Microbial communities of anaerobic digestion BMP tests fed with pot ale at different concentrations

In this study we produce methane from pot ale, a residue from the whisky distillation process, using the microbial biomass precipitated with used flocculant polymer from the sludge dewatering process. Pot ale, a combination of yeast residue and spent grain from the whisky distillation process, has limited alternative uses due the high copper content and has previously been considered difficult to digest anaerobically due to the high nitrogen content. The inoculum possesses an increased settling velocity and stability in transport when compared to the liquid counterpart. The the use of this inoculum as a microbial seed is currently unexplored. To study the potential of this novel feedstock and inoculum combination, Biomethane potential (BMP) tests were complemented by 16S rRNA DNA analysis of the microbial community grown from the used flocculant polymer. Pairwise phylogenetic tree branch node distances showed clustering of samples in relation to their initial pot ale concentration in addition to temporal changes in the microbial community. We identified a core microbiome that developed from the microbes affixed to the used flocculant polymer for pot ale digestion and confirmed the production of methane from the combination of this material. The major community variance observed over the test duration does not represent a stable microbial community for the accurate prediction of methane yields and raises questions concerning biological reproducibility between BMP tests, especially those using particulate-containing inoculum at initial timepoints, and suggest this variance is only an issue for small lab-scale studies and not full scale digesters.