Hydrogen production from food industry wastes by suspended and immobilized cells of four Thermotoga thermophilic strains

This work represents the first step of a wider study aimed at evaluating the feasibility of a cost-effective process of biological H2 production from food industry wastes under thermophilic conditions. The H2-producing performances of 4 Thermotoga strains (Th. neapolitana, Th. petrophila, Th. naphtophila, Th. maritima) were compared at 77 °C by means of tests conducted in 120-mL batch bioreactors containing 40 mL of a nutrient-rich growth medium (ATCC 1977; Van Ooteghem et al., Biotechnol. Lett., 2004, 26:1223) additioned with glucose, molasses or whey as carbon source. For all the substrate tested, Th. neapolitana resulted the best-performing strain, with a 0.50-0.68 mmol gdry weight-1 h-1 H2 specific production rate at a 10 g L-1 initial substrate concentration. To compare the H2-producing capacities of the 4 strains also under attached-growth conditions, preliminary tests were conducted with Th. neapolitana, with the goal to select the best biomass carrier among 4 porous materials utilized in the field of biofiltration. The best results were obtained with a porous ceramic product characterized by a 9 m2 g-1 interfacial area. Also under attached-growth conditions, Th. neapolitana resulted the best strain for all the 3 substrates tested, with a 0.09-0.18 mmol gdry weight-1 h-1 H2 specific production rate. Further tests aimed at optimizing the growth medium composition allowed the attainment of H2 production rates slightly lower than the above-reported values, with a significantly more simple – and thus more economical – medium composition. The preliminary results of a kinetic study of H2 production by attached cells of Th. neapolitana with glucose, molasses and whey indicate a substrate inhibition effect above 20 g L-1 for glucose and whey, but not for molasses. Finally, the process scale-up to an innovative 19-L attached-cell agitated reactor is in progress.