Treatment of cotton textile wastewater using lime and ferrous sulfate

Treatment of cotton textile wastewater using lime and ferrous sulfate

Water Research 37 (2003) 2248–2250 Technical note Treatment of cotton textile wastewater using lime and ferrous sulfate D. Georgiou*, A. Aivazidis, ...

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Water Research 37 (2003) 2248–2250

Technical note

Treatment of cotton textile wastewater using lime and ferrous sulfate D. Georgiou*, A. Aivazidis, J. Hatiras, K. Gimouhopoulos Department of Environmental Engineering, Demokritos University of Thrace, Xanthi GR-67100, Greece Received 8 November 2001; received in revised form 1 October 2002; accepted 4 October 2002

Abstract This technical note summarizes the results of a textile wastewater treatment process aiming at the destruction of the wastewater’s color by means of coagulation/flocculation techniques using ferrous sulfate and/or lime. All the experiments were run in a pilot plant that simulated an actual industrial wastewater treatment plant. Treatment with lime alone proved to be very effective in removing the color (70–90%) and part of the COD (50–60%) from the textile wastewater. Moreover, the treatment with ferrous sulfate regulating the pH in the range 9.070.5 using lime was equally effective. Finally, the treatment with lime in the presence of increasing doses of ferrous sulfate was tested successfully, however; it proved to be very costly mainly due to the massive production of solids that precipitated. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Azo reactive dyes; Coagulation; Ferrous sulfate; Flocculation; Lime; Textile wastewater

1. Experimental

1.2. Pilot plant

1.1. Materials

All experiments were performed in a pilot plant (Fig. 1) that simulated the industrial wastewater treatment plant (Fanco). Thus, the first part of the pilot plant consisted of an equalization basin, in which the wastewater was homogenized by means of an air compressor and a diaphragm. The wastewater was then transferred from the equalization basin to a fast stirring tank into which the coagulants (lime, ferrous sulfate) were introduced and well mixed. The residence time in the fast stirring tank ranged between 1 and 2 min. Coagulation/flocculation took place in the following tank that was slowly stirred (residence time: 15–20 min). Polyelectrolyte (8 mg/L of cationic type) was also introduced in the latter tank. Finally, the wastewater was led to a sedimentation tank where the solid precipitates were separated from the aqueous phase (residence time: 45 min). Five pumps were utilized for wastewater transfer, introduction of coagulants and sludge removal. Following steady-state conditions, samples were withdrawn from the equalization basin and the exit of the

Textile wastewater was obtained from a nearby cotton textile-dyehouse industry (Fanco, northeastern Greece) the mean characteristics of which are presented in Table 1. The samples were withdrawn from the equalization basin of the wastewater processing plant. The wastewater was highly colored and also had high BOD and COD values. Lime (Ca(OH)2) and ferrous sulfate (FeSO4  7H2O) of commercial grade were utilized for the experimental procedure. Lime was prepared in the form of slurry (10– 20 g/L) and ferrous sulfate as a solution (20–40 g/L) using tap water in both cases.

*Corresponding author. Tel.: +3-0541-28865; fax: +3-054162955. E-mail address: [email protected] (D. Georgiou).

0043-1354/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 3 - 1 3 5 4 ( 0 2 ) 0 0 4 8 1 - 5

D. Georgiou et al. / Water Research 37 (2003) 2248–2250 Table 1 Textile wastewater mean characteristics (Fanco S.A.)

Absorbance (m 1) 180 605

8.8

22.6

21.2

11.2

Removal (%)

BOD5 (mg/L) COD (mg/L) pH 436 nm 525 nm 620 nm

100 90 80 70 60 50 40 30 20 10 0

2249

pH = 13,3

pH = 13,5

pH = 12,4

436 nm yellow 525 nm-red 620 nm-blue COD

pH = 11,6 pH = 10,1

0

200

400 600 800 1000 Ca (OH)2 (mg/L)

Removal (%)

Fig. 2. Color and COD removal in textile wastewater vs. lime concentration.

