Enhancing methane production from lignocellulosic biomass by combined steam-explosion pretreatment and bioaugmentation with cellulolytic bacterium Caldicellulosiruptor bescii

Abstract

BackgroundBiogas production from lignocellulosic biomass is generally considered to be challenging due to the recalcitrant nature of this biomass. In this study, the recalcitrance of birch was reduced by applying steam-explosion (SE) pretreatment (210 °C and 10 min). Moreover, bioaugmentation with the cellulolytic bacterium Caldicellulosiruptor bescii was applied to possibly enhance the methane production from steam-exploded birch in an anaerobic digestion (AD) process under thermophilic conditions (62 °C).ResultsOverall, the combined SE and bioaugmentation enhanced the methane yield up to 140% compared to untreated birch, while SE alone contributed to the major share of methane enhancement by 118%. The best methane improvement of 140% on day 50 was observed in bottles fed with pretreated birch and bioaugmentation with lower dosages of C. bescii (2 and 5% of inoculum volume). The maximum methane production rate also increased from 4-mL CH4/g VS (volatile solids)/day for untreated birch to 9–14-mL CH4/g VS/day for steam-exploded birch with applied bioaugmentation. Bioaugmentation was particularly effective for increasing the initial methane production rate of the pretreated birch yielding 21–44% more methane than the pretreated birch without applied bioaugmentation. The extent of solubilization of the organic matter was increased by more than twofold when combined SE pretreatment and bioaugmentation was used in comparison with the methane production from untreated birch. The beneficial effects of SE and bioaugmentation on methane yield indicated that biomass recalcitrance and hydrolysis step are the limiting factors for efficient AD of lignocellulosic biomass. Microbial community analysis by 16S rRNA amplicon sequencing showed that the microbial community composition was altered by the pretreatment and bioaugmentation processes. Notably, the enhanced methane production by pretreatment and bioaugmentation was well correlated with the increase in abundance of key bacterial and archaeal communities, particularly the hydrolytic bacterium Caldicoprobacter, several members of syntrophic acetate oxidizing bacteria and the hydrogenotrophic Methanothermobacter.ConclusionOur findings demonstrate the potential of combined SE and bioaugmentation for enhancing methane production from lignocellulosic biomass.

Steam Explosion Pretreatment Changes Ruminal Fermentation in vitro of Corn Stover by Shifting Archaeal and Bacterial Community Structure

“…Total gas production and CH 4 production from TRT were both higher than that from CON, but the increases were both statistically insignificant. The results are not consistent from previous studies ( Lizasoain et al, 2017 ; Mulat et al, 2018 ), which reported that steam explosion pretreatment significantly increased the total gas production and CH 4 production. Steam explosion pretreatment improved the digestibility of corn stover and more readily fermentable substrates should produce more gas.…”

“…In addition, the anaerobic digestion inoculum used in the present study is rumen fluid, which is home to a vast array of ciliate protozoa, fungi, bacteria, and archaea. The compositions and interactions of different microbes are more complex than those used in the previous studies ( Lizasoain et al, 2017 ; Mulat et al, 2018 ). In the present study, the formation of propionate might be served as an alternative to H 2 formation and then reduce the utilization of H 2 in methanogenesis, shifting H 2 flow from CH 4 to propionate production.…”

Substrate-Induced Response in Biogas Process Performance and Microbial Community Relates Back to Inoculum Source

“…Caldicoprobacter has also been found to be enriched in anaerobic digesters fed lignocellulosic biomass under both mesophilic and thermophilic conditions [53,54]. Moreover, it has been shown to dominate in an anaerobic digester with high total ammonium-nitrogen (5 to 25 g/L) and, as in this study, high VFA levels (>4 g/L) [55].…”

Thermophilic Anaerobic Digestion: Enhanced and Sustainable Methane Production from Co-Digestion of Food and Lignocellulosic Wastes

“…The intricate composition of lignocellulosic materials, where cellulose fiber is tightly linked to hemicellulose and lignin, hinders their biodegradability and thus limits their use as co-substrates for AD. The recalcitrant nature of the LW necessitates the inclusion of the pretreatment step (physical, chemical or biological) for their efficient conversion into biofuels [34]. The use of thermophilic digesters can eliminate the use of costly and sometimes hazardous pretreatment steps.…”