Figure 3.2
Motor
Gas out
Shaft
Baffles
Downcomer
Riser
Draft tube
Impeller
Gas in
Sparger
(a) Stirredtank bioreactor
(b) Airlift bioreactor
50
Bacterial Cellulose
ketogluconic.acids,.which.may.be.a.reason.for.the.reduction.in.the.resulting.
BNC.. Further,. Hu. and. Catchmark. (2010a). investigated. the. influence. of. the.
inhibitor.1-methyl. cyclopropene.to.either.exogenous.or.endogenous.ethylene.
during.the.biological.senescence.of.plants.on.the.growth.of.G. xylinus.and.
its.BNC.production..A.higher.concentration.of.biomass.and.lower.BNC.formation.was.observed.in.cultures.excluding.the.additive,.while.the.cellulose.
yield.was.enhanced.up.to.25%.in.media.containing.the.inhibitor.
reactor Types
As. mentioned. earlier,. shake. flasks,. stirred. tanks,. bubble. columns,. airlift.
. reactors,. modified. airlift. reactors,. and. gaslift. bioreactors. have. been. used.
for.BNC.production.under.agitated.conditions..The.stirred-tank.and.airlift.
. reactors.are.the.most.commonly.used.bioreactors.(Figure 3.2).
In.contrast.to.a.bubble-column.reactor,.the.airlift.bioreactor.contains.of.a.
draft.tube,.which.improves.circulation.as.well.as.oxygen.transfer,.and.equalizes.shear.forces.in.the.reactor..Depending.on.the.position.of.the.draft.tube,.
the. reactor. is. called. an. airlift. bioreactor. with. an. internal. or. external. loop.
(Sakairi.et.al..1998).
An.important.process.parameter.in.such.reactors.is.the.oxygen.transfer..
High.BNC.production.rates.require.a.high.oxygen.transfer.rate.associated.
with. a. high. oxygen. transfer. coefficient. (K L a). (Kouda. et. al.. 1997).. However,.
this.may.result.in.high.energy.costs..To.minimize.these.costs,.detailed.investigations. of. agitator. configurations. have. been. made.. Since. in. an. agitated.
and.aerated.culture.BNC.production.increases.the.viscosity.and.reduces.the.
homogeneity.of.the.broth,.the.oxygen.level.in.the.broth.and.following.the.
production. rate. of. BNC. is. reduced.. As. one. of. the. first,. Kouda. et. al.. (1997).
investigated.the.effect.of.the.agitator.configuration.on.the.resulting.BNC.production..They.reported.the.level.of.mixing.and.oxygen.transfer.capacity.for.
various.types.of.impellers.in.a.stirred-tank.bioreactor.(Figure 3.3).
Figure 3.2
Bioreactors.typically.used.to.produce.BNC.(Sani.and.Daham.2009).
Motor
Gas out
Shaft
Baffles
Downcomer
Riser
Draft tube
Impeller
Gas in
Sparger
(a) Stirredtank bioreactor
(b) Airlift bioreactor
50
Bacterial Cellulose
ketogluconic.acids,.which.may.be.a.reason.for.the.reduction.in.the.resulting.
BNC.. Further,. Hu. and. Catchmark. (2010a). investigated. the. influence. of. the.
inhibitor.1-methyl. cyclopropene.to.either.exogenous.or.endogenous.ethylene.
during.the.biological.senescence.of.plants.on.the.growth.of.G. xylinus.and.
its.BNC.production..A.higher.concentration.of.biomass.and.lower.BNC.formation.was.observed.in.cultures.excluding.the.additive,.while.the.cellulose.
yield.was.enhanced.up.to.25%.in.media.containing.the.inhibitor.
reactor Types
As. mentioned. earlier,. shake. flasks,. stirred. tanks,. bubble. columns,. airlift.
. reactors,. modified. airlift. reactors,. and. gaslift. bioreactors. have. been. used.
for.BNC.production.under.agitated.conditions..The.stirred-tank.and.airlift.
. reactors.are.the.most.commonly.used.bioreactors.(Figure 3.2).
In.contrast.to.a.bubble-column.reactor,.the.airlift.bioreactor.contains.of.a.
draft.tube,.which.improves.circulation.as.well.as.oxygen.transfer,.and.equalizes.shear.forces.in.the.reactor..Depending.on.the.position.of.the.draft.tube,.
the. reactor. is. called. an. airlift. bioreactor. with. an. internal. or. external. loop.
(Sakairi.et.al..1998).
An.important.process.parameter.in.such.reactors.is.the.oxygen.transfer..
High.BNC.production.rates.require.a.high.oxygen.transfer.rate.associated.
with. a. high. oxygen. transfer. coefficient. (K L a). (Kouda. et. al.. 1997).. However,.
this.may.result.in.high.energy.costs..To.minimize.these.costs,.detailed.investigations. of. agitator. configurations. have. been. made.. Since. in. an. agitated.
and.aerated.culture.BNC.production.increases.the.viscosity.and.reduces.the.
homogeneity.of.the.broth,.the.oxygen.level.in.the.broth.and.following.the.
production. rate. of. BNC. is. reduced.. As. one. of. the. first,. Kouda. et. al.. (1997).
investigated.the.effect.of.the.agitator.configuration.on.the.resulting.BNC.production..They.reported.the.level.of.mixing.and.oxygen.transfer.capacity.for.
various.types.of.impellers.in.a.stirred-tank.bioreactor.(Figure 3.3).
Figure 3.2
Bioreactors.typically.used.to.produce.BNC.(Sani.and.Daham.2009).