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of costs in Cartagena and elsewhere, including the pilot projects in Granada and San Zenon, indicated that these parameters remained sound in spite of drastic changes in prices in Colombia since 1982. |
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1. Particle size. The particle size to which minimum cost parameters correspond is 0.02 mm. |
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2. Unit load. The unit load for the sewer design was calculated for cylindrical interceptor tanks, these being cheaper to mass produce. The rate of flow of the unit load is produced by the simultaneous discharge of all the fixtures, that is, the toilet, the kitchen sink, the laundry trough and the shower. Colombian taps and showers discharge about 0.1 1/s each for normal in-house water pressures (810 m water). Thus for these three fixtures the compound discharge is 0.3 1/s. |
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For the unit tank adopted for the pilot project (diameter: 0.90 m; length: 1.48 m; average occupancy per house: 6.8 people) the maximum possible discharge increment was 0.028 1/s for cisternflush toilets (17 1) and 0.007 1/s for pour-flush toilets (4 1). The compound rates are, therefore, 0.328 and 0.307 1/s, respectively. For rectangular tanks of equivalent capacity to the cylindrical ones, the maximum discharges are less: the tanks have a greater surface area and therefore toilet flush-water flows have less of an effect on changes in the level of the liquid. |
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Because there is so little variation in maximum discharge in relation to the type of toilet and tank shape, a conservative unit load of 0.328 1/s, rounded to 0.33 1/s, was then adopted as a basic parameter for ASAS design. |
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10.3.5
Simultaneity Equation and Design Loads |
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A suitable method for calculating the probability of simultaneous discharges is described by Gallizio (1964) which determines water demand and drainage in large buildings in which the following three parameters are taken into account to reflect the buffering effect of the interceptor tanks: peak duration, interval between repetitive discharges and duration of discharge. Gallizio's equation is: |
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