Fermentative hydrogen production enhancement by microbial community selection and enrichment through biostimulation

This paper presents a novel technique to increase hydrogen production from dark fermentation of cheese whey, conducted using open mixed cultures. Hydrogen (H-2)-producing microbial pools were selected and enriched using an innovative biostimulation technique, performed by sequential re-inocula of the interstitial microbial community using porous supports in sequential batch reactors. The supports offered a spatial refuge to the microbial community, facilitated re-inoculum procedures and reduce operational disturbance. Two different re-inoculum times (i.e. 24 h and 96 h) were tested to verify the influence of timing on the selection/enrichment. Results showed that the H-2 production rate was up to 80 times higher using a 24 h re-inoculum time than using a 96 h re-inoculum time. Under a 24 h re-inoculum time, a stable H-2 production rate was reached after two sequential re-inocula, with values ranging between 4 and 6.1 mLH(2) h(-1). The cumulative production, detected after the last re-inoculum (8 days), was 2.2 LH2 L-reactor(-1), corresponding to 42.5 mL gCOD(-1). A very low methane (CH4) production was observed and only in the first two re-inocula, as short re-inoculum intervals favoured H-2-producing bacteria. Microbiological analyses confirmed that subsequent re-inocula contributed to an increase in total microbial abundance. The proposed approach provides a concentrated inoculum in liquid medium (which is easy to use) exploiting an enrichment technique that is conceptually new and more economical/environmentally friendly than conventional thermal, acid or alkaline enrichment techniques.