Process optimization and mathematical modelling of photo-fermentative hydrogen production from dark fermentative cheese whey effluent by Rhodobacter sphaeroides OU001 in 2-L cylindrical bioreactor

In this study, organic acids present in dark fermentative cheese whey effluent (DFCWE) were utilized to produce biological hydrogen via photo fermentation by R. sphaeroides O.U.001 cells in 2-L double-walled cylindrical PBR with a working volume of 1.5 L. Plackett-Burman design-based analysis revealed organic acid concentration (OA), temperature, and light intensity as the most significant variables. Experiments were performed at different conditions of (OA, 8-16 g L-1), temperature (25-37 degrees C), and light intensity (8-12 klx). Optimum values were obtained by Box-Behnken design matrix (BBD) based on the impact on hydrogen production rate (HPR) and under optimum values (OA concentration, 12 g L-1; temperature, 31 degrees C; and light intensity, 10 klx); HPR of 41.94 mL L-1 h(-1) was obtained, which lies in close proximity with the predicted production rate of 41.65 mL L-1 h(-1) with the correlation coefficient (R-2) and coefficient of variance as 0.9801 and 0.0521, respectively. PBR performance for treating DFCWE was checked by performing mathematical modelling using four models. Kinetic study of DFCWE consumption and growth profile of the bacterial cell were investigated by fitting experimental values into Monod and logistic equations, respectively. Parameters of the modified Gompertz equation and Luedeking-Piret models gave proper simulated fitting with experimental H-2 production obtained under optimized bioprocess variables. Metabolite analysis revealed that acetic and lactic acids were utilized to produce biohydrogen under uncontrolled pH. Findings of the current investigation could be a promising strategy for obtaining better hydrogen productivity in photo fermentation.