KINETICS OF METABOLISM DURING GROWTH OF THE HYDROGEN-PRODUCING BACTERIUM RUMINOCOCCUS ALBUS ON GLUCOSE
Integration of life sciences & engineering
Integration of Life Sciences & Engineering - Poster (T5-P)
Keywords: biohydrogen, Ruminococcus albus, kinetics
I. Ntaikou1,2, H.N. Gavala1,2 and G. Lyberatos*1,2
1 Department of Chemical Engineering, University of Patras, Karatheodori 1 st., 26500 Patras, Greece, 2 Institute of Chemical Engineering and High Temperature Chemical Processes, 26504 Patras, Greece. *E-mail: lyberatos@chemeng.upatras.gr
ABSTRACT
Biohydrogen generation from renewable biomass was proposed lately in answer to the global environmental impacts of the overuse of fossil fuels. The production of hydrogen from biomass refers to the fermentation of organic, rich in carbohydrates substrates, using either photosynthetic or fermentative microorganisms. In any case the final yield of produced hydrogen seems to depend on the metabolism of each microorganism used, and is influenced by the specific environmental parameters during its growth.
Ruminococcus albus is an important fibrolytic bacterium of the rumen, where it cohabits with other bacteria and protozoa. R. albus can ferment soluble sugars and also complex carbohydrates, such as cellulose and hemillulose, after breaking them down through extracellular enzymes it produces. Regardless the initial substrate used, great amount of hydrogen evolves from the fermentation process. Previous research with pure cultures of R. albus and whole sorghum, sorghum extract and lignocellulosic residues as substrate lead to very promising hydrogen yields Therefore, it is believed that R. albus is very promising for the production of hydrogen from agricultural residues rich in lignocellulosic materials and from energy crops, such as sweet sorghum which contains soluble sugars and complex carbohydrates in almost equal amounts.
However, little is known about the metabolic paths through which hydrogen is produced, and about the factors affecting the distribution of metabolic products. It has already been reported that the amount of hydrogen, and in particular its partial pressure in continuous cultures of R. albus may influence the yields of the main metabolic products, i.e. ethanol and acetate. However, the effect of the hydrogen partial pressure on the yield and degradation rate of formic acid has not been investigated. Formic acid is an important intermediate of R. albus metabolism, which as shown from previous experiments degrades to carbon dioxide and hydrogen. Experimental data of the present study suggested that H2 partial pressure strongly influenced formic degradation rate and subsequently hydrogen generation, whereas it did not affect other metabolic products. Microbial growth was described using Monod kinetics, taking into account the inhibition factors of pH and initial substrate concentration, and the hydrogen final yield was reversely connected to the accumulation of ethanol. Batch experiments were carried out in order to calculate growth kinetics of R. albus on glucose, the degradation constant of formic acid and the PH2 inhibition factor. These values were used to simulate a CSTR performance at different steady states. The model predicted the CSTR performance quite well.
Presented Wednesday 19, 13:30 to 15:00, in session Integration of Life Sciences & Engineering - Poster (T5-P).
