This study evaluated the importance of inoculum source for start-up and operation of biogas processes. Three different inocula with different community structure were used to initiate six laboratory continuous stirred tank reactor (CSTR) processes operated with a grass manure mixture as substrate. The processes were evaluated by chemical and microbiological analysis, by targeting the overall bacterial community and potential cellulose-degrading bacteria. As expected, the results showed a large difference in community structure in the inocula and in process performance during the first hydraulic retention time (HRT). However, the performance and overall microbial community structure became similar in the reactors over time. An inoculum from a high-ammonia process, characterized by low diversity and low degradation efficiency, took the longest time to reach stability and final methane yield. The overall bacterial community was mainly shaped by the operating conditions but, interestingly, potential cellulose-degrading bacteria seemed mainly to originate from the substrate.

BackgroundMaterials rich in lignocellulose, such as straw, are abundant, cheap and highly interesting for biogas production. However, the complex structure of lignocellulose is difficult for microbial cellulolytic enzymes to access, limiting degradation. The rate of degradation depends on the activity of members of the microbial community, but the knowledge of this community in the biogas process is rather limited. This study, therefore, investigated the degradation rate of cellulose and straw in batch cultivation test initiated with inoculums from four co-digestion biogas plants (CD) and six wastewater treatment plants (WWTP). The results were correlated to the bacterial community by 454-pyrosequencing targeting 16S rRNA gene and by T-RFLP analysis targeting genes of glycoside hydrolase families 5 (cel5) and 48 (cel48), combined with construction of clone librariesResultsUniFrac principal coordinate analysis of 16S rRNA gene amplicons revealed a clustering of WWTPs, while the CDs were more separated from each other. Bacteroidetes and Firmicutes dominated the community with a comparably higher abundance of the latter in the processes operating at high ammonia levels. Sequences obtained from the cel5 and cel 48 clone libraries were also mainly related to the phyla Firmicutes and Bacteroidetes and here ammonia was a parameter with a strong impact on the cel5 community. The results from the batch cultivation showed similar degradation pattern for eight of the biogas plants, while two characterised by high ammonia level and low bacterial diversity, showed a clear lower degradation rate. Interestingly, two T-RFs from the cel5 community were positively correlated to high degradation rates of both straw and cellulose. One of the respective partial cel5 sequences shared 100 % identity to Clostridium cellulolyticum.ConclusionThe degradation rate of cellulose and straw varied in the batch tests dependent on the origin of the inoculum and was negatively correlated with the ammonia level. The cellulose-degrading community, targeted by analysis of the glycoside hydrolase families 5 (cel5) and 48 (cel48), showed a dominance of bacteria belonging the Firmicutes and Bacteriodetes, and a positive correlation was found between the cellulose degradation rate of wheat straw with the level of C. cellulolyticum.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-016-0543-9) contains supplementary material, which is available to authorized users.

In farm‐scale biogas systems, different kinds of manure are the most important substrate for anaerobic digestion, but result in low biogas yields. Biogas production can be increased by complementing the manure with forage crops, in codigestion. The aim of this study was to evaluate grass‐clover (GCS) and whole‐crop barley silages (WCB) in codigestion with manure from organic and conventional dairy production systems on biogas production, microbial community, degree of degradation and gas quality at different organic loading rates by addition of soya bean meal and wheat grain, which are rich in protein and starch. Four continuous stirred anaerobic laboratory‐scale reactors were used, and the codigestion resulted in additive effects on biogas production, but no synergistic effects. The highest biogas yield was obtained in reactors receiving WCB independently of manure types, for both experiments (7,416 ml/day and 10,978 ml/day respectively). The degradation efficiency, measured as the reduction in volatile solids was, on average, six percentage units higher in the reactors receiving manure from conventional compared with organic dairy cows, probably because of a higher concentration of undigested fibre and proteins in conventional cow manure. Microbiological analysis by illumina sequencing illustrated low impact of both manure types on the reactor community and only small differences between the reactors receiving GCS and WCB. However, addition of soya bean meal and wheat grain changed the community in all reactors. The ratio between Firmicutes and Bacteroidetes was comparably higher in reactors having the highest gas production and methane yield.

