In addition to being a strong oxidizer, ozone is not stable at
conditions typically found in stored grain. Ozone gas that is toxic to
the insects must be continually replenished to maintain entomologically
lethal concentrations in the grain mass
tested a closed-loop recirculation system to capture and
reuse ozone gas that had passed through the grain and observed
that the decay rate of ozone reached a steady state after a passivation
period that ranged from 53.5 to 84.7 h. In the same study, the
closed-loop system did recover ozone that had passed through the
grain and this reduced the amount of new ozone that needed to be
generated to maintain target concentrations lethal to insects. The
closed-loop pilot study shows that the rapid decay of ozone as it
passes through grain, poses a significant design challenge. To
maintain ozone concentrations that are lethal for insects throughout the entire grain column
recommended
several engineering measures that can be used. The velocity
of air/ozone through the grain and/or the initial
concentration of ozone can be increased. However, both of these
measures have practical limitations. Another option would be to
inject ozone to multiple points to monitor target ozone concentrations
throughout the grain mass. For moderately high structures,
where the ozone concentration at the midpoint of the grain mass is
above target levels, the direction of the flow could be reversed after
a period of time to treat the top and bottom of the grain with the
highest concentrations of ozone. This would be especially effective
for insect pests that do not penetrate deeply into the grain mass
and have greater abundance near the headspace and plenum. Humidifying
ozone (bubbling) before the application is proposed as a
solution to increase ozone effectiveness, but even in this case, the
results obtained are contradictory