TSWANE UNIVERSITY OF TECHNOLOGY

DEPARTMENT OF CHEMICAL AND METALLURGICAL ENGINEERING

REPORT GRADING FORM

Name of student : Jan Hendrik RobertsStudent number : 211236728

FLOCCULATION AND COAGULATION

3nd Semester 2 Mei 2012Index : Introduction p1 Theoretical background p1 Procedure p2,3 Results p4 Graphs experiment 1 p5-12 Graph experiment 2 p13 Abstract p14 Discussion of results p14 Conclusion and recommendation p 14 Literal cited

Introduction :Raw caused by tiny clay and silt particles. These particles have natural electric charges which keeps them in motion and prevents them from colliding and sticking together. Coagulants are chemicals which are added to the water to neutralize the charges on the particles which helps the particles to collide and stick together and form larger particles.

Theoretical Background : Coagulation is the chemical alteration of colloidal particles to help them stick together and form larger particles called flocs. Flocculation is a physical process that gives assistance in the growth of larger particles. These processes are used to remove suspended matter and colour. Jar tests are the most effective way to determine the correct coagulant, the minimum dose ,and best operating PH for coagulation and flocculation. Aluminium or iron salts are usually used to coagulate particles to form flocs.The objectives of the 2 experiments are : To do the jar test on natural surface water to determine the best dosage of aluminium sulphate needed for the removal of suspended matter and colour. To observe the rate of sedimentation and flocculation.

Procedure :Experiment 1 :Collect 800 ml of surface water in 4 beakers.Measure the PH and turbidity of the water.Add 20 g of CaCO3 in each beaker.Mix at 20 rpm to ensure that the water is completely mixed.Throw 3g, 6g, 9g, and 12 g of Al2SO3 simultaneously into each beaker and mix at 250 rpm for 1 min. Measure the PH and turbidity of each sample.Mix at 60 rpm for 9 minutes.Measure the PH and turbidity of each sample.Mix at 25 rpm for 4 minutes.Measure the PH and turbidity of each sample.Mix at 10 rpm for 2 minutes.Measure the PH and turbidity of each sample.Turn mixer of and leave samples for 20 minutes.Measure the PH and turbidity of each sample.Measure depth of sludge in each beaker.

Experiment 2 :Collect 800 ml of surface water in 4 beakers.Measure the PH and turbidity of the water.Add 20 g of CaCO3 in each beaker.Mix at 20 rpm to ensure that the water is completely mixed.Adjust the PH of each sample to 6, 7, 8, and 9 by using NaOH or H2SO4.Throw optimum dosage of Al2SO3 observed in experiment 1 in each sample simultaneously and mix at 250 rpm for 1 min. Measure the PH and turbidity of each sample.Mix at 60 rpm for 9 minutes.Measure the PH and turbidity of each sample.Mix at 25 rpm for 4 minutes.Measure the PH and turbidity of each sample.Mix at 10 rpm for 2 minutes.Measure the PH and turbidity of each sample.Turn mixer of and leave samples for 20 minutes.Measure the PH and turbidity of each sample.Measure depth of sludge in each beaker.

Results :Table 1 :Initial PH is 7.31

3g Al2SO46g Al2SO49g Al2SO412g Al2SO4

Beaker 1Beaker 2Beaker 3Beaker 4

250 RPM for 1 minPH :5.735.986.176.42

Turbidity :256771633538

60RPM for 9 minPH :6.716.376.296.17

Turbidity :675578799634

25 RPM for 4 minPH :6.926.646.736.69

Turbidity :985852727916

10 RPM for 2 minPH :6.996.76.676.62

Turbidity :593422737979

0 RPM for 20 minPH :6.966.576.476.52

Turbidity :6524.627.560.1

Length of waste at bottom :1.3 cm1.7 cm1.6 cm1.4 cm

Table 2 :PH = 6PH = 7PH = 8PH = 9

6g Al2SO46g Al2SO46g Al2SO46g Al2SO4

Beaker 1Beaker 2Beaker 3Beaker 4

250 RPM for 1 minPH :5.56.456.556.38

Turbidity :689495539530

60RPM for 9 minPH :6.287.146.746.67

Turbidity :577478530598

25 RPM for 4 minPH :6.587.346.956.81

Turbidity :891641860942

10 RPM for 2 minPH :6.77.316.866.88

Turbidity :840612982234

0 RPM for 20 minPH :6.287.026.756.75

Turbidity :11114.170.227.9

Length of waste at bottom :1.1 cm2.2 cm1.3 cm0.9 cm

Data analysis :Experiment 1 :Inverse turbidity vs. dosage.

Time vs. dosage :

Inverse turbidity vs. time :

Log inverse turbidity vs. time :

Experiment 2 :Turbidity vs. PH :

Abstract :Coagulation and flocculation are two very important processes in wastewater and water treatment. Coagulation helps suspended solids two stick together to form flocs and flocculation increases the size of the flocs , and then the solids can settle out of the water. Coagulation has two important mechanisms namely : charge neutralization and bridging. Charge neutralizing occurs when the coagulant neutralizes the charges on suspended colloidal particles. Bridging is when the colloidal particles stick together by virtue of macromolecules formed by the coagulant. When aluminium sulphate is added to water, it dissolves to form Al3+ and SO42-. Lime is added to raise the PH to get the desirable forms aluminium hydroxide. Jar tests are used to choose the best coagulant and the minimum dose. Discussion of results :In experiment 1 the reaction order is 1st order and in experiment 2 its 2nd order. Aluminium sulphate is a very good coagulant when the PH is neutral. In experiment 1 the 2nd beaker had the clearest colour thus the optimum dosage of aluminium sulphate is 6 g. In experiment 2 the 2nd beaker with the PH of 7 had the most settled solids.Conclusion and recommendation :I would recommend to use 6 g of aluminium sulphate with 20 g of carbon hydroxide in normal surface water treatment to settle out the suspended solids.Literal cited :Introduction to chemical engineering 3rd edition.Chemical engineering plant IIIA laboratory guide.Water.me.vccs.edu/courses/env115/coagulation.htmNptel.iitm.ac.in/courses/webcourse-contents/iit-kanpur/wastewater/lecture%209.htm