“…Such CEPT sludge had shown better digestibility than regular sludge [ 29 ]. Consequently, the degree of performance promotion reported here may be higher than other studies apply similar part-stream strategy [ 12 , 52 ]. Fig.…”
BackgroundPart-stream low-frequency ultrasound (LFUS) was one of the common practices for sludge disintegration in full-scale anaerobic digestion (AD) facilities. However, the effectiveness of part-stream LFUS treatment and its effect on AD microbiome have not been fully elucidated.MethodsHere we testified the effectiveness of part-stream LFUS pretreatment by treating only a fraction of feed sludge (23% and 33% total solid of the feed sludge) with 20 Hz LFUS for 70 s. State-of-the-art metagenomic and metatranscriptomic analysis was used to investigate the microbial process underpinning the enhanced AD performance by part-stream LFUS pretreatment.ResultsBy pretreating 33% total solid of the feed sludge, methane yield was increased by 36.5%, while the volatile solid reduction ratio remained unchanged. RNA-seq of the microbiome at stable stage showed that the continuous dosage of easy-degradable LFUS-pretreated feed sludge had gradually altered the microbial community by selecting Bacteroidales hydrolyzer with greater metabolic capability to hydrolyze cellulosic biomass without substrate attachment. Meanwhile, Thermotogales with excellent cell mobility for nutrient capturing was highly active within the community. Foremost proportion of the methanogenesis was contributed by the dominant Methanomicrobiales via carbon dioxide reduction. More interestingly, a perceivable proportion of the reverse electron flow of the community was input from Methanoculleus species other than syntrophic acetate-oxidizing bacteria. In addition, metagenomic binning retrieved several interesting novel metagenomic-assembled genomes (MAGs): MAG-bin6 of Alistipes shahii showed exceptional transcriptional activities towards protein degradation and MAG-bin11 of Candidatus Cloacimonetes with active cellulolytic GH74 gene detected.ConclusionsIn summary, despite the unchanged sludge digestibility, the applied part-stream LFUS pretreatment strategy was robust in adjusting the microbial pathways towards more effective substrate conversion enabled by free-living hydrolyser and beta-oxidation-capable methanogens.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1042-y) contains supplementary material, which is available to authorized users.
“…Such CEPT sludge had shown better digestibility than regular sludge [ 29 ]. Consequently, the degree of performance promotion reported here may be higher than other studies apply similar part-stream strategy [ 12 , 52 ]. Fig.…”
BackgroundPart-stream low-frequency ultrasound (LFUS) was one of the common practices for sludge disintegration in full-scale anaerobic digestion (AD) facilities. However, the effectiveness of part-stream LFUS treatment and its effect on AD microbiome have not been fully elucidated.MethodsHere we testified the effectiveness of part-stream LFUS pretreatment by treating only a fraction of feed sludge (23% and 33% total solid of the feed sludge) with 20 Hz LFUS for 70 s. State-of-the-art metagenomic and metatranscriptomic analysis was used to investigate the microbial process underpinning the enhanced AD performance by part-stream LFUS pretreatment.ResultsBy pretreating 33% total solid of the feed sludge, methane yield was increased by 36.5%, while the volatile solid reduction ratio remained unchanged. RNA-seq of the microbiome at stable stage showed that the continuous dosage of easy-degradable LFUS-pretreated feed sludge had gradually altered the microbial community by selecting Bacteroidales hydrolyzer with greater metabolic capability to hydrolyze cellulosic biomass without substrate attachment. Meanwhile, Thermotogales with excellent cell mobility for nutrient capturing was highly active within the community. Foremost proportion of the methanogenesis was contributed by the dominant Methanomicrobiales via carbon dioxide reduction. More interestingly, a perceivable proportion of the reverse electron flow of the community was input from Methanoculleus species other than syntrophic acetate-oxidizing bacteria. In addition, metagenomic binning retrieved several interesting novel metagenomic-assembled genomes (MAGs): MAG-bin6 of Alistipes shahii showed exceptional transcriptional activities towards protein degradation and MAG-bin11 of Candidatus Cloacimonetes with active cellulolytic GH74 gene detected.ConclusionsIn summary, despite the unchanged sludge digestibility, the applied part-stream LFUS pretreatment strategy was robust in adjusting the microbial pathways towards more effective substrate conversion enabled by free-living hydrolyser and beta-oxidation-capable methanogens.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1042-y) contains supplementary material, which is available to authorized users.
“…Improved methane yield from cellulosic substrate after pretreatment has also been reported by other authors [24][25][26]. Though the improvements were different, (this has something to do with the composition of the substrate and the different operational conditions [24]) these methods all can accelerate the hydrolysis process by destroying the substrate Fig. 1.…”
Section: The Effect Of Microaerobic Condition On the Thermophilic Fersupporting
h i g h l i g h t sThe effect of limited oxygen daily supplied on the AD of corn straw was studied. Daily oxygen supplied could obviously improve the AD performance of corn straw. Specific methanogenic activity under microaerobic condition improved slightly. The microbial community structure shift could explain the better AD performance. a r t i c l e i n f o
b s t r a c tConventionally, oxygen is considered as inhibit factor of anaerobic digestion (AD). However, recent studies have demonstrated that AD performance could be enhanced by introducing limited amounts of oxygen (or air) directly into the anaerobic digester or during pretreatment step. In this study, impacts of microaeration on the anaerobic digestion of corn straw and the microbial community structure were investigated. Results showed that limited air introduced into fermentation system could improve the methane yield of corn straw. Maximum cumulative methane yield of 216.8 ml/g VS substrate and maximum VS removal efficiency of 54.3% were simultaneously obtained under microaerobic condition with the air load of 12.5 ml/L R per day, which were 16.5% and 10.3% higher than those of sample under anaerobic condition, respectively. Compared to anaerobic condition, the relative abundances of phylum Firmicutes, class Clostridia and order Clostridiales, which associated with hydrolysis process of AD were raised under microaerobic condition. In addition, the relative abundances of oxytolerant Methanosarcina and Methanobacterium were both doubled under microaerobic condition. Accordingly, specific methanogenic activity (SMA) under microaerobic condition improved slightly. The microbial community shift might be the reason for improved AD performance under microaerobic condition.
“…Anaerobic digestion can thus convert over 50% of the by-product COD to biogas, which may be used as fuel within the plant [89]. Moreover, as stillage represents the partially degraded form of the biomass used within the fermentation process, the energy required for its treatment prior to anaerobic digestion can be significantly reduced [97]. Several studies reported the use of bioethanol residues for biogas production.…”
Section: The Combination Of Bioethanol and Biogas Production Processesmentioning
Abstract:In the last decades the increasing energy requirements along with the need to face the consequences of climate change have driven the search for renewable energy sources, in order to replace as much as possible the use of fossil fuels. In this context biomass has generated great interest as it can be converted into energy via several routes, including fermentation and anaerobic digestion. The former is the most common option to produce ethanol, which has been recognized as one of the leading candidates to substitute a large fraction of the liquid fuels produced from oil. As the economic competitiveness of bioethanol fermentation processes has to be enhanced in order to promote its wider implementation, the most recent trends are directed towards the use of fermentation by-products within anaerobic digestion. The integration of both fermentation and anaerobic digestion, in a biorefinery concept, would allow the production of ethanol along with that of biogas, which can be used to produce heat and electricity, thus improving the overall energy balance. This work aims at reviewing the main studies on the combination of both bioethanol and biogas production processes, in order to highlight the strength and weakness of the integrated treatment for industrial application.
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