Alternative storage technology at farm/village level
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Wherever grain is grown on a commercial basis, buying agencies often issue empty sacks to producers so that they may be filled on the farm. The buying agency may then collect the bagged grain from the farm, or the producer has to deliver it to the nearest collection point. In either case, the producer has to store the sacks of grain for some time before they are sold. During this period precautions have to be taken to ensure the safety of the grain and maintain its quality.
At the very least, the bagged grain must be kept off the ground to prevent spoilage by translocating water and/or termites. Low platforms, tarpaulins or plastic sheeting may serve this purpose; but if there is a risk of damage by rodents or other animals, high platforms fitted with rodent barriers should be used. If there is a risk of rain during the temporary storage period the bags should be covered with waterproof sheeting ( but not all the time if the grain has a moisture content much in excess of 12%). Alternatively, the sacks of grain should be stacked on dunnage or waterproof sheeting, away from walls, in a rodentproofed barn. The need for chemical methods of pest control should not arise if the storage period is short.
Where sacks are used for domestic grain storage, similar conservation measures should be adopted. However, it will be necessary to employ some form of insect pest control (see Chapter 8). Second-hand sacks must be thoroughly cleaned and disinfested before use.
Metal or Plastic Drums
Drums are often used as storage containers in the house and serve notably for the storage of cereal seeds and pulses.
Plastic drums are used intact or after having the upper part cut off to facilitate loading and unloading. Otherwise, plastic lends itself poorly to adaptation because it is relatively weak: at most, a lockable outlet can be added. If the lid is tight fitting and the drum is completely filled with grain, any insects present will deplete the oxygen in the drum and die.
Metal drums can be adapted for domestic grain storage in a similar way. A removable lid permits easy loading; but it is also possible to weld half of the lid to the rim of the drum, and provide a riveted hinge on the remaining half of the lid so that it alone can be opened.
Fitted with a padlock, such a modified drum is more secure. To make a store of greater capacity, two metal drums can be welded together end to end and fitted out as described above. Well modified and/or fitted with gaskets, metal drums can also be made airtight.
Inaccessible to rodents, efficient against insects, sealed against entry of water, drums make excellent grain containers. However, they should be protected from direct sunshine and other sources of heat to avoid condensation by being located in shaded and well ventilated places.
Alternative Solid Wall Bins
In some countries grain storage workers, rather than modifying traditional storage structures, have developed significantly different storage bins. A few examples of these are described below.
(i) The "Pusa" bin.
Developed by the Indian Agricultural Research Institute (I.A.R.I.), these silos are made of earth or sun-dried bricks; they are rectangular in shape and have a capacity of 1 to 3 tonnes.
A typical "Pusa" bin has a foundation of bricks, compacted earth, or stabilised earth. A polyethylene sheet is laid on this, followed by a concrete slab floor 10 cm thick. An internal wall of the desired height (usually 1.5 to 2 metres) is constructed of bricks or compacted earth, with a sheet of polyethylene wrapped around it. This sheet is heat-sealed to the basal sheet, and the external wall is then erected. During the construction of the wall an outlet pipe is built into its base.
The concrete slab roof is supported by a wooden frame and, like the floor, is constructed of two layers separated by a polyethylene sheet. During its construction, a man-hole measuring 60 x 60 cm is built into one corner.
The "Pusa" bin (Figure 6.10. The "Pusa" bin.) has been widely adopted in India, and has been demonstrated in some African countries. It gives good results when loaded with well dried grain.
(ii) The "Burkino" silo
Based on a traditional dome shaped type of bin, this silo is constructed with stabilised earth bricks (Figure 6.11. The "Burkino" bin.). Various models and capacities are available.
The base is made of stabilised earth resting on the ground or on concrete pillars. The domeshaped roof is also made of stabilised earth bricks, using special wooden formers. The technique of making a dome-shaped roof is not easy to master, and usually has to be done by skilled masons. A variant has been developed with the roof resting upon a wooden frame, which can be erected by unskilled farmers.
