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.

废物转化能源是实现环境可持续性的一种有前途的方法。我们研究了在无膜生物阴极微生物燃料电池（MB-MFC）中使用西瓜皮废料和含亚硝酸盐的废水发电的情况。结果表明，在分批补料模式下，内部亚硝酸盐循环的最大输出电压为294 mV，分别是不进行内部循环和连续模式时的1.4倍和1.3倍。西瓜皮在发电过程中迅速发酵成以乙酸和乳酸为主的有机酸。阴极生物膜中最主要的属是乳酸杆菌，相对丰度为74％，而严格梭状芽胞杆菌和拟杆菌属是两个主要属。阳极生物膜中的丰度相似，约为18％。三种微生物在发电和将亚硝酸盐转化为氮气方面合作良好。此外，我们发现nirS / K，conrB和nosZ的关键基因参与亚硝酸盐还原。我们的研究结果表明，利用MB-MFC的电能以西瓜皮废料为基质，含亚硝酸盐的废水为电子受体，是可行的。