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    K5301 - 20081

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    Morton Coutts (1904-2004), father ofcontinuous fermentation

    Morton Coutts' plan for continuous fermentation at DominionBreweries' Waitemata Brewery was patented as a world firstin 1956.

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    A system at which; Fresh medium is continuously being

    supplied

    Volume of culture is kept constant

    Removal of culture at same flow rate asthe feeding rate

    An extension concept of fed-batchFi, Xi, Si, Pi

    Fo, Xo, So, Po

    F, X, S, P

    D.V = Fi = Fo 0, V = constantD = Dilution rate (T-1)

    F = flow rate

    X = biomassS = substrateP = productV = volume

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    Prolong exponential growth of batchculture

    Condition of Medium; Growth is substrate limited

    Growth is not toxin limited

    Exponential growth will proceed until theadditional substrate is exhausted

    A steady state will be achievedeventually

    Under steady state condition;

    Specific growth rate is controlled by

    Steady state =Formation of new biomass isbalanced with the loss of cells

    from the vessel

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    Continuous CultureDistinguished Characteristics

    Microbial growth takes place understeady-state condition

    Growth occurs in constant rate andconstant environment

    Physical and chemical factors aremaintained constant

    Factors can also be controlledindependently by operator

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    Growth curve of batch fermentation Growth curve of continuous fermentatio

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    INTRODUCTION An apparatus for the continuous cultivation ofmicroorganisms or plant cells

    Made of two main parts :-a nutrient reservior-a growth-chamber

    Nutrients are supplied continuously to the culture vessel

    Residual nutrients and cells are removed from thevessel (fermenter) at the same rate by an overflow

    Volume of culture in the fermenter remain constant

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    The volume of the chemostat can be controlled either by using:

    Figure 1: Apump

    Figure 2: An overflowsystem

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    The nutrient medium contains an excess of allgrowth factors except one, the growth-limiting

    nutrient

    The concentration of the cells (biomass) isdependent on the concentration of the growth-limiting nutrient in the medium feed

    Increase or decrease in the concentration of thegrowth limiting factor is correspondingly expressedby increase or decrease in the growth rate of cells

    Thus the desired rate of cell growth can bemaintained by adjusting the level of concentrationswith respect to the growth limiting factor and otherconstituents

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    To grow microorganisms on very toxic nutrients

    To select mutants with a higher affinity to the growth-limitingnutrient

    To select the species that are optimally adapted to thegrowth limitation and culture conditions in a mixed population

    To study the properties of organisms at selected growthrates

    To gather steady state data about an organism in order to

    generate a mathematical model relating to its metabolicprocesses

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    Chemostat Production of Plantaricin C byLactobacillus plantarum LL441By: Barcena et. al. (1998)

    Lactobacillus plantarum LL441-isolated from

    homemade cheese whey Produces bacteriocin - Plantaricin C Characteristics of Plantaricin C:

    -3.5 kDa-resistant to harsh environmental conditions

    -active at pH values from 2.0 to 7.0-induces the formation of pores in the plasmamembrane of sensitive cells-considered to be a food preservatives

    Case study 1 :

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    Objective :

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    Plantaricin C was optimally produced

    in chemostat Kept at pH 5.0, 300C,150 rpm

    Dilution rate for different carbonsource:

    -glucose : 0.05h-1

    -sucrose : 0.10h-1

    -fructose : 0.12 h-1

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    Introduction

    A continuous culture device in which a bacterialculture is maintained at a constant volume andcell density (turbidity) by adjusting the flow rateof fresh medium into the growth tube by means

    of a photocell and appropriate electricalconnections.

    If the turbidity tends to increase, the feed rate isincreased to dilute the turbidity back to its set point.

    When the turbidity tends to fall, the feed rate is loweredso that growth can restore the turbidity to its setpoint

    Most turbidostats use a spectrophotometer orturbidometer to measure the optical density forcontrol purposes.

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    Sketch of TurbidostatK5301 - 2008

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    Turbidometer

    also known as a nephelometer

    Process;

    light shines throughout sample of water

    light strikes a colloid the light is scattered

    bounce off the colloid

    reflects upwards

    light does not strike a colloid shines through the water sample.

    The meter measures how much light isreflected off colloids in the liquid medium.

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    Case Study 2:

    Highly improved turbidity sensors was used. Algal densitywas regulated by turbidity measurements and the growthrates were monitored. The regulation system allowed an

    effective online process control.

    The turbidostat is a very good tool for such experimentsbecause it functions optimally at maximum growth rates

    The algal growth in the turbidostat is not limited bynutrients. This provides a better quality of live feed forrotifers in turbidostats than in chemostats

    Its possibility to monitoring the growth process of algae androtifers

    Algae and rotifer turbidostats:

    studies on stability of live feedcultures

    By: Walz et. al. (1997)

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    Advantages of continuousfermentation

    High productivityAbility to relieve repression under specific

    nutrient limitationThe distillery can be run at steady state

    conditions and at set-points in control. Without fluctuations during operations,

    utility requirements are constant, giving agreater economy in usage.

    Reductions in manpower.

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    Disadvantages

    Prone to contamination.

    Cost of pumps, reservoirs, sterilizers,and controls is relatively high.

    Economic benefits of improvedkinetics is small compared to cost offeed and preprocessing

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    I. Continuous cultivation of rumen

    microorganisms, a system withpossible application to the anaerobicdegradation of lignocellulosic wastematerials (Huub et al., 1986)

    II.A bioprocessing mode forsimultaneous fungal biomass proteinproduction and wastewater treatmentusing an external air-lift bioreactor(Bo et al.,2001)

    Continuous industrial microbial processesare much less common than batchprocesses, but most biological waste

    treatment steps are operatedcontinuously

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    Continuous fermentation has been

    successfully applied in

    brewing industry ( Dennis et al., 2000)

    single cell protein production (King,1982).

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    530 008

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    ReferencesBarcena, J.M.B., Sineriz F.