Key factors for biohydrogen production by dark fermentation

Abstract

AbstractAmong biological ways of hydrogen production, the dark fermentation process gives important prospects. One of the key factors of bioreactor operation is the biogas extraction. Thus, this work gives a parametric optimization of the bioreactor as a function of the sweep gas nature and flow rate.The bacterial inoculum was activated sludge of wastewater treatment plant, which was thermally treated to inhibit the activity of hydrogenotrophic and non‐hydrogen producing micro‐organisms. The fermentation was performed in a semi‐batch bioreactor with a model substrate. Biogas was analyzed online by GC‐TCD and metabolites (volatile fatty acids and alcohols) were analyzed by GC‐FID. Kinetics parameters of hydrogen production were obtained by modelling.Increase the sweep gas (N2) flow rate in the bioreactor results in an increase of hydrogen yield and cumulative production of 35 %. In the purpose of recycling the CO2 produced by fermentation, the addition of CO2 to N2 as sweep gas gives a yield improvement from 2.10 molH2/molhexose with N2 alone, to 2.37 molH2/molhexose with a mixture of CO2:N2 (75:25). In order to reduce the amount of suspended matter in initial biomass, filtration tests show an equivalent hydrogen yield but with a higher lag time than with unfiltered biomass (30 h towards 4.4 h). The presence of hydrogen producing bacteria mainly stick with the solid part of sludge was highlighted.