Figure 3.7
59
Large-Scale Production of BNC
(a)
(b)
Figure 3.7
The.substrate.aerosol.generator.(left).and.aerosol.spreading.(right).(Hornung.et.al..2007).
and.the.BNC.tended.to.separate.from.the.metallic.mesh.on.which.it.was.supposed.to.form.when.the.cellulose.layer.became.thicker..The.authors.stated.
that.these.problems.were.overcome.by.the.aerosol.bioreactor.
The. aerosol. generator. (see. Figure 3.7,. left. panel). produces. a. spray. of.
the. nutrient. broth. by. ultrasound. using. two. removable. and. sterilizable.
. chambers..These.are.filled.by.gravity.from.a.feed.tank.above.the.chambers,.
and.sterile.air.is.introduced..Then.the.spray.is.transported.into.the.aerosol.
distribution.box.(see.Figure 3.7,.right.panel)..Piezoelectric.crystals.are.used.
as.a.vibration.source.
The.spray.is.fed.to.a.rotating.disk.device.(4.rpm).that.feeds.two.of.the.eight.
exit. channels. at. any. time. to. ensure. a. homogeneous. distribution.. Flexible.
tubes.lead.the.spray.to.a.special.roof-shaped.distribution.box.situated.on.top.
of.the.culture.box..The.two.streams.come.at.the.same.time,.but.on.opposite.
sides,.horizontally.into.the.vessel.in.order.to.cause.turbulence..The.culture.
box,.with.dimensions.of.500.mm.×.900.mm.×.500.mm.is.made.of.temperatureresistant.security.glass.(see.Figure 3.8)..The.whole.construction.is.operated.
under.a.slightly.positive.pressure.to.avoid.contamination.from.the.outside..
The.average.growth.of.BNC.observed.in.this.apparatus.was.2.mm/day.or.
approximately.9.g.cellulose.dry.mass/day..The.runs.were.stopped.when.contamination.was.observed.
To.harvest.the.cellulose.layer.from.the.aerosol.bioreactor,.the.distributor.
box.is.removed.and.the.block.of.product.is.lifted.out.by.hand..In.order.to.get.
a.number.of.slices.rather.than.a.block.of.BNC.material,.the.supply.of.substrate.is.switched.off.for.a.period.of.time.
The. best. results. were. found. by. the. authors. when. a. 6. h. interruption. was.
used,.resulting.in.3–4.cm.thick.layers..One.drawback.to.the.bioreactor.is.the.
ingress. of. contaminating. organisms,. which. usually. occurs. between. 6. and.
10 weeks.after.the.start.of.the.fermentation.process..The.location.of.the.problem.is.usually.the.aerosol.generator.or.the.distribution.box,.which.cannot.be.
disinfected.during.a.production.run..The.authors.were.unsure.as.to.whether.
the. contaminating. species. come. from. outside. the. apparatus. or. arise. from.
insufficient.sterilization.of.the.nutrient.components.at.the.start.of.the.process.
59
Large-Scale Production of BNC
(a)
(b)
Figure 3.7
The.substrate.aerosol.generator.(left).and.aerosol.spreading.(right).(Hornung.et.al..2007).
and.the.BNC.tended.to.separate.from.the.metallic.mesh.on.which.it.was.supposed.to.form.when.the.cellulose.layer.became.thicker..The.authors.stated.
that.these.problems.were.overcome.by.the.aerosol.bioreactor.
The. aerosol. generator. (see. Figure 3.7,. left. panel). produces. a. spray. of.
the. nutrient. broth. by. ultrasound. using. two. removable. and. sterilizable.
. chambers..These.are.filled.by.gravity.from.a.feed.tank.above.the.chambers,.
and.sterile.air.is.introduced..Then.the.spray.is.transported.into.the.aerosol.
distribution.box.(see.Figure 3.7,.right.panel)..Piezoelectric.crystals.are.used.
as.a.vibration.source.
The.spray.is.fed.to.a.rotating.disk.device.(4.rpm).that.feeds.two.of.the.eight.
exit. channels. at. any. time. to. ensure. a. homogeneous. distribution.. Flexible.
tubes.lead.the.spray.to.a.special.roof-shaped.distribution.box.situated.on.top.
of.the.culture.box..The.two.streams.come.at.the.same.time,.but.on.opposite.
sides,.horizontally.into.the.vessel.in.order.to.cause.turbulence..The.culture.
box,.with.dimensions.of.500.mm.×.900.mm.×.500.mm.is.made.of.temperatureresistant.security.glass.(see.Figure 3.8)..The.whole.construction.is.operated.
under.a.slightly.positive.pressure.to.avoid.contamination.from.the.outside..
The.average.growth.of.BNC.observed.in.this.apparatus.was.2.mm/day.or.
approximately.9.g.cellulose.dry.mass/day..The.runs.were.stopped.when.contamination.was.observed.
To.harvest.the.cellulose.layer.from.the.aerosol.bioreactor,.the.distributor.
box.is.removed.and.the.block.of.product.is.lifted.out.by.hand..In.order.to.get.
a.number.of.slices.rather.than.a.block.of.BNC.material,.the.supply.of.substrate.is.switched.off.for.a.period.of.time.
The. best. results. were. found. by. the. authors. when. a. 6. h. interruption. was.
used,.resulting.in.3–4.cm.thick.layers..One.drawback.to.the.bioreactor.is.the.
ingress. of. contaminating. organisms,. which. usually. occurs. between. 6. and.
10 weeks.after.the.start.of.the.fermentation.process..The.location.of.the.problem.is.usually.the.aerosol.generator.or.the.distribution.box,.which.cannot.be.
disinfected.during.a.production.run..The.authors.were.unsure.as.to.whether.
the. contaminating. species. come. from. outside. the. apparatus. or. arise. from.
insufficient.sterilization.of.the.nutrient.components.at.the.start.of.the.process.