Removal of acid and direct dye by epichlorohydrin–dimethylamine: Flocculation performance and floc aggregation properties

Bioresource Technology 113 (2012) 265–271

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Removal of acid and direct dye by epichlorohydrin–dimethylamine: Flocculation performance and floc aggregation properties Yuan-Fang Wang, Bao-Yu Gao ⇑, Qin-Yan Yue, Yan Wang, Zhong-Lian Yang Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, No. 27 Shanda South Road, 250100 Jinan, China

a r t i c l e

i n f o

Article history: Received 1 September 2011 Received in revised form 21 November 2011 Accepted 25 November 2011 Available online 11 December 2011 Keywords: Epichlorohydrin–dimethylamine Flocculation Dye removal Floc aggregation Chemical interaction

a b s t r a c t A cationic organic flocculant epichlorohydrin–dimethylamine (EPI–DMA) was employed for the treatment of acid and direct dye. The study aims at investigating the flocculation performance of EPI–DMA for the model dye, and corresponding floc aggregation properties, which were determined by jar test and photometric dispersion analysis, respectively. The interactions between cationic flocculant and anionic dye were investigated through spectra analysis. The results showed that EPI–DMA effectively decolorized the tested acid and direct dye. The viscosity and cationicity of EPI–DMA had different influence on the removal of different dye. Chemical interaction was observed between quaternary ammonium of EPI– DMA and sulfonic group of dye. The flocculation dynamic process showed that flocs with better aggregation and sedimentation properties were produced by EPI–DMA with higher viscosity and cationicity for acid dye. Contrarily, flocs with the best aggregation and sedimentation properties were produced by EPI– DMA with the lowest viscosity and cationicity for direct dye. Ó 2011 Elsevier Ltd. All rights reserved.

1. Introduction Effluents from textile, printing, papermaking and food industries contain large quantities of dye compounds. The presence of dye in water can result in water environmental degradation, and even threaten human health due to the production of carcinogenic substances. Effective treatment process is needed to remove dye compounds from water and reduce the toxicity of effluents. The removal of dye by coagulation/flocculation is one of the most popular treatment processes (Allegre et al., 2004; Gao et al., 2007a,b; Golob et al., 2005; Guibal and Roussy, 2007; Szygula et al., 2009). Different with the biological treatment, there is no toxic intermediate produced during the flocculation process of dyeing wastewater. Moreover, relatively high cost effectiveness ratio can be achieved during the large scale flocculation operation (Lee et al., 2006; Mo et al., 2007; Papic´ et al., 2004). During the flocculation process, decolorization efficiency depends on the flocculant used and the treated dye. Different color removal efficiency is obtained by different flocculants for the same dye, and also different color removal efficiency is obtained by the same flocculant for different dyes. Inorganic coagulant such as traditional aluminum and ferric salts, with a wide application in drinking water treatment, has limitations in removing some high-soluble and low molecular dyes

⇑ Corresponding author. Tel.: +86 531 88364832; fax: +86 531 88364513. E-mail address: [email protected] (B.-Y. Gao). 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.11.106

(Joo et al., 2007; Kim et al., 2004; Shi et al., 2007). Organic polymeric flocculant has drawn increasing attention in various industries. Recently, the research and application of novel polymeric flocculant has been particularly active for the removal of dissolved and colloidal solids (Ovenden and Xiao, 2002; Sarika et al., 2005). Many organic polymers were synthesized and used as the flocculant to remove dye. Gao et al. (2007a,b) and Kang (2007) employed polydimethyldiallylammonium chloride as the flocculant and found that high removal efficiency was achieved for treating reactive and disperse dyes. The copolymer of acrylamide and 2-[(methacryloyloxy)ethyl]trimethyl ammonium chloride was effective to removal reactive, acid and direct dyes from water under certain conditions (Shen et al., 2006). The organic flocculant used in this study, epichlorohydrin–dimethylamine (EPI–DMA) polymer, is a poly-quaternary polymer produced by the reaction of dimethylamine and epichlorohydrin. Similar polymer prepared from ethylenediamine and epichlorohydrin was used in removing nitrite ions by Bíçak and Sßenkal (1998). Recently, EPI–DMA was employed as the flocculant. The decolorization performance of EPI–DMA has been studied for reactive and disperse dyes in our previous research. In this study, Acid Cyanine 5R and Direct Violet N dyes were chosen as the model dye compounds. The flocculation process can be explored by analyzing floc aggregation properties. Flocs are formed after the addition of flocculant, and floc size increases due to aggregation. A steady state of floc size occurs eventually due to the equilibrium between floc aggregation and breakage. All the floc aggregation rate and floc size can be used to compare flocculation effectiveness.

