CIVL 375 Experiment REMOVAL OF COLLOIDAL PARTICLES BY COAGULATION Introduction Coagulation is the destabilisation and initial aggregation of colloidal and finely divided suspended matter (colloidal particles) by addition of floc-forming chemical such as aluminium sulphate (alum) or one of the iron coagulants The flocculation process is the agglomeration of collected and finely divided suspended matter after coagulation by gently stirring through either mechanical or hydraulic means Optimum removal of colloidal particles from water and wastewater depends on, among other factors, the type of coagulant used, the dose, and the pH Objective To determine the optimum coagulant dosage for removal of colloidal particles from the provided sample Equipment and Reagents (a) Equipment and glassware Jar test apparatus pH meter Turbidimeter Six 1-L beakers Five 100-ml beakers Pipettes (b) Reagents A coagulant (either aluminium sulphate (Al 2(SO4)3.16H2O or ferric chloride FeCl3) at a concentration of 1% Every ml of this coagulant solution gives a concentration of 10 mg/L when added to liter of sample Schematic of the Jar Test Apparatus Procedure Transfer liter of the sample to each 1-L beaker and place on stirrer base Immerse paddles to a fixed depth below liquid surface in the beakers Set paddles to rotate at 100 RPM Add a given volume of the coagulant solution to each of the five 100-ml beakers as directed by the engineer (commonly 1, 2, 5, 10, and 20 ml with one beaker is left without addition of coagulant) Add the coagulant dose in the 100-ml beakers to five of the 1-L beakers while the paddles are rotating Make sure that there is no significant time difference between the additions of coagulant to different beakers Use the sixth 1-L beaker as a blank (i.e don’t add a coagulant to this beaker) Stir for approximately minute at 100 RPM, then reduce the speed of stirring to 30 RPM for additional 20 minutes Rapid mixing allows distributing the coagulant uniformly within the solution while slow mixing allows flocculation of the particles Stop stirring, lift the paddles from the solution, and allow sample to stand for about 30 minutes Sample the supernatant of each beaker without shaking or stirring the settled portion Measure the pH, alkalinity and suspended solids of the withdrawn sample from each beaker 10 A table similar to the one shown below should be filled Beaker Coagulant dose ml Coagulant dose mg/l 0 blank pH Alkalinity Suspended solids mg/l Requirements: Fill out the provided experiment data sheet and carry out the required calculations If you are requested to submit a report of this experiment then your report should contain (a) an introduction that ends with the objective (b) methodology including sample identification (c) results and discussion (d) conclusion (e) references and (f) an appendix that contains the filled data sheet CIVL375: Experiment Data Sheet REMOVAL OF COLLOIDAL PARTICLES BY COAGULATION Name ID Experimental Conditions Experiment date Sample identification Coagulant used Coagulant solution concentration, % Sample suspended concentration, mg/l Sample alkalinity, mg/l as CaCO3 Rapid mixing time, seconds Slow mixing time, minutes Settling time, minutes Jar Test Results Jar No Coagulant dose (ml of coagulant solution) Coagulant dose (mg/l) pH Suspended solids (mg/l) Required Calculations Plot pH versus coagulant dose (mg/l) Plot suspended solids versus coagulant dose (mg/l) Plot alkalinity versus coagulant dose (mg/l) What is the optimum dose? Alkalinity (mg/l as CaCO3)