The production of hydrogen from food wastes was studied in a two-stage (dark fermentation-digestion) process under mesophilic conditions. The effect of a recycling stream, from the methanogenic phase to the fermentation phase, over H2 production and alkali consumption was evaluated in a semicontinuous fermentation process. The cases of no-recycling, direct recycling, and membrane permeate recycling of methanogenic supernatant (using an ultrafiltration and nanofiltration membrane) were evaluated.
Adding a recycling stream from a methanogenic reactor to the hydrogen-producing reactor significantly reduced the need of external alkali addition for pH control, up to 52%. The performance of the hydrogen-producing reactors receiving the recycling stream was similar in all cases tested, with values of specific hydrogen production of about 30 mL g−1 VSadded. This value was also similar to that one obtained from the no-recycling configuration. The use of a membrane pretreatment stage proved to be not necessary. Operating conditions established in the fermentation stage were enough to avoid any detrimental effect associated to methanogenic microflora predominance. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 227–233, 2015