Biomedical Engineering Reference
In-Depth Information
TABLE 5.8
Composition of Typical CAs Easily Created in Sealed Grain Storages
Composition (%)
Type of CA
Atmosphere Source
O
2
CO
2
N
2
Ar
Low O
2
Nitrogen from liquid or other source (<0.1% O
2
)
0.5
99.4
Low O
2
Propane burner
0.5
13.4
85.1
1.0
Low O
2
Producer gas burner
0.5
20.8
78.2
0.5
Low O
2
CO
2
from liquid or other source (<0.1% O
2
)
0.5
97.5
2.0
Hermetic storage
Metabolism within the storage
2.0
18.0
81.0
1.0
High-CO
2
CO
2
from liquid or other source (>98% pure)
4.2
80.0
15.6
0.2
High-CO
2
CO
2
from liquid or other source (>98% pure)
8.4
60.0
31.2
0.4
High-CO
2
CO
2
from liquid or other source (>98% pure)
12.6
40.0
46.9
0.5
From Banks, H.J. and Fields, P.G., Physical methods for insect control in stored-grain ecosystems, in
Stored Grain Ecosystems,
Jayas, D.S., White, N.D.G., and Muir, W.E., Eds., Marcel Dekker, Inc., New
York, 1995, 353. With permission.
reaction observed with CA involves CO
2
in concrete silos.
60
Carbon dioxide is bound
by concrete through carbonation, which can result in reduced pressures developing
in well-sealed new concrete bins. Also, carbonation of concrete can gradually extend
to a depth where reinforcing steel is exposed and the steel may eventually corrode
and weaken the storage structure.
E
FFECT OF
C
ONTROLLED
A
TMOSPHERES ON
M
ORTALITY OF
I
NSECTS
The effectiveness of CA in eliminating insects is dependent on several abiotic (e.g.,
gaseous composition, relative humidity, temperature, exposure time, and total gas
pressure) and biotic (e.g., insect species, life stage, and infestation level and distri-
bution) factors. Interaction of all these factors must be understood to create an
environment that is lethal to all the pests in the stored grain. Researchers around the
world have been conducting empirical studies to define atmospheric conditions for
eliminating several pest species from grain.
Harein and Press
61
studied the mortality of adults and larvae of the beetle
Tribolium castaneum
(Herbst), and larvae of the moth
Plodia interpunctella
(Hub-
ner), when exposed to binary and ternary combinations of the atmospheric gases
(CO
2
, N
2
, and O
2
) at various temperatures (15.6, 26.7, and 37.8°C). In general, the
mortality of insects increased with a decrease in O
2
concentration, an increase in
CO
2
concentration, an increase in length of exposure (from 7 to 14 day), and an
increase in temperature (15.6 to 37.8°C). Atmospheres containing >36% CO
2
were
lethal to test insects even when O
2
concentration was as high as 15%. In the absence
of CO
2
, however, the O
2
concentration must be reduced to <1% to obtain lethal
gaseous atmospheres.
P
.
interpunctella
larvae were more susceptible than
T
.
casta-
neum
adults or larvae under all test environments. Lindgren and Vincent
62
determined
the mortality of all life stages of the weevil
Sitophilus granarius
(L.) and
S
.
oryzae
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