Hydrogen production and microbial kinetics of Clostridium termitidis in mono-culture and co-culture with Clostridium beijerinckii on cellulose.

Cellulose utilization by hydrogen producers remains an issue due to the low hydrogen yields reported and the pretreatment of cellulose prior to fermentation requires complex and expensive steps. Clostridium termitidis is able to breakdown cellulose into glucose and produce hydrogen. On the other hand, Clostridium beijerinckii is not able to degrade cellulose but is adept at hydrogen production from glucose; therefore, it was chosen to potentially enhance hydrogen production when co-cultured with C. termitidis on cellulose. In this study, batch fermentation tests were conducted to investigate the direct hydrogen production enhancement of mesophilic cellulolytic bacteria C. termitidis co-cultured with mesophilic hydrogen producer C. beijerinckii on cellulose at 2 g l-1 compared to C. termitidis mono-culture. Microbial kinetics parameters were determined by modeling in MATLAB. The achieved highest hydrogen yield was 1.92 mol hydrogen mol-1 hexose equivalentadded in the co-culture compared to 1.45 mol hydrogen mol-1 hexose equivalentadded in the mono-culture. The maximum hydrogen production rate of 26 ml d-1 was achieved in the co-culture. Co-culture exhibited an overall 32 % enhancement of hydrogen yield based on hexose equivalent added and 15 % more substrate utilization. The main metabolites were acetate, ethanol, lactate, and formate in the mono-culture, with also butyrate in the co-culture. Additionally, the hydrogen yield of C. beijerinckii only in glucose was 2.54 mol hydrogen mol-1 hexose equivalent. This study has proved the viability of co-culture of C. termitidis with C. beijerinckii for hydrogen production directly from a complex substrate like cellulose under mesophilic conditions.

Performance of mesophilic biohydrogen-producing cultures at thermophilic conditions.

In this study, batch tests were conducted to investigate the performance of mesophilic anaerobic digester sludge (ADS) at thermophilic conditions and estimate kinetic parameters for co-substrate fermentation. Starch and cellulose were used as mono-substrate and in combination as co-substrates (1:1 mass ratio) to conduct a comparative assessment between mesophilic (37 °C) and thermophilic (60 °C) biohydrogen production. Unacclimatized mesophilic ADS responded well to the temperature change. The highest hydrogen yield of 1.13 mol H2/mol hexose was observed in starch-only batches at thermophilic conditions. The thermophilic cellulose-only yield (0.42 mol H2/mol hexose) was three times the mesophilic yield (0.13 mol H2/mol hexose). Interestingly, co-fermentation of starch-cellulose at mesophilic conditions enhanced the hydrogen yield by 26% with respect to estimated mono-substrate yields, while under thermophilic conditions no enhancement in the overall yield was observed. Interestingly, the estimated overall Monod kinetic parameters showed higher rates at mesophilic than thermophilic conditions.

Microbial kinetics of Clostridium termitidis on cellobiose and glucose for biohydrogen production.

OBJECTIVE: To determine Monod kinetics parameters (µmax, Ks, kd and YX/S) of the mesophilic H2 producer Clostridium termitidis grown on glucose and cellobiose by modeling in MATLAB. RESULTS: Maximum specific growth rates (µmax) were 0.22 and 0.24 h(-1) for glucose and cellobiose respectively; saturation constants (Ks) were 0.17 and 0.38 g l(-1) respectively and the biomass yields (YX/S) were 0.26 and 0.257 g dry wt g(-1) substrate. H2 yields of 1.99 and 1.11 mol H2 mol(-1) hexose equivalent were also determined for glucose and cellobiose respectively. CONCLUSION: The microbial kinetics of this model microorganism will enhance engineering biofuel production applications.