Long-term anaerobic digestion of food waste at semi-pilot scale: Relationship between microbial community structure and process performances

Stability and performance of long term semi-continuous Anaerobic Digestion of food waste at semi-pilot scale is here evaluated based on the integration of multiple lines of evidence. In order to elucidate the main microbial components, the core microbiome dynamics were assessed by high-throughput 16 S rRNA gene sequencing over the reactor operation together with the data related to the AD performances. The experimental reactor, after a successful start-up, was operated for more than 200 days at a moderate OLR (Organic Loading Rate) of 1.6 +/- 0.4 g VS L(-1)d(-1). The availability of readily biodegradable substrate, in particular carbohydrates, favored the fermentative functional redundancy of bacteria promoting the rapid accumulation of acetate first, and propionate afterwards, due to limited methanogenesis. The prolonged operation, despite the moderate OLR, nurtured propionate accumulation, because H-2 concentration exceeded the level capable to render the reaction endergonic, hampering the propionate uptake process. The application of a Pulsed Feeding strategy increased the hydrogenotrophic Methanomicrobiales favoring the consumption of propionate most likely through hydrogen utilization.