Digestão anaeróbia de glicerol visando a produção de biohidrogênio

Abstract

Alternative energy sources have been gaining ground in the current scenario, and thus the bioprocesses for sustainable energy production have been more intensively investigated. The use of industrial waste as alternative sources of carbon has gained prominence, among which glycerol is a source of carbon highly assimilable by microorganisms. Anaerobic digestion is a bioprocess that uses microorganisms for the degradation of organic matter and biogas production. Besides being used, primarily, for the stabilization of organic matter, it is currently a promising way to produce energy. The association of this bioprocess with microbial fuel cells brings an innovative and interesting concept for the use of acidogenic reactor residues. The objective of this work was to evaluate the production of hydrogen from the anaerobic digestion of glycerol, in addition to the reduction of organic matter and energy production. It was carried out tests with the carbon/nitrogen ratio (C/N) 40, 80 and 120, varying the agitation in continuous agitation (100 rpm), agitation of 4 h (100 rpm) and without agitation at 55 °C. After determining the best condition for removal of organic matter, the production of hydrogen was verified with the application of heat treatment to the inoculum of 80 °C for 30 min and 105 ° C for 15 h. A UASB reactor and a microbial fuel cell reactor (MFC), continuously operated, the hydraulic retention time (HRT) of the UASB reactor was 24 h and the temperature was 35 ° C. The chemical oxygen demand (COD), pH, volatile organic acids (AOV), glycerol consumption, hydrogen concentration, biogas volume, current density and power were determined in the tests. In the initial tests, the best condition was obtained for organic matter removal in the C/N 40 condition (62.22 %) without agitation, with no significant difference between the other forms of agitation. The highest hydrogen production was obtained at 105 °C for 15 h, 0.345 mmol L-1 and glycerol removal of 58 %. In the treatment at 80 °C for 30 min the presence of methane was identified from 18 h of process, with maximum hydrogen production of 0.261 mmol L-1 and glycerol removal of 99.74 % at the end of 168 h. When the TRH was evaluated in the UASB reactor as a form of methanogenic bacteria control, it was not possible to control only with the HRT, with the presence of methane. However, the energy production in the CFM was higher in the C/N 120 test, with a power density of 40 mW m-2. Therefore, the C/N ratio had an influence on the removal of organic matter and the hydrogen production was favored by the application of the thermal treatment at 105 °C for 15 h to the sludge, with no methane present. MFC is an innovative and appropriate process for the use in acidogenic reactors, generating energy and aiding in the removal of organic matter.