Changes in the prokaryotic communities occurring along a two-stage anaerobic digestion system treating the organic fraction of solid waste

Abstract

Two-stage anaerobic digestion is useful for recycling of the organic fraction of municipal solid waste and wastewater; the prokaryotic communities involved in this process were characterized using massive sequencing of 16S rRNA gene amplicons. During the 60-day study the prokaryotic communities were stable in time but were affected by their position in the system. The first stage of solid waste digestion was operated in an anaerobic-hydrolytic leach bead reactor with high organic solids content, the microbial communities were dominated by members of the orders Bacteroidales (62%), Selenomonadales (15%), Lactobacillales (13%), Clostridiales (4%) and Rhodospirillales (1%). At this stage, a vertical stratification acted as a transition zone from aerobic to anaerobic environments modifying significantly the composition and structure of bacterial communities.The second stage occurred in an up-flow anaerobic sludge bed reactor specialized in acidogenesis-methanogenesis, where the leachate of the first stage was co-fed with municipal wastewater. In this stage, the bacterial community was dominated by members of the orders Pseudomonadales, Clostridiales, Burkholderiales, Bacteroidales and Syntrophobacterales (accounting for 52%), while the most abundant orders of the archaeal community corresponded to Methanosarcinales (72%) and Methanobacteriales (13%), both of them with methanogenic capacity.