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The main objectives of this study were to investigate the performance of EPI–DMA with different intrinsic viscosity and cationicity in the flocculation of acid and direct dyes, to investigate the floc aggregation properties of these EPI–DMA flocculants, and to explore the relationship between flocculation mechanisms and properties of flocculant.

steady state region

4

growth region

Ratio

3 sedimentation region 2 sedimentation slope

2. Methods 1

slope

2.1. Materials The cationic cross-linked polymer epichlorohydrin–dimethylamine (EPI–DMA) was synthesized by the polycondensation of epichlorohydrin and dimethylamine. The intrinsic viscosity (g) and cationicity (s) of obtained polymers were as follows: g = 120 mPa s and s = 4.25 mmol/g, g = 1000 mPa s and s = 4.83 mmol/g, g = 3200 mPa s and s = 5.36 mmol/g. Then, 10 g/L of EPI–DMA stock solution was prepared by dissolving designated amount of polymer with distilled water. Two azo dyes (Acid Cyanine 5R and Direct Violet N) purchased from Jinan No.2 Textile Dyeing Mill (Shandong, China) were used during the flocculation process.

0 0

2.3. Analysis of floc growth and aggregation Both the growth and sedimentation rate of floc and floc size can be determined by monitoring and analyzing the formation process of floc. Floc aggregation process was on-line monitored using a photometric dispersion analyzer (PDA2000, Brother, U.K.). Fig. 1 showed the variation of typical ratio values obtained from dynamic experiments with time. In the growth region where floc size increases gradually, slope value indicated the growth rate of floc, and was calculated using Eq. (1):

Slope ¼ Dratio=Dtime

ð1Þ

In the steady state region, floc size remains stable with time due to the dynamic equilibrium between floc growth and breakage. The time-weighted average steady state ratio value (denoted as R) was calculated using Eq. (2): N P

R ¼ i¼1

ðratioi  timei Þ N P i¼1

ð2Þ timei

1000

1500

2000

Time(s) Fig. 1. Variation of typical ratio value with flocculation time.

where ratioi is the typical ratio value at a certain flocculation time and timei is the flocculation time value. The time-weighted ratio variance of steady state ratio value (denoted as RV) indicated the floc size difference and range of steady state region, and was calculated using Eq. (3):

2.2. Flocculation experiments Synthetic dyeing wastewater was prepared by adding 0.1 g dye to 1 L of tap water. The absorbance values of raw wastewater recorded on a UV-754 spectrophotometer (Shanghai Analytical Instrument Factory, China) were 1.596 for Acid Cyanine 5R dye at 550 nm of kmax, and 0.756 for Direct Violet N dye at 514 nm of kmax. Flocculation experiments were conducted with a jar test apparatus (DC-506 Laboratory Stirrer, Shanghai Huahui New Technology Development Co., Ltd., China). After the addition of EPI–DMA flocculant, dye solution was mixed rapidly for 3 min at 120 rpm, followed by mixing slowly for 12 min at 40 rpm and a settling process for 20 min. Next, the absorbance values of supernatant samples were determined using a UV-754 spectrophotometer at the kmax of each dye. Therefore, the color removal efficiency of flocculant was calculated by comparing the absorbance difference between raw dyeing wastewater and supernatant sample. The zeta potential of floc formed was determined using a JS94H micro-electrophoresis analyzer (Shanghai Zhongchen Digital Technology Equipment Co., Ltd., China).

