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

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/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.Electronic supplementary materialThe online version of this article (10.1007/s00253-018-9243-7) contains supplementary material, which is available to authorized users.

Microbial Responses to Different Operating Practices for Biogas Production Systems

“…Animal manure and sludge are commonly used in co-digestion with straw (corn, rice, tobacco, wheat) and in these processes the two orders Clostridiales (phylum Firmicutes) and Bacteroidales (phylum Bacteroidetes) often dominate. However, the phyla Proteobacter, Chloroflexi, and Fibrobacteres also often increase in response to addition of lignocellulosic materials, with some variation depending on codigestion material and prevailing environmental conditions [118,202,[204][205][206][207][208]. The microbial community structure in AD of rice straw has been shown to be influenced by temperature, with a higher ratio of Firmicutes to Bacteroidetes being reported at higher temperature [208].…”

Metagenomic and Metatranscriptomic Analyses Revealed Uncultured Bacteroidales Populations as the Dominant Proteolytic Amino Acid Degraders in Anaerobic Digesters

“…The order Bacteroidales is one of the most prevalent in AD, and its abundance can reach as high as 15% in a community (Mei et al, 2016(Mei et al, , 2018Narihiro et al, 2018;Zealand et al, 2018;Nobu et al, 2020). It is also widely distributed in different non-AD habitats (Gupta, 2004) such as animal intestinal microflora (Dick et al, 2005) and marine bacterioplankton (Fernández-Gomez et al, 2013).…”

Recent Advance in Anaerobic Co-digestion Technology: A Review

“…Moreover, the addition of magnetite (Fe 3 O 4 ) eases the consumption of dihydrogen by the microorganisms (Li et al, 2019). It should be noted that a long-term acclimation of microbes was proven to be a powerful method for improving the inoculum quality for AD of a given substrate (Kumar, Prajapati, Malik, & Vijay, 2019) (Zealand et al, 2018) (Akshaya & Jacob, 2020).…”

“…This is an important factor in the AD process and is dependent on carbon-and protein-rich substrates (Akshaya & Jacob, 2020) (Salama et al, 2019). The balance of the C/N ratio of the feedstock was shown to enhance the methane production of anaerobic co-digestion (Mozhiarasi et al, 2019) (Zealand et al, 2018) (Ngan et al, 2019). The proportion between carbon and nitrogen improves the buffering capacity and minimizes the effect of inhibitory compounds (accumulation of organic acids, ammonia, VFAs) (Elalami et al, 2019) (Fragoso et al, 2020) (Shen et al, 2019) (Sahoo & Rao, 2019).…”

“…The microbial community in the biogas process is important (Achinas & Euverink, 2019) since it was suggested that specific dominant operational taxonomic units might be more significant to methane production than a variety of microorganisms (Zealand et al, 2018). The addition of co-substrate may bring in many variate species (Rabii et al, 2019) that do not correspond to methane generation itself but more associated with intermediate reactions (Latifi et al, 2019).…”