Springer Nature is making Coronavirus research free. View research | View latest news | Sign up for updates

Coagulation of highly turbid suspensions using magnesium hydroxide: effects of slow mixing conditions

  • 448 Accesses

  • 14 Citations


Laboratory experiments were carried out to study the effects of slow mixing conditions on magnesium hydroxide floc size and strength and to determine the turbidity and total suspended solid (TSS) removal efficiencies during coagulation of highly turbid suspensions. A highly turbid kaolin clay suspension (1,213 ± 36 nephelometric turbidity units (NTU)) was alkalized to pH 10.5 using a 5 M NaOH solution; liquid bittern (LB) equivalent to 536 mg/L of Mg2+ was added as a coagulant, and the suspension was then subjected to previously optimized fast mixing conditions of 100 rpm and 60 s. Slow mixing speed (20, 30, 40, and 50 rpm) and time (10, 20, and 30 min) were then varied, while the temperature was maintained at 20.7 ± 1 °C. The standard practice for coagulation-flocculation jar test ASTM D2035-13 (2013) was followed in all experiments. Relative floc size was monitored using an optical measuring device, photometric dispersion analyzer (PDA 2000). Larger and more shear resistant flocs were obtained at 20 rpm for both 20- and 30-min slow mixing times; however, given the shorter duration for the former, the 20-min slow mixing time was considered to be more energy efficient. For slow mixing camp number (Gt) values in the range of 8,400–90,000, it was found that the mixing speed affected floc size and strength more than the time. Higher-turbidity removal efficiencies were achieved at 20 and 30 rpm, while TSS removal efficiency was higher for the 50-rpm slow mixing speed. Extended slow mixing time of 30 min yielded better turbidity and TSS removal efficiencies at the slower speeds.

This is a preview of subscription content, log in to check access.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9


  1. American Public Health Association (APHA), American Water Works Association (AWWA), Water Environment Federation (WEF) (2012) Standard methods for the examination of water and wastewater, 22nd edn. American Public Health Association, Washington

  2. ASTM D2035-13 (2013) Standard practice for coagulation-flocculation jar test of water. ASTM International

  3. Ayoub GM, Merhebi F (2002) Characteristics and quantities of sludge produced by coagulating wastewater with seawater bittern, lime and caustic. Adv Environ Res 6(3):277–284

  4. Ayoub GM, Merehbi F, Abdallah R, Acra A, El Fadel M (1999) Coagulation of alkalinized municipal wastewater using seawater bittern. Water Environ Res 71:443–453

  5. Ayoub GM, El-Fadel M, Acra A, Abdallah R (2000a) Critical density index for the solar production of bittern from seawater. Int J Environ Stud 58(1):85–97

  6. Ayoub GM, Merhebi F, Acra A, El-Fadel M, Koopman B (2000b) Seawater bittern for the treatment of alkalized industrial effluents. Water Res 34(2):640–656

  7. Ayoub GM, Semerjian L, Acra A, El Fadel M, Koopman B (2001) Heavy metal removal by coagulation with seawater liquid bittern. J Environ Eng 127(3):196–207

  8. Ayoub GM, Hamzeh A, Al-Hindi M (2013) The impact of process sequences on pollutant removal efficiencies in tannery wastewater treatment. Water Air Soil Pollut 224:1379

  9. Barbot E, Dussouillez P, Bottero JY, Moulin P (2010) Coagulation of bentonite suspension by polyelectrolytes or ferric chloride: floc breakage and reformation. Chem Eng J 156(1):83–91

  10. Cornwell DA, Bishop MM (1983) Determining velocity gradients in laboratory and full-scale systems. J Am Water Works Assoc 75(9):470–475

  11. Ebeling JM, Sibrell PL, Ogden SR, Summerfelt ST (2003) Evaluation of chemical coagulation-flocculation aids for the removal of suspended solids and phosphorus from intensive recirculating aquaculture effluent discharge. Aquacult Eng 29(1–2):23–42

  12. Fitzpatrick CSB, Fradin E, Gregory J (2004) Temperature effects on flocculation, using different coagulants. Water Sci Technol 50:171–175

  13. Ghernaout D, Ghernaout B (2012) Sweep flocculation as a second form of charge neutralisation-a review. Desalination Water Treat 44(1–3):15–28

  14. Gregory J (2004) Monitoring floc formation and breakage. Water Sci Technol 50:163–170

  15. Gregory J (2009) Monitoring particle aggregation processes. Adv Colloid Interface Sci 147-148(C):109–123

  16. Gregory J, Dupont V (2001) Properties of flocs produced by water treatment coagulants. Water Sci Technol 44:231–236

  17. Jarvis P, Jefferson B, Parsons S (2004) The duplicity of floc strength. Water Sci Technol 50:63–70

  18. Jarvis P, Jefferson B, Gregory J, Parsons SA (2005a) A review of floc strength and breakage. Water Res 39(14):3121–3137