(iii) The "USAID" silo
This silo is based on the "Burkino" silo and examples have been erected in Nigeria; holding one tonne of maize grain, the silo rests on stone or concrete pillars supporting a reinforced concrete slab 1.5 metres in diameter. The walls are made of stabilised earth bricks and are plastered inside and out with cement reinforced with chicken wire mesh. The top is domeshaped with a central round opening, and covered with a cone-shaped earthen cap. This is plastered with cement, and rests on bamboos or on a metallic drum base. An outlet door, consisting of a 15 x 30 cm plate 1.5 mm thick which is smeared with grease for easy sliding, is let into the base concrete slab.
(iv) Concrete/cement silos
Such silos are 'cement rich', and often include other materials which normally have to be imported into developing countries. Therefore they are potentially (and usually) expensive structures, which can be seriously considered only when improvements to traditional storage bins cannot be practically applied. Their redeeming feature, given that they are properly constructed and used, is that they are robust and should give many years of satisfactory service.
The Ferrocement Bin ("Ferrumbu")
Developed in Cameroon (Østergaard, 1977), and tested in a number of African countries, this bin is similar to the "Burkino" bin in shape but consists mainly of chicken wire plastered inside and out with cement mortar. Details of its construction may be found in Bodholt and Diop (1987).
The wall varies in thickness from 3.5 cm for a bin of 0.9 m3 capacity, to 6 cm for one of 14.4 m3 capacity.
The "Dichter" stave silo
This cylindrical silo (Figure 6.12. The "Dichter" concrete stave bin.) was developed in Benin, and is constructed with trapezoidal section concrete blocks (staves) supported externally by tightened steel wire. Both internal and external surfaces are rendered smooth with cement, and the outside may be treated with coaltar to ensure water-proofness. The floor and cover slab consist of reinforced concrete cast in situ, and the whole structure is raised off the ground on four concrete block pillars. A manhole is located in one side of the cover slab, and an 'anti-theft' outlet is built into the bottom of the wall. Construction details may be found in Dichter (1978).
Other types of ferrocement or concrete block bins have been designed and tested, notably that developed in Thailand for rice storage (Smith and Boon-Long, 1970) (Figure 6.13. Ferrocement bin for rice, Thailand.). However, as far as is known, none has enjoyed more than local popularity.
A principal technical difficulty with such bins is that they are poorly insulated, which encourages the development of moulds if the moisture content of the grain is higher than 13%. This means that the bins must be constructed indoors, or at least protected by shelters with a wide overhang to reduce extreme variations in temperature. With tall bins, such as the larger Ferrumbu, this is not very practical.
(v) Metal Silos
Economically valid for storing large quantities (over 25 tonnes), metal silos are often regarded as too costly for small scale storage. Nevertheless certain projects have been successful in introducing small metal silos, of 0.4 to 10 tonne capacity, at farm/village level in developing countries: Swaziland (Walker, 1975), Bolivia (Anon, 1982), India (Anon, no date), to mention just a few. Metal silos are reported to have been used on farms and in villages in Guatemala for over 50 years (Breth, 1976) and in Swaziland, on a small scale, for possibly longer.
Such silos are made of smooth or corrugated galvanised metal, and are cylindrical in shape with a flat metal top and, usually but not always, a flat metal bottom. A man-hole with a cover, which may be hinged but is nevertheless lockable, is located, usually to one side, in the top panel; and an outlet pipe provided with a padlock is fitted at the base of the wall.
Metal silos should be placed on platforms or plinths, to facilitate emptying. Large capacity silos are usually constructed without base plates on raised concrete slabs. In this case, bitumen or cement mortar is plastered around the base of the wall to prevent penetration by water and pests.
As with concrete silos, it is essential to provide cover, to avoid excessive variations in temperature and moisture translocation (Figure 6.14).
(vi) Synthetic Silos
Various attempts have been made to develop small scale storage bins, using synthetic materials such as butyl rubber (O'Dowd, 1971) and high density polyethylene (CFTRI, 1975). However, such bins proved to be either too expensive (Figure 6.15. 500 kg butyl rubber/weldmesh silo for cowpea storage, Nigeria.) or prone to damage by pests. Also the management level required by such storage facilities is probably too high for most rural situations.
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