Study of Hydrodynamics Factor (Off-Bottom Clearance) in Enhancing Hydrogen Gas Production as a Renewable Energy in a Stirred Bioreactor

Hydrogen has been recognized as an ideal energy source that is environmentally friendly and widely used in various industries. Burning hydrogen does not pollute the environment, can be produced from renewable materials and produce a higher energy yield compared to hydrocarbon fuels. During this time, hydrogen production process by fermentation (biohydrogen) more review in terms of chemical and biological factors, whereas physical factors such as hydrodynamic factors are rarely studied. Hydrodynamic factor is one of the important factor affecting the biohydrogen production processes involving multiphase system. Therefore, this research aims to study the influence of hydrodynamic factor that is off-bottom clearance (position of the impeller from the bottom of the tank) influence to the hydrogen production process by fermentation. Off-bottom clearance is one of the important hydrodynamic factor because it can affect the flow pattern and then can affect the distribution of microbes in the media and mass transfer of hydrogen gas from liquid phase to the gas phase. Hydrogen was produced using glucose as substrate and Enterobacter aerogenes (NBRC 13534) as the bacteria. The reactor used is a stirred tank equipped with a single impeller, 45o-6 blades, Pitched Blade Turbine (PBT) type at constant rotation speed of 200 rpm. While off bottom clearance was varied 0.25 H, 0.5 H and 0.75 H. The results showed that at the same impeller speed, impeller position does not affect to the speed of consumption of glucose by bacteria that are used as a carbon source for metabolism, but the position of the impeller effect on the capacity of hydrogen gas. A lower off bottom clearance provides better performance in an effort to increase the hydrogen production capacity. The highest yield was 0.0029 mol H2/mol glucose, which was obtained at impeller position 0.25 H. Keyword: hydrodynamics, biohydrogen, off bottom clearance, pitched blade turbin