1 Lake water (raw) Flocculation Flash mix Gentle mix Quiescent condition Sedimentation Precipitation Coagulant

Coagulation Flocculation/Sedimentation 2

Coagulation Flocculation 3

Jar Test 4 Objective: To determine the best coagulant and optimum coagulant dose Reference: ASTM D Standard Practice for Coagulation-Flocculation Jar Test of Water

Jar Test - Procedure 1.Place 2000 mL of raw water in each 2 L nominal size beaker and set them on the jar tester. 2.To simulate flash mixing, begin by initiating mixing for all six beakers at 100 rpm. Then, add a predetermined amount of coagulant solution to each beaker as quickly as possible. Note that if a coagulant aid is added, it should be added separately 3.To simulate tapered flocculation, mix as follows: 7.5 min at a mixing speed of 70 rpm 7.5 min at a mixing speed of 40 rpm 7.5 min at mixing speed of 25 rpm 4.Settle for 20 min and analyze the supernatant 5

Advantage of 2-L Square Jars  Better mixing  Mixing curve available  Plexglas®: Better insulating properties  More water for testing – 2 liters  Standard Sampling location (10 cm) used to set settling velocity  Do not use glass beaker due to poor insulation and inability of simulating mixing conditions in the field 6

Velocity Gradient vs. Mixing Speed Velocity Gradient, G, s Rotational Speed of Paddle, rpm 10°C < t  32°C (µ = 1.29 × N·sec/m 2 ) 1°C  t  10°C (µ = 2.57 × N·sec/m 2 ) A p : × C D : 1.8 : ×  : V 7

Jar Test - Measurements 1.Time: Record the minimum time required to form “pinpoint” floc during flocculation step. 2.Size: At the end of the flocculation step, record the size of the majority floc: 3.Water quality: Measure temp., turbidity, and pH 4.Filtrability: Filter 70 mL of the supernatant through Whatman No. 1 or similar filter paper (1~2 µm pore size) and record the time required to filter 50 mL of the sample. Measure the turbidity of the filtrate mm A B C D E F G Size Settleable floc 8

Jar Test - Optimization 1.Optimization of Coagulant: Alum or ferric chloride with cationic polymers as a coagulant aid 2.Proper Dosage: (1) a wide range of dosages: 2.5, 5, 10, 20, 40, and 80 mg/L of coagulant; (2) a refinement Optimization of Coagulant Aid: The suggested dosages are 0.25, 0.5, 1.2, and 4 mg/L Example Dosage Alum (mg/L) polymer (mg/L)

Coagulation - A Multidimensional View 10

Coagulation - Data Fitting Jar Test TOC Result 3-D Plot 11

Coagulation - Fitting Data Contour plot Best way of determining the optimum condition 12

Alum Contour Mapping Turbidity DOC Experimental condition Optimum pH 5.9 & Alum 41 mg/L Optimum pH 5.82 & Alum 47 mg/L Select optimum condition based on the goal of water treatment 13

Floc Settling Velocity Measurement Procedure: 1.After the completion of flocculation, collect mL samples at 1, 2, 4, 8, and 16 minutes by pipetting or siphoning from a fixed depth of 10 cm from the original water level and measure turbidity. The fixed depth represents settling velocities of 10, 5, 2.5, 1.25, and 0.63 cm/min, respectively. 2.Plot the turbidity of the settled water samples at the designated times divided by velocities and the corresponding settling velocity in the log- probability scale. 14

Two-Liter Jar for Bench-Scale Testing Jar test reference: 15

Example Plot % Turbidity remaining Initial turbidity = 500 NTU 100 NTU 10 NTU Settling velocity, ft/sec Overflow rate, gpd/ft 2 16

17 Flocculation tank in a water treatment plant

Gravity Settlement Conventional/traditional Sedimentation tank Flocculation tank 18