GB2134540A

GB2134540A - Biological conversion system

Info

Publication number: GB2134540A
Application number: GB08401731A
Authority: GB
Inventors: Charles David Scott
Original assignee: US Department of Energy
Current assignee: US Department of Energy
Priority date: 1983-02-08
Filing date: 1984-01-23
Publication date: 1984-08-15
Also published as: JPS59154981A; BR8400494A; GB8401731D0; DE3403607A1

Abstract

A system for bioconversion of organic material comprises a primary bioreactor column (10) wherein a biological active agent converts the organic material to a product, a rejuvenator column (24) wherein the biological activity of said biological active agent is enhanced, and means for circulating said biological active agent between said primary bioreactor column and said rejuvenator column. The system maybe used to convert sugar into alcohol using a flocculent strain of Zymomonas mobilis as biological active agent. <IMAGE>

Description

SPECIFICATION Biological conversion system This invention, which resulted from a contract with the United States Department of Energy, relates to a biological conversion system ofthetype used for converting a dissolved organic material to an alternate form, such as conversion of alcohol to sugar.

Forvarious reasons, the use of batch-type process equipment (e.g., vats) snot suitable for biologically induced conversion of dissolved organic material to other substances (e.g., sugar to alcohol) on a largescale production basis. It has consequently been proposed heretofore to convert an organic material in an aqueous solution to anothersubstance as the solution flows continuously through a column containing microorganisms which effect this conversion (which microorganisms will be referred to hereinafter as biological active agents). In previously used continuous flow systems for conversion of dissolved organic material to other substances, nutrients have been introduced into a bioreactorcolumnto keep the biological active agent from losing its efficacy.This practice results in the addition of a burdensome quantity of nutrients to the column, much of which passes from itwithout being used. Furthermore, if too much nutrient material is allowed to accumulate in a column, the activity of the biological active agent therein can be reduced.

It is therefore an object ofthis invention to provide a more efficient system for converting an organic material such as sugar to another substance such as alcohol.

Another object of the invention is to provide a system for converting a dissolved organic material to another substance in a continuousflow-type operation which is not subjectto a reduction in the activity of a biological active agent, such as occurs in known process apparatus used for the same purpose.

These objects are attained by preferred embodi mentsoftheinventioncomprising: (1)a primary bioreactorwherein a biological active agent converts organic material to a product, (2) a rejuvenator wherein the biological activity of said biological active agent is enhanced, and (3) means for circulating said biological active agent between said primary bioreac torand said rejuvenator.

Figures 1 and 2 diagrammatically illustrate two bioreactorsystems constructed in accordance with the principles ofthe invention.

In Fig. 1, reference number 10 designates a primary bioreactorcolumn the lower end of which is connected by a conduit 12 to the upper end of a mixing vessel 14 (which mixing vessel may not be required in all applications ofthe inventions), a valve 16 being located in said conduitto control fluid flow therethrough. An inlet conduit 18 and an outlet conduit 20 are connected to the side of vessel 14, and the lower end of the vessel is connected buy a conduit 22 to the upper end of a biological agent rejuvenation column 24, hereinafter referred to as the rejuvenator.

The lower end ofthe rejuvenator is in turn connected to the upper end of primary bioreactor column 10 by a conduit 26 provided with a flow control valve 28. Inlet and outlet conduits 30,32 are respectively connected to the lower and upper ends of rejuvenator 24, inlet conduit 30 being connected to a pump P1 and outlet conduit 32 being connected to a suitable waste disposal means. Inlet and outlet conduits 34, 36 are likewise respectively connected to the lower and upper ends of column 10, inlet conduit 34 being connected to a pump P2. Conduit 38 is connected to conduit 12 and to a pump P3, and a conduit 40 is connected to a conduit 26 and ta a pump P4.

In the embodiment of the invention illustrated in Fig.

