Lab Bench – Scale Jar Testing for Coagulants & Flocculants

Process wastewater treatment typically involves the removal of suspended particles from solution, referred to as solid/liquid separation.  The suspended particles of concern in the tests procedures discussed below are metallic precipitate.  Such particles are removed by settling, filtration, flotation, or other such means.

Coagulants and flocculants are used to facilitate the removal of suspended particles from waste waters.  Although jar tests procedures should be tailored to closely match actual plant conditions, some experimentation is required since full scale conditions are only approximated in jar testing.  The suggested procedures that follow can be used to determine the most effective dilution ratio and/or dosage of the recommended coagulants and flocculants.  The results obtained using these procedures are influenced by the chemical dosage, mixing energy, and length of mixing.


  1. Draw a sample of the wastewater, after the pH adjustment and precipitation operations, in a clear beaker. A visual inspection of the sample may determine whether coagulants and/or flocculants are required to assist in the removal of suspended particles. If the solution appears hazy or cloudy, the suspended particles are colloidal (finely dispersed throughout the solution) and will not settle. A coagulant with a cationic charge must be used to destabilize the particles and form larger particles (flocs). If the particles appear to be settling but need assistance to accelerate their settling, a flocculant with an anionic charge may be all that is needed to accelerate the settling of the stabilized particles.
  2. Pour an equal amount of the sample into several beakers. Number each beaker and prepare a log sheet to record the activity for each beaker..
  3. To determine the proper dilution ratio for the coagulant or flocculant, start with the recommended dilution ratio on the Product Information Bulletin, and pour it in a beaker. Then prepare different dilution ratios in several beakers and go to step 5. Record the data for each beaker.
  4. To determine the proper dosage, prepare the dilution ratio recommended on the Product Information Bulletin, or as determined in step 3 above, and put varying amounts of the same dilution ratio in each beaker. Record the amounts for each beaker.
  5. Mix the solutions using a lab-type magnetic or mechanical stirrer. Coagulants are dosed with high energy to disperse them in the water and promote agglomeration by increased frequency of particle collisions. The duration may be short, less than 1 to 3 minutes. Flocculants are typically added during the last few seconds of the rapid mix (used for coagulants), followed by a slow mix to allow floc building. After slow mixing for an optimum period of time, which is determined by repeat tests usually from 5 to 15 minutes, place the jars side-by-side and allow to settle for 5-10 minutes.
  6. Observe, compare and record the results. Compare floc formation and settling rates, final clarity or suspended solids content, and volume of sludge produced (if measurable) between jars. For most wastewater treatment purposes, the results can be judged by eye, although instrumentation provides more accurate measurement.

To test each of the above procedures for effectiveness in removing particles containing toxic metals from wastewater, filter the treated solution after each test and analyze the filtrate for metals of interest with an analytical instrument, such as an atomic adsorption spectrophotometer (AA).


To determine the settling attributes of an anionic flocculant, graduated cylinders can be used in place of the beakers . Number the cylinders to record each test and proceed with testing as described in items 2,3 and 4 above. Mix the solutions by inverting each cylinder (equal number for each). Set the cylinders upright and observe the interface between the water and the settling solids. Record and compare time and solids levels for each cylinder.

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