Effect of acclimation on inoculum functioning and dynamics within a microbial community

Highlights: • The Effect of acclimation on microbial community was studied. • The addition of KH₂PO₄ and food waste improves inoculum function. • This study provides the basis for acclimating an efficient inoculum for FW biogas, and the FW inoculum produced higher microbial diversity and gas production. -- Abstract: Anaerobic digestion of food waste in a bioreactor requires efficient system operations in order to achieve acclimation of the sludge inoculum prior to initiation of the start-up for the digestion process. However, the acclimation process and the underlying microbial mechanisms involved have not yet been fully explicated. This study investigated the effects of food waste and KH₂PO₄ on inoculum acclimation within the microbial community utilizing the 16S rRNA MiSeq Illumina platform. The acclimated inoculum was created by adding 1 g/d food waste, 1360 mg/L KH₂PO_4, and then acclimated from the 8th d to 21st d. This medium produced superior inoculum with high gas production, high microbial diversity, and a stable process system. Bacteroidetes, Proteobacteria, Firmicutes, Euryarchaeota, and Chloroflexi were predominantly found within the microbial community, which played an active role during anaerobic digestion. Moreover, microbial diversity, composition, and relative abundance varied by acclimation process. The relative abundance of Bacteroidetes, Chloroflexi, Firmicutes, Synergistetes, and Fusobacteria had increased in the acclimated inoculum, while that of Proteobacteria and Euryarchaeota had decreased. Pearson correlation analysis revealed that the relative abundance of Firmicutes and Fusobacteria when based upon the number of Operational Taxonomic Units was positively correlated with biogas production. This study provides new insights into the understanding of variation, as it relates to inoculum functioning and the microbial community during acclimation. Thus, this process could be utilized to obtain superior inoculum, while optimizing reactor conditions to produce higher biodegradation efficiency from food waste.