The Acetone-Butanol-Ethanol Fermentation: Recent ...

Biotechnology and Genetic Engineering Reviews

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The Acetone-Butanol-Ethanol Fermentation: Recent Progress in Technology Ian S. Maddox To cite this article: Ian S. Maddox (1989) The Acetone-Butanol-Ethanol Fermentation: Recent Progress in Technology, Biotechnology and Genetic Engineering Reviews, 7:1, 189-220, DOI: 10.1080/02648725.1989.10647859 To link to this article: http://dx.doi.org/10.1080/02648725.1989.10647859

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5 The Acetone-Butanol-Ethanol Fermentation: Recent Progress inTechnology

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IAN

s.

MADDOX

Biotechnology [Jepartnlellf. Mas.\'ey UniversitYJ !)ll!J17ersfon North. Zealand

JVe~v

Introduction The acetone-butanol-ethanol (ABE) fermentation process. using Clostridiu111 beijerinckii ~ epitomizes the problenls of all fermentation processes vis-a-vis chenl ical synthesis:

(lcetobutylicu111 or C...

1. 2.

Lo\\' reactor productivities; Presentation of a dilute aq ueous sol utian for product recovery.

In particular.. the process is subject to severe product inhibition" at concentrations no greater than 20 g r- I and this~ in turn . restricts the concentration of sugar that can be fermented. ~rhe purpose of this chapter is to revie\v sonle recent developnlcnts in fermentation technology as applied to the ABE process. The ainl of such technologies is to increase reactor productivity and/or retnove product inhibition. In this way., the economics of the overall process can be inlproved. Detailed accounts of the nlicrobiology and biochemistry of the ABE process (outlined in Figure J) have been presented in several recent reviews (e.g. L.inden . Moreira and Lenz . 1985: Ennis.. Gutierrez and Maddox . 1986; Jones and Woods~ 1986; Awang . Jones and Ingledew~ 1988). In this article . techniques for improving productivity in batch fermentation \vill be considered first . followed by the use of continuous culture techniques and some novel fermentation technologies ~ such as the application of imll10bilized ceHs. Finally . sonle integrated fermentation/product recovery technologies \vill be described, because the key to future conlmercia] developnlent of the process may depend on minimizing product inhibition \\,hiIe reducing the costs of product recovery. 'I

Ahbrcviations: I\BE, (,cct()ne-butan{)l-c!th~lnol:CFtv1. capillary cross1l0\V Inicrofiltration: CSTR. continuous stirred t~nk reactor. 1J;()lt~dln()Jog\'mul G{~tr(~(i(" EJl~l.!iJ,('(·rill~~ l~(O\'it'n's

n264-H72;/~9107/1 R9,~220 520.00

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Carbohydrate

! Glucose.. 6..phosphate /

GIYCeralidehYde-3-PhOSPhate \

/ /

1

~ Acids

Solvents

~J"

CO 2 • H2 I:i~ure

I.

