Figure 3.3
Turbine
Maxblend
Helical ribbon
Screw
Gate with
with Draft Tube Turbine
51
Large-Scale Production of BNC
Figure 3.3
Agitator.configurations.including.turbine.and.maxblend.impellers.used.in.BNC.production.
(Kouda.et.al.1997).
They.found.that.the.Maxblend.and.gate.with.turbine.impellers.mix.culture.
broths.more.effectively.than.the.other.agitators.investigated..In.consequence,.
larger. K L a values. were. achieved.. They. recommended. smaller. distances.
between.the.area.of.the.culture.broth.and.the.impeller.in.order.to.further.
increase.the.K L a..They.argue.that.this.characteristic.should.reduce.the.high.
viscosity.of.the.culture.broth,.where.the.shear.speed.is.low..Moreover,.the.
impeller.should.induce.a.high.shear.region.around.the.sparger.in.order.to.
increase.the.dispersion.of.bubbles.and.K L a.
Agitated Cultivation by Shaking
As. very. simple. bioreactors,. shaken. flasks. can. be. used. for. BNC. generation.in.the.form.of.spheres..Czaja.et.al..(2004b).focused.their.investigations.
on. the. structural. influence. of. BNC. formed. in. agitated. culture. conditions..
Furthermore,. they. were. interested. in. bacteria. behavior. and. BNC. product.
accumulation.during.the.biosynthesis..They.found.that.the.G. strain.ATCC.
53582.effectively.synthesizes.BNC.in.the.form.of.unique,.large.spheres.and.in.
large.amounts.similar.to.stationary.culture.after.7.days..Other.authors.have.
investigated.the.influence.of.the.bioreactor.vessel.size.on.the.production.of.
BNC.spheres..By.utilizing.150.and.100.ml.Erlenmeyer.flasks.under.the.same.
conditions.(medium.volume.and.rotation.speed),.the.size.of.the.spheres.was.
decreased.by.one.order.of.magnitude.(Hu.and.Catchmark.2010b).
Most.of.the.cells.have.been.found.to.be.distributed.at.the.sphere.surface.
and.only.a.few.of.them.are.randomly.scattered.inside..Based.on.the.hypothetical. formation. process,. cells. are. assumed. to. become. attached. around.
the.surface.of.air.bubbles.existing.in.the.agitated.liquid..The.bacteria.then.
start.to.proliferate.and.synthesize.cellulose.ribbons,.resulting.in.a.compact.
structure.. Close. observation. by. Czaja. et. al.. (2004b). revealed. that. cellulose.
characterized. by. uniaxially. oriented. ribbons. is. formed. in. stationary. culture,. whereas. cellulose. synthesized. under. agitated. conditions. possesses.
a.structure.of.disordered,.curved,.and.overlapping.ribbons.with.a.smaller.
Turbine
Maxblend
Helical ribbon
Screw
Gate with
with Draft Tube Turbine
51
Large-Scale Production of BNC
Figure 3.3
Agitator.configurations.including.turbine.and.maxblend.impellers.used.in.BNC.production.
(Kouda.et.al.1997).
They.found.that.the.Maxblend.and.gate.with.turbine.impellers.mix.culture.
broths.more.effectively.than.the.other.agitators.investigated..In.consequence,.
larger. K L a values. were. achieved.. They. recommended. smaller. distances.
between.the.area.of.the.culture.broth.and.the.impeller.in.order.to.further.
increase.the.K L a..They.argue.that.this.characteristic.should.reduce.the.high.
viscosity.of.the.culture.broth,.where.the.shear.speed.is.low..Moreover,.the.
impeller.should.induce.a.high.shear.region.around.the.sparger.in.order.to.
increase.the.dispersion.of.bubbles.and.K L a.
Agitated Cultivation by Shaking
As. very. simple. bioreactors,. shaken. flasks. can. be. used. for. BNC. generation.in.the.form.of.spheres..Czaja.et.al..(2004b).focused.their.investigations.
on. the. structural. influence. of. BNC. formed. in. agitated. culture. conditions..
Furthermore,. they. were. interested. in. bacteria. behavior. and. BNC. product.
accumulation.during.the.biosynthesis..They.found.that.the.G. strain.ATCC.
53582.effectively.synthesizes.BNC.in.the.form.of.unique,.large.spheres.and.in.
large.amounts.similar.to.stationary.culture.after.7.days..Other.authors.have.
investigated.the.influence.of.the.bioreactor.vessel.size.on.the.production.of.
BNC.spheres..By.utilizing.150.and.100.ml.Erlenmeyer.flasks.under.the.same.
conditions.(medium.volume.and.rotation.speed),.the.size.of.the.spheres.was.
decreased.by.one.order.of.magnitude.(Hu.and.Catchmark.2010b).
Most.of.the.cells.have.been.found.to.be.distributed.at.the.sphere.surface.
and.only.a.few.of.them.are.randomly.scattered.inside..Based.on.the.hypothetical. formation. process,. cells. are. assumed. to. become. attached. around.
the.surface.of.air.bubbles.existing.in.the.agitated.liquid..The.bacteria.then.
start.to.proliferate.and.synthesize.cellulose.ribbons,.resulting.in.a.compact.
structure.. Close. observation. by. Czaja. et. al.. (2004b). revealed. that. cellulose.
characterized. by. uniaxially. oriented. ribbons. is. formed. in. stationary. culture,. whereas. cellulose. synthesized. under. agitated. conditions. possesses.
a.structure.of.disordered,.curved,.and.overlapping.ribbons.with.a.smaller.