同海大学 Tongji University 2.Flocculent settling Particles in a rather dilute suspension flocculate during the settling operation,resulting a increase in particle mass and a faster settling velocity For example,the removal of TSS in untreated wastewater in primary settling facilities,and in upper portions of secondary settling facilities,also the removal of chemical floc in settling tanks
Tongji University 2. Flocculent settling Particles in a rather dilute suspension flocculate during the settling operation, resulting a increase in particle mass and a faster settling velocity. For example, the removal of TSS in untreated wastewater in primary settling facilities, and in upper portions of secondary settling facilities, also the removal of chemical floc in settling tanks
同©大学 Tongji University 3.Hindered settling Also called zone settling,it refers to s suspensions of intermediate concentration,in which inter-particle forces are sufficient to hinder the settling of neighboring particles.The particles tend to remain in fixed position with respect to each other,and the mass of particles settles as a unit.A distinct solid-liquid interface formed at the top of the settling mass. For example,the removal of biomass and sludge in secondary settling facilities used in conjunction with biological treatment process
Tongji University 3. Hindered settling Also called zone settling, it refers to suspensions of intermediate concentration, in which inter-particle forces are sufficient to hinder the settling of neighboring particles. The particles tend to remain in fixed position with respect to each other, and the mass of particles settles as a unit. A distinct solid-liquid interface formed at the top of the settling mass. For example, the removal of biomass and sludge in secondary settling facilities used in conjunction with biological treatment process
同傍大学 Tongji University 4.Compression settling. Refers to settling in which the particles are of such concentration that a structure is formed,and further settling can occur only by compression of the structure.Compression takes place from the weight of the particles,which are constantly being added to the structure by the sedimentation from the supernatant liquid. Usually occur in the lower layers of a deep solids or bio-solids mass, such as in the bottom of secondary settling tank and in sludge- thickening facilities
Tongji University 4. Compression settling. Refers to settling in which the particles are of such concentration that a structure is formed, and further settling can occur only by compression of the structure. Compression takes place from the weight of the particles, which are constantly being added to the structure by the sedimentation from the supernatant liquid. Usually occur in the lower layers of a deep solids or bio-solids mass, such as in the bottom of secondary settling tank and in sludgethickening facilities
同海大学 Tongji University The settling characteristics of activated sludge For the settling process of activated sludge,there exists all the four types of sedimentation in sequence from the water surface to the bottom of settling basin,as shown in figure bellow. Discrete Settling Flocculent Settling Hindered Settling Compression Settling time
Tongji University The settling characteristics of activated sludge For the settling process of activated sludge, there exists all the four types of sedimentation in sequence from the water surface to the bottom of settling basin, as shown in figure bellow. time water depth Discrete Settling Flocculent Settling Hindered Settling Compression Settling
同©大学 Tongji University Variation of drag coefficient Cpwith Reynolds Number Re 10000 1000 S : 100 Region Region Region Region (a) (b) (c) :(d 10 6ed 0.44 0.1 0.2 ·500 0.01 0.01 0.1 1 10 100 1000 10000 1000001000000 Reynolds Number,Re For Region (a) 104<Re<0.2 For region (b) 0.2<Re<500to1000, For region (c) 500<Re<2*105, In region (d) Re<2*I05
Tongji University For Region (a) 10-4＜Re ＜0.2； For region (b) 0.2 ＜Re ＜500 to 1000； For region (c) 500＜Re ＜2*105； In region (d) Re ＜2*105 Variation of drag coefficient CD with Reynolds Number Re