Tvla.ior

Ethanol, Acetone, Butanol rl1~Lab()hh:s

pr(}duc~d

Acetic acid, Butyric acid

fn)nl carhohydrah.' on

ana~rohic r,~rrncnlation

hy


C/osrridiuul an' /ollllf,r{icuIII (or ('. bl!~jetillkii)_

Batch fermentation pl-·I AND INITIAL SUGAR CC)NCENTRATION

It has been known for 111any years that the culture pH value has a strong influence on the course of the ABE ferrnentation. The general concensus has been that fermentations performed at relatively high pH values produced acids rather than solvents. whereas in fermentations perfornled at relatively low pI-I values~ the reverse was true (e.g. Monot, Engasser and Petitdemange . 1983). However, there have been several reports of solvents (i.e. total butanol + ethanol + acetone) being produced at pI-I values approaching neutrality . and it is now clear that there is a strong interaction bet\veen the pH value and the initial sugar concentration, and also the strain of bacteriunl used. Thus~ higher initial sugar concentrations encourage solvent production, even at pH values approaching neutrality (Monot et lll.~ 1982:. George. and Chen~ 1983~ Monot, Engasser and Petitdenlange, 1983; Holt" Stephens and Morris, 1984; Ennis and Maddox~ 1987). Marchal, Blanchet and Vandecasteele (1985), working with a substrate derived from the Jerusaleln artichoke (Helillnthus tuberosus) re-emphasized the marked influence of pH value, and shovved that while a lo\v pH value favoured solvent production over acid production, it also led to an increase in the total fermentation time. Their solution to the problem was to control the pH profile during the process. Two such profiles \vere described. In one, the pH was held at plwI6·(}-6·S during the growth phase~ and was then allowed to decrease by self.. acidification. In the second, the pH \vas similarly held during the growth phase, and was then allo\ved to drop by self-acidification. On reaching pH 5·3.. it was re-adjusted to pH 6·5, followed by another natural decrease. By this means" substantial improvements in solvent production were achieved. A similar approach has been described by Ennis and Maddox (1987), \vorking with a substrate of\vhey permeate. I'hey reconfirmed that at relatively low sugar (lactose) concentrations (45 g l-l)~ lo\\' pH favoured soivcntogcnesis.. but gro\vth and sugar utilization \vere poor. Conversely . at higher pH values~ although growth and sugar utilization \vere much improved, solvent production was poor. The pH profile that was developed to optimize the fermentation involved holding the pll near neutrality during the growth phase~ and then allowing it to fall naturally to the optimum value for the solvent 'I

Acetone-butanol-ethanol {ern1entatioll

191

production rate (pH 5-1.-5-5) ~ at which point it was maintained by addition of

alkali (ammonia)_ The conclusion thHt can be drawn from these studies is that to achieve a high

solvent productivity ~ it is necessary to control the pH profile during the process, rather than siJnply to maintain a constant pl-[ value. "[he oplinlUITI profile for a given substrate and bacterial strain is probably case-specific~ and should be evaluated for each situation. AGrrATIC)N AND l-IE/\D-SPACE PRESSURE


Spivey (1978), in his article describing the cOInmercial process then operating at National Chemical Products. South Africa. stated t~at during the fernlentation the head-space pressure was allo\vcd to rise to 35 KPa ahove ambient pressure (due to the carbon dioxide and hydrogen produced by bacterial mctaholislll). Further. the fernlcntation vessels \\'ere not fitted \vith nlechanical agitators. Presunlably.. sufficient 1l1ixing occurred due to gas evolution so that agitation \vas not required. Maddox . Gapes and L,arsen (1981 ) pcrforJned expcrinlen ts in a stai nless steel fernlcntation vessel \vhcrc the head...space pressure could be controlled. Pressure.s of up to 105 KPa \vcre generated naturally . and held at the required value using a relief valve. It \vas shown that nlaintenallce of a positive head-space pressure resulted in a lllarked improvenlent in solvent productivity . the val ue increasing fronl 0-05 gil. h to 0-2 glLh \vhen the process vias conducted at 105 KPa above alllbicnt pressure rather than at atll10spheric pressure. Furthernlore. it \"las deillonstratcd that sparging O[ s\vceping the culture \vith hydrogen gas at atnl0sphcric pressure had no effect on the solvent productivity'l and it \vas suggested that this is because the partial pressure \vas not sufficiently high to achieve the necessary concentration of hydrogen in solution. It \vas postulated. based on renlarks by Spivey (] 978). that the hydrogen gas produced early in the fernlcntation is subsequently reused by the hacteriulTI to provide reducing povver for butanol

production. In contrast to the above, Griffith, Compere and Googin (1983) reported that at a head-space pressure of 1400 KPa~ produced by pressurizing \vith hydrogen gas, there was a slight decrease., rather than an increase . in butanol production. Unfortunately., no details were provided for production rates or yields. In support of the beneficial effects of an increased head-space preSSl1re~ Doremus~ IJnden and Moreira (1985) compared fertnentations pcrfornlcd at 105 KPa with those performed under non-pressurized conditions. They demonstrated a 6()7 x 109 cells ml- 1) during his description of a multistage pilot plant process. Unfortunately~there has been no further study into this phenomenon. despite its potential commercial application with regard to the novel fermentation technologies described belo\v. In conclusion . free-cell continuous culture allows superior productivities (up to 2·5 gll.h) to be achieved when compared with batch culture. Such systems are notoriously unstable, although multistage systems may provide a solution to the problem. Unfortunately. the solvent concentrations that are achieved in continuous culture are considerably lo\\'er than in batch culture~ aggravating the problem of economic product recovery. Novel fermentation technologies CONTINU()US CULTl]RE WITH CELL RECYCLE

