Conversion of vegetable wastes to organic acids in leaching bed reactor: Performance and bacterial community analysis

Vegetable wastes (VWs), which contained abundant solid content, were digested in a leaching bed reactor (LBR). The tested VWs for acidification in the LBR included cabbage, potato, and tomato vine. The digestion in the LBR was carried out at the same organic loading rate of 25 g volatile solid (VS) per liter. It was found that cabbage and potato produced much more volatile fatty acids (VFAs) than tomato vine, probably because readily degradable components were more abundant in cabbage and potato. The retention time to digest each feedstock was different. It took 4, 5, and 8 days for cabbage, potato, and tomato vine to completely disappear in the reactor, respectively. The profiles of the VFAs generated from the three VWs were examined. In all cases, the predominant VFAs were acetic acid and butyric acid, although the relative abundance of individual VFA varied across the tested leachate samples. The bacterial community compositions of the leachates were analyzed by high throughput sequencing, and it was found that the feedstock strongly affected the bacterial community structure in the acidogenic process. All leachates had distinct bacterial community structure, although they did share a common set of core communities that included Proteobacteria, Firmicutes, and Bacteroidetes.