Chemostat - Mass and Kinetic Balances Flashcards

1
Q

What makes a continuous fermentation process a chemostat?

A

Keeping one element (typically the substrate) constant as the limiting reactant.

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2
Q

What assumptions do we make for a Chemostat reactor?

A

Ideal mixing, no concentration gradients

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3
Q

When the substrate is the limiting agent, what is the specific growth rate equal to?

A

The dilution rate (D)

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4
Q

What is the dilution rate and what are it’s units?

A

The dilution rate is the flux (flow in OR flow out) divided by the reactor volume D = F/V. The units are time^-1

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5
Q

What is the equation that shows that D = u?

A

dx/dt - ux - Dx (dx/dt = 0) => D = u

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6
Q

What is the general balances for substrate, product and biomass concentration?

A

Assume they are constant
Sub: 0 = -rs x + D(csf - cs)
Prod: 0 = rpi x + D(cpf - cp)
Bio: 0 = (u - D)x

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7
Q

What are the solutions for substrate, product, and biomass concentration?

A

Assume they are constant
cs = (DKs)/(Umax - D)
cp = (rp x)/D
x = D(cfs - cs)/rs

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8
Q

What is the critical dilution rate?

A

It is the maximum Flow over reactor volume that can be used. If this amount is exceeded, biomass will be washed out of the reactor faster than it can replicate.

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9
Q

What are the 8 characteristics of a chemostat reactor?

A

Chemostat characteristics:
Volume is constant (Fout > 0)
One limiting substrate, D = u
Both flow in and flow out. Inflow contains no biomass, outflow contains cells and product in same concentration as the reactor.
Steady state: x, Cs, Cp, etc… are constant
Cs depends on D not on Csf (not on substrate concentration in feed: Csf)
High productivity can maintained for long periods of time.
Most often lower product concentration than in a fed-batch
Problems with contamination and strain stability (random mutations affect productivity)

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10
Q

How does a chemostat start?

A

It starts as a batch reactor (no feed or outflow) and eventually the outflow and feed streams are started.

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