Process for the production of ethanol and butanol

1. A process for the production of ethanol and butanol using two separate fermentation steps comprising:

a) first fermentation step comprising fermenting feedstock;

wherein subjecting said feedstock to anaerobic fermentation in the presence of acetogenic bacteria, further comprising a mixture of bacterial strains, at a pH below 6.0, at a temperature in the range 20 to 70 degree C, converting said feedstock to a product predominantly comprising acetic acid and butyric acid; wherein ratio of acetic acid to butyric acid is at least 2:1;

b) treating said product predominantly comprising acetic acid and butyric acid of step a) to separate a solution comprising the acetic acid and butyric acid by:

(i) separating residual solids; and

(ii) separating bacteria; optionally pasteurizing; optionally sterilising said solution comprising the acetic acid and butyric acid;

c) second fermentation step comprising fermenting in the presence of solventogenic bacteria said solution comprising the acetic acid and butyric acid from step b) to form ethanol and butanol.

2. A process according to claim 1 wherein said product predominantly comprising acetic acid and butyric acid from step a) has a concentration of acetic acid in solution of 2 to 5 wt % and a concentration of butyric acid in solution of 0.2 to 0.75 wt %.

3. A process according to claim 2 wherein said products ethanol and butanol from step c) comprises ethanol at a concentration of ethanol in solution in the range 2 to 5 wt % and butanol at a concentration of butanol in solution in the range 0.2 to 0.75 wt %.

4. The process of claim 1 , wherein step a) uses a mixture of bacterial strains; including at least some of the bacteria present in the feedstock.

5. The process of claim 1 , wherein the pH in step a) is maintained in the range 3.0 to 5.5.

6. The process of claim 1 , wherein the temperature in step a) is the range 40 to 70 degree C.

7. The process of claim 1 , wherein the conditions in said first fermentation step are such that the acetic acid and butyric acid in said product predominantly comprising acetic acid and butyric acid from step a) are present in a combined concentration of at least 60 wt % of the total weight of carboxylic acids.

8. A process according to claim 1 wherein said product predominantly comprising acetic acid and butyric acid from step a) comprises at least a 4:1 weight ratio of acetic acid to butyric acid and a combined concentration of the acetic acid and butyric acid of at least 90 wt % of the total weight of carboxylic acids.

9. The process of claim 1 , wherein step b) comprises filtration to remove any residual solids.

10. The process of claim 1 , wherein step b) comprises pasteurisation or sterilisation of the solution.

11. The process of claim 1 , wherein step c) uses a solventogenic bacteria selected from Acetogenium kivui, Acetobacterium woodii, Acetoanaerobium noterae, Clostridium aceticum, Butyribacterium methylotrophicum, Clostridium acetobutylicum, Clostridium thermoaceticum, Eubacterium limosum, Clostridium ljungdahlii, Peptostreptococcus productus, Clostridium carboxydivorans, Clostridium beijerinkii, Clostridium aurantibutyricum , and Clostridium tetanomorphum.

12. The process of claim 1 , wherein said biomass feedstock is landfill leachate.

13. A process according to claim 1 wherein the said solventogenic bacteria in step c) are selected Acetogenium kivui, Acetobacterium woodii, Acetoanaerobium noterae, Clostridium aceticum, Butyribacterium methylotrophicum, Clostridium acetobutylicum, Clostridium thermoaceticum, Eubacterium limosum, Clostridium ljungdahlii, Peptostreptococcus productus and Clostridium carboxydivorans.

14. A process according to claim 1 wherein said solventogenic bacteria in step c) is selected from Clostridium ljungdahlii and Clostridium carboxydivorans.