Transcript What is hermetic storage?

Effects of modified
atmospheres on insects with
special reference to silo-bags
Prof. Shlomo Navarro
Green Storage Ltd. Israel
e-mail: [email protected]
October 14, 2014
Navarro - Effects of MA on insects in
silo-bags
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Modified atmospheres and
hermetic storage take advantage
of the basic fact that
Storage insects are aerobic
organisms requiring oxygen for
their survival
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Action of modified
atmospheres on insects
1- Desiccation
2- Anoxia
3- Hypercarbia
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A moth larva with spiracles along the body
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What is hermetic storage?
hermetic storage
is a type of
biogenerated MA
It consists of generation of an
oxygen-depleted and carbon
dioxide-enriched interstitial
atmosphere by the respiration of
the living organisms in the
ecological system of a sealed
storage.
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Organisms that contribute to
the generation of MAs
• Insects and mites
• Aerobic microflora
• Anaerobic microflora
• Seed germ
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Bio-generation of MAs in relation to the atmospheric gas
composition and the humidity of their environment
Aerobic conditions
Anaerobic conditions
High oxygen
Low carbon dioxide
Oxygen (%)
20
Low oxygen
High carbon dioxide
Insects & mites
65% RH
<
15
Aerobic fungi, seed germ
65 to 85% RH
10
Anaerobic bacteria
5
>85% RH
0
0
10
20
30
40
50
60
70
80
Carbon dioxide (%)
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90
100
First challenge in MA and
hermetic storage
Maintaining a well sealed
storage structure
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Night
Day
Heated air expands
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Cooled air contracts
9
Atmospheric pressure
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At low atmospheric pressure At high atmospheric pressure
Inside atmosphere moves out
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External atmosphere moves in
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Parameters to determine
GASTIGHTNESS of the
structure
1- Leaks of the structure. Can
be assessed using pressure
test.
2- Permeability of the
membrane, particularly in
flexible structures. Should be
measured in a laboratory.
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Second challenge in MA
and hermetic storage
Preventing permeation of
oxygen through the
flexible liners
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Oxygen permeability [mL/(m 2 24 h)]
Oxygen permeability requirements [mL/(m2 24 h)] of liners in relation
to various storage capacities (m3) and oxygen ingress rates (%/24 h)
for successful application of hermetic storage of dry grain.
O2 ingress rate (0.15%/24h)
450
400
350
O2 ingress rate (0.10%/24h)
300
250
200
O2 ingress rate (0.05%/24h)
150
100
50
0
0
100
200
300
400
3
Volume of the structure (m )
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500
Third challenge in MA and
hermetic storage
Absorption
and
adsorption
of carbon
dioxide by
the
commodity
Gas tight s tr ucture
Le ak y s tr uctur e
A – Carbon dioxide
distribution
B - Exposure period
C - Aeration period
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Recommended ranges for variable pressure test
carried out in structures destined for gaseous
treatments to control storage insects.
Type of
gaseous
treatment
Structure
volume in cubic
meters
Controlled
atmospheres
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95% Full
1. 5
500 to 2,000
4
2
2,000 to 15,000
6
3
6
3
7
4
11
6
10
5
500 to 2,000
12
6
2,000 to 15,000
18
9
<500
<
500 to 2,000
2,000 to 15,000
Modified atmospheres
including airtight
storage
Empty structure
3
<500
Fumigants
Variable pressure test decay
time (min) 250 to 125 Pa
<500
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Phosphine loss from an empty structure of 7.5 m3 capacity
in relation to half-life pressure decay time. Phosphine loss
should not exceed 100 ppm/day.
250
PH3 loss (ppm/day)
225
Exposed
200
Shaded
175
150
125
100
75
50
25
0
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1
2
3
4
5
Minutes for half-life pressure decay
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Fourth challenge in MA and
hermetic storage
Liner durability:
1. Insect damage
2. Rodent damage
3. Weather damage, mainly UV.
4. Mechanical damage
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Low O2 ingress level, is
difficult to maintain in
rigid structures, but is
achievable in practice
using flexible liners
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Measured CO2 concentration during storage time of three silo-bags with
soybeans at 11.5%, 12.9% and 14.9% m.c. and average ambient
temperature (adapted from Bartosik, 2008).
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Calculated O2 and CO2 concentration in silo-bags containing
wheat of initial m.c. at 12, 14 and 16% w.b. for locations
at Pergamino and Balcarce. Initial ‫ס‬at Saenz Pe
temperature 25oC (adapted from Baretto et al., 2012).
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Application of
BIOGENERATED
atmospheres on
dry cereal grain
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The process ofO2 ingress
hermetic storage
Residual O2
Insect respiration
20
Residual oxygen within the
hermetic storage
Oxygen (%)
15
10
Critical point
Insect respiration
Oxygen ingress rate 0.05 %/day
5
0
0
1
2
3
4
5
6
7
8
9
10
11
12
Weeks
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13
14
15
16
Modified atmosphere generated by respiration of insects in
hermetic storage (calculated theoretical). Based on grain mass
containing different infestation levels of insects with an oxygen ingress ra‫א‬e of O.24%/day.
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Calculated weight-loss from a grain mass containing initial
infestation of 2 insects/kg, at different oxygen ingress
rates.
Target gas tightness level
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Target gas tightness to control
storage insects in dry cereals, in
hermetic storage structures
Daily oxygen ingress rate:
1- Below 0.05 % O2/day prevents
oscillated oxygen concentration and
increased weight loss.
2- Between 0.05 and 0.24 % O2/day
allows oscillated oxygen
concentration and increased weight
loss.
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Conclusions
• MA or hermetic storage are very promising quality
preservation and insect control technologies.
• There are a number of challenges in the application
of MA or hermetic storage:
1. Maintaining a well sealed storage structure.
2. Preventing permeation of gas through the structural
membrane (by improved liners).
3. Consider absorption and adsorption of carbon dioxide by
the commodity.
4. In flexible storages improve liner durability; to insect
damage; to rodent damage; to weather; and to mechanical
damage.
5. For silo-bags daily oxygen ingress rate should be below
0.10 % O2/day.
6. For silo-bags oxygen permeability requirements of liners
should be below 400 [mL/(m2 24 h)]
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Thank you for your
attention !!!
Silobags for sealed
storage of grain
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