Addition of microbial consortium to the rice straw biomethanization: effect on specific methanogenic activity, kinetic and bacterial community

Abstract

Abstract The biomethanization of lignocellulosic residues is still an inefficient and complex process due to the lignin structures that hinder the hydrolysis step. Therefore, one of the strategies has been the application of biological treatments using cellulolytic microorganisms. The objective of this work was to evaluate a microbial consortium obtained from the technology of effective microorganisms and enriched with microorganisms isolated from different agricultural soils, for bioaugmentation and/or pretreatment strategies during the biomethanization of rice straw. A laboratory-scale experiment was carried out in batch reactors, using anaerobic sludge from swine manure as inoculum, following two strategies: i) pretreatment of rice straw during 48 h using the enriched microbial consortium (dilution 1:100), and ii) addition of this enriched microbial consortium (dilution 1:100) directly to the anaerobic reactors (bioaugmentation). The kinetic behavior of the digestion process was described through three models. As a result, the molecular characterization of the enriched microbial consortia showed 58 different bacterial species responsible for the positive effect obtained in bioaugmented and pretreated reactors. The abundance of anaerobic species and the different metabolic pathways supported the higher methane yields (290 LNCH4/kgVS), even after 30 days of digestion, influenced by the addition of enriched microorganism consortia. All the kinetic models applied in this study fitted well with the experimental cumulative methane yield data, although the modified Hill model showed the best fit in all cases. The methane yield obtained from the pretreatment and bioaugmentation strategies demonstrates that these biological methods are efficient in the degradation of lignocellulosic biomass.