Storage platform
This was one of two, and consisted of a 20-cm reinforced concrete floor with a peripheral support wall 1 m high and 15 cm thick, and a surrounding apron 80 cm wide outside the wall. The platform was 75 m long and 25 m wide and set on an east west axis with all four corners angled at 45º by wall sections 3.5 m long to form an octagon. The platform had two entrances on the southern side, each one 5 m wide to permit loading and unloading with trucks, and the platform was constructed with a gentle slope towards the entrances.
Loading, sampling and sealing
Before loading, strips of 0.25 mm thick polyethylene underliner were laid transversely over the floor and walls. To keep the plastic from being torn by the concrete walls, two layers of 2-3 cm thick strips of insulation material formed from synthetic fiber were glued along the top of the wall before the underliner was placed in position. Loading was started by truck at the far end of the platform and as it progressed, successive strips of underliner were placed in overlapping position and joined together with adhesive tape. After the floor had been covered, the two entrances were sealed with wooden planks and loading was continued with screw conveyors that raised the grain along a central peak to a height of ca. 7 m at which stage the peripheral grain level was about 25 cm below the upper lip of the wall. After loading was completed, the grain bulk surface was trimmed to fill depressions.
The platform was loaded with 4018 tonnes of locally harvested barley (a mixture of cvs. Cantara and Athinais) during September 1989.
The platform was sealed using a 0.83 mm thick PVC formulated overliner. Rolls of the liner 10 m wide and 34 m long were placed over the wall, and were pulled over the top of the grain bulk. They were then welded together to form a continuous liner. The gaslight seal was obtained by folding the over- and underliners together at the base of the wall and securing with sand-bags. A series of 15 cm wide polyester-woven fabric strips were placed at 10-m intervals across the platform above the overliner and these were anchored to the concrete apron. These strips prevented flapping of the overliner in high winds that frequently occur in the area.
After sealing, eight screw-cap inspection ports were welded along the peak from east to west, within which thermocouple cables and gas-sampling tubing were inserted to depths of 0.3, 1.0 and 3.0 m, respectively. The platform was sealed on 21st-22nd September 1989, and uncovered after 34 months storage.
In-storage monitoring and sampling
Grain: Samples were withdrawn from the inspection ports at one- to two-months intervals, and at three depths (0-0.3, 1.0, and 3.0 m). Each sample (ca. 500-600 g) was examined for moisture content (MC) by oven-drying ground samples at 130°C for 2 h, and insect infestation (using a sieve with 1 x 10-mm slots). A Probe-A-Vac vacuum sampler was used to withdraw the samples from the different depths.
Viability: After 19 months storage, the samples from 1- and 3-m depths were mixed to form four composite samples that were tested for viability by the tetra-zolium method (Moore, 1962).
Temperature: Measurements at all ports were carried out at the same intervals.
Intergranular atmospheric composition: Oxygen (O2) and carbon dioxide (CO2) concentrations in the grain bulk were measured monthly by withdrawing gas samples through the plastic tubing inserted into the grain, and analyzing using a Gow-Mac portable analyzer for CO2 concentration, and a Herman-Moritz analyzer for O2 concentration determination. Towards the end of storage, gas monitoring was reduced by taking only one reading from a depth of 1.5 m at each sampling port.
Ambient conditions: Ambient temperatures, and rainfall during the storage period were taken from available meteorological data at the nearest meteorological station (Nicosia) and are provided in Fig. 1.
Equilibrium relative humidity: An equilibrium relative humidity (ERH)/MC curve for local barley varieties was determined separately using barley samples of mixed cvs. (Cantara and Athinais) at different MCs taken from a previous hermetically sealed platform. The barley MC was determined using the oven-drying method. The equilibrium relative humidity of the interstitial air space of the same barley was determined using a Novasina electronic humidity sensor suspended in a gaslight 350-ml plastic container that contained the sample. The ERH/MC curve is given in Fig. 2.
Unloading and sampling
Before unloading, the overliner was removed and additional grain samples were withdrawn as follows: (a) from three areas of visible mould at the apex (0-30 cm) for moisture and mycofloral analysis; and (b) surface samples (0-15 cm) from the four slopes (north, south, east, and west) for moisture and insect infestation analyses. From each slope surface samples were collected (approximately from every 1-m distance in each of the slopes) from two locations: at a distance of 1 m from the retaining wall, and mid-way between the wall and the platform apex. In addition, samples were taken from a depth of 1 m from a location mid-way between the wall and the apex over each slope using a hand sampler.
Fig. 2. ERM/MC curve for local barley at 25°C.
After removal of the overliner, mouldy barley that was located at the apex, was carefully separated manually from sound grain and removed from the platform. During unloading (with front-end loaders), 1-1.5 kg samples were taken from each truck. Samples from 20 consecutive trucks were pooled to form nine composite samples which were reduced to 5 kg each. The composite samples were used to determine germination (4 x 100 replicates sand), chemical analysis (protein, fat, fiber, and MC), and physical analyses (test weight, purity, weed seeds, and broken kernels). One pooled composite sample was used for aflatoxin analyses by high-pressure thin-layer chromatography (HPTLC) fluorotensiometric method.
© 1995 Elsevier Science B.V. All rights reserved.