500

RV ¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi PN PN 2 i¼1 ½ðratioi  RÞ  timei = i¼1 timei R

 100%

ð3Þ

In the sedimentation region where floc settled, sedimentation slope value indicated the sedimentation rate of floc, and was calculated using Eq. (4):

Sedimentation slope ¼ jDratio=Dtimej

ð4Þ

2.4. FTIR analysis of EPI–DMA, dye and floc formed The FTIR spectra of three EPI–DMA flocculants, two azo dyes and flocs formed were obtained on a Nicolet FT/IR-20SX Model Fourier transform infrared spectrometer in 4000–400 cm1 region. 3. Results and discussion 3.1. Interactions between EPI–DMA flocculant and dye To investigate the interaction between EPI–DMA flocculant and Acid Cyanine 5R dye, the FTIR spectra of EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g), Acid Cyanine 5R dye and floc formed were determined. The band at 996.43 cm1 was assigned to the special vibration of quaternary ammonium (R4N+) of EPI–DMA, and was weakened in intensity and shifted to 876.85 cm1 in the spectrum of floc. The bands assigned to sulfonic group ð—SO 3 Þ of Acid Cyanine 5R dye molecule were observed at 1023.22, 1076.91 and 1101.16 cm1, and shifted to 1019.97, 1074.85 and 1099.16 cm1 in the spectrum of floc. The bands between 3410 and 3450 cm1 reflected the OH deformation of water. The intensity of floc band (3419.58 cm1) was stronger than that of Acid Cyanine 5R dye band (3437.88 cm1), which was probably due to the increased hydrophilic nature of dye molecule after the addition of EPI– DMA. These spectral changes confirmed the reaction between R4N+ of EPI–DMA and —SO 3 of Acid Cyanine 5R dye molecule. The FTIR spectra of EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/ g), Direct Violet N dye and floc were also investigated. It is observed that the band at 996.43 cm1 corresponding to R4N+ of EPI–DMA, shifted to 966.52 cm1 with weak intensity in the spectrum of floc. The bands at 1037.86 and 1054.57 cm1 corresponded to the vibration of —SO 3 of Direct Violet N dye molecule, which shifted to 1034.88 and 1052.28 cm1 in the spectrum of floc. As for the

Y.-F. Wang et al. / Bioresource Technology 113 (2012) 265–271

OH deformation of water, the intensity of floc band at 3419.23 cm1 was stronger than that of Direct Violet N dye band at 3441.33 cm1. These results indicated that R4N+ of EPI–DMA reacted with —SO 3 of Direct Violet N dye molecule.

3.2. Decolorization performance of EPI–DMA for Acid Cyanine 5R dye Flocculation experiment for the removal of Acid Cyanine 5R dye was conducted using different characteristics of EPI–DMA within the dosage range of 0–40 mg/L. The variations of color removal efficiency and zeta potential with flocculation dosage were presented in Fig. 2. From Fig. 2(a), similar color removal efficiency was obtained by these three EPI–DMA flocculants within the low dosage range. The color removal efficiency of these flocculants increased dramatically and almost 90% of efficiency was achieved at 10 mg/L of dosage. The result indicated that these EPI–DMA flocculants were highly effective in treating synthetic Acid Cyanine 5R dyeing wastewater. Differences on the changing trend of color removal efficiency were appeared with dosage further increasing. With EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g) as the flocculant, color removal efficiency increased slightly with dosage and then remained constant until 40 mg/L of dosage. In the case of EPI–DMA (g = 1000 mPa s and s = 4.83 mmol/g) and EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g), however, particle restabilization phenomenon was observed after the highest removal efficiency was achieved. Moreover, the more serious particle restabilization resulted from the flocculation of EPI–DMA flocculant with higher cationicity. The observable particle restabilization can be explained by the differences of decolorization mechanism among these three EPI– DMA flocculants.

Color removal (%)

100

(a)

80 60 40 20

120 mPa.s 1000 mPa.s 3200 mPa.s

0 0

Zeta potential (mV)

20

10

(b)

20 30 Dosage (mg/L)

