Hydrogen production from cheese whey with ethanol-type fermentation: Effect of hydraulic retention time on the microbial community composition

The effects of different hydraulic retention times (HRTs) of 4, 2, and 1 h and varying sources of inoculum (sludge from swine and sludge from poultry) on the hydrogen production in two anaerobic fluidized bed reactors (AFBRs) were evaluated. Cheese whey was used as a substrate, and 5000 mg COD L−1 was applied. The highest hydrogen yield (HY) of 1.33 mol mol−1 lactose and highest ethanol yield (EtOHY) of 1.22 mol EtOH mol−1 lactose were obtained at the highest HRT (4 h). When the reactors were operated at an HRT of 1 h, methane (0.68 L CH4 h−1 L−1) was produced concurrently with hydrogen (0.51 L H2 h−1 L−1). The major metabolites observed were soluble ethanol, methanol, acetic acid, and butyric acid. Cloning of the 16S rRNA gene sequences indicated that the microbial community were affiliated with the genera Selenomonas sp. (69% of the sequences), and Methanobacterium sp. (98% of the sequences).