|
|
|
|
|
|
|
fails and excessive solids (e.g. slaughterhouse blood and offal) are passed into the sewer system. |
|
|
|
|
|
|
|
|
5.4.8
Methods for Cleaning Sewers |
|
|
|
|
|
|
|
|
Rodding is a manual technique for the clearing of blockages that occur within small-diameter, shallow sewer systems, generally not exceeding 225300 mm diameter and less than 2 m deep. For sewers greater than 300 mm diameter, the rods tend to wander within the sewer, and are not very effective. The distance from the access point (manhole or inspection chamber) is limited to about 25 m, above which the operation becomes ineffective. |
|
|
|
|
|
|
|
|
Rods are generally of 1-2m lengths of steel, plastic or cane which are screwed together to form a semirigid construction. The screwed joint should not be capable of becoming detached during operation. Although the steel and cane rods operate much more effectively in tension and torsion, plastic rods are extremely effective when working in compression, in order to push the blockage material to the next manhole. Consequently the most effective strategy is the complementary use of both types of rods, with the choice dependent on the type of blockage. This decision may be readily made by an experienced operator. |
|
|
|
|
|
|
|
|
Personal experience in Ghana suggests that rodding is probably the most cost-effective method of alleviating blockages within specific parts of the sewer system. If a blockage cannot be cleared by rodding, then jetting or another suitable technique should be used. The benefit of rodding is that it requires minimum labour and capital costs. However, it is essential that the operators should remove, whenever possible, the debris causing the blockage. |
|
|
|
|
|
|
|
|
Sewer jetting involves the eroding and removal of sediment or blockage material from the sewer system. Jetting machines can clear sewer blockages, and erode sewer sediment within the pipe to a point where removal can take place. |
|
|
|
|
|