Efficacy and fumigation characteristics of ozone in stored maize

This study evaluated the efficacy of ozone as a fumigant to disinfest stored maize. Treatment of 8.9 tonnes (350 bu) of maize with 50ppm ozone for 3 d resulted in 92-100% mortality of adult red flour beetle, Tribolium castaneum (Herbst), adult maize weevil, Sitophilus zeamais (Motsch.), and larval Indian meal moth, Plodia interpunctella (Hübner) and reduced by 63% the contamination level of the fungus Aspergillus parasiticus Speare on the kernel surface. Ozone fumigation of maize had two distinct phases. Phase 1 was characterized by rapid degradation of the ozone and slow movement through the grain. In Phase 2, the ozone flowed freely through the grain with little degradation and occurred once the molecular sites responsible for ozone degradation became saturated. The rate of saturation depended on the velocity of the ozone/air stream. The optimum apparent velocity for deep penetration of ozone into the grain mass was 0.03 m/s, a velocity that is achievable in typical storage structures with current fans and motors. At this velocity 85% of the ozone penetrated 2.7 m into the column of grain in 0.8 d during Phase 1 and within 5 d a stable degradation rate of 1 ppm/0.3 m was achieved. Optimum velocity for Phase 2 was 0.02 m/s. At this velocity, 90% of the ozone dose penetrated 2.7 m in less than 0.5 d. These data demonstrate the potential usefulness of using ozone in managing stored maize and possibly other grains.