EXPERIMENT#5Removal of Contaminants in water sample (JAR

TEST)

Prepared by: Engr.Iftikhar Azim

Introduction Naturally occurring silt particles suspended in water are difficult to remove because they are very small, often colloidal in size, and possess negative charges, and are thus prevented from coming together to form large particles that could more readily be settled out.

The removal of these particles by settling requires first that their charges be neutralized and second that the particles be encouraged to collide with each other.

Introduction

The charge neutralization is called coagulation, and the building of larger flocs from smaller particles is called flocculation.

Introduction Flocculation or floculation, is the process of adding a flocculant, coagulant or other catalyst to dirty water or wastewater. The flocculant then binds with the contaminants to form flocculent or floc. This process is a critical part of virtually all wastewater treatment. Separating solids from liquid is the primary basis of the treatment of "wastewater"

Continued…

Flocculants are the chemicals or substances that facilitate flocculation or floccing up of suspended solids in liquid, the resulting floc or wooly mass itself is called flocculent with an "e" however sometimes the terms are used interchangeably

Continued… Flocculation normally follows coagulation and essentially is the 'bridging' of coagulated particles to form larger flocs which can then settle (or float) quicker.

Coagulation is a preferred method for water treatment, in wastewater treatment it is mostly used when finely dispersed colloids with lower mass concentration have to be removed. On the other end for sludge dewatering flocculation is preferred.

Continued… Flocculation: Process by which clumps of solids in water or sewage aggregate through biological or chemical action so they can be separated from water or sewage.

 Coagulation: Clumping of particles in wastewater to settle out impurities, often induced by chemicals such as lime, alum, and iron salts

Jar Testing

Purpose  of the test The primary purpose of the coagulation/flocculation process is the removal of turbidity from the water.  Turbidity is a cloudy appearance of water caused by small particles suspended therein.  Water with little or no turbidity will be clear.

Why do we need such a complex process to remove particles from water?

Some particles would settle out of the water on their own, given enough time.  But other particles would resist settling for days or months due to small particle size and to electrical charges between the particles. 

Apparatus required Ferric Chloride

Calcium bi-carbonate or Sodium Hydroxide

Electric Stirrer

Turbidimeter

Procedure Prepare a bucket of turbid water by adding soil and a little clay to a bucket of tap water.

Prepare a solution of Ferric chloride (coagulant).

Fill each of six 1-liter beakers with the turbid water making sure that the same volume of water is added to each beaker, and that the water is of uniform turbidity.

Place the beakers on the stirrer, and stir the contents of all beakers at maximum speed.

Rapidly add varying doses of coagulant to the beakers. Record time. Stir at maximum speed for one minute (Rapid mixing).

Continued… Reduce the speed to half of the last speed and stir for 5 minutes. Reduce speed to half of the last speed and stir for another 5 minutes. (This promotes floc formation.)

Compare the floc sizes and characteristics in the six beakers.

Stop the stirrer and observe the settling of floc particles. Compare the clarity of water in different beakers.

Measure and record the turbidity of settled water in each beaker.

Plot measured turbidity as a function of coagulant dose.

50 100 150 200 250 300 350 4000

2

4

6

8

10

12

Alum dose

Alum dose

Optimum dose

Turbidit

y remainin

g