Solvent production
The invention relates to a process and system for the production of a solvent using monophasic solventogenic Clostridia in a single stage process. More particularly, the process and system relate to the use of a culture vessel for culturing monophasic solventogenic Clostridia, wherein cell growth of the Clostridium is monitored and optimized by the addition of controlled amounts of culture media and/or the removal of controlled amounts of solvent. The process and system may particularly be used to produce solvents such as butanol, acetone and ethanol.
1. A single-stage fed-batch or single-stage continuous process for the production of one or more solvents, the process comprising the steps:
(a) culturing cells of a monophasic solventogenic Clostridium saccharoperbutylacetonicum cells in a liquid culture medium in a culture vessel and producing one or more solvents in the same vessel;
(b) monitoring cell growth of the monophasic solventogenic Clostridium saccharoperbutylacetonicum cells in the culture vessel;
(c) continuously or semi-continuously introducing fresh culture media and/or nutrients into the culture vessel;
(d) continuously or semi-continuously removing a stream or portion of liquid culture medium comprising solvent(s) from the culture vessel and passing said liquid culture medium to a solvent remover to extract the one or more solvents;
(e) maintaining or increasing cell density within the culture vessel; wherein cell growth in the culture vessel is regulated and/or optimized by controlling:
(i) the amount or rate of fresh culture medium or nutrients which are introduced into the culture vessel, and/or
(ii) the amount or rate of liquid culture medium comprising one or more solvents which is removed from the culture vessel.
2. The process as claimed in claim 1 , wherein step (e) comprises:
increasing cell density within the culture vessel;
wherein cell growth in the culture vessel is optimized by controlling:
(i) the amount or rate of fresh culture medium or nutrients which are introduced into the culture vessel, and/or
(ii) the amount or rate of liquid culture medium comprising one or more solvents which is removed from the culture vessel,
wherein the process maintains cell growth and optimizes cell density within the culture vessel, and maximizes sugar utilization and solvent production.
3. The process as claimed in claim 1 , wherein the monophasic solventogenic Clostridium saccharoperbutylacetonicum cells:
(a) naturally display simultaneous growth and solvent production during the major growth phase of batch fermentations;
(b) have been chemically mutated to produce solvents during growth; or
(c) have been genetically modified to produce solvents during growth.
4. The process as claimed in claim 3 , wherein the monophasic Clostridium saccharoperbutylacetonicum is a monophasic Clostridium saccharoperbutylacetonicum N1 strain.
5. The process as claimed in claim 1 , wherein step (b) comprises monitoring cell growth by one or more of:
(i) monitoring production of one or more gases;
(ii) monitoring production of one or more acids;
(iii) monitoring the pH of the culture medium;
(iv) monitoring the utilization of sugar;
(v) monitoring cell density; and
(vi) monitoring the production of one or more solvents.
6. The process as claimed in claim 1 , wherein in step (b) the monitored level of cell growth is compared to a reference level and fresh media or nutrients are introduced into the culture vessel and/or liquid media comprising solvents are removed from the culture vessel if the monitored level is lower than the reference level.
7. The process as claimed in claim 1 , wherein step (d) comprises continuously or semi-continuously removing a stream or portion of the liquid culture medium from the culture vessel and passing the stream/portion via a cell separator to the solvent remover.
8. The process as claimed in claim 1 , wherein the one or more solvents is extracted continuously.
9. The process as claimed in claim 1 , wherein in step (d) liquid culture medium comprising one or more solvents is removed from the culture vessel at a rate which maintains the solvent concentration in the liquid culture below a defined solvent concentration point, wherein the concentration point is the toxicity threshold of that solvent for the monophasic solventogenic Clostridium saccharoperbutylacetonicum.
10. The process as claimed in claim 9 , wherein the solvent is butanol and wherein the defined solvent concentration point is 8-10 g butanol/L.
11. The process as claimed in claim 1 , wherein the solvent is butanol and wherein the butanol concentration in the culture vessel does not exceed 10 g/L.
12. The process as claimed in claim 1 , wherein in step (e) the cell density is maintained or increased within the culture vessel by:
(i) recycling cells which are removed from the liquid culture medium comprising one or more solvents back to the culture vessel; and/or
(ii) continuously or semi-continuously feeding cells from a cell seeder into the culture vessel; and/or
(iii) immobilization of some or all of the cells within the culture vessel.
13. The process as claimed in claim 1 , wherein the liquid culture medium comprises sugar and wherein the amount of sugar in the liquid culture medium is maintained at 5-30 g/L.
14. The process as claimed in claim 1 , wherein the monophasic solventogenic Clostridium saccharoperbutylacetonicum cells are cultured in the liquid culture medium in the culture vessel with no prior anaerobic purge.
15. The process as claimed in claim 4 , wherein the monophasic solventogenic Clostridium saccharoperbutylacetonicum N1 strain is:
(i) Clostridium saccharoperbutylacetonicum N-1(HMT) deposited under accession number ATCC 27021 or Clostridium saccharoperbutylacetonicum N1-504 deposited under accession number ATCC 27022; or
a monophasic and solventogenic variant or derivative thereof.
16. The process as claimed in claim 7 , wherein:
(i) cells are removed from the liquid culture medium in the cell separator and the cells are returned to the culture vessel (optionally via a cell seeder), and/or
(ii) wherein solvent is removed from the liquid culture medium in the solvent remover and the residual liquid culture medium is returned to the culture vessel.
17. A process as claimed in claim 1 , wherein the solvent is butanol.
18. A process as claimed in claim 1 , wherein the process is a single-stage fed-batch process.
19. A process as claimed in claim 1 , wherein the process is a single-stage continuous process.