Dataset Information

Molecular microbial ecology of stable versus failing rice straw anaerobic digesters.

ABSTRACT: 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.

SUBMITTER: Zealand AM

PROVIDER: S-EPMC6681398 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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Molecular microbial ecology of stable versus failing rice straw anaerobic digesters.

Zealand Andrew M AM Mei Ran R Roskilly Anthony P AP Liu WenTso W Graham David W DW

Microbial biotechnology 20190610 5

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 ...[more]

PMID: 31233284

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Project description:The formation of dense, well-settling methanogenic granules is essential for the operation of high-rate, up-flow anaerobic bioreactors used for wastewater treatment. Granule formation (granulation) mechanisms have been previously proposed, but an ecological understanding of granule formation is still lacking. Additionally, much of the current research on granulation only examines the start-up phase of bioreactor operation, rather than monitoring the fate of established granules and how new granules emerge over time. This paper, therefore, attempts to provide an insight into the microbial ecology of granule formation outside the start-up phase of bioreactor operation and develop an ecological granulation model. The microbial communities of granules actively undergoing growth, breakage, and reformation were examined, and an ecological granulation model was proposed. A distinct pregranular microbial community, with a high proportion of acidogenic organisms, such as the Streptococcaceae, was identified and suggested to have a role in initiating granulation by providing simpler substrates for the methanogenic and syntrophic communities which developed during granule growth. After initial granule formation, deterministic influences on microbial community assembly increased with granule size and indicated that microbial community succession was influenced by granule growth, leading to the formation of a stepwise ecological model for granulation. IMPORTANCE Complex microbial communities in engineered environments can aggregate to form surface-attached biofilms. Others form suspended biofilms, such as methanogenic granules. The formation of dense, methanogenic granules underpins the performance of high-rate, anaerobic bioreactors in industrial wastewater treatment. Granule formation (granulation) has been well studied from a physico-chemical perspective, but the ecological basis is poorly understood. We identified a distinct, flocculent, microbial community, which was present alongside granules, comprising primary consumers likely key in providing simpler substrates to granules. This flocculent community is understudied in anaerobic digestion and may initiate, or perpetuate, granule formation. We propose that it may be possible to influence bioreactor performance (e.g., to regulate volatile fatty acid concentrations) by manipulating this community. The patterns of microbial community diversity and assembly revealed by the study indicate that cycles of granule growth and breakage lead to overall diversification of the bioreactor meta-community, with implications for bioreactor process stability.

Project description:BackgroundConsiderable interest has been expressed in the development of anaerobic digestion (AD) of straw to solve the environmental problems caused by the dumping and burning of straw and to generate clean energy. However, the poor biodegradability of straw and the low efficiency of energy generation achieved during its AD are problematic. Studying the parameter changes involved in the process of AD is helpful for clarifying its micro-mechanisms and providing a theoretical basis for improving its efficiency. Currently, most research into process parameters has focused on gas production, methane content, pH, and volatile fatty acid (VFA) content; limited research has focused on carbon migration and functional gene changes during the AD of straw.ResultsCarbon migration and changes in metagenomic characteristics during the AD of rice straw (RS) were investigated. Accumulated biogas production was 388.43 mL/g VS. Carbon in RS was consumed, and the amount of carbon decreased from 76.28 to 36.83 g (conversion rate 51.72%). The degree of hydrolysis rapidly increased during the first 5 days, and a large amount of carbon accumulated in the liquid phase before migrating into the gas phase. By the end of AD, the amount of carbon in the liquid and gas phases was 2.67 and 36.78 g, respectively. According to our metagenomic analysis, at the module level, the abundance of M00357, M00567, M00356, and M00563 (the modules related to the generation of methane) during AD were 51.23-65.43%, 13.96-26.88%, 16.44-22.98%, and 0.83-2.40%, respectively. Methyl-CoM, 5-methyl-5,6,7,8-tetrahydromethanopterin, and Acetyl-CoA were important intermediates.ConclusionsCarbon was enriched in the liquid phase for the first 5 days and then gradually consumed, and most of the carbon was transferred to the gas phase by the end of AD. In this study, AD proceeded mainly via aceticlastic methanogenesis, which was indicated to be a dominant pathway in methane metabolism. Batch AD could be divided into three stages, including initiation (days 1-5), adaptation (days 6-20), and stabilization (days 21-50), according to biogas production performance, carbon migration, and metagenomic characteristics during AD.

Dataset Information

Molecular microbial ecology of stable versus failing rice straw anaerobic digesters.

Publications

Molecular microbial ecology of stable versus failing rice straw anaerobic digesters.

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