Most industrial fermentations are operated under vigorous aeration and the air supplied to the fermenter must be sterilized To prevent contamination of either the fermentation by airborne Microorganisms or the environment by aerosols generated within the fermenter both air input and air exhaus ID: 525110
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Slide1
Sterilization of air: Methods
Most industrial fermentations are operated under vigorous aeration and the air supplied to the fermenter must be sterilized.
To prevent contamination of either the fermentation by airborne.
Microorganisms or the environment by aerosols generated within the fermenter, both air input and air exhaust ports have air filters attached.Slide2
Suspended solids may be separated from a fluid
during filtration by the following mechanisms:
(j) Inertial impaction.
(ii) Diffusion.
(iii) Electrostatic attraction.
(iv) Interception.Slide3
Advantages of continuous sterilization over batch Sterilization
(i) Superior maintenance of medium quality.
(ii) Ease of scale-up - discussed later.
(iii) Easier automatic control.
(iv) The reduction of surge capacity for steam.
(v) The reduction of sterilization cycle time.
(vi) Under certain circumstances, the reduction of fermenter corrosion.Slide4
Advantages of batch sterilization over continuous sterilization
Lower capital equipment costs.
(ii) Lower risk of contamination -
continuous
processes require the aseptic transfer of the
sterile broth to the sterile vessel.
(iii) Easier manual control.
(iv) Easier to use with media containing a high
proportion of solid matter.Slide5
Filters and design of depth filters
Filtration is one of the most common processes
used at all scales of operation
to separate suspended particles
from a liquid or gas,
using a porous medium called filter
which retains the particles
but allows the liquid or gas when pass through filter.Slide6
The theory of depth filters:
Aiba
et al.
(1973) have given detailed quantitative analysis of these mechanisms but this account will be limited to a description of the overall efficiency of operation of fibrous filters.
It is assumed that if a particle touches a fibre it remains attached to it, and that there is a uniform concentration of particles at any given depth in the filter, then each layer of a unit thickness of the filter should reduce the population entering it by the same proportion; which may be expressed mathematically as:
dN/dx
=
-KN 1
Where,
N
is the concentration of particles in the air at a depth,
x,
in the filter and
K
is a constant.Slide7
On integrating equation (1) over the length of the filter it become:
N/No = e
-kx
------------2
where
No
is the number of particles entering the filter and
N
is the number of particles leaving the filter.
On taking natural logarithms, equation (2) becomes:
In
(N
/
No)
=
-Kx. ----------3
Equation (3) is termed the log penetration relationship.Slide8
The efficiency of the filter is given by the ratio of the number of particles removed to the original number present, thus:
E
=
(No
-
N)/No --------4
where
E
is the efficiency of the filter.
(No
-
N)/No
= 1 -
(N
/
No). ------5
Substituting
N/No = e
-Kx ,
Therefore
(No
-
N)/No
1
e-Kx -----6
and E
= 1 - e
-KxSlide9
The log penetration relationship [equation (3)] has been used by Humphrey and Gaden (1955) in filter design, by using the concept
X
9O
'
the depth of filter required to remove 90% of the total number of particles entering the filter; thus:
If
No
were 10 and
x
were
X
9O
'
then
N
would be 1:
In (1/10) =
-KX
90
or 2.303 10glO(1/IO) = -
KX
9O
2.303( -1) = -KX
90
therefore,
X
90
=
2.303/K. ------ 7