Improvement of biohydrogen and usable chemical products from glycerol by co-culture of Enterobacter spH1 and Citrobacter freundii H3 using Different Supports As surface Immobilization

Glycerol is a by-product of biodiesel production which is yielded at about 10% (w/w). In the present work an improvement of the dark fermentation of glycerol was proposed by immobilization of the microorganisms on supports. Four different supports were employed: maghemite (Fe₂O₃), activated carbon (AC), silica gel (SiO₂) and alumina (γ-Al₂O₃). A newly isolated co- culture of Enterobacter spH1 and Citrobacter freundii H3 was immobilized in these supports. Effect of iron species on the dark fermentation was also studied by its impregnation over AC and SiO₂.

The fermentative metabolites were mainly composed by ethanol, 1,3-propanediol, lactate, H₂ and CO₂. Modeling using Gompertz equation for the batch dark fermentation were elucidate :

i)                    Maximum H₂ productivity (mmol/L) and yield(mol H₂/mol glycerol consumed) were higher in the order of: Fe/AC> AC> Fe/SiO₂>SiO₂ >Fe₂O₃> γ-Al₂O₃ > FC

_ii)                                         Maximum Ethanol productivity (mmol/L) were higher in the order of : AC > Fe/AC > Fe/SiO₂ >SiO₂ > γ-Al₂O₃ > Fe₂O₃> FC and yield (mol EtOH/mol glycerol consumed)were higher in order of: γ-Al₂O₃ > AC>SiO₂> Fe/SiO₂ Fe/AC>Fe₂O₃> FC (

_iii)                                       Maximum 1,3-propanediol productivity (mmol/L) were higher in the order of: FC > Fe/AC > Fe₂O₃> AC > Fe/SiO₂ >SiO₂ > γ-Al₂O₃

iv)                Maximum Lactate productivity (mmol/ L) were higher in the order of: FC > Fe₂O₃> Fe/AC > Fe/SiO₂> AC  >SiO₂ > γ-Al₂O₃

These results indicate that support immobilization enhance the productivity of H₂ might be due to specific surface area attachment, biofilm formation of the microorganism and hydrogenase enzyme activation by iron species