Identificação e caracterização de consórcios microbianos produtores de hidrogênio e outros coprodutos a partir de vinhaça de cana-de-açúcar, após pré-tratamento do inóculo

Abstract

The use of hydrogen as a fuel is considered a promising alternative for the next decades, as a clean energy source and produce only water as a product of its combustion. The biological production of hydrogen can be carried out using various agroindustrial residues. Vinasse is a residue of ethanol production generated in the proportion of 12 to 15 liters per liter of ethanol produced. Currently, vinasse is mainly used as fertilizer, in the sugarcane crop itself, however, the environmental agencies are limiting the amount of vinasse that can be applied to the soil due to its high pollutant. The process of converting vinasse into hydrogen can be carried out using pure cultures or microbial consortia. The use of consortia may be more advantageous because they are easier to handle and does not require sterile media. However, some microorganisms may be contained in the consortia H2 consumers, which makes it necessary to subject the inoculum to a pretreatment to suppress the activity of these bacteria. Thus, the objective of this work was to evaluate three methods of thermal pretreatment of the inoculum for the production of hydrogen and volatile fatty acids at different initial values of pH using vinasse as substrate and to compare the composition of the microbial community. The tests for H2 production were performed using vinasse at 37 °C with the following pretreatments of the inoculum: 90 °C / 10min; 105 °C / 120min and 120 °C / 20min. The effect of vinasse concentration and initial pH (5, 6 and 7) and acid production were also evaluated. The microbial communities were analyzed by isolation, PCR-DDGE and high-performance sequencing of the 16S and 18S rRNA genes. The increase of the vinasse concentration positively affected the hydrogen production, with the maximum production of hydrogen (Hmax) (821.34 mL) and yield (4.75 mmol H2g-1COD) obtained using undiluted vinasse at pH 6 and pretreatment of the inoculum 90 °C / 10min (T1). The assays T2 (105°C / 120 min pH 5) and T3 (121°C / 20 min pH 6) produced 687.58 mL and 697.68 mL, respectively. In the experiments with the best production of H2, the butyric metabolic route was favored. The highest number of copies of the Fe-hydrogenase gene is correlated with the sample of higher H2 production. Isolation and DGGE showed the presence of facultative anaerobic microorganisms (Bacillus and Enterobacter) and Clostridium in the microbial communities. High performance sequencing analyzes revealed a high prevalence of the genus Clostridium in the pretreated samples, with a predominance of Firmicutes. Other genus, such as Bacillus, Syntrophomonas, Geobacter, Syntrophus and Sulfurimonas, were also detected in the higher H2 production assay (T1). Analysis of the 18S rRNA gene for the T1 showed the prevalence of Candida (47%) and also the presence of Agaricomycetes, Pezizomycotina and Aspergillus. The results of this study show the prevalence of Clostridiaceae in the 3 trials (T1, T2 and T3) and decrease of the microbial diversity with the increase of the temperatures of the pretreatments. The assay T1 (T90 pH 6) improved performance favored microorganisms described as producing H2. The results of this study show the complexity of 14 microbial consortia with the involvement of bacteria and fungi, suggesting the need for interactions between them in the production of hydrogen and volatile fatty acids from degradation of fresh vinasse, making the process ecologically friendly. [resumo fornecido pelo autor]