40

120 mPa.s 1000 mPa.s 3200 mPa.s

10

267

The decolorization mechanism of EPI–DMA can be explored by the analysis of zeta potential of flocs. Within the dosage range lower than 20 mg/L, zeta potential fluctuations were slight for these three flocculants. It is interested that during this flocculation phase, color removal efficiency increased rapidly and the highest removal efficiency of these three flocculants was already achieved at 20 mg/L of dosage. Many authors reported that charge neutralization and adsorption bridging of flocculant were responsible for the treatment of dye (Allegre et al., 2004; Golob et al., 2005; Wang et al., 1995; Yu et al., 2001). Flocs with negative surface charge were highly precipitated, probably because EPI–DMA with a long molecular chain provided strong adsoprtion bridging ability. This suggested that the flocculation of acid dye by EPI–DMA was mainly supported by adsorption bridging other than charge neutralization when flocculation dosage was not excessive. In contrast, charge neutralization of flocculant dominated the removal of dye when zeta potential increased with flocculation dosage and was in good agreement with the flocculation efficiency (Kim et al., 2004). In additional, similar removal efficiency was obtained by these three flocculants with different viscosity in this flocculation phase, indicating that viscosity of EPI–DMA has no influence on the decolorization of acid dye. With the dosage above 20 mg/L, zeta potential increased gradually with dosage, and increased with cationicity at the same dosage. The zeta potential of EPI–DMA (s = 4.25 mmol/g) was always negative within the tested dosage range. Whereas the zeta potential of EPI–DMA (s = 4.83 mmol/g) and EPI–DMA (s = 5.36 mmol/g) shifted to positive after certain dosage. The results corresponded to the changing trends of color removal efficiency. The charge neutralization ability of EPI–DMA was stronger with the increase of cationicity, therefore, the surface charge of floc was higher and shifted to positive more earlier. Consequently, the electrostatic repulsion force was stronger and then particle restabilization was more serious. The variation of zeta potential with respect to flocculation dosage was dependent with the charge neutralization of flocculant. The linear equation of zeta potential with flocculation dosage and correlation coefficient were shown in Table 1. There is no linear relationship between zeta potential and the dosage of EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g) with 0.33 of correlation coefficient. Moreover, isoelectric point (IEP) was not reached within the whole tested dosage range. The results explained why no particle restabilization was observed as dosage increased. The result also indicated that adsorption bridging was dominant during the flocculation by EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g). The linear relationship between zeta potential and the dosage of EPI–DMA (g = 1000 mPa s and s = 4.83 mmol/g) or EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g) was either bad. However, the IEP of these two flocculants was reached at certain dosage. Therefore, a reduction in color removal efficiency was observed with the further increase of dosage, which was due to the increasing charge neutralization of these two flocculants with dosage. 3.3. Decolorization performance of EPI–DMA for Direct Violet N dye

0 -10 -20 -30 0

10

20 30 Dosage (mg/L)

40

Fig. 2. Decolorization performance of EPI–DMA for Acid Cyanine 5R dyeing wastewater: (a) decolorization efficiency and (b) zeta potential.

Removal of Direct Violet N dye was performed using a series of EPI–DMA flocculants with different g and s. Within the dosage range of 2–60 mg/L, the plots of color removal efficiency and zeta potential of flocs versus flocculation dosage were illustrated in Fig. 3. It can be observed that, above 80% of color removal efficiency was achieved at 2 mg/L of dosage. Color removal efficiency increased rapidly, and was already higher than 90% at 6 mg/L of dosage. Compared with the removal of Acid Cyanine 5R dye, these three EPI–DMA flocculants with much lower dosage were more effective for the removal of Direct Violet N dye. The result suggested that the color removal efficiency of EPI–DMA flocculant

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Table 1 Relationship between zeta potential and dosage during the flocculation process for Acid Cyanine 5R dyeing wastewater. EPI–DMA flocculant

Equation

Correlation coefficient

120 mPa s, 4.25 mmol/g 1000 mPa s, 4.83 mmol/g 3200 mPa s, 5.36 mmol/g

y = 29.5 + 0.2x

0.33

–

y = 30.4 + 0.6x

0.63

38

y = 31.8 + 0.9x

0.66

33

96

Dosage at IEP (mg/L)

(a)

Color removal (%)

92 88 84 80 76 120 mPa.s 1000 mPa.s 3200 mPa.s

72 68 0

20

10

20 30 40 Dosage (mg/L)

50

60

(b)

Zeta potential (mV)

15 10 5 0 -5 -10 120 mPa.s 1000 mPa.s 3200 mPa.s

-15 -20 -25

0

10

20 30 40 Dosage (mg/L)

50

60

Fig. 3. Decolorization performance of EPI–DMA for Direct Violet N dyeing wastewater: (a) decolorization efficiency and (b) zeta potential.

