Immobilized Cell System• Immobilized cells

Provide high cell concentrationReuse cellEliminate washout problem at high dilution rate and cell recovery May provide favorable microenvironmental conditionsMay prove genetic stabilityProtect against shear damageCan perform multi-step biosynthesis reactions that are not practical purified immobilized enzyme preparation.

Disadvantages:Diffusional limitation are important.Growth and gas evalution may lead to significant mechanical disruption of the immobilizing matrix.

Immobilized Cell System• Immobilized methods:

- immobilization of cellsEntrapment and Bindingsimilar to immobilized enzyme except covalently

binding (toxic agents, e.g. glutaraldehyde)

- immobilization of cells: biological film.Multi-layer growth of cells on solid surface.e.g. common in biological waste water treatment and mold fermentationthick biofilm: high concentration but diffusion problem

• Bioreactor consideration:- hydrodynamic shear: packed-column, fluidized-bed or airlift reactors.

Bioreactor Operation Consideration

Mixing - Agitation and Aeration To provide adequate mixing of its contents is one the

most factors to consider in design a fermenter.- to disperse the air bubbles- to suspend the organism cells- to enhance heat and mass transfer in the medium

: providing mixing : providing oxygen and mixing in aerobic

systems

Scale-up bubble columnstirred-tank reactor

airlift loop reactor propeller loop reactor

jet loop reactor

Bioreactor Operation Consideration

Some basic bioreactor types for aerobic cultivation of suspended cells:

- Reactors with Internal mechanical agitation.high KLa, flexible, medium with high viscosity

- Bubble column relying on gas sparging for agitation must avoid plugging of spargers

-Loop reactors: mixing and liquid circulation are induced by the motion of an injected gas, by a mechanical pump, or by a combination of the two.

similar to the above.

Bioreactor Operation Consideration

- Internal mechanical AgitationRushton impeller: impeller diameter 30-40% of the tank diameter, 1980s

Axial flow system hydrofoil impellers:increasingly popular

Baffle: to augment mixing and gas dispersion

Bioreactor Operation ConsiderationVolumetric oxygen mass transfer coefficient determination

Unsteady state method:

An examined reactor filled with pure water or a medium, no organism cells.

re temperatuaat oxygen ofconstant law sHenry' theis )(

oxygen of pressure partial theis

law sHenry' )(

*

)*ln(

)*(

2

2

TH

op

TH

opC

taLkLCC

LCCaLkdtLdC

Bioreactor Operation Consideration

- : internal coil and jacketed vessel

- : increases pressure drop, decreases gas flow and provide a pathway for contaminated cells’ entry- mechanical foam breaker - surfactant (toxic)The working volume is 75% of the total fermenter volume.

- : pressurized steam for in-place sterilization of reactors, seals, probes and valves.limited openings.

- : spray balls for clean-in-place

Instrumentation and control• Parameters: to be monitored and controlled• Temperature• Pressure• Agitator shaft power• Flowrate• Liquid level• Viscosity• Turbidity• pH• Redox potential• Ion concentration• DORead pages 308-310 in the text book.