Produção de hidrogênio e metano a partir de manipueira com adição de glicerol residual por biodigestão anaeróbia

Abstract

In Brazil, although most energy demand is supplied through hydroelectric power, the study and optimization of other renewable energy sources has grown due to concern about the constant low levels of water reservoirs observed in recent years. In this context, biogas production has increasingly gained the attention of researchers, who have mainly aimed at optimizing the process through the codidigestion of two or more waste. Despite the significant increase in biogas and methane production provided by the addition of glycerol to agroindustrial residues when subjected to anaerobic biodigestion, few studies are directed to the production of hydrogen using this residue. Thus, the present study evaluated the anaerobic biodigestion in two stages of Manipueira with the addition of residual glycerol, aiming to maximize the production of hydrogen and methane. In this study we used inoculum of residual swine water, which was evaluated by the isolation of anaerobic microorganisms, DNA extraction and genetic sequencing, revealing that this inoculum contained bacteria of the genus Brevundimonas, from the subgroup Bacillus subtilis and Bacillus Cereus, and one of the species Bacillus licheniformis. For the study of gas production, a 32 factorial design was delineated aiming to evaluate the effects of glycerol temperature and concentration on the production of hydrogen and methane, and it was verified that the addition of glycerol provided an increase in the production of Hydrogen. While the production of hydrogen in the treatments without the addition of glycerol ranged from 215.1 to 243.5 mL, in the best conditions obtained in this study (4% of glycerol and temperature of 38.5 oC), the production was 1102.6 mL, an increment higher than 400%. The effluent analysis of these treatments evidenced the need for additional treatment. Thus, a two-stage biodigestion study was carried out, which employs the use of physically separated acidogenic and methanogenic reactors. At this stage the methane production was optimized, evaluating the effects of temperature in the range between 36.0 and 39.0 oC and the concentration of sodium bicarbonate (between 2.0 and 6.0 gL-1), which was added to the effluent of a pilot-scale acidogenic biodigester with volume of 50 L and operating in the optimized conditions of hydrogen production. The ideal conditions for the methanogenic stage were at a temperature of 39.0 oC and a concentration of sodium bicarbonate of 5.0 gL-1. In these conditions, the removal of COD was 93.4%, and biogas was produced with 64.5% of methane, which resulted in a volume of 2819.4 mL of this biofuel. Thus, the use of two-stage biodigestion made it possible to maximize both hydrogen and methane production, and 861.4 mLH2 and 1762.1 mLCH4 were obtained for each liter of treated waste. Thus, it is concluded that the substrates and inoculum used in the study are adequate to the anaerobic biodigestion process, and can contribute to the reduction of dependence on fossil energy sources.