Safeguarding grain with gas
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CTA. 1996. Safeguarding grain with gas. Spore 62. CTA, Wageningen, The Netherlands.
Permanent link to this item: http://hdl.handle.net/10568/47307
Insect pests can quickly turn grain stocks into a pile of dust, and to prevent this happening methyl bromide has been used for many years to fumigate grain. Although this gas is an excellent fumigant, it is now known to be one of the causative...
Insect pests can quickly turn grain stocks into a pile of dust, and to prevent this happening methyl bromide has been used for many years to fumigate grain. Although this gas is an excellent fumigant, it is now known to be one of the causative agents of the depletion of the ozone layer in the earth's atmosphere. Countries that are signatories to the Montreal Protocol will probably phase it out by the year 2006. In the search for alternatives to methyl bromide, scientists at the UK's Natural Resources Institute (NRI) have teamed up with the Kenyan Agricultural Research Institute (KARI) to test the effect of carbon dioxide, a gas more commonly associated with fizzy drinks but which is toxic to insects at high concentration. Stocks of maize, which form part of Kenya's national reserve held in silos at Nakuru, are treated with carbon dioxide which is supplied by a local Kenyan company, Carbacid, who operate a well to tap local volcanic sources. The silos in the tests each hold about 2,000 tonnes of maize and to supply enough gas for fumigation, liquid carbon dioxide is delivered eight tonnes at a time by tanker. The liquid, which is delivered at 56°C, is fed into one end of a heat exchanger and emerges at the other as CO2 gas at ambient temperature: this gas is then fed into the base of the silo cell. CO2 is heavier than air, so as the silo fills from below, air is displaced through an open hatch at the top. Once the concentration at the hatch has reached 80% the silo is sealed and the gas left to do its work of fumigation. Initial studies have overcome a number of technical problems and results have been promising. However the development of a fully operational fumigation technique that can be used in place of methyl bromide is dependant on additional research into maintaining high gas concentrations for long periods. The necessary investigations are being funded by Britain's Overseas Development Administration (ODA) and will be completed by the end of 1996. Dr. Rick Hodges NRI Chatham Maritime, Kent ME4 4TB, UK