1. JARTEST FOR OPTIMUM COAGULANTDOSE
AIM: To determine the optimumdosage of givencoagulant.
GENERAL: Chemical coagulation,flocculationandsedimentationtogetherreduce suspendedand
colloidal solidsandorganicmatter.Alum, ferrousandferricsalts,whenusedforclarification,resultin
producingbettereffluentthanbythe plainsedimentation.The exactdosesof these coagulantscannot
be theoreticallycalculatedandtherefore,laboratorytestshave tobe carriedoutusingthe jar test
procedure.
Remove particulate impurities,especiallynon-settleable solidsandcolorfromthe water beingtreated
Non-Settleable solidsincludecolloidal material thatexhibitsslightlynegativechargesrepellingone
anotherand stayinginSuspension These containmicrobesincludingpathogens
Theory:The amount of coagulantrequiredforcoagulationdependsonthe turbidityof the waste water.
The use of optimumamountof coagulantisindicatedbythe formationof the large featheryflakes.This
can be approximatelydeterminedinthe laboratory byJar test.The testinvolvesrapidmixingtodisperse
the chemicals(coagulants) inthe sample andslow mixingforthe flocformation.
PRINCIPLE:Metal saltshydrolyse inpresence of the natural alkalinitytoformmetal hydroxides.The
multivalentactionscanreduce the zeta-potential.The metal hydroxidesare goodadsorbentsandhence
remove the suspendedparticlesbyenmeshingthem.
REAGENT: StandardAlum/ Ferrous/ Ferricsaltsolution
Prepare standardchemical solutionsuchthat1 ml of solutioncontains10 mg of salt inthe solution.
PROCEDURE:
1. Measure initial turbidityof the sample.
2. Measure 1 literquantitiesof the watertobe testedintoa seriesof glassjars.
3. Place the filledjarsonthe gangstirrer,withthe paddlespositioned identicallyineachbeaker,Attach
to stirringdevice.( Jartestapparatus).
4. Addprogressive volumesof the chemical solutiontoeachof the jars coveringthe range of chemical
dosage expected.
5. Mix rapidlyeachsample for1 minute.
6. Reduce the speedtoabout 10 rpm and mix for15 minutes,(Flocculation).
7. Allowthe floestosettle for15minutes.
8. Measure turbidityof eachsettledsample.
2. 9. Plotgraph % removal of turbidityVs.Coagulantdose andselectthe optimumdosage.% Removal of
TurbidityCoagulantdose
PRECAUTIONS:
1. Add coagulantdosessimultaneouslytoall glassjarswhile stirring.
2. It is advisable tosiphonoutthe settledsample fromthe jarssoas not to disturbthe settledfloc.
OBSERVATIONS:Initial Turbidityof the sample - ---- NTU
3. JAR No 1 2 3 4 5 6
Chemical,
mg/1
Flashmix
time,
inminutes
Slowmix
speed
inr.p.m
Slowmix
time,
inminutes
Temperature,
°C
Time for first
floc
formationin
min
pH
Colour
Turbidity,
NTU
(Initial)
Turbidity,
NTU
(Final)
% removal of
Turbidity
