Potential process 'hurdles' in the use of macroalgae as feedstock for biofuel production in the British Isles

This review examines the potential technical and energy balance hurdles in the production of seaweed biofuel, and particular for the MacroBioCrude processing pipeline for the sustainable manufacture of liquid hydrocarbon fuels from seaweed in the UK. The production of biofuel from seaweed is economically, energetically and technically challenging at scale. Any successful process appears to require both a method of preserving the seaweed for continuous feedstock availability and a method exploiting the entire biomass. Ensiling and gasification offer a potential solution to these two requirements. However there is need for more data particularly at a commercial scal

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

Background: Biogas 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). Results: Overall, 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. Conclusion: Our findings demonstrate the potential of combined SE and bioaugmentation for enhancing methane production from lignocellulosic biomass

The microbiome of biogas reactors treating lignocellulosic substrates revealed different mechanisms for carbohydrates utilization.

The present study dissected the microbiome of biogas reactors treating lignocellulosic substrate and swine manure by means of high throughput Illumina sequencing. A comparative metagenomic analysis allowed to identify the microbial species firmly attached to the digested lignocellulosic particles and to distinguish them from the planktonic microbes floating in the liquid medium. Proteobacteria and Firmicutes were the most abundant phyla identified respectively in the liquid samples and firmly attached to the grass, and accounted approximately 17 and 22% of the total microbial counts. Additionally, Actinobacteria were also presented in both samples but in lower relative abundance. Assembly of the shotgun reads followed by a binning process led to the extraction of 151 genome bins, out of which 80 microbial species were completely new and not previously deposited in any database. Moreover, it was shown that 25 microbial genomes were more enriched (>2 fold) in the firmly attached grass samples compared to the liquid phase. A bioinformatic approach based on multiple databases for functional annotation (KEGG, COG, SEED and dbCAN) demonstrated that these microbial species encode enzymes related to carbohydrate utilisation and present numerous carbohydrate binding modules. Finally, it was found that apart from the cellulosome multi-enzyme complex, specific microbes, such as Bacteroidetes, present different mechanisms for binding and degrading the lignocellulose due to the presence of multiple CBM6 modules in beta-xylosidase and endoglucanase proteins or SLH modules in unknown proteins

Process performance and comparative metagenomic analysis during co-digestion of manure and lignocellulosic biomass for biogas production

Mechanical pretreatment is considered to be a fast and easily applicable method to prepare the biomass for anaerobic digestion. In the present study, the effect of mechanical pretreatment on lignocellulosic silages biodegradability was elucidated in batch reactors. Moreover, co-digestion of the silages with pig manure in continuously fed biogas reactors was examined. Metagenomic analysis for determining the microbial communities in the pig manure digestion system was performed by analysing unassembled shotgun genomic sequences. A comparative analysis allowed to identify the microbial species firmly attached to the digested grass particles and to distinguish them from the planktonic microbes floating in the liquid medium. It was shown that the methane yield of ensiled grass was significantly increased by 12.3% due to mechanical pretreatment in batch experiments. Similarly, the increment of the methane yield in the co-digestion system reached 6.4%. Regarding the metagenomic study, species similar to Coprothermobacter proteolyticus and to Clostridium thermocellum, known for high proteolytic and cellulolytic activity respectively, were found firmly attached to the solid fraction of digested feedstock. Results from liquid samples revealed clear differences in microbial community composition, mainly dominated by Proteobacteria. The archaeal community was found in higher relative abundance in the liquid fraction of co-digestion experiment compared to the solid fraction. Finally, an unclassified Alkaliphilus sp. was found in high relative abundance in all samples

Enhancing anaerobic digestion of agricultural residues by microaerobic conditions

Biogas plants treating agricultural residues are associated with limited bioenergy output due to the high content of hardly degradable lignocellulosic fibers in the feedstock. Hence, effective treatment techniques are needed to enhance holocellulose deconstruction, and thus, increase the energy budget of anaerobic digestion (AD) process. In the present research, microaerobic conditions were applied in reactors that were previously operated under strict anaerobic conditions as a tool to increase the biodegradability of the lignocellulosic material and thereby improve the methane production in lignocellulose-based AD. Initially, two levels of oxygen loads (i.e., 5 and 15 mLO 2 /gVS) were examined during the AD of lignocellulosic biomass at batch mode. Low and high oxygen loads were connected with positive (+ 10%) and negative (− 4%) impact in methanation process, respectively. Subsequently, the experimental results were validated by the amended BioModel. Furthermore, continuous mode experiments were conducted to more closely mimic real-life applications. Monitoring of a continuous digester fed with agricultural residues showed that the injection of 7.3 mLO 2 /gVS/day—which value was defined from mathematical optimization—was capable of improving the methane yield by ∼ 7%. In addition, oxygen injection did not create any risk of inhibition incidents. Concerning microbial community structure, the bacterial population was relatively robust and was not markedly affected by oxygen addition. In contrast, some archaeal representatives were found to have increased relative abundance on oxygen exposure. More specifically, the aero-tolerant Methanosarcina and Methanobacterium spp. were the most dominant methanogens at microaerobic conditions