This document provides an overview of sedimentation as a process for separating solids from liquids by gravity settling. It defines sedimentation and describes types such as plain sedimentation and sedimentation with coagulation. Batch sedimentation is explained through different settling zones. Rate of sedimentation and applications are discussed. Common equipment for batch sedimentation include thickeners and clarifiers. Thickeners are used to concentrate solids while clarifiers purify liquids. Circular and parallel plate clarifiers are described.

1. NAME : SAKHARELIYA SHUBHAM A.
ENROLLMENT NO. : 180470105047
BRANCH : CHEMICAL ENGINEERING
SUBJECT : MECHANICAL OPERATION
PRESENTATION REPORT
SEDIMENTATION

2. OUTLINE
• SEDIMENTATION
 WHAT IS SEDIMENTATION?
 TYPES OF SEDIMENTATION
 TYPES OF SETTLING
 BATCH SEDIMENTATION
 RATE OF SEDIMENTATION
 APPLICATIONS OF SEDIMENTATION
 EQUIPMENTS USED FOR BATCH SEDIMENTATION
 THICKENERS
 CLARIFIERS

3.  WHAT IS SEDIMENTATION ?
 SEDIMENTATION, OR CLARIFICATION, IS THE PROCESS OF LETTING SUSPENDED
MATERIAL SETTLE BY GRAVITY.
 SUSPENDED MATERIAL MAY BE PARTICLES, SUCH AS CLAY OR SALTS, ORIGINALLY
PRESENT IN THE SOURCE WATER.
 MORE COMMONLY, SUSPENDED MATERIAL IS CREATED FROM MATERIAL IN THE
WATER AND THE CHEMICAL USED IN COAGULATION OR IN OTHER TREATMENT
PROCESSES, SUCH AS LIME SOFTENING.
 SEDIMENTATION IS ACCOMPLISHED BY DECREASING THE VELOCITY OF THE WATER
BEING TREATED TO A POINT BELOW WHICH THE PARTICLES WILL NO LONGER REMAIN
IN SUSPENSION.
 WHEN THE VELOCITY NO LONGER SUPPORTS THE TRANSPORT OF THE PARTICLES,
GRAVITY WILL REMOVE THEM FROM THE FLOW.

4.  TYPES OF SEDIMENTATION
 PLAIN SEDIMENTATION :
 WHEN IMPURITIES ARE SEPERATED FROM SUSPENDING FLUID BY ACTION OF NATURAL
FORCE ALONE, WITHOUT AID OF ANY COAGULANT, IS CALLED PLAIN SEDIMENTATION.
 SEDIMENTATION WITH COAGULATION :
 A CHEMICAL PROCESS THAT INVOLVES A NEUTRALISING CHARGE ON THE PARTICLES.
 THIS OCCURS WHEN A COAGULANT IS ADDED TO WATER TO DESTABILISE COLLOIDAL
SUSPENSIONS.

5.  TYPES OF SETTLING
DESCRETE FLOCCULANT HINDERED COMPRESSION

6.  TYPES OF SETTLING
1. DESCRETE SETTLING :
 IN DISCRETE SETTLING INDIVIDUAL
PARTICLES SETTLE INDEPENDENTLY.
 IT OCCURS WHEN THERE IS A
RELATIVELY LOW SOLIDS
CONCENTRATION.
2. FLOCCULANT SETTLING :
 IN FLOCCULANT SETTLING, INDIVIDUAL
PARTICLES STICK TOGETHER INTO CLUMPS
CALLED FLOES.
 THIS OCCURS WHEN THERE IS A GREATER
SOLIDS CONCENTRATION AND CHEMICAL
OR BIOLOGICAL REACTIONS ALTER PARTICLE
SURFACES TO ENHANCE ATTACHMENT.

7.  TYPES OF SETTLING
3. HINDERED SETTLING :
 IN HINDERED SETTLING, PARTICLE
CONCENTRATION IS GREAT ENOUGH TO
INHIBIT WATER MOVEMENT.
 WATER MUST MOVE IN SPACES
BETWEEN PARTICLES.
4. COMPRESSION SETTLING :
 COMPRESSION SETTLING OCCURS
WHEN PARTICLES SETTLE BY
COMPRESSING THE MASS BELOW.

8.  BATCH SEDIMENTATION
1 2 3 4 5

9.  BATCH SEDIMENTATION
 THERE ARE MANY ZONES IN SEDIMENTATION PROCESS.
 FIRST SOLID IS UNIFORMLY DISTRIBUTED IN THE LIQUID.
THE TOTAL DEPTH OF THE SUSPENSION IS ZO.
 AFTER A SHORT TIME THE SOLIDS HAVE SETTLED TO GIVE
A ZONE OF CLEAR LIQUID, ZONE A AND ZONE D OF SETTLED SOLIDS.
 ABOVE D IS A TRANSITION LAYER ZONE C, IN WHICH THE SOLIDS CONTENT VARIES FROM
THAT IN THE ORIGINAL PULP TO THAT IN ZONE D.
 IN ZONE B THE CONCENTRATION IS UNIFORM AND EQUAL TO THE ORIGINAL
CONCENTRATION, SINCE THE SETTLING RATE IS THE SAME THROUGHOUT.
 THE BOUNDARIES BETWEEN ZONES D AND C AND BETWEEN C AND B MAY NOT BE
DISTINCT BUT THE BOUNDARY BETWEEN ZONES A AND B IS USUALLY SHARP.
1 2 3 4 5

