同济大学：《给水工程原理与技术》课程电子教案（课件讲稿）Sedimentation

同©大学 Tongji University Lesson v Sedimentation Tang Yulin March 2017

Tongji University Lesson V Sedimentation Tang Yulin March 2017

同©大号 Tongji University Second pump station Raw water 个 Coagulation- Settler Tank High-speed flocculation Tank (Multifo) Filter Tank Backwash Pre-thickener Sludge Buffer wastewater tank Tank Sludge Dewatering Sludge balance Thickener process Tank Tank

Tongji University Coagulation￾flocculation Tank Settler Tank （Multifo） High-speed Filter Tank Raw water Second pump station Backwash wastewater Pre-thickener tank Thickener Tank Sludge Buffer Tank Sludge balance Tank Sludge Dewatering process

同©大学 Tongji University Description Sedimentation or Settling is employed for the removal of suspended solids that are heavier than water by gravity separation, such as the removal of grit,Total Suspended Solid (TSS)in primary settling basins,biological floc in activated sludge basin,and chemical floc when chemical flocculation is used. Sedimentation is the most widely used physical process in water treatment,with low cost,simple maintenance,and high efficiency.It may appear more than once in a treatment flow chart. Another kind of sedimentation is Accelerated Gravity Settling which removes particle in an accelerated flow field.but,it is not widely used

Tongji University Description • Sedimentation or Settling is employed for the removal of suspended solids that are heavier than water by gravity separation, such as the removal of grit, Total Suspended Solid (TSS) in primary settling basins, biological floc in activated sludge basin, and chemical floc when chemical flocculation is used. • Sedimentation is the most widely used physical process in water treatment, with low cost, simple maintenance, and high efficiency. It may appear more than once in a treatment flow chart. • Another kind of sedimentation is Accelerated Gravity Settling which removes particle in an accelerated flow field. but, it is not widely used

同©大学 Tongji University I. Types of Sedimentation Based on the concentration and the nature of particle, especially the tendency of particle to interact with neighboring ones. 4 types of gravitational settling can occur,including 1.Discrete particle settling, 2.Flocculent settling, 3.Hindered or Zone settling, 4.Compression settling

Tongji University I. Types of Sedimentation Based on the concentration and the nature of particle, especially the tendency of particle to interact with neighboring ones. 4 types of gravitational settling can occur, including: 1.Discrete particle settling, 2.Flocculent settling, 3.Hindered or Zone settling, 4.Compression settling

同海大学 Tongji University 1.Discrete particle settling The particle maintains its individuality and does not interact with neighboring particles,does not change in size,shape,or density during the settling process.Particles are i usually in low solid concentration,and maintain l a constant settling velocity For example,the removal of grit or sand in preliminary treatment

Tongji University 1. Discrete particle settling The particle maintains its individuality and does not interact with neighboring particles, does not change in size, shape, or density during the settling process. Particles are usually in low solid concentration, and maintain a constant settling velocity. For example, the removal of grit or sand in preliminary treatment

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 sludge￾thickening 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