Transition of microbial communities and degradation pathways in anaerobic digestion at decreasing retention time

Tuning operational variables is a common practice to control the anaerobic digestion process and, in advanced applications, to promote the accumulation of fermentation products. However, process variables are interrelated. In this study, the hydraulic retention time (HRT) was decoupled from the organic loading rate (OLR) to isolate the effect of HRT as selective pressure on: (i) process performance, (ii) metabolic rates (hydrolytic, acetogenic, and methanogenic) and (iii) microbial community. Four mesophilic continuous anaerobic digesters were subjected to a sequential decrease in HRT from 15 to 8 to 4 to 2 days while keeping the OLR constant at 1 g COD Lr 1 d-1