Methane Production Using Brewery Spent Grain: Optimal Hydrothermolysis, Fermentation Of Waste And Role Of Microbial Populations

The hydrothermolysis variables temperature (150 - 210 °C) and time (10 - 20 minutes) were assessed to improve hydrolysis efficiency of brewery spent grain (BSG) for renewable energy generation. The intensification of the pretreatment was expressed by the severity variation (2.8 - 4.5) and the process was optimized with methane production of 411.6 ± 7.2 mL. g -1 STV (severity 4.2). The fermentation-methanogenesis of BSG and hydrolysate resulting from BSG hydrothermolysis process under severity of 4.2 (210 o C for 10 min.) was evaluated by central composite design (CCD) with the variables operation temperature (30 - 60 °C), BSG concentration (7.3 - 20.7 g.L -1 ) and hydrolysate (0 - 12.4 mL). The higher methane production observed was 305.8 mL.g -1 STV, with 14 g.L -1 of BSG, without hydrolysate at 45 °C. The main soluble metabolites were acetic acid (233.17 mg.L -1 ) and butyric acid (156.0 mg.L -1 ). On other hand, the lower methane production (108.5 ± 2.0 mL. g -1 STV) verified was 14 g.L -1 of BSG, 6.5 mL of hydrolysate at 60 °C, which revealed that in this condition propionic acid (947.4 mg.L -1 ) and acetic acid (599.2 mg.L -1 ) were expressive. In the optimal fermentation-methanogenic condition of pretreated BSG, Macellibacteroides and Sphaerochaeta (15.9 and 14.7%, respectively) were identified, as well as archaea similar to Methanosaeta (80.4%), favoring the acetoclastic methanogenic pathway.

Vitamin and amino acid auxotrophy in anaerobic consortia operating under methanogenic condition

Syntrophy among Archaea and Bacteria facilitates the anaerobic degradation of organic compounds to CH4 and CO2. Particularly during aliphatic and aromatic hydrocarbon mineralization, as in crude oil reservoirs and petroleum-contaminated sediments, metabolic interactions between obligate mutualistic microbial partners are of central importance1. Using micro-manipulation combined with shotgun metagenomic approaches, we disentangled the genomes of complex consortia inside a short chain alkane-degrading cultures operating under methanogenic conditions. Metabolic reconstruction revealed that only a small fraction of genes in the metagenome-assembled genomes of this study, encode the capacity for fermentation of alkanes facilitated by energy conservation linked to H2 metabolism. Instead, inferred lifestyles based on scavenging anabolic products and intermediate fermentation products derived from detrital biomass was a common feature in the consortia. Additionally, inferred auxotrophy for vitamins and amino acids suggests that the hydrocarbon-degrading microbial assemblages are structured and maintained by multiple interactions beyond the canonical H2-producing and syntrophic alkane degrader–methanogen partnership2. Our study uncovers the complexity of ‘interactomes’ within microbial consortia mediating hydrocarbon transformation under anaerobic conditions.

Influence of the addition of sulphate and ferric ions in a methanogenic anaerobic packed-bed reactor treating gasoline-contaminated water

Benzene, toluene and xylene (BTX) are relatively soluble aromatic compounds of gasoline. Gasoline storage tank leakages generally lead to an extensive contamination of groundwater. In the natural environment for instance, these compounds might be biodegraded under a variety of reducing potentials. The objective of this work was to examine the influence of the addition of sulphate and Fe(OH)3 in a methanogenic horizontal-flow anaerobic immobilized-biomass reactor treating gasoline-contaminated water. Three different conditions were evaluated: methanogenic, sulphidogenic and sulphidogenic with the addition of ferric ions. Methanogenic condition showed the higher BTX degradation rates and the addition of sulphate negatively affected BTX removal rates with the production of H2S. However, the addition of ferric ions resulted in the precipitation of sulphur, improving BTX degradation by the consortium. Metanosphaera sp., Methanosarcina barkeri and Methanosaeta concilii were identified in the consortium by means of 16S and directly related to the addition of ferric ions.