuel cell

Waste-to-energy is a promising approach for environmental sustainability. We examined the usage of watermelon rind waste coupled with nitrite-containing wastewater for electricity production in a membraneless biocathode microbial fuel cell (MB-MFC). Results showed that the maximum voltage output with internal nitrite circulation in a fed-batch mode was 294 mV, which was 1.4 and 1.3 times of that without internal circulation and in a continuous mode, respectively. Watermelon rind was quickly fermented to organic acids dominated with acetate and lactate during electricity generation. The most dominant genus in cathodic biofilm was Lactobacillus with a relative abundance of 74%, while the two dominative genera of Clostridium sensu stricto and Bacteroides in anodic biofilm had a similar abundance of approximately 18%. Three microbes cooperated well in producing electricity and converting nitrite to nitrogen gas. Additionally, we found the key genes of nirS/K, conrB and nosZ involved in nitrite reduction. Our results suggest the feasibility of harnessing electrical energy from MB-MFC with watermelon rind waste as substrates and nitrite-containing wastewater as electron acceptor.