Environmental Engineering Lab 1 Coagulation and Flocculation

I. Introduction Coagulation and flocculation are important unit processes utilized in water treatment. Coagulation involves the addition of chemicals (coagulants) during relatively intensive mixing to destabilize naturally occurring particles and macromolecules and/or to precipitate additional particles. In flocculation, a period of less intense mixing is utilized to promote the aggregation of destabilized particles into larger flocs which can be removed subsequently by sedimentation and/or filtration. During coagulation and flocculation, various dissolved ions and molecules may be adsorbed by particles or may be precipitated, depending on the type and concentration of species considered and on the overall solution chemistry. A useful laboratory experiment for evaluating coagulation and flocculation is the jar test. This test involves an examination of the effects of coagulant addition, mixing and settling on water quality parameters such as turbidity, color, total organic carbon, pH, dissolved ions, and alkalinity. The jar test is often utilized during the design of treatment facilities and in the routine operation of treatment plants. Jar tests are used primarily to determine the optimal chemical dosages for the removal of turbidity (particles), color, organic matter, metals (e. g., arsenic), and to assess the need for pH adjustment. The test can also be used to examine issues such as: the effect of powder activated carbon or polymer addition; the effect of mixing intensity and duration on coagulation/flocculation; the effect of detention time on floc sedimentation; the kinetics of particle aggregation; and/or the removal of trace constituents. II. Objective To conduct jar tests on a natural surface water in order to estimate an optimum dosage of Alum (aluminum sulfate - hydrous) and Ferric Chloride for removal of suspended matter and organics and to observe the rate of formation and the sedimentation of floc. III. Materials 0 Six-place laboratory jar test apparatus 0 Turbidimeter 0 pH meter o Hach Hardness Kit 0 Hach Alkalinity Test Kit 0 Chemicals - alum solution, ferric chloride, polymer IV. Procedure Three stations of jar tests will be conducted to test 3 different coagulants: Jar Test Station #1- Alum (A12(SO4)3) Jar Test Station #2- Ferric Chloride (FeCl3) Jar Test Station #3- Ferric Chloride (FeCl3) + 1 mg/L of Polymer Each jar test station has 6 jars, corresponding to the following coagulant dosages: 0, 10, 20, 30, 40, 50 mg/L.