*3.6.1 Carbon dioxide (CO2)*

Treatment with CO2 involves displacing the air inside a gas-tight silo with CO2 at concentrations high enough to be toxic to grain pests. This requires a seal impermeable to gases, measured by a half-life pressure test of no less than five minutes. In order to eliminate all life stages of the main grain pests, CO2 must be retained at a minimum concentration of 35% for 15 days [14]. To achieve a 35% concentration level of CO2 for 15 days, 30 kg (size G) cylinder per 15 tones of storage capacity is required. CO2 is an odorless, colorless, non-flammable gas that is approximately one and a half times heavier than air. Food grade CO2 comes in form of a liquid in pressurized cylinders and when released from the cylinder, changes to a gas. Carbon dioxide is less effective at temperatures below 20°C. This is because insects are less active at this temperature, so the CO2 concentration must be maintained for an extended period.

#### *3.6.2 Nitrogen*

Grains stored in a nitrogen saturated environment ensure the control of insects and preserve product quality without the use of chemicals [13]. Nitrogen-based storage systems maintain the quality of canola and pulses through the inhibition of the respiration process that causes oxidation, which may result in the increase in free fatty acids, loss of color, and seed deterioration [13]. Grain treatment with nitrogen (for the purpose of pest control) is safe, environmentally friendly, and involves the usage of electricity for its major operations. Nitrogen produces no residues when used, so grains can be sold instantaneously whenever decided as against what is practiced for chemical fumigants which have recommendation period for

#### *Postharvest Preservation Technology of Cereals and Legumes DOI: http://dx.doi.org/10.5772/intechopen.102739*

withholding after fumigation [13]. The use of nitrogen as an insect control technique involves the use of Pressure Swinging Adsorption (PSA) technology in adjusting the atmospheric composition of the grain storage system to expel other gases other than nitrogen, thus depriving the pests of the needed oxygen. The method of application entails purging the silo to its base with gas majorly composed of nitrogen. This is done in order to force out from the silo the oxygen-rich air through the top of the silo. Several hours of operation are required for PSA to build up about 99.5% pure nitrogen and before the air composition reduces to 2% oxygen. It is difficult for adult insects to thrive in 2% concentration of oxygen, provided this concentration is maintained for 21 days at 25°C or above for the temperature of the grain [14]. The inhibition of the different stages of the life cycle of insects (eggs, larvae, and pupae) will be difficult below these recommended temperatures and the number of days for grain storage. For grain temperatures below 25°C, this treatment duration should further be extended to a 28-day period. Additional purging of the silo may be needed to get rid of oxygen that has diffused from the grains and it must be re-evaluated 24 hours after fumigation in order to achieve effective and efficient pest control.
