Coagulation and Coagulation and FlocculationFlocculation

CE 544CE 544

BackgroundBackground

Importance of the ProcessesImportance of the Processes Destabilization of particles Destabilization of particles

(coagulation)(coagulation) Formation of bigger particles Formation of bigger particles

(flocculation)(flocculation) Remove Suspended Solids and colorRemove Suspended Solids and color

Why experimentWhy experiment Needed to design treatment plantsNeeded to design treatment plants

CoagulantsCoagulants

Aluminum and Iron salts are usedAluminum and Iron salts are used Form settleable floc composed of Form settleable floc composed of

hydrous metal oxides and impuritieshydrous metal oxides and impurities Coagulate particlesCoagulate particles

Jar TestJar Test

Used to control of plant operationsUsed to control of plant operations Routinely used by operatorsRoutinely used by operators Indicate optimum coagulant doseIndicate optimum coagulant dose Indicates optimum pHIndicates optimum pH Indicates rate of agglomeration as a Indicates rate of agglomeration as a

function of energy input (paddle function of energy input (paddle speed)speed)

Jar TestJar Test

Indicates settleability of formed flocsIndicates settleability of formed flocs Indicates clarity and pH of Indicates clarity and pH of

supernatantsupernatant Used to study kinetic reactionUsed to study kinetic reaction Indicates removal of trace Indicates removal of trace

constituentsconstituents

ObjectivesObjectives

Conduct jar tests on synthetic surface Conduct jar tests on synthetic surface water to:water to:

estimate optimum coagulant dose and estimate optimum coagulant dose and optimum pHoptimum pH

observe rate of floc formationobserve rate of floc formation observe rate of flocculationobserve rate of flocculation

Optimum DoseOptimum Dose

1.1. Constitute 50 liters of synthetic Constitute 50 liters of synthetic surface water and determine:surface water and determine:

pHpH TurbidityTurbidity Color (after filtration)Color (after filtration) AlkalinityAlkalinity Water temperatureWater temperature Ambient temperatureAmbient temperature

2.2. Use coffee and clay to augment Use coffee and clay to augment turbidity (40 NTU) and color (80 turbidity (40 NTU) and color (80 color units)color units)

3.3. Calculate alkalinity required to react Calculate alkalinity required to react with max dose of coagulantwith max dose of coagulant

4.4. If alkalinity is not enough, use If alkalinity is not enough, use NaNa22COCO33 to reach at least 0.5 meq/l to reach at least 0.5 meq/l (25 mg/l as CaCO(25 mg/l as CaCO33) and measure pH) and measure pH

5.5. Prepare coagulants: Aluminum and Prepare coagulants: Aluminum and ferric sulfatesferric sulfates

6.6. Use the jar test apparatus (6 jars)Use the jar test apparatus (6 jars)

7.7. Add coagulant to 5 jars and perform Add coagulant to 5 jars and perform rapid mix at 100 rpm for 1 minute rapid mix at 100 rpm for 1 minute (keep the sixth jar as a control)(keep the sixth jar as a control)

8.8. Flocculate at three different speeds Flocculate at three different speeds and for three different timesand for three different times

9.9. In each case, record elapsed time In each case, record elapsed time before a visible floc is formedbefore a visible floc is formed

10.10. Remove paddles and settle till most Remove paddles and settle till most of the flocs are removed from of the flocs are removed from suspensionsuspension

11.11. Collect samples every two minutes Collect samples every two minutes till settling is completetill settling is complete

12.12. Analyze samples for turbidity and Analyze samples for turbidity and plot turbidity vs. timeplot turbidity vs. time

13.13. Measure pH and depth of sludgeMeasure pH and depth of sludge

14.14. Estimate volume of sludgeEstimate volume of sludge

15.15. Select optimum dose based on Select optimum dose based on clarity of supernatant and clarity of supernatant and settleability of flocssettleability of flocs

16.16. Repeat test with different range of Repeat test with different range of coagulant dose, if results are not coagulant dose, if results are not satisfactory or need to narrow satisfactory or need to narrow down the range of optimum dose down the range of optimum dose

Optimum pHOptimum pH

1.1. Repeat the test using optimum Repeat the test using optimum coagulant dose but adjusting pH to 6, coagulant dose but adjusting pH to 6, 7, 8, 9 with NaOH or H7, 8, 9 with NaOH or H22SOSO44 before before adding the coagulantadding the coagulant

2.2. Measure final pH and turbidity of each Measure final pH and turbidity of each collected samplecollected sample

3.3. Measure depth of sludgeMeasure depth of sludge

4.4. Plot turbidity vs initial pH and final pHPlot turbidity vs initial pH and final pH

5.5. Select optimum pHSelect optimum pH

Microscopic ExaminationMicroscopic Examination

1.1. Examine samples of water before Examine samples of water before and after treatmentand after treatment

2.2. Describe the nature of materials Describe the nature of materials observedobserved

3.3. Estimate the size of particleEstimate the size of particle

Coagulation + Activated Coagulation + Activated CarbonCarbon

1.1. If color was not removed If color was not removed efficiently, use activated carbon at efficiently, use activated carbon at different dosesdifferent doses

2.2. Develop a procedure such that Develop a procedure such that color can be removed effectivelycolor can be removed effectively

Effect of Mixing Time Effect of Mixing Time (Tapered)(Tapered)

1.1. Prepare identical optimum coagulant Prepare identical optimum coagulant dose for all the six jarsdose for all the six jars

2.2. Use rapid mix for all (as before)Use rapid mix for all (as before)

3.3. Reduce mixing to 30 rpm (slow mixing)Reduce mixing to 30 rpm (slow mixing)

4.4. Use different times for slow mixing (5, Use different times for slow mixing (5, 10, 15, 20, 30, 45 minutes) for the six 10, 15, 20, 30, 45 minutes) for the six jarsjars

5.5. Stop mixing and carefully lift the Stop mixing and carefully lift the paddlespaddles

6.6. Allow 30 minutes for settlingAllow 30 minutes for settling

7.7. Measure turbidity and pH of the Measure turbidity and pH of the supernatantsupernatant

Removal of Removal of MicroorganismsMicroorganisms

With prepared culture, examine the With prepared culture, examine the efficiency of removal at optimum efficiency of removal at optimum dose and pHdose and pH

Analysis and ProblemsAnalysis and Problems

See manualSee manual