Prytula I. Regularity of hydrogen production by spore-forming bacteria during fermentation of food waste

Dissertation is devoted to establishing the regularities of molecular hydrogen formation by spore-forming communities of Bacillus and Clostridium during the fermentation of ecologically hazardous mixed food waste and the development of theoretical bases of biotechnology-driven production of hydrogen. Environmentally friendly energy carrier H2 (54 l/kg dry weight) and biofuel (liquid combustible compounds: alcohols, fatty acids, ketones etc., 198 g/kg dry weight) were obtained as a result of food waste fermentation. It was shown that spore-forming community of aerobic bacteria genus Bacillus and anaerobic bacteria genus Clostridium are technologically promising for production of H2 and liquid energy carriers. Biological significance in the formation of energy carriers was defined for Bacillus and Clostridium. Microorganisms providing destruction of waste and energy carriers' formation were isolated from the soil microbial community and identified. On the basis of phenotypic and phylogenetic analyzes aerobic strains were identified as Bacillus licheniformis and Bacillus atrophaeus, anaerobic strain - as the Clostridium butyricum. It was shown that for efficient energy carriers' production microbial metabolisms can be regulated by such primary factors as pH, Eh and periodic stirring. Regulation of microbial metabolism provided predominant formation or H2, or liquid combustible compounds (i.e. biofuels). Alcohols were proven to be predominantly produced in acidic and weakly acidic medium, whereas H2 was produced in the neutral and weakly alkaline medium. To study distribution of H2 producers and isolation of the most efficient ones screening of ecosystems was conducted: natural (soil, cow manure, bird droppings, "indigenous" community waste) and manmade (activated sludge of aeration tank and digested sludge of methane tank). Producers of H2 and biofuels, which utilize effectively both model single-component and mixed food waste, were present in all ecosystems. The most efficient producers were microbial community of soil, digested sludge of methane tank and bird droppings. Thus, they produced 34-54 liters H2/kg, 74-80 g ethanol/kg and 69-180 g VFA/kg absolutely dry weight (ADW) of food wastes. Basic engineering and technological parameters (ETP) of energy carriers' formation while neutralizing food waste were obtained on the developed modular pilot bioreactor. Those parameters were: coefficient of destruction (Cd), time of destruction (T) and mass balance of the formation of H2 (L/kg ADW) and liquid fuel compounds (g/kg ADW). The obtained results are the basis for new universal technologies allowing to neutralize environmentally hazardous food waste (depending on the composition of the waste absolutely dry weight decreases in 7-27 times for 7-12 days) and get energy carriers on an industrial scale - 33000-54000 liters H2 and 119-198 kg of liquid combustible compounds from 1 ton of food waste.