BackgroundWaste lipids are attractive substrates for co-digestion with primary and activated sewage sludge (PASS) to improve biogas production at wastewater treatment plants. However, slow conversion rates of long-chain fatty acids (LCFA), produced during anaerobic digestion (AD), limit the applicability of waste lipids as co-substrates for PASS. Previous observations indicate that the sulfide level in PASS digesters affects the capacity of microbial communities to convert LCFA to biogas. This study assessed the microbial community response to LCFA loads in relation to sulfide level during AD of PASS by investigating process performance and microbial community dynamics upon addition of oleate (C18:1) and stearate (C18:0) to PASS digesters at ambient and elevated sulfide levels.ResultsConversion of LCFA to biogas was limited (30% of theoretical biogas potential) during continuous co-digestion with PASS, which resulted in further LCFA accumulation. However, the accumulated LCFA were converted to biogas (up to 66% of theoretical biogas potential) during subsequent batch-mode digestion, performed without additional substrate load. Elevated sulfide level stimulated oleate (but not stearate) conversion to acetate, but oleate and sulfide imposed a synergistic limiting effect on acetoclastic methanogenesis and biogas formation. Next-generation sequencing of 16S rRNA gene amplicons of bacteria and archaea showed that differences in sulfide level and LCFA type resulted in microbial community alterations with distinctly different patterns. Taxonomic profiling of the sequencing data revealed that the phylum Cloacimonetes is likely a key group during LCFA degradation in PASS digesters, where different members take part in degradation of saturated and unsaturated LCFA; genus W5 (family Cloacimonadaceae) and family W27 (order Cloacimonadales), respectively. In addition, LCFA-degrading Syntrophomonas, which is commonly present in lipid-fed digesters, increased in relative abundance after addition of oleate at elevated sulfide level, but not without sulfide or after stearate addition. Stearate conversion to biogas was instead associated with increasing abundance of hydrogen-producing Smithella and hydrogenotrophic Methanobacterium.ConclusionsLong-chain fatty acid chain saturation and sulfide level are selective drivers for establishment of LCFA-degrading microbial communities in municipal sludge digesters.

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The use of straw for biofuel production is encouraged by the European Union. A previous study showed the feasibility of producing biomethane in upflow anaerobic sludge blanket (UASB) reactors using hydrolyzed, steam-pretreated wheat straw, before and after dark fermentation with Caldicellulosiruptor saccharolyticus, and lucerne. This study provides information on overall microbial community development in those UASB processes and changes related to acidification. The bacterial and archaeal community in granular samples was analyzed using high-throughput amplicon sequencing. Anaerobic digestion model no. 1 (ADM1) was used to predict the abundance of microbial functional groups. The sequencing results showed decreased richness and diversity in the microbial community, and decreased relative abundance of bacteria in relation to archaea, after process acidification. Canonical correspondence analysis showed significant negative correlations between the concentration of organic acids and three phyla, and positive correlations with seven phyla. Organic loading rate and total COD fed also showed significant correlations with microbial community structure, which changed over time. ADM1 predicted a decrease in acetate degraders after a decrease to pH ≤ 6.5. Acidification had a sustained effect on the microbial community and process performance.

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The main idea was to solve the problem related to oil contamination of soil using bioremediation with bioaugmentation with modeled microorganism strains. The paper aimed to develop a bacterial consortium for petroleum hydrocarbon degradation during the biological treatment of oil-contaminated soils using electronic databases. The research methodology included an analysis of the mechanisms and metabolic pathways of petroleum hydrocarbon degradation and an assessment of the possible reaction modulus and enzymatic systems for the degradation of aromatic compounds. The taxonomic classification and review of oil compound transformation metabolic pathways were carried out using electronic KEGG, MetaCyc, and EzTaxon databases. The KEGG database was used to create a microbiological consortium of certain strains of bacteria that improved hydrocarbon degradation process performance. Identification of bacteria’s complete genome using Island Viewer 4 allowed to create of a consortium of oil-destructive bacteria consisting of such strains: Pseudoxanthomonas spadix BD-a59, Rhodococcus jostii RHA1, Rhodococcus aetherivorans IcdP1, Pseudomonas putida ND6, Pseudomonas stutzeri 19SMN4, Pseudomonas fluorescens UK4, Acinetobacter lactucae OTEC-02, Bacillus cereus F837/76.7.9. The ratio between the mentioned strains of microorganisms in the consortium was set at 20 % : 20 % : 15 % : 10 % : 10 % : 5 % : 5 % : 15 %. This bacterial consortium for aromatic hydrocarbons was created according to the metabolic information of basic enzymatic systems and the predominant transformation of particular oil compounds using the BacDive database.