100 90 80 70 60 50 40 30 20 10 0

436 nmyellow 525 nm-red 620 nm-blue COD

0 Fig. 1. Flow sheet of the pilot-plant installation.

200 400 600 800 FeSO4 7 H2O (mg/L)

1000

Fig. 3. Color and COD destruction in textile wastewater vs. ferrous sulfate concentration (pH=9.070.5).

pilot plant and they were analyzed for color and COD values. 2.2. Application of ferrous sulfate 2. Results and discussion 2.1. Application of lime Several tests proved that pure lime (Ca(OH)2) could effectively remove the color from the textile wastewater. Fig. 2 summarizes the results from a series of such tests. A lime concentration of over 600 mg/L was needed to effectively remove the color from the wastewater. Color removal reached approximately 80% (absorbance at 436 nm—yellow) and around 90% (absorbance at 525 nm—red, and 620 nm—blue) when lime concentration was 1 g/L of wastewater. At the same time COD removal reached 60%. The undesired result of this process was the rise of pH, which was attributed to the partial dissolution of lime in the wastewater. Neutralization with hydrochloric acid followed prior to rejection of the wastewater.

Experiments were run during which ferrous sulfate was applied at an increasing concentration while the pH was maintained constant (9.070.5). As Fig. 3 presents a ferrous sulfate concentration of over 600 mg/L was necessary for an efficient removal of color and COD from the wastewater. Almost 80% of the yellow color and 90% of the red and blue colors were removed when ferrous sulfate concentration ranged between 800 and 1000 mg/L. At the same time COD removal reached 50%. Lime was utilized in order to maintain the pH constant (9.070.5) the consumption of which ranged between 250 and 350 mg/L. 2.3. Application of lime in the presence of ferrous sulfate The application of lime in the presence of increasing doses of ferrous sulfate was also studied. The concentration of ferrous sulfate was kept constant for each

D. Georgiou et al. / Water Research 37 (2003) 2248–2250

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Table 2 Summary of different textile wastewater treatments No.

Lime (mg/L)

Ferrous sulfate (mg/L)

pH

Color removal (%)

COD removal (%)

Solid precipitates (mg/L)

1 2 3 4 5 6 7

800 800 800 800 800 800 350

0 200 400 600 800 1000 800

13–13.5 12.5–13 12.5–13 12–13 12–13 12–12.5 8.5–9.5

70–90 75–90 80–90 70–90 70–90 85–95 70–90

50–60 50–60 50–55 60–70 60–70 60–70 45–50

530 1315 1240 1395 1285 1410 650

series of experiments during which lime concentration was increasing (200–1000 mg/L). Ferrous sulfate concentration varied between 200 and 1000 mg/L for different series of experiments. Despite the high amount of coagulants (lime and ferrous sulfate) utilized only a very slight improvement (compared to the previous applications) in color and COD removal was observed. Destruction of color and COD reached its peak (85– 95% and 70%, respectively) when lime and ferrous sulfate were applied at a concentration of 800 and 1000 mg/L, respectively. 2.4. Production of solid precipitates The treatment of textile wastewater with lime alone or lime and ferrous sulfate resulted in the production of solids that precipitated. Utilizing lime alone and for an efficient color and COD removal the production of solids reached 500–600 mg/L of wastewater. A slightly higher amount of solids (600–700 mg/L) was produced utilizing ferrous sulfate at a constant pH (9.070.5). However, a massive production of solids (mainly due to the formation of iron hydroxides) was observed when lime was applied in the presence of ferrous sulfate. For an efficient color and COD removal the production of

solids that precipitated reached 1200–1400 mg/L. Table 2 summarizes the most efficient treatments in terms of color and COD removal. The amounts of the raw materials used, the solids that precipitated and the pH of the wastewater treated are also shown. It becomes evident from Table 2 that the treatment with lime in the presence of ferrous sulfate was not advantageous since it required increased amounts of raw materials, it led to high pH values and most importantly it led to the production of high amounts of solids that precipitated. Treatment with lime alone could be considered as competitive to the treatment with ferrous sulfate at a constant pH (9.070.5). Both methods showed the same efficiency in removing the color and the COD of the wastewater at almost the same cost. However, further investigation is required regarding the characterization and the quality of the solids that the two methods produced.

Acknowledgements Fanco S.A. is gratefully acknowledged for its assistance and support.