Drapoi D. Obtaining hydrogen from cellulose-containing raw materials

Thesis are devoted to scientific and technical bases of fermentation agricultural waste with obtaining hydrogen. In the research an effective association of microorganisms - cellulose destructors and hydrogen producers has been isolated. Natural microbial association from the soil has been taken as a basis, as it contains a reduced amount of hydrogen consumers - sulfate-reducing microorganisms, compared to natural associations from the silt and from the flowing body of water. It has been experimentally determined that to neutralize methane-producing microorganisms it is necessary to carry out heat treatment of the inoculum at t = 90ºC for 1 hour. Under this treatment, microorganisms of the genera Clostridium and Bacillus form spores that germinate in 2 days under favorable conditions. It has been determined that additional enrichment of the microbial association of Clostridium and Bacillus genera leads to an increase in hydrogen yield compared to the original association. Moreover, hydrogen content in biogas depends on the number and ratio of microorganisms added. It has been established that enrichment of the microbial association by the microbial culture of Clostridium and Bacillus genera at the ratio 1:2.5 increases hydrogen yield by 2.3 times. This is due to the fact that for the optimal viability of the microorganisms of Clostridium genus, a completely anaerobic environment is required. And the microorganisms of Bacillus genus require presence of a certain amount of oxygen. If the number of microorganisms of Bacillus genus is insufficient, a certain amount of oxygen remains in the gas phase and the optimal environmental conditions for the development of Clostridium are not be reached. This in turn reduces their enzymatic activity, which leads to a reduction in hydrogen yield. A rational method of raw materials pre-treatment has been determined (3h, 20% NaOH); it allows to increase hydrogen yield by 3 times. The alkali effectively removes lignin from biomass, improves cellulose availability and increases the adsorption area of substrate for the microorganisms. The thesis proposes a mathematical description of biogas production depending on the pH value and substrate concentration; it allows to model an arbitrary nature of the process and determine the optimal conditions for hydrogen production depending on the variable parameters of the process. The main technological parameters of cellulose-containing raw materials fermentation process with hydrogen production have been determined: process temperature - 35ºC, pH - 7-7.5, raw material concentration - 50 ± 5 g / dm3, inoculum to substrate ratio - 1:4, constant removal of hydrogen from the fermentation zone. This allows to obtain biogas with hydrogen content of 87.5 ± 4.2%.