International Journal of Environment Science and Technology Center for Environment and Energy Research and Studies (CEERS) ISSN: 1735-1472 EISSN: 1735-2630 Vol. 3, Num. 2, 2006, pp. 153-157

International Journal of Enviornmental Science and Technology, Vol. 3, No. 2, Spring 2006, pp. 153-157

The removal of color and COD from wastewater containing water base color by coagulation process

^*H. Asilian, Sh. Moradian fard, A. Rezaei, S. B. Mortazavi and A. Khavanin

Department of Occupational and Environmental Health, Faculty of Medical Sciences, Tarbiat Modares University, Tehran, Iran

Received 8 January 2006; revised 12 March 2006; accepted 20 March 2006; available online 20 April 2006

*Corresponding Author, E-mail: asilianm@yahoo.com

Code Number: st06019

ABSTRACT

In this study acrylic water base color was removed from synthetic wastewater using coagulation process. Experiments were conducted on the sample containing 100 mg/L and 400 mg/L of acrylic water base color. Destruction of color by means of coagulation/flocculation techniques using ferrous sulfate, alum, lime and polyelectrolyte (cationic, anionic and non ionic).The study was performed in a systematic approach searching optimum values of alum and FeSO₄ concentration, pH and temperature. All the experiments were run in a laboratory scale .The obtained results show that treatment with alum and ferrous sulfate alone proved to be very effective in removing the color (> 99 %) and part of COD (60-70 %) from aqueous solution. Lime alone did not significant change on COD and color removal.

Key words: Color and COD removal, coagulation, ferrous sulfate, alum, lime, aqueous solution

INTRODUCTION

Water base paint were the earliest type of paint and go to the dawn of history .water born coating have been around in one form or another for decades but have demonstrated greatly improved performance characteristics in recent years Water base or aqueous coating can be divided roughly in to three types. Water-soluble or water-reducible coating are coatings in which a resin in actually dissolved in the water phase. Colloidal or water solubilized dispersion coating are on intermediate between water soluble and emulsion coatings. Latex or emulsion coatings have resins dispersed in water that are stabilized by emulsifiers rather than dissolved. Acrylic paint is a synthetic media made by suspending pigment in synthetic polymer emulsified by water. They are essentially plastic paints that are water soluble and have good adhesive qualities. They are very stable and resist oxidation and chemical decomposition and will not yellow over time. The releas of colore wastewater in the environment is considerable source of non aesthetic pollution and eutrophication and can originate dangerous by products through oxidation; hydrolysis or other chemical reaction taking place in the wastewater phased colorization of dye effluents has therefore received increasing attention. For removal of color pollutants, adsorption on activated carbon, ultrafiltration, reverse osmosis, coagulation by chemical agent, ion exchange on synthetic adsorbent resins, ozonation and advanced oxidation processes (O₃/UV, H₂ O₂/UV, O_{3 /}H₂ O₂ /UV, Fe²⁺/H₂ O₂) can be used. (Azbar et al., 2004 and Kusvuran et al., 2004).

MATERIAL AND METHODS

Coagulation and flocculation

Experimental study was designed to obtain maximum COD and color removal at optimum pH temperature and FeSO₄ and alum doses.Aluminum sulfate (Al₂ (SO₄)₃ .18 H₂O) and ferrous sulfate (FeSO₄.7H₂O) of commercial grade were utilized for the experimental procedure. A series of jar test experiment after adding coagulants applying 2 min rapid mixing at 120 rpm, 20 min slow mixing at 30 rpm and 45 min settling was conducted by using 500 mL dye solution. (Georgiou, et al., 2003).

Analytical methods

COD was measured according to standard methods. Absorbance measurements were made using pu 8700 series uv/vis spectrophotometer for color removal. The supernatant in each beaker were filtered by 0.45 µm millipore membrane filter before measuring COD and absorbance at maximum wave length. Removal efficiency of COD and color were obtained according to the formula given below. (Georgiou, et al., 2003).

Removal (%) = (c/c₀)/ c₀

Where c₀ and c are the initial and final absorbance or COD values of simulated wastewater, respectively.

RESULTS

Coagulation with ferrous sulfate

Basic equations occurring during the coagulation process for ferrous sulfate is given with equation 1:

Varying ferrous sulfate concentration (1000 mg/L) keeping pH constant (9) were applied for the treatment of wastewater. A ferrous sulfate concentration of 200 mg/L and 100 mg/L was necessary for an efficient COD removal for 400 and 100 mg/L color concentration and did not significant change COD removal.

Coagulation with aluminum sulfate

Alumininum ion,AL^+3, behaves verymuch like Fe+³. When alum is added to water or wastewater AL (OH)₃ precipitations occurs as described by the following equation 2:

Similar to ferroussulfate experiment, varing aluminum sulfate concentration, keeping pH at the optimum condition 10 were applied for the treatment of wastewater. An alum concentration of 600 mg/L and 300 mg/L was necessary for an efficient COD removal for 400 and 100 mg/L color concentration.Al₂ (SO₄)_3.18 H₂O and FeSO₄.7H₂o coagulant were used during the chemical treatment experimens with varying dosages under varying pH condition. For comparison the COD and color removal results of under best pH condition are given in Figs. 1,2 ,3, 4 and Table 1.

Optimum pH and temperature for each coagulant was found to be as follow: pH =3, T=40 for alum and pH= 9, T= 30 for FeSO₄.7H₂O. In term of COD removal, alum and ferrous sulfate used behaved same from the practical point of view as follow: 70 % COD (COD in effluent = 120 mg/L) and 99.99 % color removal were observed in experiments using Al₂ (SO₄)_3.18 H₂O with a dose of 600 mg/L For 400 mg/L of WBA, and for 100 mg/L WBA 69 % COD (COD in effluent = 124 mg/L) and color removal by Al₂(SO₄)₃. 18 H₂O with a dose of 300 mg/L was 99.8 %. While the COD removal at a FeSO₄ dose of 200 mg/L resulted in an effluent COD of 124 mg/L (69% COD removal) for 400 mg/L WBA and by 100 mg/L FeSO₄ for 100 mg/L WBA 67% COD removal (COD in effluent = 132 mg/L) were observed. Color removal by lime with a dose of 2000 mg/L and 1000 mg/L was 37 % and 15 % for 400 and 100 mg/L color concentration, respectively. COD removal by lime was very low. By using 10 mg/L polyelectrolyte (cationic, anionic and non ionic) with alum and ferrous sulfate did not significant change on flocculation and size of floces.

DISCUSSION AND CONCLUSION

Degradation of acrylic water base color in aqueous solutions by the coagulation process was performed. Color removal by coagulation process by use of alum and ferrous sulfate was > 99 % and COD removal is approximately 70 %. But lime was not effective on color and COD removal and polyelectrolyte did not significant change on flocculation. Before treatment wastewater by alum and ferrous sulfate pH must be adjusted and so alkanity was necessary to coagulation that must be adjusted by lime or calcium carbonate, but in this study alkanity of sample was enough. But due to the high chemical sludge production and increasing of hardness and corrosion it seems coagulation was not applicable for color removal in the wastewater containing color.

ACKNOWLEDGEMENTS

The authors are most appreciated to the laboratory staff of the Department of Occupational and Environmental Health, Faculty of Medical Sciences, Tarbiat Modarres University.

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