2, reference number 42 designates a primary bioreac torcolumnthelowerendofwhich is connectedto the lower end of a biological agent rejuvenation column 44 (or rejuvenator) through a conduit 46, a pump P5, and a conduit 48. The upper end of column 42 also connects with rejuvenator 44via a conduit 50 con nectedtoconduit46,and a waste conduit52 branches from conduit 50. Also connected to the upper end of column 42 are two outlet conduits 54, 56. The upper and lower ends of rejuvenator 44 are connected to the lower end of column 42 by means of conduits 58-62 associated with a pump P6.An inlet conduit 64 and associated pump P7 connect with conduit 62, another inlet conduit 66 and associated pump P5 connect with conduit 58, an inlet conduit 68 and associated pump Pg connect with the lower end of rejuvenator 44, and outlet conduits 70, 72 connect with the upper end of said rejuvenator.

In the operation of the embodimentofthe invention illustrated in Fig. 1, a stream consisting old a suitable transportfluid (e.g., water) and an organic reactant which is convertible by a biological active agentto a different product material is injected by pump P2 into the lower end of primary bioreactor 10. The reactant may be a fermentable aqueous solution ofthe kind described in "Evaluation of Substrates for Butanol Production", an article by A. Compere and W. Griffith which appeared in Volume 20 of Developments In Industrial Microbiology, published by the Societyfor industrial Microbiologyin 1979.In column 10,the organic reactant is converted to afluid product buy a biological active agent, this product being removed through conduit 36. The biological active agent may be attached to or retained in mobile particulate material such as polymeric organic substances, or it may be an agent agglomerating in separate bodies, such as the floccu lent strain of Zymomonas mobilis that is registered under accession number NRRL B-1 2526 in the Agricultural Research Culture Collection, International DepositoryAuthority(NRRL),1815 N. University Street, Peoria, Illinois. Transportfluid, devitalized biological active agent, a, nd organic reactant may be drawn out ofthe lower end of column 10 through conduit 12 either continuously or periodically during the operation ofthesystem, these materials passing into mixing vessel 14 when needed together withtransportfluid (e.g.,water) addedto conduit 12 through conduit 38. Fresh biological active agent and/or additional organic reactant can be added to mixing vessel 14(when used) through conduit 18, while excess biological active agent and organic reactant can also be withdrawn from the system through conduit 20.From mixing vessel 14 biological active agent and thetransportfluid and organic reactant combined therewith pass into the upper end of rejuvenator 24throygh conduit 22. Material which serves as a nutrient for the biological active agent is pumped into the lower end of rejuvenator24 via conduit 30, the flow rate of the agent th rough the rejuvenator being controlled by valves 16 and 28 so thatthe agent is revitalized by the nutrient material while it is retained in the rejuvenator. Additional organic reactant can be introduced into rejuvenator 24 with nutrient feed if desired.From the rejuvenator the revitalized biological active agent passes into the upper end of primary bioreactor 10, together with additionaltransportfluid added to conduit 26 through conduit40 if desired. Thus, the activity ofthe biological active agent in converting the organic feed to a product in primary bioreactor 10 is maintained at a predetermined level as the described system is operated on a continuous basis.

In the operation of the embodiment of the invention illustrated in Fig. 2, a stream consisting of a suitable transportfluid and an organic reactant is injected through conduits 64,62 into the lower end of primary bioreactor42, wherein a biological active agent converts the organic reactant to a fluid product drawn offthrough conduit 54. Transportfluid, devitalized biological active agent, and organic reactant may be continuously or periodically drawn out of either the upper or lower ends of primary bioreactor 52 through conduits 46 and 50 and passed through said conduit 46 and conduit48 to eitherthe upper or lower end of rejuvenator 44. A portion of the recycle stream from bioreactor42 may be discharged through conduit 52 if desired.Nutrients for the devitalized biological active agent are added to the recycle stream through conduit 66, and additional organic reactant and associated transportfluid may also be introduced into rejuvenator44through conduit 68. Biological active agent which has feasted on nutrients in rejuvenator 44 is returned to the lower end of primary bioreactor 42 through conduits 58,60,62. Excess materials are discharged from the system through conduit 70, and gas is vented from the rejuvenator44th rough conduit 72.

An aqueous solution containing 140 grams per liter of glucose was subjected to microbial action in the form ofthe above-mentioned flocculent strain of Zymomonas mobilis, using a coupled bioreactorrejuvenator system similar to that illustrated in Fig. 2.

