Abstract
The present study investigated the effect of rumen fluid (RF) concentration on the methane production through anaerobic digestion of wheat straw in batch mode, and compared the microbial communities in RF and RF inoculated reactors by 16S rRNA genes sequencing. Six levels of RF concentration including 1%, 5%, 10%, 15%, 20% and 25% (v/v) were used in reactors R1, R5, R10, R15, R20 and R25 respectively. The results revealed that lower than or equal to 5% RF concentrations resulted in reactor acidification and low methane production. The highest methane yield of 106 mL CH4 g VS−1 was achieved in R10, whereas higher RF concentrations than 10% could not improve the methane production significantly. Methanosarcina barkeri was abundant in the well-working reactors, and Methanobacterium was dominant in the poor-working reactors, implying the archaeal communities in reactors had changed greatly from the Methanobrevibacter-dominated RF. Although the relative abundance of Clostridium and Ruminococcus were greatly different between RF and reactors, the Bacteroidetes and Firmicutes communities were dominant in all the tested samples. The results indicated that the in vitro anaerobic conditions had altered the rumen methanogenic communities significantly and the facultative acetoclastic Methanosarcina was important for the methane production in the RF seeded reactors.
Highlights
Lignocellulosic materials include a large fraction of municipal solid waste, crop residues, animal manures, woodlot arisings, forest residues, and/or dedicated energy crops [1]
In reactors that contained more than 10% rumen inoculum, the inoculum was prepared by removing certain volume of supernatant after the active rumen fluid (RF) was centrifuged at 14,000 × g for 30 min (e.g., 25% RF was Sustainability 2017, 9, 243 prepared by removing of 9 mL of supernatant out of 15 mL of centrifuged RF)
It was observed that no archaeal operational taxonomic unit (OTU) derived from RF were detected from reactor samples and only one RF bacterial OTU was detected from R1 and R25 (Figure 3)
Summary
Lignocellulosic materials include a large fraction of municipal solid waste, crop residues, animal manures, woodlot arisings, forest residues, and/or dedicated energy crops [1]. Because they are abundant in renewable biomass with low treatment costs, they are broadly employed for methane production in recent years [2]. Experiments were performed using different RF concentrations for the wheat straw anaerobic digestion to (1) explore the appropriate RF concentration for methane production and (2) characterize the bacterial and archaeal communities in RF and RF seeded reactors
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