Comparison of Flocculation Characteristics of Humic Acid by Inorganic and Organic Coagulants: Effects of pH and Ionic Strength

  • Xu Mei-Lan (Division of Civil and Environmental Engineering, Cheju National University) ;
  • Lee Min-Gyu (Division of Applied Chemical Engineering, Pukyong National University) ;
  • Kam Sang-Kyu (Division of Civil and Environmental Engineering, Cheju National University)
  • Published : 2005.08.01


The effects of pH (5, 7 and 9) and ionic strength of different salts on the flocculation characteristics of humic acid by inorganic (alum, polyaluminum chloride (PAC) with degree of neutralization, r=(OH/Al) of 1.7) and organic (cationic polyelectrolyte) coagulants, have been examined using a simple continuous optical technique, coupled with measurements of zeta potential. The results are compared mainly by the mechanisms of its destabilization and subsequent removal. The destabilization and subsequent removal of humic acid by PAC and cationic polyelectrolyte occur by a simple charge neutralization, regardless of pH of the solution. However, the mechanism of those by alum is greatly dependent on pH and coagulant dosage, i.e., both mechanisms of charge neutralization at lower dosages and sweep flocculation at higher dosages at pH 5, by sweep flocculation mechanism at pH 7, and little flocculation because of electrostatic repulsion between negatively charged humic acid and aluminum species at pH 9. The ionic strength also affects those greatly, mainly based on the charge of salts, and so is more evident for the salts of highly charged cationic species, such as $CaCl_2$ and $MgCI_2.$ However, it is found that the salts have no effect on those at the optimum dosage for alum acting by the mechanism of sweep flocculation at pH 7, regardless of their charge.


Flocculation;Humic Acid;pH;Ionic strength;Inorganic and organic coagulants;Zeta potential


  1. Smeds, A., R. Franzen and L. Kronberg, 1995, Occurrence of some chlorinated enol lactones and cyclopentane-1,3-diones in chlorine-treated waters, Environ. Sci. Technol., 29(7), 1839-1844
  2. Nobukawa, T. and S. Sanukida, 2000, Genotoxicity of halogenated by-products in the disinfected waters, Text of Posters of 1st IWA World Water Congress, Paris, France, Np-049
  3. Vik, E. A. and B. Eikebrokk, 1989, Coagulation process for removal of humic substances from drinking water, In Suffet, I. H. and P. MacCarthy (eds.,), Influence on fate and Treatment of Pollutants, American Chemical Society, Washington D.C., 385-408pp
  4. Rebhun, M. and M. Lurie, 1993, Control of organic matter by coagulation and floc separation, Water Sci. Technol., 27(11), 1-20
  5. Tipping, E., 1993, Modelling ion binding by humic acids, Colloids & Surfaces A, 73, 117-131
  6. Hintelmann, H., P. M. Welbourn and R. D. Evans, 1997, Measurement of complexation of methylmercury(II) compounds by freshwater humic substances using equilibrium dialysis, Environ. Sci. Technol., 31(2), 489-495
  7. Duan, J. and J. Gregory, 2003, Coagulation by hydrolysing metal salts, Adv. Colloid Interface Sci., 100-102, 475-502
  8. Semmens, M. J. and T. K. Field, 1980, Coagulation: Experiences on organics removal, J. Am. Water Works Assoc., 72, 476-483
  9. Kam, S. K., C. S. Moon, D. K. Kim, B. C. Ko and C. G. Hu, 2002, Effects of mixing intensity and dosages on flocculation of particles in water by cationic polyelectrolytes, Bull. Mar. Environ. Res. Inst. CNU, 26, 79-87
  10. Gregory, J., 1996, Polymer adsorption and flocculation, In Finch, C. A. (ed.), Industrial Water Soluble Polymers, Royal Society of Chemistry, Cambridge, UK, 62-75pp
  11. Kretzschmar, R., H. Holthoff and H. Sticher, 1998, Influence of pH and humic acid on coagulation kinetics of kaolinite: a dynamic light scattering study, J. Colloid Interface Sci., 202, 95-103
  12. Lee, M. G. and S. K. Kam, 2005, Charge determination of cationic polyelectrolytes by visual titrimetry and spectrophotomemrty, J. Environ. Sci., 14(6), 525-532
  13. Lee, S. Y., 1991, The flocculation of charged particles in aqueous solutions by cationic polyelectrolytes, Ph.D. Thesis, University College London, UK, 164pp
  14. Wang, D., H. Tang and J. Gregory, 2002, Relative importance of charge neutralization and precipitation on coagulation of kaoline with PACl: effect of sulfate ion, Environ. Sci. Technol., 36, 1815-1820
  15. Lee, S. Y. and J. Gregory, 1990, The effect of charge density and molecular mass of cationic polymers on flocculation kinetics in aqueous solution, Water Supply, 8, 11-17
  16. Kam, S. K., D. K. Kim, C. S. Moon, B. C. Ko and M. G. Lee, 2002, Flocculation characteristics of kaoline suspensions in water by cationic polyelectrolytes, J. Environ. Sci., 11(2), 93-102
  17. Gregory, J. and D. W. Nelson, 1986, Monitoring of aggregates in flowing suspensions, Colloids & Surfaces, 18, 175-188
  18. Letterman, R. D. and S. G. Vandebrook, 1983, Effect of solution chemistry on coagulation with hydrolyzed Al(III): significance of sulfate ion and pH, Water Res., 17(2), 195-204
  19. Dentel, K., 1991, Coagulant control in water treatment, CRC Crit. Rev. Environ. Control, 21, 41-135
  20. Hall, E. S. and R. F. Packham, 1965, Coagulation of organic matter with hydrolyzing coagulants, J. Am. Water Works Assoc., 57(9), 11-49
  21. Edzwald, J. K. and J. E. Tobiason, 1999, Enhanced coagulation: US requirements and a broader view, Water Sci. Technol., 40(9), 63-70
  22. Park, S. J., H. S. Lee and T. I. Yoon, 2002, Evaluation of dominant mechanisms for soluble humic acid removal in coagulation process by aluminum sulfate, J. Kor. Soc. Environ. Eng., 24(9), 1623-1631
  23. Gregory, J. and V. Dupont, 2001, Properties of floes produced by water treatment coagulants, Water Sci. Technol., 44(10), 231-236
  24. Wall, N. A. and G. R. Chopp in, 2003, Humic acids coagulation: influence of divalent cations, Appl. Geochem., 18, 1573-1582
  25. Kam, S. K. and J. Gregory, 2001I, The interaction of humic substances with cationic polyelectrolytes, Water Res., 35(15), 3557-3566