Fermentative H2 production using a switchgrass steam exploded liquor fed to mixed anaerobic cultures: Effect of hydraulic retention time, linoleic acid and nitrogen sparging

Fermentative hydrogen (H2) production from a steam exploded switchgrass liquor using inhibited mixed anaerobic microbial communities was studied in upflow anaerobic sludge blanket reactors (UASBRs). Increasing the H2 yield was accomplished by treating the inoculum with linoleic acid (LA), varying the hydraulic retention time (HRT) and sparging liquid phase with nitrogen (N2). A maximum H2 yield of 2.56 ± 0.10 mol mol−1 hexose, was obtained at a 6 h HRT in LA treated cultures sparged with N2. Sparging or LA treatment alone was able to enhance the H2 yield by 46 ± 5% and 38 ± 3%, respectively, in comparison to control cultures operating at a 6 h HRT. Of the different methods employed, N2 sparging in combination with LA treatment proved to be more effective in enriching the H2 producing bacteria belonging to Clostridium sp. Species belonging to Propionibacterium, Bacteroides and Eubacterium, which were associated with H2 consumption and reduced byproducts formation, were observed in addition to Clostridium sp. in unsparged control cultures.