Molecular microbial ecology of stable versus failing rice straw anaerobic digesters

Abstract

Summary Waste rice straw (RS) is generated in massive quantities around the world and is often burned, creating greenhouse gas and air quality problems. Anaerobic digestion (AD) may be a better option for RS management, but RS is presumed to be comparatively refractory under anaerobic conditions without pre‐treatment or co‐substrates. However, this presumption assumes frequent reactor feeding regimes but less frequent feeding may be better for RS due to slow hydrolysis rates. Here, we assess how feeding frequency (FF) and organic loading rate (OLR) impacts microbial communities and biogas production in RS AD reactors. Using 16S rDNA amplicon sequencing and bioinformatics, microbial communities from five bench‐scale bioreactors were characterized. At low OLR (1.0 g VS l−1 day−1), infrequently fed units (once every 21 days) had higher specific biogas yields than more frequent feeding (five in 7 days), although microbial community diversities were statistically similar (P > 0.05; ANOVA with Tukey comparison). In contrast, an increase in OLR to 2.0 g VS l−1 day−1 significantly changed Archaeal and fermenting Eubacterial sub‐communities and the least frequency fed reactors failed. ‘Stable’ reactors were dominated by Methanobacterium, Methanosarcina and diverse Bacteroidetes, whereas ‘failed’ reactors saw shifts towards Clostridia and Christensenellaceae among fermenters and reduced methanogen abundances. Overall, OLR impacted RS AD microbial communities more than FF. However, combining infrequent feeding and lower OLRs may be better for RS AD because of higher specific yields.

The Effect of Operating Strategies on the Anaerobic Digestion of Gentamicin Mycelial Residues: Insights into the Enhancement of Methane Production and Attenuation of Gentamicin Resistance

“…This discrepancy of methanogen abundances in MMAD and MAcoD was likely caused by the addition of WS. The optimal pH for Methanobacterium (i.e., 6.0) was lower than that for Methanosarcina (i.e., neutral), suggesting that a lower pH environment created during WS decomposition was favorable for the growth of Methanobacterium . , …”

“…This discrepancy of methanogen abundances in MMAD and MAcoD was likely caused by the addition of WS. The optimal pH for Methanobacterium (i.e., 6.0) was lower than that for Methanosarcina (i.e., neutral), 47 suggesting that a lower pH environment created during WS decomposition was favorable for the growth of Methanobacterium. 7,48 Under the thermophilic conditions, methanogens in TAcoD were overwhelmingly dominated by Methanosarcina with an abundance of 76.00%−92.02%, and almost all of the rest of the methanogens were identified as Methanobacterium (6.39%− 20.06%).…”