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discharge vertically into the tank. The pour-flush toilet discharges 5 cm above the liquid level, and the floor drain pipe discharges 10 cm below the liquid level to produce a hydraulic seal (see Figure 10.3). The kitchen sink and the laundry fixture have a common drain connected to the tank vent pipe through a waterseal trap unit. |
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The maintenance of an ASAS system essentially involves desludging the interceptor tanks. Occasionally, a small piece of cloth or other floating material will need removing from the control box. More rarely, accidental obstruction in a sewer will require attention. Desludging of the interceptor tanks can be done hygienically with vacuum tankers. To avoid the need for large, complex equipment and the need to desludge a large number of tanks at any one time, a desludging programme that enables a few tanks at a time to be cleaned on a daily or weekly basis is recommended. Sludge can be disposed of in a drying bed. |
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The ratio of the volume of the contents of an interceptor tank to the total daily discharge in an ASAS system is so small (approximately 1200) that the sludge can be disposed of without problems in a standard treatment facility. For San Zenon, for instance, the ratio is 0.88192 m3/day. Even if several tanks are desludged each day, the effect of the added load of solids, BOD5 and nutrients is negligible. |
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10.3.13
Wastewater Treatment |
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The interceptor tanks retain about 80 per cent of the solids and reduce BOD5 by about 4060 per cent. For this reason the effluents require only simple treatment, for example in facultative waste stabilization ponds that are designed for a lower organic loading than would be the case for conventional sewage. |
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For the Cartagena project the ASAS costs (1982 prices) per household were Col$15400 (US$42) for vitrified clay pipe sewers |
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