Temporal analysis of the microbiota involved in the anaerobic degradation of sugarcane vinasse in a full-scale methanogenic UASB reactor

The treatment of sugarcane vinasse is still a challenge to develop a sustainable bioethanol production. Anaerobic digestion (AD) is the most promising treatment of vinasse since energy in the form of biogas can be recovered. The aim of this work was to understand the dynamics of the microbial community in a 100-m(3) upflow anaerobic sludge blanket (UASB) methanogenic reactor at start-up and during two periods of bioethanol production. An inter-harvest period in which the reactor was not fed was also studied. Metabarcoding analysis of the V4 region of the 16S rRNA gene showed that Firmicutes, Synergistetes, Chloroflexi, and Proteobacteria were the dominant phyla. Firmicutes was abundant, suggesting that this group plays a specific role in the treatment of vinasse. The inoculum adaptation to vinasse was correlated with the microbiota diversity and dynamics. The microbiota diversity was higher during the first harvest and reflected the initial microbial composition. During the second harvest, the increasing organic loading rate (OLR) and the adaptation to the new effluent selected a less diverse community which produced the biogas in the reactor. The qPCR of the mcrA gene and methanogenic activity tests showed that the abundance of methanogens increased over time and remained stable even after the stop period. This work shows the plasticity of the microbial community, which adapted its structure to the changes in the feed and persisted during starvation periods in the reactor. A time-series of microbiological information is necessary to a comprehensive understanding of full-scale reactor maintenance.