Kinetics of thermophilic acidogenesis of typical Brazilian sugarcane vinasse

The kinetics of the acidogenic phase during anaerobic digestion of sugarcane vinasse in differential reactors containing immobilized cells was investigated. The maximum substrate conversion rate (rmax), substrate saturation constant (Ks) and constant of inhibition by excess substrate (Kis) were determined using vinasse with and without pH adjustment. Simulation and scaling-up of a thermophilic-hydrogen production system were performed. The rmax values obtained at different pH were similar and near 0.9 mg-Total carbohydrates g-VS−1 h−1. The Ks obtained from the system without pH adjustment was 10,762.3 mg-Total carbohydrates L−1 (i.e., 2.5 times higher than the system with pH adjustment). No inhibition by excess substrate was achieved in the system without pH adjustment, indicating that sugarcane vinasse can be used to produce hydrogen without input costs. The simulation revealed that hydrogen production is a sensitive process that requires careful balancing of various operational parameters. The payback for the investment in system implementation is 4.4 years.