Waste Activated Sludge Addition Assures the Stable Anaerobic Digestion of Food Waste: Microbiome Changes and Link with Key Process Parameters

Anaerobic digestion (AD) process was investigated in ten different semi-continuous reactors treating only food waste (FW) or FW and waste activated sludge (WAS) in co-digestion, in order to evaluate the AD performances and elucidate the dynamics of main microbial groups selected under different operating conditions. The analysis was performed by high-throughput 16S rRNA gene sequencing combined with in situ detection techniques. The instability of the AD process was observed in all reactors fed with only FW, mirrored by the volatile fatty acids (VFAs) accumulation due to dramatic decrease of methanogenic activity. On the contrary, WAS addition improved the AD performance assuring the process stability also at OLRs higher than those imposed to the mono-digestion systems. A clear link between microbial composition and AD performance was found. A distinctive selection of fermentative bacteria and methanogens was found in mono- and co-digestion systems.