Enhanced hydrogen production by a sequential dark and photo fermentation process: Effects of initial feedstock composition, dilution and microbial population

Two-stage process of dark fermentation (DF) and photo fermentation (PF), using fruit and vegetable waste (FVW) and cheese whey powder (CWP), was used as an approach to enhance the hydrogen (H₂) production. FVW and CWP at C/N ratios of 34, 39, 60, 71 and 82 were tested as substrates for DF. Dilution (1:2, 1:5, 1:10) of the DF effluents was used as a coupling strategy. DF effluents with low-butyrate and high lactate concentrations were obtained as a function of an increased C/N ratio, which results in high H₂ production during the PF. Maximum overall H₂ yields of 793.7 and 695.4 mLH₂/gChemical Oxygen Demand (COD) were obtained using a 1:10 dilution, at a C/N ratio of 60 and 70, respectively. These H₂ yields were higher than those obtained with the individual processes. The C/N ratio at the DF stage regulate not only H₂ production but also the distribution and concentrations of by-products. These metabolites, in turn, control the H₂ production during the PF. Predominant microbial population for both processes (DF: C/N = 34 Acetobacter lovaniensis, Clostridium butyricum; C/N = 39 C. butyricum, Enterobacter sp, Bifidobacterium; C/N = 82 Lactobacillus casei; PF: Rhodopseudomonas palustris) were in accordance with the final metabolic products.