Immobilized Cell System Provide high cell concentration Reuse cell Elimination of washout problem at high dilution rate and cell recovery May provide favorable microenvironmental conditions May prove genetic stability Protect against shear damage Can 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: - Active immobilization of cells Entrapment and Binding similar to immobilized enzyme except covalently binding (toxic agents, e.g. glutaraldehyde) - Passive immobilization of cells: biological film. Multi-layer growth of cells on solid surface. e.g. common in biological waste water treatment and mold fermentation thick biofilm: high concentration but diffusion problem Bioreactor consideration: - low 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 Agitation: providing mixing Aeration: providing oxygen and mixing in aerobic systems

Scale-up stirred-tank reactor bubble column jet loop reactor airlift loop reactor propeller 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 Agitation Rushton 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 Consideration Volumetric oxygen mass transfer coefficient determination Unsteady state method: An examined reactor filled with pure water or a medium, no organism cells.

Bioreactor Operation Consideration - Heat removal: internal coil and jacketed vessel Foam: 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. Sterility: pressurized steam for in-place sterilization of reactors, seals, probes and valves. limited openings. - Clean: 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 DO Read pages 308-310 in the text book.