The primary bioreactor ofthetested system consisted of a vertical column which was 50 cm long and which tapered from an inside diameter of 1.27 cm at its upper end to an inside diameter of 10.2 cm at its lower end.

The primary bioreactor column nominally contained flocs ofthe identified flocculent strain of Zymomonas mobilis havi ng a diameter in the range of about 0.5cm to about cm, the ilocs being in the form of a fluidized bed in the primary bioreactorwhile the feed solution was flowing.therethrough. The primary bioreactorcolumn communicated with a rejuvenator column which was cm long and which tapered from an inside diameter of 1.27 cm at its lower end to a diameter of 2.54 cm at its upper end.A recycle aqueous solution and particu late Zymomanas mobilis suspended therein were moved from the bottom of the primary bioreactorto the top of the rejuvenator and returned from the bottom of the rejuvenator to the top ofthe primary bioreactor by a peristaltic pump.- The glucose-containing feed solution was introduced into the lower portion of the primarybioreactor, and a nutrient-containing solution was introduced into the lower portion ofthe rejuvenator during part ofthe test procedure.

The described fluidized-bed reactor system was initially operated with a feed of 12 milliliters per minute of the aqueous feed solution containing 140 grams per liter of glucose. An aqueous nutrient solution containing 5 grams per liter of yeast extract, 1 gram per liter of (NH4)2SO4, 0.5 gram per liter of MgSO4.7H2O,and 1 gram per liter of KH2PO4was simultaneously introduced into the primary bioreactorwith the aforesaid glucose solution during a first period in which flocs ofthe above-identifiedflocculent strain of Zymomonas mobilis were formed in the primary bioreactor.After an appreciable amount of flocculent Zymomonas mobilis had accumulated in the primary bioreactor, the flow ofthe described nutrient solution was terminated and the flow ofthe aqueous glucose solution into the primary bioreactor was continued until the bioconversion of glucoseto ethanol and carbon dioxide in the column reached a quasi-steady state. Without the introduction of nut rients into the primary bioreactor,the conversion rate in the column decreased significantly within 4 hours and within 24 hours reached a level of less than 10% of that during the addition of nutrients to the column.At that point, recycle of the floccuient Zymomonas mobilisto the rejuvenator column and back to the primary bioreactorwas initiated, a nutrient feed solution containing 20 grams per liter of glucose and the same concentrations of the nutrients mentioned above being simultaneously introduced into the bottom ofthe rejuvenatorcolumn at a rate of 2 milliliters per minute. Within 1.5 hou rs of operation of the system in this mode, the bioconversion rate of glucose to ethanol intheprimarybioreactorhad increased by morethan 60%. The bioconversion rate in the primary bioreactor continued to increase thereafter, reaching a level that was more than 6times the rate without recycle ofthe biological active agent to the rejuvenator, although the rate of introduction of the nutrient solution intotherejuvenatorwasonly 17% ofthatused when nutrients were introduced into the primary bioreactorwith the aqueous glucosefeed stream. Hence, it is manifestthat a bioconversion system ofthetype disclosed herein is extremely efficient in operation.

Claims

1. Asystem for bioconversion of organic material, comprising: a primary bioreactorwherein a biological active agent converts said organic material to a product; a rejuvenator wherein the biological activity of said biological active agent is enhanced; and means for circulating said biological active agent between said primary bioreactor and said rejuvenator.

2. Thesystemofclaim 1 wherein said organic material comprises a sugar and said product is alcohol.

3. The system of claim 2wherein a nutrientforsaid biological active agent is introduced into said rejuve nator.

4. The system of claim 3wherein said biological active agent is a flocculent strain ofZymomonas mobilis.

5. The system of claim 4wherein said nutrient comprises yeast extract.

6. The system of claim Swherein said nutrient further comprises (NH4)2S04, MgSOs7H20 and KH2PO4.

7. Thesystem of claim 6 wherein sugar is introduced into said rejuvenator and then passed to said primary bioreactorwith said Zymomonas mobilis.

8. The system of claim 7 wherein said sugar is glucose.