Production of biobutanol from white grape pomace by Clostridium saccharobutylicum using submerged fermentation
MetadataShow full metadata
The use of agricultural residues for the production of biofuel such as butanol is one potential alternative to fossil fuels. The abundance of white grape pomace in the wine industry in New Zealand makes grape pomace a potential substrate for the production of butanol using Clostridium saccharobutylicum (formerly known as Clostridium acetobutylicum P262). Chardonnay grape pomace was fermented with C. saccharobutylicum using submerged fermentation. The concentration of reducing sugars was measured using the Dinitrosalicylic acid reagent while the pH was monitored using a pH meter. Gas Chromatography was used to measure acetone, butanol, ethanol, acetic acid and butyric acid. The growth of Clostridium saccharobutylicum was determined by viable plate count, which was converted to dry weight for evaluation of kinetic parameters. The kinetic parameters of the fermentation which included total ABE (acetone butanol ethanol) production, total solvent yield (solvents/substrate), total solvent productivity (g/L/h), reducing sugar utilisation (g/L/h), and specific growth rate (g/g/h) were determined. The parameters necessary for a solventogenic fermentation of grape pomace (12.5 % wet weight/volume) by C. saccharobutylicum were first established. This study demonstrated that the parameters that enabled the production of solvents in grape pomace (12.5 % w/v) were the concentration of 11 % (v/v) inoculum, a concentration of 1 % (w/v) yeast extract, and the adjustment of pH 5.5 with potassium phosphate buffer (1M). The fermentation in white grape pomace with these parameters resulted in the production of ABE (acetone, butanol, ethanol) at 8.76 g/L, a total solvent yield of 0.30 g/g, and productivity of 0.21 g/L/h. The bioprocess and kinetic parameters were lower than a typical batch fermentation indicating that the presence of inhibitors could have hindered the fermentation of grape pomace. Copper and zinc are known to be found in grape pomace which could exert inhibitory effects on C. saccharobutylicum. Polyphenolic compounds are other potential growth inhibitors in grape pomace. This study found that an alternative to Yeast Extract for the grape pomace fermentation involved the use of manganese sulphate (MnSO4.H2O), magnesium sulphate (MgSO4.3HO2), ferrous sulphate (FeSO4.7H2O), potassium diphosphate (KH2PO4), dipotassium hydrogen phosphate (K2HPO4) and ammonium sulphate ((NH4)2SO4). The addition of these mineral salts to grape pomace resulted in a total production of solvents 9.08 g/L, a solvent yield of 0.36 g/g, and a productivity of 0.19 g/L/h. The fermentation with the mineral salts produced a higher total solvent production and solvent yield (based on substrate) than those of a fermentation supplemented with yeast extract. Fermentation in the presence of these mineral salts was successful probably due to the presence of ferrous sulphate which might have repressed the growth inhibitory effect of copper and zinc in grape pomace. The optimisation of the fermentation process which enabled the grape pomace to remain submerged led to an acidogenic fermentation due to oxygen being re-introduced to the substrate when the magnetic rod was activated. This shows that controlled agitation and controlled pH using a batch bioreactor should be applied instead. The production of butanol by fermentation using grape pomace as substrate is promising, particularly if all toxic components in grape pomace could be removed.