Microbial community composition and diversity in rice straw digestion bioreactors with and without dairy manure

A. M. Zealand, R. Mei, P. Papachristodoulou, A. P. Roskilly, W. T. Liu, David W. Graham*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)


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/day; 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/day). 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.

Original languageEnglish
Pages (from-to)8599-8612
Number of pages14
JournalApplied Microbiology and Biotechnology
Issue number19
Publication statusPublished - 1 Oct 2018
Externally publishedYes

Bibliographical note

Funding Information:
Funding This work was partially supported by the Energy from Rice Straw project (EP/L002477/1) funded by EPSRC, DFID and DECC as part of the Energy & International Development: USES programme; the Natural Environment Research Council (NE/L501748/1); the Sir Joseph Swan Centre for Energy Research; and the Xiamen-Newcastle Joint Strategic Partnership Fund. A special acknowledgement goes to Wen- Tso’s group at the University of Illinois at Urbana, USA, without which, this microbial analysis would not have been possible.

Publisher Copyright:
© 2018, The Author(s).


  • 16S rDNA amplicon
  • Anaerobic digestion
  • Feeding frequency
  • Illumina sequencing
  • Methane yields
  • Organic loading rate
  • Rice straw


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