Coagulation and Flocculation CE 544 Coagulation and Flocculation

Background Importance of the Processes Why experiment Destabilization of particles (coagulation) Formation of bigger particles (flocculation) Remove Suspended Solids and color Why experiment Needed to design treatment plants

Coagulants Aluminum and Iron salts are used Form settleable floc composed of hydrous metal oxides and impurities Coagulate particles

Jar Test Used to control of plant operations Routinely used by operators Indicate optimum coagulant dose Indicates optimum pH Indicates rate of agglomeration as a function of energy input (paddle speed)

Jar Test Indicates settleability of formed flocs Indicates clarity and pH of supernatant Used to study kinetic reaction Indicates removal of trace constituents

Objectives Conduct jar tests on synthetic surface water to: estimate optimum coagulant dose and optimum pH observe rate of floc formation observe rate of flocculation

Optimum Dose Constitute 50 liters of synthetic surface water and determine: pH Turbidity Color (after filtration) Alkalinity Water temperature Ambient temperature

Use coffee and clay to augment turbidity (40 NTU) and color (80 color units) Calculate alkalinity required to react with max dose of coagulant If alkalinity is not enough, use Na2CO3 to reach at least 0.5 meq/l (25 mg/l as CaCO3) and measure pH Prepare coagulants: Aluminum and ferric sulfates Use the jar test apparatus (6 jars)

Add coagulant to 5 jars and perform rapid mix at 100 rpm for 1 minute (keep the sixth jar as a control) Flocculate at three different speeds and for three different times In each case, record elapsed time before a visible floc is formed Remove paddles and settle till most of the flocs are removed from suspension Collect samples every two minutes till settling is complete

Analyze samples for turbidity and plot turbidity vs. time Measure pH and depth of sludge Estimate volume of sludge Select optimum dose based on clarity of supernatant and settleability of flocs Repeat test with different range of coagulant dose, if results are not satisfactory or need to narrow down the range of optimum dose

Optimum pH Repeat the test using optimum coagulant dose but adjusting pH to 6, 7, 8, 9 with NaOH or H2SO4 before adding the coagulant Measure final pH and turbidity of each collected sample Measure depth of sludge Plot turbidity vs initial pH and final pH Select optimum pH

Microscopic Examination Examine samples of water before and after treatment Describe the nature of materials observed Estimate the size of particle

Coagulation + Activated Carbon If color was not removed efficiently, use activated carbon at different doses Develop a procedure such that color can be removed effectively

Effect of Mixing Time (Tapered) Prepare identical optimum coagulant dose for all the six jars Use rapid mix for all (as before) Reduce mixing to 30 rpm (slow mixing) Use different times for slow mixing (5, 10, 15, 20, 30, 45 minutes) for the six jars Stop mixing and carefully lift the paddles

Allow 30 minutes for settling Measure turbidity and pH of the supernatant

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

Analysis and Problems See manual