View
0
Download
0
Category
Preview:
Citation preview
04/04/2014
1
SEDIMENTATION-1 TEKNOLOGI PENGOLAHAN LIMBAH
Definition separation of unstable and destabilized
suspended solids from a suspension by the
force of gravity
04/04/2014
2
Applications in Wastewater
Treatment
grit removal
suspended solids removal in primary
clarifier
biological floc removal in activated
sludge (secondary clarifier)
Settling of particles from
suspension depends on:
1. Characteristics of the Particles
Discrete Particle: particles whose size, shape and specific gravity do not change with time.
Flocculating particles: particles whose surface properties are such that they aggregate upon contact. Thus, changing in size, shape, and perhaps specific gravity with each contact
04/04/2014
3
Settling of particles from
suspension depends on:
2. Concentration of Particles in Suspension:
Dilute suspension: suspensions in which the
conc. of particles is not sufficient to cause
significant displacement of water as they settle
or in which the particles will not be close
enough for velocity field interference to occur
Concentrated Suspension: suspensions in which
the conc. of particles is too great to meet the
conditions mentioned for dilute suspensions
Basic Theory of Settling
pwpG gVF
2
pwpd
D
vACF
04/04/2014
4
Velocity of Settling
18
)( 2
pwp
p
dgv
Coefficient of drag as a
function of Reynolds Number
04/04/2014
5
SETTING VELOCITY VS PARTICLE DIAMETER
Settling in a Tank
04/04/2014
6
Discrete Settling in 3 types of Basin
GRIT REMOVAL
Sandy material, mostly inorganic, is grit
Mostly between 0.05 and 1 mm in diameter
Considered to be “non-sticky” particles, but are mostly “sticky” particles. Coated with fats, oils and grease in the sewers, increasing buoyancy (upward force)
Need to know true grit size to determine the settling velocity –wet sieving versus dry sieving
If not removed in grit tanks, ends up in digesters
Grit characteristics change with flow rates to the plant
04/04/2014
7
HORIZONTAL-FLOW GRIT CHAMBER
The flow passes through the chamber in a
horizontal direction and the straight-line
velocity
Flow is controlled by the dimensions of the
unit, an influent distribution gate, and a
weir at the effluent end.
Horizontal-flow
Rectangular Square
HORIZONTAL-FLOW GRIT CHAMBER
04/04/2014
8
Typical design information for
horizontal-flow grit chamber
Unit Range Typical
Detention Time s 45-90 60
Horizontal Velocity m/s 0.25-0.4 0.3
Settling velocity for removal of
0.21 mm material m/min 1.0-1.3 1.15
0.15 mm material m/min 0.6-0.9 0.75
Headloss in control section as percent of depth in channel % 30-40 36
Added length allowance for inlet and outlet turbulence % 25-50 30
Aerated Grit Chamber
Nominally designed to remove 0.21-mm-diameter or larger, with 2-to-5-minute detention periods at the peak hourly rate of flow.
Air is introduced along one side of a rectangular tank to create a spiral flow pattern perpendicular to the flow through the tank.
The heavier grit particles that have higher settling velocities settle to the bottom of the tank.
Lighter, principally organic, particles remain in suspension and pass through the tank.
04/04/2014
9
Typical Section Through on Aerated Grit Chamber
04/04/2014
10
Helical Flow Pattern in An Aerated Grit Chamber
Aerated grit chamber with traveling-bridge type grit removal system
04/04/2014
11
Typical design information for aerated grit chamber
Unit Range Typical Detention time at peak flow rate min 2-5 3
Dimensions:
Depth min 2-5
Length min 7.5-20
Width min 2.5-7
Width-depth ratio ratio 1:1 -5:1 1.5:1 Length-width ratio ratio 3:1 - 5:1 4:1 Air supply per unit of length m3/m.min 0.2-0.5
Grit quantities m3/103m3 0.004-0.29 0.0015
04/04/2014
12
VORTEX GRIT CHAMBER
Used in small plants and these require lesser area
Grit is removed with vortex flow pattern
Due to inertia the grit particle will remain in the
chamber and liquid free from grit will only
escape
1. The rotating turbine maintains constant flow velocity, and its adjustable pitch blades promote separation of organics from the grit.
2. The action of the propeller produces a toroidal flow path for grit particles.
3. The grit settles by gravity into the hopper in one revolution of the basin's contents.
4. Solids are removed from the hopper by a grit pump or an airlift pump.
5. Grit removed by a grit pump can be discharged to a hydro-clone for removal of the remaining organic material.
6. Grit removed by an airlift may be dewatered on a wedge wire screen.
04/04/2014
13
Typical design for Vortex grit
chamber
Unit Range Typical
Detention time of average flow rate s 20-30 30
Diameter
Upper chamber m 1.2-7.2
Lower chamber m 0.9-1.8
Height m 2.7-4.8
Removal rates
0.3 mm % 92-98 95
0.24 mm % 80-90 85
0.15 mm % 60-70 65
04/04/2014
14
Next week………
Primary sedimentation tanks
Design calculation for all
sedimentation tanks………….
Recommended