On the modeling of metabolic products distribution during fermentative hydrogen production
Multi-scale and/or multi-disciplinary approach to process-product innovation
Analysis of Energy Issues (T3-3a)
Keywords: ADM1, fermentation, hydrogen, metabolic products, modeling
Hariklia N. Gavala1,2,3*, Ioannis V. Skiadas1,2,3 and Gerasimos Lyberatos1,2
1Department of Chemical Engineering, University of Patras, Karatheodori 1 st., 26500 Patras, Greece
2Institute of Chemical Engineering and High Temperature Chemical Processes, 26504 Patras, Greece.
3Present address: Bioprocess Science and Technology group, Biocentrum-DTU, building 227, Technical University of Denmark, 2800 Lyngby, Denmark
*e-mail: hng@biocentrum.dtu.dk, gavala@chemeng.upatras.gr
Renewable energy sources have received great interest from the international community during the last decades. Biomass is one of the oldest and the most promising energy sources and nowadays, it provides approximately 14% of the global energy needs. There are several conversion technologies for the energy exploitation of biomass, that is, direct combustion, gasification, pyrolysis, and biological treatment. During biological treatment, biomass can be converted to fuels, such as ethanol, methanol, methane and hydrogen, which was recently characterized as the fuel of the future. Hydrogen is a clean and environmentally friendly fuel, which is converted to water instead of greenhouse gases when combusted and it possesses a high-energy yield (122 kJ/g). Furthermore, hydrogen could be directly used to produce electricity through fuel cells. Biological fermentative hydrogen production, one of the several ways to produce hydrogen, has received special attention during the last decade. Carbohydrates are the main source of hydrogen during fermentative processes and therefore wastes/wastewater or agricultural residues rich in carbohydrates can be considered as potential sources of hydrogen. Fermentation of sugars is accompanied by the production of hydrogen and various metabolic products, mainly volatile fatty acids (acetic, propionic and butyric acids), lactic acid and ethanol. The hydrogen yield varies proportionally to the final metabolic products. Production of acetic and butyric acids favors production of hydrogen, with the fermentation to acetic acid giving the highest theoretical yield of 4mol H2/mol hexose, while low H2 yields are associated with more reduced end products, i.e. propionic and lactic acids and ethanol. Hydrogen partial pressure, pH and substrate concentration are the main macroscopic factors influencing the distribution of metabolic products and consequently hydrogen yield. In fact, hydrogen yield depends on the ratio of the intracellular reduced and oxidized form of coenzymes, i.e. NAD, which transfer the electron produced and/or consumed during the biochemical reactions.
In the present study a mathematical model has been developed able to predict the distribution of the various metabolic products depending on the ratio of reduced to oxidized NAD. Glucose was chosen as sugars representative, model compound and the products distribution among acetic, propionic, butyric and lactic acids and ethanol as well as hydrogen production was studied at different values of pH and loading rate. The novelty of the present study lies on the fact that the model allows the yield of metabolic products to vary depending on the microbial growth conditions and it was developed using the same platform as the Anaerobic Digestion Modeling No1 (ADM1). In addition, this modeling approach can be applied not only in hydrogen production area but also in maximizing the production of other important metabolites as well, i.e. lactic acid and ethanol.
Presented Monday 17, 15:40 to 16:00, in session Analysis of Energy Issues (T3-3a).
