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Microbial Community Composition and Diversity in Rice Straw Digestion Bioreactors with and without Dairy Manure

Lookup NU author(s): Dr Andrew Zealand, Professor Tony Roskilly, Professor David Graham

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


Abstract

Anaerobic digestion (AD) uses a range of substrates to generate biogas, including energy crops such as globally abundant rice straw (RS). Unfortunately, RS is high in lignocellulosic material and has high to C:N ratios (~80:1), which makes it (alone) a comparatively poor substrate for AD. Co-digestion with dairy manure (DM) has been promoted as a method for balancing C:N ratios to improve RS AD whilst also treating another farm waste and co-producing a potentially useful fertiliser. However, past co-digestion studies have not directly compared RS AD microbial communities with and without DM additions, which has made it hard to assess all impacts of DM addition to RS AD processes. Here four RS:DM ratios were contrasted in identical semi-continuous-fed AD bioreactors, and 100% RS was found to produce the highest specific methane yields (112 mL CH4/g VS/d; VS, volatile solids), which is over double yields achieved in the reactor with the highest DM content (30:70 RS:DM by mass; 48 mL CH4/g VS/d). To underpin these data, microbial communities were sequenced and characterised across the four reactors. Dominant operational taxonomic units (OTUs) in the 100% RS unit were Bacteroidetes/Firmicutes, whereas the 30:70 RS:DM unit was dominated by Proteobacteria/Spirochaetes, suggesting major microbial community shifts occur with DM additions. However, community richness was lowest with 100% RS (despite higher specific yields), suggesting particular OTUs may be more important to yields than microbial diversity. Further, ambient VFA and VS levels were significantly higher when no DM was added, suggesting DM-amended reactors may cope better with higher organic loading rates (OLR). Results show that RS AD without DM addition is feasible, although co-digestion with DM will probably allow higher OLRs, resulting in great RS throughput in farm AD units.


Publication metadata

Author(s): Zealand AM, Mei R, Papachristodoulou P, Roskilly AP, Liu WT, Graham DW

Publication type: Article

Publication status: Published

Journal: Applied Microbiology and Biotechnology

Year: 2018

Volume: 102

Issue: 19

Pages: 8599-8612

Print publication date: 01/10/2018

Online publication date: 27/07/2018

Acceptance date: 13/07/2018

Date deposited: 30/07/2018

ISSN (print): 0175-7598

ISSN (electronic): 1432-0614

Publisher: Springer

URL: https://doi.org/10.1007/s00253-018-9243-7

DOI: 10.1007/s00253-018-9243-7


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