Theoretical Study of High- Rate Sedimentation

The term high-rate sedimentation used here refers to the use of shallow gravitational settlers with detention periods of not more than 15 min to achieve comparable or better settling efficiencies normally obtained in conventional rectangular settling tanks having detention periods of usually more than 2 hr. The settlers can be rectangular, circular, or any other convenient shape. They can be either horizontal or inclined. One obvious advantage is the significant saving in capital cost of construction, land, and piping. The short detention periods required make the high-rate settlers extremely attractive in waste water treatment. For instance, a short detention in final settling in the activated sludge process could eliminate the possibility of developing anaerobic conditions which may be detrimental to the aerobic microorganisms. ' ) The main feature of a high-rate 'settler is its shallow "depth" which is usually not more than a few inches. The idea appears to be suggested originally by Hazen in 1904 (1) and was explored by Camp in 1946 (2). Hansen and Gulp successfully demonstrated that, by using circular tubes of 0.5 to 4 in. in diameter (1.3 to 10.2 cm) and up to 8 ft in length (2.44 m), turbidity removal as high as 96 percent could be obtained (3). A number of installations using high-rate settlers actually have been constructed by industries and municipalities (4).