Avaliação da digestão anaeróbia do bagaço de malte submetido a pré-tratamentos físicos >/sup<

Abstract

Brewers spent grain (BSG), the major by-product of brewing industry, can be used in anaerobic digestion for methane production, which can provide energy for brewery process. This study evaluated the methane production in batch reactors, in triplicates, at 37 ± 1°C, without agitation, from BSG under the following conditions: (1) raw, (2) pretreated in hydrothermal system (3) pretreated in autoclave. The inoculum source was obtained from upflow anaerobic slugde blanket reactor used in slaughterhouse of poultry. At first, an evaluation was accomplished using BSG (a) raw, (IN), pretreated, ground (T) milled (M), (b) raw and pretreated in hydrothermal system (INH), ground and pretreated in hydrothermal system (TH) and milled and pretreated in hydrothermal system. Hydrothermal pretreatment occurred at 180°C for 15 minutes under 9.6 bar. The highest methane production was observed in MH (320.64 ± 7.72 mL.g -1 STV) and higher volatile fatty acids was verified in M and MH, mainly butyric acid in M (388.32 mg.L -1 ) and acetic acid in MH (192.47 mg.L -1 ). A central composite design (CCD) involving two factors was held for evaluate the interaction between (x 1 ) hydrothermal pretreatment temperature and (x 2 ) hydrothermal pretreatment time for BSG. The range of temperature was 150-210 °C with runtime of 10 -20 minutes. Seven batch reactors assays was reached and the highest methane production (411.64 mL.g -1 STV) was verified for BSG pretreated at 210°C for 10 minutes under 12 bar. In this assay was observed carbohydrates consume of 90.45% (from 142 ± 1.41 mg.L -1 to 14.0 ± 1.41 mg.L -1 ) and COD removal of 81.12% (from 3.900 mg.L -1 to 627.5 ± 3.53 mg.L -1 ). BSG pretreated under this condition was employed in a CCD, with seventeen batch reactors condition, involving three variables (x 1 ) incubation temperature, (x 2 ) BSG concentration and (x 3 ) hydrolizate liquid from hydrothermal pretreatment. According to methodology of the CCD and response surface, the highest methane production was predicted in assay at 36°C, with 18 mg.L -1 and 3 mL of hydrolizate liquid. A CCD using BSG pretreated in autoclave was reached with two variables (x 1 ) incubation temperature and (x 2 ) BSG concentration. For this purpose, eleven batch reactors conditions were conducted, in triplicates, at temperature in the range of 30,86 -59,14°C and BSG concentration in the range of 8.34 a 19.66 mg.L -1 . By means of methodology of the CCD and response surface, the optimal predicted condition was at 35°C and 14 mg.L -1 with methane production of 289.10 mL.g -1 STV.