58
Bacterial Cellulose
oxygen. content,. as. well. as. the. pH. value. and. the. temperature.. For. example,.
Watanabe.and.Yamanaka.(1995).examined.the.effect.of.oxygen.tension.in.the.
gaseous.phase.on.the.production.and.physical.properties.of.BNC.formed.under.
static.cultivation.conditions..They.stated.that.the.cellulose.production.was.much.
higher.at.oxygen.tensions.of.10%.or.15%.than.under.atmospheric.conditions.
Likewise,.Verschuren.et.al..(2000).investigated.the.development.of.oxygen.
concentration.gradients.and.the.effective.diffusion.coefficient,.D e ,.of.oxygen.
in.a.cellulose.pellicle.generated.under.static.conditions..They.obtained.an.oxygen.flux.of.9.1.×.10 −6 .mol/m 2 /s.at.a.pH.value.of.4.0..The.effective.diffusion.coefficient.of.oxygen.was.equal.to.1.4.×.10 −9 .m 2 /s.under.all.conditions.investigated.
Levy.et.al..(2004).suggested.producing.sheets.and.membranes.of.BNC.using.
a.tray.with.culture.medium.that.is.prepared.in.a.mechanical.mixer..The.reactor. is. furnished. with. a. jacket. for. temperature. control. and. heat. exchange,.
whereas.the.temperature.is.controlled.and.maintained.through.the.circulation. of. hot. or. cold. water.. The. BNC. sheets. produced. are. collected. from. the.
surface.of.the.culture.medium.and.are.then.submitted.to.a.process.of.purification,.passing.through.a.semicontinuous.system.of.rollers.and.belt.conveyors.
made.of.adsorbent.material..The.approach.has.been.improved.by.Farah.et.al..
(2006).so.that.replacement.of.the.culture.medium.in.the.tray.is.not.necessary..
The.resulting.BNC.fleece.is.drained.via.the.box.and.the.cultivation.is.complete..This.procedure.can.be.repeated.until.a.volume.of.only.15%–25%.of.the.
initial.volume.occurs..Then.new.growth.medium.had.to.feed.in.
Benefits and Limitations of Static Cultivation Forms in Batch Vessels
Because.the.BNC.is.formed.at.the.air–liquid.interface,.any.commercial.production. process. based. on. this. type. of. cultivation. is. area. intensive.. Often.
the. process. is. also. less. automated. than. agitated. cultivation. in. deep. tank.
. fermenters.and.therefore.demands.more.manual.work.and.higher.personnel.
costs..Moreover,.the.synthesized.flat.BNC.material.depends.on.the.reaction.
. vessels.used,.and.thus.is.limited.in.size.and.not.variable..Under.batch.conditions,.the.concentration.of.nutrients.changes.during.cultivation,.limiting.the.
. maximum.cultivation.time.and.requiring.regular.costly.holding.times.
Fed-Batch Cultivation
The. cultivation. time. of. static. cultivation. can. be. prolonged. by. the. feeding.
of.new.culture.medium.during.the.bioprocess..Toda.et.al..(1994).reported.a.
yield.increase.of.BNC.using.a.culture.with.a.continuous.or.periodic.supply.
of.carbon.sources.from.underneath.the.cellulose.pellicles.
In.2007.Hornung.et.al..presented.the.aerosol.bioreactor..They.reported.that.
earlier. experiments. with. a. self-constructed. rotating. disk. system. resulted.
in. nonhomogeneous. BNC. with. low. quality. and. BNC. sections. that. were.
mechanically.weaker.than.others..Furthermore,.unwanted.cellulose.grew.in.
the.substrate.reservoir,.interfering.with.the.movement.of.the.rotating.disk.
Bacterial Cellulose
oxygen. content,. as. well. as. the. pH. value. and. the. temperature.. For. example,.
Watanabe.and.Yamanaka.(1995).examined.the.effect.of.oxygen.tension.in.the.
gaseous.phase.on.the.production.and.physical.properties.of.BNC.formed.under.
static.cultivation.conditions..They.stated.that.the.cellulose.production.was.much.
higher.at.oxygen.tensions.of.10%.or.15%.than.under.atmospheric.conditions.
Likewise,.Verschuren.et.al..(2000).investigated.the.development.of.oxygen.
concentration.gradients.and.the.effective.diffusion.coefficient,.D e ,.of.oxygen.
in.a.cellulose.pellicle.generated.under.static.conditions..They.obtained.an.oxygen.flux.of.9.1.×.10 −6 .mol/m 2 /s.at.a.pH.value.of.4.0..The.effective.diffusion.coefficient.of.oxygen.was.equal.to.1.4.×.10 −9 .m 2 /s.under.all.conditions.investigated.
Levy.et.al..(2004).suggested.producing.sheets.and.membranes.of.BNC.using.
a.tray.with.culture.medium.that.is.prepared.in.a.mechanical.mixer..The.reactor. is. furnished. with. a. jacket. for. temperature. control. and. heat. exchange,.
whereas.the.temperature.is.controlled.and.maintained.through.the.circulation. of. hot. or. cold. water.. The. BNC. sheets. produced. are. collected. from. the.
surface.of.the.culture.medium.and.are.then.submitted.to.a.process.of.purification,.passing.through.a.semicontinuous.system.of.rollers.and.belt.conveyors.
made.of.adsorbent.material..The.approach.has.been.improved.by.Farah.et.al..
(2006).so.that.replacement.of.the.culture.medium.in.the.tray.is.not.necessary..
The.resulting.BNC.fleece.is.drained.via.the.box.and.the.cultivation.is.complete..This.procedure.can.be.repeated.until.a.volume.of.only.15%–25%.of.the.
initial.volume.occurs..Then.new.growth.medium.had.to.feed.in.
Benefits and Limitations of Static Cultivation Forms in Batch Vessels
Because.the.BNC.is.formed.at.the.air–liquid.interface,.any.commercial.production. process. based. on. this. type. of. cultivation. is. area. intensive.. Often.
the. process. is. also. less. automated. than. agitated. cultivation. in. deep. tank.
. fermenters.and.therefore.demands.more.manual.work.and.higher.personnel.
costs..Moreover,.the.synthesized.flat.BNC.material.depends.on.the.reaction.
. vessels.used,.and.thus.is.limited.in.size.and.not.variable..Under.batch.conditions,.the.concentration.of.nutrients.changes.during.cultivation,.limiting.the.
. maximum.cultivation.time.and.requiring.regular.costly.holding.times.
Fed-Batch Cultivation
The. cultivation. time. of. static. cultivation. can. be. prolonged. by. the. feeding.
of.new.culture.medium.during.the.bioprocess..Toda.et.al..(1994).reported.a.
yield.increase.of.BNC.using.a.culture.with.a.continuous.or.periodic.supply.
of.carbon.sources.from.underneath.the.cellulose.pellicles.
In.2007.Hornung.et.al..presented.the.aerosol.bioreactor..They.reported.that.
earlier. experiments. with. a. self-constructed. rotating. disk. system. resulted.
in. nonhomogeneous. BNC. with. low. quality. and. BNC. sections. that. were.
mechanically.weaker.than.others..Furthermore,.unwanted.cellulose.grew.in.
the.substrate.reservoir,.interfering.with.the.movement.of.the.rotating.disk.