10.  BATCH SEDIMENTATION
 AS THE SETTLING CONTINUES, THE DEPTHS OF A AND D
INCREASE. THE DEPTH OF C REMAINS CONSTANT AND OF
B DECREASES.
 EVENTUALLY ZONE B DISAPPEARS AND ALL THE SOLIDS
ARE IN ZONES C AND D.
 THE GRADUAL ACCUMULATION OF SOLIDS PUT STRESS ON THE MATERIAL AT THE
BOTTOM, WHICH COMPRESSES SOLIDS IN LAYER D.
 COMPRESSION BREAKS DOWNS THE STRUCTURE OF THE FLOCS OR AGGREGATES AND
LIQUID IS EXPELLED INTO THE UPPER ZONES.
 WHEN THE WEIGHT OF THE SOLID IS BALANCED BY THE COMPRESSIVE STRENGTH OF THE
FLOCS, THE SETTLING PROCESS STOPS.
 THE ENTIRE PROCESS IS CALLED BATCH SEDIMENTATION.
1 2 3 4 5

11.  RATE OF SEDIMENTATION
 DURING EARLY STAGES OF SETTLING THE VELOCITY IS
CONSTANT, AS SHOWN BY THE FIRST CURVE. WHEN ZONE
B DISAPPEARS, THE RATE OF SETTLING STARTS TO
DECREASE AND STEADILY DROPS UNTIL THE ULTIMATE
HEIGHT IS REACHED.
 THE INITIAL RATE IS A FUNCTION OF THE FEED
CONCENTRATION BUT IN LATE STAGES THE SETTLING
RATE ALSO DEPENDS UPON THE INITIAL HEIGHT, SINCE
COMPRESSION EFFECTS ARE MORE IMPORTANT WITH
THICKER SLUDGE LAYERS.
 EXPERIMENTAL STUDIES OF THE SETTLING RATE FOR
DIFFERENT INITIAL HEIGHTS AND CONCENTRATIONS ARE
NEEDED TO DESIGN A THICKENER.

12.  APPLICATION OF SEDIMENTATION
 APPLICATIONS IN WATER TREATMENT :
 SETTLING OF COAGULATED AND FLOCCULATED WATERS PRIOR TO FILTRATION.
 SETTLING OF COAGULATED AND FLOCCULATED WATERS IN A SOFTENING PLANT.
 SETTLING OF TREATED WATERS IN AN IRON AND MANGANESE REMOVAL PLANT.
 APPLICATIONS IN WASTE WATER TREATMENT :
 IN THE PROCESS OF GRIT REMOVAL.
 SUSPENDED SOLIDS REMOVAL IN PRIMARY CLARIFIER.
 BIOLOGICAL FLOC REMOVAL IN ACTIVATED SLUDGE.

13.  EQUIPMENTS USED FOR BATCH SEDIMENTATION
 THERE ARE TWO TYPES OF EQUIPMENTS WHICH ARE USED FOR SEDIMENTATION :
 thickenerS
 CLARIFIERS
 THICKENERS AND CLARIFIERS ARE BOTH USED TO SEPARATE LIQUIDS AND SOLIDS BY
SETTLING.
 THICKENERS ARE USED TO CONCENTRATE SOLIDS, WHILE CLARIFIERS ARE USED TO PURIFY
LIQUIDS.

14.  THICKENERS
 IN THE TYPE OF THICKENER EQUIPMENT WE USE GRAVITY thickener.
 THICKENING IS THE PROCESS BY WHICH BIO SOLIDS ARE CONDENSED TO PRODUCE A
CONCENTRATED SOLID PRODUCTS.
 THICKENING WASTEWATER SOLID REDUCES THE VOLUME OF RESIDUALS, IMPROVES
OPERATION, AND REDUCES COST FOR SUBSEQUENT STORAGE, PROCESSING, TRANSFER,
END USE, OR DISPOSAL.
 GRAVITY THICKENING USES THE NATURAL TENDENCY OF HIGHER-DENSITY SOLIDS TO
SETTLE OUT OF LIQUID TO CONCENTRATE THE SOLIDS.
 GRAVITY THICKENERS CONSIST OF A CIRCULAR TANK (USUALLY WITH A CONICAL BOTTOM)
THAT IS FITTED WITH COLLECTORS OR SCRAPERS AT THE BOTTOM.
 PRIMARY AND/OR SECONDARY SOLIDS ARE FED INTO THE TANK THROUGH A CENTER
WELL, WHICH RELEASES THE SOLIDS AT A LOW VELOCITY NEAR THE SURFACE OF THE TANK.

