H₂ consumption by anaerobic non-methanogenic mixed cultures

The impact of H₂ consumption, by homoacetogens, on the overall hydrogen yield in mixed culture fermentation is the focus of this study. Batch reactors were used to test the ability of anaerobic digested sludge, heat treated to eliminate methanogens, to produce and consume molecular hydrogen. The measured average hydrogen production rate from 4.2 g glucose/L was 44 ± 4 mmol H₂/L sludge · d, while the H₂ consumption rate varied much more, in the range from 4 to 62 mmol H₂/L sludge · d. Hydrogen consumption rate depends on acetic acid concentration, headspace H₂ partial pressure and mass transfer rates. Different but relatively long lag-phases for hydrogen consumption were observed. It is concluded that homoacetogenesis can have a significant negative effect on bio-H₂ production by mixed cultures, limiting the possibilities for sustainable solutions.