Automated sewage screen

Abstract

Sewage and waste water originate in houses, factories and other establishments and are collected to the street sewers which normally lie only a few feet below the ground. The street sewers are laid in an inclined position so that the liquid could flow by gravity away from its original source. In Malta and Gozo there exist four physical types of sewer construction: - surface sewers consisting of circular pipes laid in trenches; - open galleries provided with circular sewage pipes; - open galleries in which a channel has been constructed; - closed galleries in which circular sewage pipes have been laid. These galleries are closed off by walls at shafts. The street pipes are laid in such a way that the sewage will be diverted into the main sewers. Obviously, the latter should be large enough to receive sewage directly from nearby buildings as well as from other small sewers. The main sewer drops the liquid into a large pit constructed at a low point in the area. A number of pumps, depending on the volume of liquid flowing into the pit, deliver the sewage into a larger pipe at a higher level. From here, the sewage flows on until it reaches a major pumping station to be finally pumped either out into the sea or to a purification plant. INCLINATION OF SEWERS The inclination of the sewers is a very important factor and must always be given careful consideration when the existing sewerage system is being extended. If the gradient of the pipe is very small, most of the solids present in the sewage are liable to be left behind. The accumulation of these solids will eventually cause a blockage. Therefore, there exists a minimum gradient, depending upon the diameter of the pipe at which it can be laid. On the other hand, the gradient of the pipe cannot exceed a particular standard value. For if the gradient is too large, the solids will be left behind just the same. Table 1 shows the standard values of minimum and maximum gradients applied by the Drainage Section of the Works Department [...].