Biohydrogen Production from Glycerol using Thermotoga spp

Given the highly reduced state of carbon in glycerol and its availability as a substantial byproduct of biodiesel production, glycerol is of special interest for sustainable biofuel production. Glycerol was used as a substrate for biohydrogen production using the hyperthermophilic bacterium, Thermotoga maritima and Thermotoga neapolitana. Both species metabolized glycerol to mainly acetate and hydrogen. At glycerol concentrations of 2.5 g/L, hydrogen was produced with a yield of 2.75 and 2.65 mol H2/mol glycerol consumed by T. maritima and T. neapolitana respectively. Additionally, the effect of initial pH (ranging between pH 5.0-8.5) and yeast extract concentrations (0.5, 1, 2, 4 g/L) on glycerol fermentation by T. neapolitana was investigated in batch systems. An initial pH value of around 7 was optimal for hydrogen production by T. neapolitana. Lower concentration of yeast extract resulted in a lower H2 production, however increasing the concentration from 2 to 4 g/L did not affect H2 productio

Glycerol fermentation to hydrogen by Thermotoga maritima: Proposed pathway and bioenergetic considerations

The production of biohydrogen from glycerol, by the hyperthermophilic bacterium Thermotoga maritima DSM 3109, was investigated in batch and chemostat systems. T. maritima converted glycerol to mainly acetate, CO2 and H2. Maximal hydrogen yields of 2.84 and 2.41 hydrogen per glycerol were observed for batch and chemostat cultivations, respectively. For batch cultivations: i) hydrogen production rates decreased with increasing initial glycerol concentration, ii) growth and hydrogen production was optimal in the pH range of 7–7.5, and iii) a yeast extract concentration of 2 g/l led to optimal hydrogen production. Stable growth could be maintained in a chemostat, however, when dilution rates exceeded 0.025 h-1 glycerol conversion was incomplete. A detailed overview of the catabolic pathway involved in glycerol fermentation to hydrogen by T. maritima is given. Based on comparative genomics the ability to grow on glycerol can be considered as a general trait of Thermotoga species. The exceptional bioenergetics of hydrogen formation from glycerol is discusse

Dark fermentative hydrogen and ethanol production from biodiesel waste glycerol using a co-culture of Escherichia coli and Enterobacter sp.

In previous comparative studies, Enterobacter spH1 was selected as the best hydrogen and ethanol producer (Knothe, 2010). Here, glycerol fermentation was compared between three other strains: Escherichia coli CECT432, Escherichia coli CECT434 and Enterobacter cloacae MCM2/1. E. coli CECT432 was found to perform best with a H2 productivity of 69.1 mM (1307 mL/L). A co-culture of this E. coli CECT432 strain with the earlier selected Enterobacter spH1 showed a 3.1-fold higher H2 productivity (4767 mL/L) from pure glycerol and higher biomass production. Remarkably, the hydrogen yield per mol of glycerol also increased from 0.61 to 1.26 mol H2/mol glycerol. The co-culture was also tested using waste glycerol from biodiesel. Waste glycerol was characterized and found to consist of (w/v): glycerol 47.5%, water 40.5%, ash content 4.8% and non-glycerol organic matter (MONG) 7.2%. The amount of total soluble organic carbon (TOC) in the crude glycerol was 317 g/L. A maximum H2 yield and ethanol yield of 1.53 and 1.21 mol/mol glycerol was obtained on the waste glycerol, respectively. These yields are the highest reported to date using mesophilic strains. The strains metabolized the crude glycerol without any purification step. The ability to produce H2 without prior purification of the waste glycerol is attractive because it avoids extra costs in the process.</p