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Hindered (Zone) Settling

الكلية كلية الهندسة     القسم  الهندسة البيئية     المرحلة 3
أستاذ المادة جبار حمود عبد النبي البيضاني       11/07/2018 08:30:39
In systems that contain a high concentration of suspended solids, both hindered or zone settling and compression settling occur in addition to discrete ( free) settling and flocculent settling . The settling phenomenon that occur when a concentrated suspension, initially of uniform concentration throughout, is placed in a gradual cylinder, is illustrated on the presented figure of this lecture. Because of the high concentration of particles, the liquid tends to move up through the interstices of the contacting particles. As a result, the contacting particles tend to settle as a zone or (blanket), maintain the same relative position with respect to each other. The phenomenon is known as hindered settling. As the particles settle, a relatively clear layer of water is produced above the particles in the settling region. The scattered, relatively light particles maintain usually settle as discrete or flocculent particles, as discussed previously. In most cases, an identifiable interface develops between the upper regions of the figure shown in the context of the lecture. The rate of settling in the hindered settling region is a function of the concentration of solids and their characteristics. As settling continues, a compressed layer of particles begins to form on the bottom of the cylinder in the compression settling region. The particles apparently form a structure in which there is close physical contact between the particles. As the compression layer forms, region containing successively low concentration of solids that those in the compression region extend upward in the cylinder. Thus, in actuality the hindered settling region contains a gradation in solids concentration from that found at the interface of the settling region to that found in the compression settling region (Metcalf & Eddy, 2003).



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