Spatial separation of metabolic stages in a tube anaerobic baffled reactor: reactor performance and microbial community dynamics.

Spatial separation of metabolic stages in anaerobic digesters can increase the methane content of biogas, as realized in a tube anaerobic baffled reactor. Here, we investigated the performance and microbial community dynamics of a laboratory-scale mesophilic anaerobic baffled reactor with four compartments treating an artificial substrate. Due to the activity of fermentative bacteria, organic acids mostly accumulated in the initial compartments. The methane content of the biogas increased while hydrogen levels decreased along the compartments. Microbial communities were investigated based on bacterial 16S rRNA genes, hydA genes encoding Fe-Fe-hydrogenases, and mcrA genes/transcripts encoding the methyl-CoM reductase. The metaproteome was analyzed to identify active metabolic pathways. During the reactor operation, Clostridia and Bacilli became most abundant in the first compartment. Later compartments were dominated by Sphingobacteriia, Deltaproteobacteria, Clostridia, Bacteroidia, Synergistia, Anaerolineae, Spirochaetes, vadinHA17, and W5 classes. Methanogenic communities were represented by Methanomicrobiales, Methanobacteriaceae, Methanosaeta, and Methanosarcina in the last compartments. Analysis of hydA and mcrA genes and metaproteome data confirmed the spatial separation of metabolic stages. In the first compartment, proteins of carbohydrate transport and metabolism were most abundant. Proteins assigned to coenzyme metabolism and transport as well as energy conservation dominated in the other compartments. Our study demonstrates how the spatial separation of metabolic stages by reactor design is underpinned by the adaptation of the microbial community to different niches.

Influence of trace substances on methanation catalysts used in dynamic biogas upgrading.

The aim of this work was to study the possible deactivation effects of biogas trace ammonia concentrations on methanation catalysts. It was found that small amounts of ammonia led to a slight decrease in the catalyst activity. A decrease in the catalyst deactivation by carbon formation was also observed, with ammonia absorbed on the active catalyst sites. This was via a suppression of the carbon formation and deposition on the catalyst, since it requires a higher number of active sites than for the methanation of carbon oxides. From the paper findings, no special pretreatment for ammonia removal from the biogas fed to a methanation process is required.

Dynamic biogas upgrading based on the Sabatier process: thermodynamic and dynamic process simulation.

This study aimed to investigate the feasibility of substitute natural gas (SNG) generation using biogas from anaerobic digestion and hydrogen from renewable energy systems. Using thermodynamic equilibrium analysis, kinetic reactor modeling and transient simulation, an integrated approach for the operation of a biogas-based Sabatier process was put forward, which was then verified using a lab scale heterogenous methanation reactor. The process simulation using a kinetic reactor model demonstrated the feasibility of the production of SNG at gas grid standards using a single reactor setup. The Wobbe index, CO2 content and calorific value were found to be controllable by the H2/CO2 ratio fed the methanation reactor. An optimal H2/CO2 ratio of 3.45-3.7 was seen to result in a product gas with high calorific value and Wobbe index. The dynamic reactor simulation verified that the process start-up was feasible within several minutes to facilitate surplus electricity use from renewable energy systems.

Biotechnological screening of microalgal and cyanobacterial strains for biogas production and antibacterial and antifungal effects.

Microalgae and cyanobacteria represent a valuable natural resource for the generation of a large variety of chemical substances that are of interest for medical research, can be used as additives in cosmetics and food production, or as an energy source in biogas plants. The variety of potential agents and the use of microalgae and cyanobacteria biomass for the production of these substances are little investigated and not exploited for the market. Due to the enormous biodiversity of microalgae and cyanobacteria, they hold great promise for novel products. In this study, we investigated a large number of microalgal and cyanobacterial strains from the Culture Collection of Algae at Göttingen University (SAG) with regard to their biomass and biogas production, as well antibacterial and antifungal effects. Our results demonstrated that microalgae and cyanobacteria are able to generate a large number of economically-interesting substances in different quantities dependent on strain type. The distribution and quantity of some of these components were found to reflect phylogenetic relationships at the level of classes. In addition, between closely related species and even among multiple isolates of the same species, the productivity may be rather variable.