15.  THICKENERS
 THE SOLIDS SETTLE TO THE BOTTOM OF THE TANK BY GRAVITY, AND THE SCRAPERS
SLOWLY MOVE THE SETTLED, THICKENED SOLIDS TO A DISCHARGE PIPE AT THE BOTTOM
OF THE TANK.
 A V-NOTCH WEIR LOCATED AT THE TOP OF THE TANK ALLOWS THE SUPERNATANT TO
RETURN TO A CLARIFIER.
 GRAVITY SETTLING OCCURS WHEN SOLID PARTICLES TRAVEL DOWNWARD DUE TO THEIR
WEIGHT.
 SETTLEMENT CONTINUES AS SOLIDS BEGIN TO CONCENTRATE NEAR THE BOTTOM OF THE
TANK, BUT THE SETTLEMENT RATE DECREASES AS THE SOLIDS CONCENTRATIONS
INCREASE.

16.  THICKENERS
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17.  THICKENERS
 SOLIDS AT THE BOTTOM OF THE TANK CAN REACH AS HIGH AS 15 PERCENT TOTAL
SOLIDS(TS). A MORE TYPICAL RESULT IS 4 TO 6 PERCENT.
 LIQUID AT THE SURFACE OF THE TANK IS NEARLY CLEAR, WITH SUSPENDED SOLIDS
CONCENTRATIONS AS LOW AS 200 MG/L.

18.  CLARIFIERS
 THERE ARE TWO TYPES OF CLARIFIERS : 1. CIRCULAR CLARIFIERS
 2. PARALLEL PLATE CLARIFIER
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19.  CLARIFIERS
 CIRCULAR CLARIFIERS :
 THICKENERS AND CLARIFIERS USE
SLOWLY ROTATING RAKE ARMS TO
SEPARATE SOLID PARTICULATE.
 A LIQUID FEED WITH SUSPENDED SOLIDS
IS FED INTO A TANK WITH A DIAMETER
OF 5 TO 500 FEET. AS THE PARTICLES
SETTLE, ANGLED RAKE ARMS MOVE THE
CONCENTRATED SLURRY TOWARD THE
CENTER OF THE TANK, WHERE IT IS
REMOVED.
 CLEAR LIQUID OVERFLOWS AT THE TOP
OF THE TANK AND COLLECTED.
 IN THE THICKENER SHOWN BELOW,
CABLES CONTROLS THE HEIGHT OF THE
RAKE ARMS.
 WHEN HEAVY SLUDGE BUILDS UP AT THE
BOTTOM, THE RAKES ARE RAISED
SLIGHTLY.
 ONCE THE BLOCKAGE HAS BEEN
DISPERSED, THE RAKE ARMS ARE
LOWERED BACK TO NORMAL POSITION.
 ADJUSTABLE RAKE ARMS INCREASE
OPERATING EFFICIENCY BY REDUCING
MAINTENANCE DOWNTIME.

20.  CLARIFIERS
 APPLICATIONS OF CIRCULAR CLARIFIERS :
 CLARIFIERS IS OFTEN USED IN WATER
AND WASTEWATER TREATMENT PLANTS
TO REMOVE SOLIDS, CHEMICALS,
MICROBES AND OTHER IMPURITIES.
 CLARIFIERS IS ALSO USED IN THE PAPER
INDUSTRY, THE URANIUM INDUSTRY, AND
IN ALUMINA, COAL, COPPER, AND IRON
ORE PRODUCTION.
 ADVANTAGES :
 EFFECTIVE SOLID-LIQUID SEPARATION.
 CAN BE USED FOR A VARIETY OF LIQUID-
SOLID SEPARATIONS.
 DISADVANTAGES :
 INEFFICIENT FOR SMALL SCALE
OPERATION.
 LARGE INITIAL INVESTMENT.
 REQUIRES LARGE INSTALLATION AREA.

21.  CLARIFIERS
 PARALLEL PLATE CLARIFIER :
 PARALLEL PLATE CLARIFIERS ARE
DESIGNED TO CREATE LAMINAR FLOW,
ALLOWING GRAVITY TO SEPARATE
HEAVIER ELEMENTS FROM THE REST OF
THE FLUID, AS SHOWN IN FIGURE.
 AS SHOWN IN FIGURE THE SOLID
PARTICLES ARE MOVES TOWARD DOWN
SIDE, OIL PARTICLE RISING ON THE
SURFACE OF OUR LIQUID.

22.  CLARIFIERS
 APPLICATIONS OF PARALLEL PLATE
CLARIFIER :
 PARALLEL PLATE CLARIFIERS ARE OFTEN
USED TO SEPARATE SOLIDS AND LOW
DENSITY LIQUIDS, SUCH AS OILS.
 THEY CAN BE SUITABLE FOR MANY
APPLICATIONS, INCLUDING CHEMICAL
PROCESSING, COOLANT SYSTEMS, FOOD
PROCESSING, OIL REFINERY, PAPER
MAKING, AND INDUSTRIAL WASTE
MANAGEMENT.
 ADVANTAGES :
 LOW SPACE REQUIREMENT.
 NO MOVING PARTS IN SETTLING AREA.
 NO FILTER MEDIA REQUIRED.
 DISADVANTAGES :
 Cannot be used operations larger than
2000 GPM.