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The innovative idea that formed the basis of this project was to develop a structure where the grain is contained within a sealed flexible plastic liner, while rigidity is obtained using a thin but rigid polypropylene (PP) sheath.
The constraining condition was that the granary would be socially acceptable to village societies where cheapness is essential, since traditional granary construction materials are usually freely available.
Unique features in the structure were designed to enable the grain to be loaded and unloaded, with the possibility of periodic removal of limited quantities of grain, after which the lower unloading sleeve is sealed. By these means it was possible to maintain grain condition, without affecting significantly the principle of gas-tightness and hermetic storage needed for control of insect pests. This storage system obviates the need for employing residual insecticides and fumigants with the accompanying hazards they pose to the users and the environment.
Evaluations have been carried out in Israel and the Philippines over the last three years, and have formed the basis for both structural and procedural modifications, in order to optimise the system.
We believe that through the development of a series of prototype storage structures, we have now obtained a structure that will fulfil the storage needs of small scale farmers at a minimal and affordable cost.
The concept: The basic concept lies in the development of a hermetically sealable "big-bag" in which the grain is stored.
Respiration by stored-product insects inside the bag changes the composition of the inter-granular atmosphere to an extent where the insects are no longer able to survive. Although hermetic storage is not new, neither is the use of plastic bags for grain storage, the concept of introducing this modern grain storage technology at the village level by using a hermetically sealable bag placed inside a simulated traditional storage structure had not been developed previously.
The two major problems we faced were:
To overcome these problems "bags" of 700 Liter (and later 1300 Liter) nominal capacity were fabricated in the form of a cylindrical PVC liner equipped with an upper conical sleeve for in-loading and a lower cylindrical sleeve for out-loading the grain.
The bag is placed on a wooden platform about 100 cm above ground provided with a central hole through which the lower sleeve is inserted to facilitate unloading by gravitation from beneath the platform. The lower sleeve is sealed with a screw-on cap.
To provide stability to the granary and to maintain the shape of the bag, a strip of rigid white polypropylene (PP) board is curved round the liner to form a cylindrical sheath, the overlapping edges of which are screwed together on to a wooden strut 135 cm long, 40 mm wide and 30 mm thick. An identical strut is then screwed to the outside of the sheath diametrically opposite the first one.
The grain is then loaded into the liner through the upper sleeve using buckets. This sleeve is equipped with a welded strap and buckle so that when loading is completed the sleeve can be rolled over a horizontal wooden strut and firmly sealed using the pressure of the strap.
One necessary design aspect was the need to prevent accumulation of rain-water on top of the bag where an inverted cone would form at the upper surface when grain is removed from the bottom. This was achieved by lifting the horizontal strut that seals the loading sleeve, and positioning it across the top of the granary so that two holes at each end of the strut are fitted over pins screwed into the top of the vertical struts that serve to stabilize the PP sheath. Consequently as grain is removed from below, and the grain level drops, the top of the bag remains suspended beneath the horizontal strut, but collapses from the sides so that the volume of headspace remains minimal. Furthermore, because the granary volume decreases when grain is removed, no pressure differential is created between the inside and outside of the granary and consequently no significant amount of air enters during unloading.
Donahaye, E.J. and Messer, Ellen 1992. Reduction in grain storage losses of small-scale farmers in tropical countries. Research Report RR-91-7, The Allan Shawn Feinstein World hunger Program, Brown University, USA, 19pp.
Emekci , M., Navarro, S., Donahaye, E., Rindner Miriam, Azrieli, A. 1997. Respiration rates of storage insects in airtight conditions. IOBC/WPRS, Study Group, Integrated Protection of Stored Foodstuffs and Other Commodities, Zurich (in press).
Emekci , M., Navarro, S., Donahaye, E., Rindner Miriam, Azrieli, A. 1997. Respiration rates of Tribolium castaneum (Herbst) storage insects in airtight conditions. IOBC/WPRS, Study Group, Integrated Protection of Stored Foodstuffs and Other Commodities, Zurich (in press).
Ferizli, A.G., Navarro, S., Donahaye, E.J. Miriam Rindner
and Azrieli, A.(2001). Airtight granary for use by subsistence farmers. In: Donahaye, E.J., Navarro, S. and Leesch J.G. [Eds.] (2001) Proc. Int. Conf. Controlled Atmosphere and Fumigation in Stored Products, Fresno, CA. 29 Oct. - 3 Nov. 2000, Executive Printing Services, Clovis, CA, U.S.A. pp. 37-43
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Donahaye, E.J., Navarro, S. (1999). A sealed structure for grain storage by small-scale farmers: GrainSafe. Final Report of Project 417-0400-98 submitted to Haogenplast Projects Ltd (Project #22950 funded by the Chief Scientist, Ministry of Commerce & Industry). August 1999, 36 pages.
Navarro S., Donahaye, E.J., Ferizli, G.A., Miriam Rindner and Azrieli, A. (1998). A sealed granary for use by small-scale farmers. p. 434-443 (Vol. I) (In) Proc. 7th Int. wkg. Conf. Stored-Product Protection, (Eds. Zuxun, J., Quan, L., Yongsheng, L., Xianchang, T., and Lianghua, G.) 14-19 October Beijing China.
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