Continuous culture (using free cells) with cell recycle is a technique by which the cells in the effluent stream are collected and recycled to the ferlnenter. "fhe result of this is that higher biomass concentrations are achieved in the fermenter, and this should lead to higher reactor productivities. Furthermore, the higher bionlass concentration \vithin the fernlenter may allow the process to operate at higher product concentrations than in conventional systems, \vith the resuit that the higher productivities achieved are not entirely at the expense of product concentration. Potential disadvantages of cell recycle include the need for additional capital equipment . and the process nlay be complex and difficult to operate. Table 1 summarizes the studies using this technology. 1":tble 1.

C~II

recycle

Recycle lcnUll~nts

l)O m~ hUt~Hl0llu r~sin

Xl\Dscrics

the i\BE

similar 10

~iHcalit~

lVtikston,-= and Bihh\' ( IlJX I): rvtaddux ( ILJH2): Larsson ~uld rv1uttias~on ( 19H..l)~ Ennis. Ourc:shi and l\i1aduox ( IlJX7) (jroot and l..ll\"h~n ( PJ~6): Das. Soni and Ghnse ( I ()S7): En nis ~ Ulu,-=shi ,~nl! r\fladdox (19X7): Ni...·lst..·n (,(tll. (19X~)

~lay adsorb sorllt: nt1tri~nts


Bonoport..•

l\dsnrpti(Hl capal'ity Silllihu· to silicalitc l)~ l~S not adsorh nulri.. .· nts

Larsson ,111uty!icurn in extractive fernlcntation system. Journal of (~henlicl;/ Engineeri"g Japan 18.. 125-130. JOBSES. I.M.L. AND I{OELS, J .A. (1983). Experience "lith solvent production by C'/oscridiurn beijeriJlckii in continuous culture. Biotechnology find Bioengineering 25. 1187~1 J94. JONES. D.T. AND \VOOl)S. D.I~. (1986). Acetone-butanol fernlentation revisited.

A4ic/'obi%gical l~evien's 50,484-524. A.tv!., JANATI-IoRISSl .. R.• PETITDEt\·1ANGE, I-I. AND GAY. R. (1988). Iron effect on acetone·-butflnol fermentation. C"lll"renl fltficrobi%gy 17,299-303,

JUNELlES ..

T. S. AN D K Hv1. B. Y. (1988). Electron flow shift in (''los/ric/bun tlcelobu tyliCliln fernle ntation by e lectrochenlicaII yin t roduced reduci ng equivalen t. BiOleclr" ology

KI1\1.

KI~L

Letter.";· ]0, 123-128. B.l·I.. BELLO\VS. P.• DATTA .. R.

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electron

fl()\\f

fernlenter.

Lliolechn%gy lind

Bioengineering 25,281-299.

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S.T., LONG. S., SANTANGELO, J.D., JONES, D.T. AND WOODS. D.R, (1985), lmnlobilized (Jostridilll1l llcetobulyliclun P262 Illutants for solvent production. Applied and £11 vironfnen tal Microbiology 50 ~ 477--481.

LARGIER t

Aceto1Ze-bu{aJlol~ethllll()1 ferntentatioll

217

extraction through pervaporation in acetobutylic fernlentation. Biotechnology and Bio(!ngineel"illg 3"'O~ 692-696.

LARRAYOZ.. M.A. AND PlHGJANER. L. (19H7). Studv of butanol

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LARSSON,

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MADDOX..

MADD()X~

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MILESTONE.

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PIERROT~

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fernlentatioJl. Biotechnology llnd Bioengineering 27, 1297-1305. YERUSHALMl t L. AND VOLESKY .. B. (1987). Culture conditions for gro\vth and solvent biosynthesis by a modified Clostridilll1l acetobuty!iC:lilll. Applied Nlicrobiology and Biotechnology 25 .. 513-520. YERUSHAL~fI, L':t VOLESKY, B. AND SZCZESNY, T. (1985). Effect of increased hydrogen partial pressure on the acetone-butanol fermentation by (Jostridilll1 I acetobutylicunl. Applied Microbiology and Biotechnology 22. 103-107.