Microbial Kinetics

Question 1

What do engineers use microbial kinetic for?

Answer 1

To design biological systems.

Question 2

What is all growth limited by?

Answer 2

Substrate

Question 3

What does Yield link?

Answer 3

Growth and substrate use

Question 4

Where does batch growth take place?

Answer 4

In a single reactor without influent or effluent.

Question 5

What is the process for batch growth? (4)

Answer 5

1) Fill container with wastewater
2) Air-ate it, let the sludge settle down
3) Then drain off the water from the top
4) Send that off for disinfection

Question 6

What type of growth do you notice in a batch growth system?

Answer 6

A logarithmic growth

Question 7

What is the equation for growth rate (rg) and state what the components are?

Answer 7

rg=μX=dX/dt
where:
μ= specific growth rate (time^-1)
X=microorganism concentration (mass per unit volume)

Question 8

What are the 4 phases to batch growth?

Answer 8

1) Leg phase
2) Logarithmic phase
3) Stationary phase
4) Death phase

Question 9

Sketch a log base 10 cells against time (hours) graph and label all the import phases on it.

Answer 9

See notes

Question 10

What is the general equation for exponential growth and state what the components are?

Answer 10

Xt=X0e^μt
where:
Xt= amount of biomass at time t
X0= the initial amount (therefore at t=0)
μ= growth rate (h^-1)
t= time (h)

Question 11

What is Liebigs law of limiting factors?

Answer 11

In reality nothing grows forever, something limits the growth and growth is limited by some factor. In this case you try and make your pollutant the limiting factor.

Question 12

Define substrate.

Answer 12

It is the amount of “food” necessary for growth (the substance on which an enzyme acts).

Question 13

Sketch a graph to show the relationship between the growth rate and substrate concentration (Monod Kinetics).

Answer 13

See notes

Question 14

What part of the graph will be different if we have different bacteria?

Answer 14

Different bacteria will have different slopes depending on the ecology of the organism.

Question 15

State the Monod Equation and state what the components are.

Answer 15

μ=μmax(S/S+ks)
where:
S= substrate concentration 
ks= saturation coefficient 
μ= growth rate

Question 16

Define a functional group.

Answer 16

Bacteria doing the same job.

Question 17

How much BOD is in a clean river?

Answer 17

2mg/l

Question 18

What should the BOD not exceed in a river?

Answer 18

4mg/l

Question 19

What is the required dilution in a river?

Answer 19

1:8

Question 20

How can you calculate Ld effluent (concentration)?

Answer 20

Using Monod kinetics.

Question 21

What does net growth rate equal?

Answer 21

Net growth rate (μ) = Growth rate (μmax(S/S+ks) - death rate (m)

Question 22

If a substrate S growing on an organism maximum specific growth rate 5d^-1 with a value of ks of 2mg/l. What is the effluent substrate concentration if the system was at equilibrium so that death =growth and death rate = 8d^-1?

Answer 22

If growth equals death then:
0 = μmax(S/S+ks)-m
Rearranging:
S = -ksm/m-μmax
Effluent= 5.3mg/l

Question 23

What does the amount of biomass produced depend on?

Answer 23

The yield

Question 24

What does yield ratio equal?

Answer 24

mass of biomass/mass of substrate consumed.

Question 25

What is rg equal linking yield?

Answer 25

rg = -rsuY
Where:
rg= growth rate
rsu= growth rate
Y= yield (mass/mass)

Question 26

What is rsu equal to?

Answer 26

rsu = -μmax(1/Y)(S/S+ks)
where:
rsu= growth rate
Y= yield
S= substrate concentration  
ks= saturation coefficient 
μmax= growth rate maximum

Question 27

What happens if we switch from treating the wastewater anaerobically to aerobically?

Answer 27

It is more energy efficient, produces some green energy and means not as much sludge disposal.