Efficiency of selected shapes of grit chamber troughs

TR Number



Journal Title

Journal ISSN

Volume Title


Virginia Polytechnic Institute


Grit is usually removed from sewage flow just prior to treatment by some type of grit chamber, often little more than a wide channel with a depressed trough to trap the grit. Three shapes of grit chamber troughs were studied in a model to determine which was the most efficient for the selective capture of grit. The model was constructed of wood, with plastic, interchangeable troughs, and was six inches wide by about ten feet long, including a three foot approach channel to the chamber. The three troughs were six inches deep with 2:1, side slopes and differed, therefore, only in bottom length. Trough 1 tapered to a point, Trough 2 had a four inch bottom length, and Trough 3 had an eight inch bottom length.

Water from a town main was run through the apparatus at velocities varying from 0.11. to 0.8 fps and depths from 0.1 to 0.33 feet. Grit was added, as the flow entered the approach channel, through a funnel. Ordinary construction sand was used as grit after being sieved to obtain 0.1 and 0.2 mm diameter particles. When all the grit had been added the flow was stopped and all grit which had not passed the trough was removed and measured. This measurement when compared with the known amount of grit which was added produced a value of per cant grit passing the trough for each run.

Trough 2, the medium length trough, was found to be relatively most efficient for the selective capture of grit.