  19. Jarvis P, Jefferson B, Parsons SA (2005b) Measuring floc structural characteristics. Rev Environ Sci Biotechnol 4(1–2):1–18

  20. Judkins JF, Hornsby JS (1987) Color removal form textile dye waste using magnesium carbonate. Water Pollut Control Fed 50:2446–2456

  21. Kan C, Huang C, Pan JR (2002a) Coagulation of high turbidity water: the effects of rapid mixing. J Water Supply: Res Technol - AQUA 51(2):77–85

  22. Kan C, Huang C, Pan JR (2002b) Time requirement for rapid-mixing in coagulation. Colloids Surf, A 203(1–3):1–9

  23. Kang LS, Cleasby JL (1995) Temperature effects on flocculation kinetics using Fe(III) coagulant. J Environ Eng 121(12):893–901

  24. Leentvaar J, Rebhun M (1982) Effect of magnesium and calcium precipitation on coagulation-flocculation with lime. Water Res 16(5):655–662

  25. Lin JL, Huang C, Pan JR, Wang D (2008) Effect of Al(III) speciation on coagulation of highly turbid water. Chemosphere 72:189–196

  26. Liu T, Chen ZL, Yu WZ, Shen JM, Gregory J (2011) Effect of two-stage coagulant addition on coagulation-ultrafiltration process for treatment of humic-rich water. Water Res 45(14):4260–4268

  27. Manning AJ, Dyer KR (1999) A laboratory examination of floc characteristics with regard to turbulent shearing. Mar Geol 160(1–2):147–170

  28. Muyibi SA, Evison LM (1995) Optimizing physical parameters affecting coagulation of turbid water with Moringa oleifera seeds. Water Res 29(12):2689–2695

  29. Photometric Dispersion Analyser PDA (2000) Operating Manual. (n.d.). Rank Brothers Ltd, Cambridge

  30. Rossini M, Garrido JG, Galluzzo M (1999) Optimization of the coagulation-flocculation treatment: influence of rapid mix parameters. Water Res 33(8):1817–1826

  31. Semerjian L, Ayoub GM (2003) High-pH–magnesium coagulation–flocculation in wastewater treatment. Adv Environ Res 7(2):389–403

  32. Solomentseva I, Bárány S, Gregory J (2007) The effect of mixing on stability and break-up of aggregates formed from aluminum sulfate hydrolysis products. Colloids Surf, A 298(1–2):34–41

  33. Spicer PT, Pratsinis SE, Raper J, Amal R, Bushell G, Meesters G (1998) Effect of shear schedule on particle size, density, and structure during flocculation in stirred tanks. Powder Technol 97(1):26–34

  34. Xiao F, Yi P, Pan XR, Zhang BJ, Lee C (2010) Comparative study of the effects of experimental variables on growth rates of aluminum and iron hydroxide flocs during coagulation and their structural characteristics. Desalination 250(3):902–907

  35. Yeung A, Gibbs A, Pelton R (1997) Effect of shear on the strength of polymer-induced flocs. J Colloid Interface Sci 196(1):113–115

  36. Yu W, Gregory J, Campos L, Li G (2011) The role of mixing conditions on floc growth, breakage and re-growth. Chem Eng J 171(2):425–430

  37. Yukselen MA, Gregory J (2004) The reversibility of floc breakage. Int J Miner Process 73(2–4):251–259

  38. Zhao J, Lin W, Chang Q, Liu W, Wang S, Lai Y (2012) Effects of operational conditions on the floc formation time and rate in magnesium hydroxide coagulation process. Desalination Water Treat 45(1–3):153–160

  39. Zouboulis AI, Traskas G (2005) Comparable evaluation of various commercially available aluminium-based coagulants for the treatment of surface water and for the post-treatment of urban wastewater. J Chem Technol Biotechnol 80(10):1136–1147

Download references


The authors would like to thank the Environmental Engineering Research Center at the American University of Beirut for providing all necessary equipment and assistance during the experimental work.

Author information

Correspondence to Sara W. BinAhmed.

Additional information

Responsible editor: Bingcai Pan

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Ayoub, G.M., BinAhmed, S.W., Al-Hindi, M. et al. Coagulation of highly turbid suspensions using magnesium hydroxide: effects of slow mixing conditions. Environ Sci Pollut Res 21, 10502–10513 (2014).

Download citation


  • Coagulation
  • Flocculation
  • Liquid bittern
  • Magnesium hydroxide
  • Mixing speed
  • Mixing time