swt jar testing
DESCRIPTION
Swt Jar TestingTRANSCRIPT
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JAR TESTING: CONSIDERATIONSAND PROCEDURE
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Purpose of Coagulation andFlocculation
�� Remove particulate impurities, especiallynon-settleable solids and color from thewater being treated
�� Non-Settleable solids include colloidalmaterial that exhibits slightly negativecharges repelling one another and staying inSuspension
�� These contain microbes including pathogens
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Removal of Turbidity byCoagulation & Production of Floc
�� Neutralization of repulsive charges
�� Precipitation with sticky flocs
�� Bridging of suspended matter
�� Providing “agglomeration sites” for larger floc
�� Weighting down of floc particles
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Factors Affecting the CoagulationProcess
�� pH (Al from 5 – 7; Fe from 5 – 8)
�� Alkalinity of water (> 30 ppm residual)
�� Concentration of Salts (affect efficiency)
�� Turbidity (constituents and concentration)
�� Type of Coagulant used (Al and Fe salts)
�� Temperature (colder requires more mixing)
�� Adequacy of mixing (dispersion of chemical)
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Primary Coagulants
�� Primary coagulants are lime, aluminumsulfate (alum), ferrous sulfate, ferric sulfateand ferric chloride
�� These inorganic salts will react with thealkalinity in the water to form insoluble flocswhich will trap the suspended matter inthem
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Use of Alum as a Coagulant�� Earliest and Most Widely Used
Coagulant
�� Effective Range pH 5.0 to 7.0 (6.5 optimal)
�� Reacts with Alkalinity
�� Results in drop in pH
�� For every 2 mg/L Alum 1 mg/L Lime is
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Use of Ferrous Sulfate (Copperas)and Lime for Coagulation
�� Combination produces Ferric Hydroxide
�� pH 8.4 range to 9.0
�� Oxygen must added by aeration or chemically such as chlorine
�� Very effective for turbid water
�� Care must be taken because color not removed at high pH
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Use of Ferric Chloride as a Coagulant
�� Has wider pH range than Ferrous Sulfate
�� Typically used where color removal is also desirable
�� Does not require oxygen supplement
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Use of Ferric Sulfate as a Coagulant
�� Does not require oxygen supplement
�� Effective over wider pH ranges
�� Lower doses required that Ferrous Sulfate
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Secondary Coagulants or Coagulant Aids
�� Coagulant aids are often added to help stimulate the production of floc
�� They include sodium aluminate, sodium silicate and various synthetic organic water
soluble polyelectrolytes or polymers
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Desirable Floc Quality�� The best floc are smooth circular
particles that tend to settle quicker
�� Irregular shaped particles settle slower
�� Large clumps (popcorn floc) settle fast but are caused by chemical overdosing
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Performance Measurement Usingthe Jar Test
�� A jar test is a laboratory procedure where varying dosages of coagulant are tested in a series of glass or plastic jars under identical conditions
�� The jars are injected with coagulant dosages and mixed to match flash mix & flocculation field conditions as closely as possible
�� After mixing and settling the jars are observed to determine which dosage produce the largest, strongest floc or which dosage produces the floc that settles the fastest
�� Other laboratory tests sometimes include a jar test to determine the optimal pH or determine the turbidity of the
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Factors Affecting the CoagulationProcess Revisited
�� pH range: 5 – 7
�� Alkalinity of water > 30 PPM residual
�� Concentration of Salts affects efficiency
�� Turbidity (constituents and concentration)
�� Type of Coagulant used (Al and Fe salts)
�� Temperature (colder requires more mixing)
�� Adequacy of mixing (dispersion of chemical)
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Jar Test Apparatus and Procedures
�� Four or six paddles
�� Typically, one container is used as control
�� RPM gauge allows for mixing speeds to match plant conditions for flash mix and flocculation
�� Can be programmable or manual
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Determining Mixing Scheme
10 20 30 40 50 60 70 80 90 100 200
Speed, rpm
500
400
300
200
100
80
60
50
40
30
20
10
G, s-1
Find energy from plant
Then determine mixing speed from graph
Graph Created by Camp, 2930s
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Evaluation of Jar Test Results�� Rate of Floc Formation
�� Type of Floc Particles
�� Clarity of the Water between the Floc
�� Size of the Floc
�� Amount of Floc
�� Clarity of Water above Settled Floc
�� Volume of Floc
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Jar Test Plot for Low AlkalinityWater
�� Alum initially reacts with low alkalinity
�� With Ferric Chloride requires chemical to reach optimal pH before reacting
�� Adding too much l t
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Jar Test Plot for Higher AlkalinityWater
�� Higher Coagulant doses are needed for high alkalinity waters
�� Ferric Chloride required more chemical but reached lower turbidity
�� Since Alum did not produce water <1 NTU a coagulant aid is
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Additional Analyses for Jar Testing�� TOC
�� Alkalinity
�� pH
�� Turbidity of Supernatant
�� Filtered Turbidity of Supernatant
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JAR TESTING PROCEDURE
PurposeTo determine the optimum concentration of coagulant to be added to the source water