Chitosan flocculation associated with biofilms of C. saccharolyticus and C. owensensis enhances biomass retention in a CSTR

Cell immobilization and co-culture techniques have gained attention due to its potential to obtain high volumetric hydrogen productivities (Q_H2). Chitosan retained biomass in the fermentation of co-cultures of Caldicellulosiruptor saccharolyticus and C. owensensis efficiently, up to a maximum dilution rate (D) of 0.9 h⁻¹. Without chitosan, wash out of the co-culture occurred earlier, accompanied with approximately 50% drop in Q_H2 (D > 0.4 h⁻¹). However, butyl rubber did not show as much potential as carrier material; it did neither improve Q_H2 nor biomass retention in continuous culture. The population dynamics revealed that C. owensensis was the dominant species (95%) in the presence of chitosan, whereas C. saccharolyticus was the predominant (99%) during cultivation without chitosan. In contrast, the co-culture with rubber as carrier maintained the relative population ratios around 1:1. This study highlighted chitosan as an effective potential carrier for immobilization, thereby paving the way for cost – effective hydrogen production.