A flushing system for combined sewer cleansing

Full-scale tests were conducted on two variable-slope test sewers (12- and 18- inch diameters), during which solids were first allowed to build up by passing domestic sewage through the sewers for durations of 12 to 40 hours and then were removed by hydraulic flushing. Formulas were developed which gave satisfactory predictions of several cleansing efficiencies and wave depths for the flush waves and sewer sizes studied. A prototype flush station developed can be inserted in a manhole to provide the functions necessary to pick up sewage from the sewer, store it in a coated fabric tank, and release the stored sewage as a flush wave upon receipt of an external signal. An estimate of costs of periodically flushing combined sewer laterals are given.