Material flow analysis of feedstock for enhancing its conversion efficiency during continuous photo-hydrogen production

The practical application of photofermentative hydrogen production process has been generally limited by the low feedstock conversion efficiency. In this work, material flow analysis (MFA) was applied into continuous photohydrogen to investigate the material flow of feedstock. Maximum feedstock utilization for hydrogen production (31.87%) was obtained at an hydraulic retention time of 60 h and influent acetate concentration of 40 mmol l^-1, corresponding to maximum hydrogen yield of 1.89 mol H₂ mol^-1 acetate. MFA showed that due to the poor flocculation, photofermentative bacteria (PFB) cannot be efficiently separated from supernatant and rushed out with effluent continuously. To replenish the biomass washout, most of feedstock was continuously utilized for cell growth rather than hydrogen production, which caused low feedstock conversion efficiency. The results showed that poor flocculation of PFB resulting in low biomass retention capacity of photobioreactor was the origin of low feedstock conversion efficiency. Therefore, enhancing flocculation of PFB and using high biomass retaining operation modes are essential to further develop photofermentative hydrogen production process.