48
Bacterial Cellulose
(2009).used.a.modified.airlift-type.bubble.column.bioreactor.to.transfer.an.
agitated. cultivation. process. of. BNC. into. pilot. scale. . Furthermore,. recently.
a. novel. bioreactor,. called. a. horizontal. lift. reactor. (HoLiR),. was. developed.
by.Kralisch.et.al..(2010a,.2010b)..It.allows.for.semicontinuous.cultivation.of.
flat. fleeces. and. foils. of. BNC. with. undisturbed. nanostructure. comparable.
to.those.gained.from.static.cultivation,.but.in.a.more.efficient.manner..The.
HoLiR. approach. has. been. transferred. to. pilot-scale. processing. combined.
with.continuous.downstream.processing.and.extensively.tested.under.variations.of.the.bacteria.strain..In.this.way.the.transferability.of.the.concept.as.
well.as.the.robustness.and.scalability.of.the.process.could.be.demonstrated.
Agitated Forms of Cultivation
introduction
Because.of.many.years.of.experience.in.the.use.of.microorganisms.for.food.
turing.methods.for.large-scale.production.of.BNC.were.based.on.fermentation. processes.. The. nutrient. medium. within. a. typical. fermenter. relies. on.
agitation,.thus.diffusion.of.nutrient.components.is.enhanced.by.mixing.of.
the.culture.medium..Also.the.oxygen.solubility.is.increased.by.this.mixing.
compared.to.static.cultivation..Because.of.this,.early.approaches.for.the.bioprocess.intensification.and.for.the.production.of.BNC.on.a.larger.scale.were.
dominated.by.agitated.cultivation.forms.
As.one.of.the.first.companies,.Weyerhaeuser.tested.the.production.of.bacterial.cellulose.called.“Cellulon,”.produced.by.stirred.fermenters.(1988;.U.S..
Patent.4863965).
Since. then. several. kinds. of. culture. devices,. such. as. shake. flasks,. stirred.
tanks,. airlift. reactors,. and. modified. airlift. or. gas-lift. bioreactors. have. been.
tested.for.BNC.production.under.agitated.conditions..At.this.time,.stirred-tank.
and.air-.or.oxygen-supplying.reactors.have.been.used.most.often.(Sani.and.
Dahman.2009)..Spherical.particles.or.fiberlike.structures.are.usually.formed.
within.such.devices.
Benefits and Limits of Agitated Cultivation Forms
Applying. agitated. cultivation. techniques. including. submerged. cultures.
in. shaken. flasks. or. in. stirred. aerated. fermenters,. the. cultivation. time. can.
be. reduced. up. to. 10. times. in. comparison. with. static. fermenters. (Dudman.
1960),. whereas. the. space–time. yield. increases. in. a. significant. manner..
However,.the.idea.of.enhancing.the.BNC.yield.by.higher.air.flow.rates.was.
not.. successful.(Ross.et.al..1991)..It.led.to.a.decrease.in.the.BNC.yield,.since.
Bacterial Cellulose
(2009).used.a.modified.airlift-type.bubble.column.bioreactor.to.transfer.an.
agitated. cultivation. process. of. BNC. into. pilot. scale. . Furthermore,. recently.
a. novel. bioreactor,. called. a. horizontal. lift. reactor. (HoLiR),. was. developed.
by.Kralisch.et.al..(2010a,.2010b)..It.allows.for.semicontinuous.cultivation.of.
flat. fleeces. and. foils. of. BNC. with. undisturbed. nanostructure. comparable.
to.those.gained.from.static.cultivation,.but.in.a.more.efficient.manner..The.
HoLiR. approach. has. been. transferred. to. pilot-scale. processing. combined.
with.continuous.downstream.processing.and.extensively.tested.under.variations.of.the.bacteria.strain..In.this.way.the.transferability.of.the.concept.as.
well.as.the.robustness.and.scalability.of.the.process.could.be.demonstrated.
Agitated Forms of Cultivation
introduction
Because.of.many.years.of.experience.in.the.use.of.microorganisms.for.food.
turing.methods.for.large-scale.production.of.BNC.were.based.on.fermentation. processes.. The. nutrient. medium. within. a. typical. fermenter. relies. on.
agitation,.thus.diffusion.of.nutrient.components.is.enhanced.by.mixing.of.
the.culture.medium..Also.the.oxygen.solubility.is.increased.by.this.mixing.
compared.to.static.cultivation..Because.of.this,.early.approaches.for.the.bioprocess.intensification.and.for.the.production.of.BNC.on.a.larger.scale.were.
dominated.by.agitated.cultivation.forms.
As.one.of.the.first.companies,.Weyerhaeuser.tested.the.production.of.bacterial.cellulose.called.“Cellulon,”.produced.by.stirred.fermenters.(1988;.U.S..
Patent.4863965).
Since. then. several. kinds. of. culture. devices,. such. as. shake. flasks,. stirred.
tanks,. airlift. reactors,. and. modified. airlift. or. gas-lift. bioreactors. have. been.
tested.for.BNC.production.under.agitated.conditions..At.this.time,.stirred-tank.
and.air-.or.oxygen-supplying.reactors.have.been.used.most.often.(Sani.and.
Dahman.2009)..Spherical.particles.or.fiberlike.structures.are.usually.formed.
within.such.devices.
Benefits and Limits of Agitated Cultivation Forms
Applying. agitated. cultivation. techniques. including. submerged. cultures.
in. shaken. flasks. or. in. stirred. aerated. fermenters,. the. cultivation. time. can.
be. reduced. up. to. 10. times. in. comparison. with. static. fermenters. (Dudman.
1960),. whereas. the. space–time. yield. increases. in. a. significant. manner..
However,.the.idea.of.enhancing.the.BNC.yield.by.higher.air.flow.rates.was.
not.. successful.(Ross.et.al..1991)..It.led.to.a.decrease.in.the.BNC.yield,.since.