53
Large-Scale Production of BNC
Based.on.these.results,.higher.shear.stresses,.which.are.necessary.for.high.
oxygen.transfer,.seem.to.be.unsuited.for.cultivation.of.most.cellulose-producing.
bacteria. strains.. In. comparison,. bubble. columns. have. low. shear. stresses,.
but. they. are. also. characterized. by. low. oxygen. transfer. and. poor. mixing..
Because.of.the.sensitivity.of.some.bacteria.cells.to.shear.stress.and.the.necessity.for.high.oxygen.consumption.rates,.both.the.stirred-tank.fermenter.and.
the.bubble.column.seem.to.be.unfavorable..To.solve.this.problem,.Wu.et.al..
(2001). developed. a. modified. bubble. column,. whereby several. wire. mesh.
draft.plates.were.installed.inside.the.column..Thus.the.air.from.the.sparger.
entered.the.column.between.two.wire.mesh.draft.plates,.resulting.in.a.20.l.
column.with.three.modules.of.draft.plates..In.the.proposed.modified.bubble.
column,. higher. values. of. gas. holdup. and. of. the. volumetric. mass. transfer.
coefficient,.as.well.as.lower.mixing.times.than.those.in.the.bubble.column.
without.wire.mesh.draft.plates,.were.estimated..Experimental.testing.of.the.
proposed. modified. column. to. cultivate. sensitive. G. xylinus. confirmed. the.
improvement.with.better.production.yields.
Further.investigation.from.Zhou.et.al..(2007b).dealt.with.BNC.production.
by. G. xylinus. strain. NUST4.1. in. shake. flasks. and. in. a. stirred-tank. reactor.
by.adding.sodium.alginate.into.the.medium..They.found.that.an.addition.
of.0.04%.(w/v).sodium.alginate.into.a.shake.flask.produced.a.BNC.yield.of.
6.0 g/l..The.conversion.rate.from.sugar.to.cellulose.was.27%,.compared.with.
3.7. g/l. and. 24%. under. static. conditions.. Using. a. stirred-tank. reactor,. the.
addition.of.sodium.alginate.influenced.the.BNC.morphology.from.irregular.clumps.and.fibrous.masses.entangled.in.the.internals.to.discrete.masses.
dispersed.in.the.broth..The.authors.assumed.that.sodium.alginate.hinders.
the.formation.of.large.clumps.of.BNC.and.enhances.the.cellulose.yield..As.a.
result,.some.differences.in.reticulated.structures.and.ribbon.width.as.well.as.
lower.crystallinity.(decreased.from.78%.to.59%).and.a.smaller.crystallization.
size.of.BNC.produced.with.sodium.alginate.added.were.observed.
Batch Fermentation under Stirring using Plastic Composite Supports
Cheng.et.al..(2009).recently.described.the.implementation.of.different.types.
of.plastic.composite.supports.(PCSs).in.a.submerged.fermentation.process.to.
enhance.the.resulting.yield.and.material.properties.of.BNC..The.general.idea.
followed. was. the. generation. of. BNC. biofilms. growing. on. a. solid. support.
zation..The.PCSs.were.an.extrusion.product.of.a.mixture.between.polypropylene.and.nutritious.compounds.(Pometto.et.al..1997)..The.polypropylene.
was.used.as.a.matrix.integrating agricultural.mixtures.(e.g.,.ground.soybean.
hulls, soybean. flour,. and. microbial. nutrients. such. as. bovine albumin,. red.
blood.cells,.yeast.extract,.and.peptone).as well.as.mineral.salts.and.released.
these. nutrients. slowly. during. fermentation.. The. fermentations. were. conducted.at.30°C.in.a.1.25 l.Bioflo.3000.fermenter.(New.Brunswick.Scientific,.
Edison,.NJ).using.a.working.volume.of.1.l.and.an.agitation.rate.of.100.rpm..
Large-Scale Production of BNC
Based.on.these.results,.higher.shear.stresses,.which.are.necessary.for.high.
oxygen.transfer,.seem.to.be.unsuited.for.cultivation.of.most.cellulose-producing.
bacteria. strains.. In. comparison,. bubble. columns. have. low. shear. stresses,.
but. they. are. also. characterized. by. low. oxygen. transfer. and. poor. mixing..
Because.of.the.sensitivity.of.some.bacteria.cells.to.shear.stress.and.the.necessity.for.high.oxygen.consumption.rates,.both.the.stirred-tank.fermenter.and.
the.bubble.column.seem.to.be.unfavorable..To.solve.this.problem,.Wu.et.al..
(2001). developed. a. modified. bubble. column,. whereby several. wire. mesh.
draft.plates.were.installed.inside.the.column..Thus.the.air.from.the.sparger.
entered.the.column.between.two.wire.mesh.draft.plates,.resulting.in.a.20.l.
column.with.three.modules.of.draft.plates..In.the.proposed.modified.bubble.
column,. higher. values. of. gas. holdup. and. of. the. volumetric. mass. transfer.
coefficient,.as.well.as.lower.mixing.times.than.those.in.the.bubble.column.
without.wire.mesh.draft.plates,.were.estimated..Experimental.testing.of.the.
proposed. modified. column. to. cultivate. sensitive. G. xylinus. confirmed. the.
improvement.with.better.production.yields.
Further.investigation.from.Zhou.et.al..(2007b).dealt.with.BNC.production.
by. G. xylinus. strain. NUST4.1. in. shake. flasks. and. in. a. stirred-tank. reactor.
by.adding.sodium.alginate.into.the.medium..They.found.that.an.addition.
of.0.04%.(w/v).sodium.alginate.into.a.shake.flask.produced.a.BNC.yield.of.
6.0 g/l..The.conversion.rate.from.sugar.to.cellulose.was.27%,.compared.with.
3.7. g/l. and. 24%. under. static. conditions.. Using. a. stirred-tank. reactor,. the.
addition.of.sodium.alginate.influenced.the.BNC.morphology.from.irregular.clumps.and.fibrous.masses.entangled.in.the.internals.to.discrete.masses.
dispersed.in.the.broth..The.authors.assumed.that.sodium.alginate.hinders.
the.formation.of.large.clumps.of.BNC.and.enhances.the.cellulose.yield..As.a.
result,.some.differences.in.reticulated.structures.and.ribbon.width.as.well.as.
lower.crystallinity.(decreased.from.78%.to.59%).and.a.smaller.crystallization.
size.of.BNC.produced.with.sodium.alginate.added.were.observed.
Batch Fermentation under Stirring using Plastic Composite Supports
Cheng.et.al..(2009).recently.described.the.implementation.of.different.types.
of.plastic.composite.supports.(PCSs).in.a.submerged.fermentation.process.to.
enhance.the.resulting.yield.and.material.properties.of.BNC..The.general.idea.
followed. was. the. generation. of. BNC. biofilms. growing. on. a. solid. support.
zation..The.PCSs.were.an.extrusion.product.of.a.mixture.between.polypropylene.and.nutritious.compounds.(Pometto.et.al..1997)..The.polypropylene.
was.used.as.a.matrix.integrating agricultural.mixtures.(e.g.,.ground.soybean.
hulls, soybean. flour,. and. microbial. nutrients. such. as. bovine albumin,. red.
blood.cells,.yeast.extract,.and.peptone).as well.as.mineral.salts.and.released.
these. nutrients. slowly. during. fermentation.. The. fermentations. were. conducted.at.30°C.in.a.1.25 l.Bioflo.3000.fermenter.(New.Brunswick.Scientific,.
Edison,.NJ).using.a.working.volume.of.1.l.and.an.agitation.rate.of.100.rpm..