might be influenced by the molecular properties of tested dye, such as molecular weight and structure. The molecular weight of Direct Violet N dye is higher than that of Acid Cyanine 5R dye, and the chemical structure of Direct Violet N dye molecule is prone to linear and planar. Therefore, Direct Violet N dye was easier to be adsorbed by EPI–DMA polymer. As shown in Fig. 3(a), the color removal efficiency obtained by EPI–DMA (g = 1000 mPa s and s = 4.83 mmol/g) or EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g) exhibited the following changing trend: increasing rapidly with dosage until the maximum was achieved, and then decreasing as dosage further increased. Similar trend on the decolorization efficiency of direct dye was obtained by the flocculation of P(AM–DMC), however, the required optimum dosage was higher (Shen et al., 2006). In the case of EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g), color removal efficiency exhibited different changing trend after rapid increase: slow increase with dosage, then followed by a plateau, and no particle restabilization was observed within the tested dosage range.

From Fig. 3(b), it was noted that with dosage lower than 10 mg/ L, all the zeta potential values were highly negative and increased slightly with the dosage of these EPI–DMA flocculants, which suggested that the high removal of Direct Violet N dye was not achieved through the charge neutralization of EPI–DMA with low dosage. With dosage further increasing, zeta potential increased gradually, and also increased as the cationicity of EPI–DMA polymer increased. The results suggested that the charge neutralization ability of EPI–DMA polymer corresponded well with its cationicity. Table 2 showed the linear equation of zeta potential over flocculation dosage and the corresponding correlation coefficient. For EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g) with 0.99 of correlation coefficient, zeta potential was linear correlation with dosage, but almost all of zeta potential was negative within the tested dosage range. For the other two flocculants with high correlation coefficient, there was also linear relationship between zeta potential and dosage. The dosage required to reach IEP was 28 mg/L of EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g), 32 mg/L of EPI– DMA (g = 1000 mPa s and s = 4.83 mmol/g). As shown in Fig. 3(a), the maximum color removal efficiency for these three flocculants was appeared when zeta potential was highly negative and far away from their IEP. The results implied that both adsorption bridging and charge neutralization were the flocculation mechanism of EPI–DMA in the treatment of direct dyeing wastewater, but the former was the dominant. 3.4. Floc aggregation properties of EPI–DMA for Acid Cyanine 5R dye The flocculation dynamic process of these three EPI–DMA flocculants was investigated by a photometric dispersion analyzer, and the experimental results for Acid Cyanine 5R dye were shown in Fig. 4. As shown in Fig. 4(a), (b) and (c), the changing trends of three floc aggregation parameters were similar for EPI–DMA (g = 1000 mPa s and s = 4.83 mmol/g) and EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g), and different with those of floc aggregation parameters obtained by EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g). For the two EPI–DMA flocculants with higher g and s, slope, R and sedimentation slope of flocs increased with dosage until the highest values were achieved at certain dosage, and then decreased dramatically with dosage further increasing. At the same dosage, these three floc aggregation parameters obtained by EPI–DMA with the highest g and s were always higher than those of EPI–DMA with 1000 mPa s of g and 4.83 mmol/g of s. Contrarily, slope, R and sedimentation slope of flocs formed by EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g) kept increasing with flocculation dosage. These three floc aggregation parameters obtained by EPI–DMA with the lowest g and s were the lowest in most cases compared with those obtained by the other two flocculants. From Fig. 4(d), the RV of flocs formed by these three flocculants showed similar changing trend: increasing gradually with dosage and decreasing as dosage further increased. It was noticed that the highest RV values were achieved by EPI–DMA (g = 1000 mPa s and s = 4.83 mmol/g) not EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g). The RV values obtained by EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g) were still the lowest within the whole dosage range. The results indicated that floc formation and growth were significantly influenced by the properties of flocculant and flocculation dosage. In the treatment of EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g), floc increased to the largest size with the highest grow rate, and then settled rapidly with the highest sedimentation rate. Moreover, RV was not the highest, which suggested that floc size was in a relatively narrow range. It can be concluded that large and dense flocs were produced through the strong adsorption bridging of flocculant. The reduction in the floc grow rate, sedi-

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flocs with different slope, R, sedimentation slope and RV. As shown in Fig. 5, these four floc aggregation parameters obtained by EPI– DMA (g = 1000 mPa s and s = 4.83 mmol/g) and EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g) had a similar changing trend: increasing with dosage, following by the maximum at the optimum dosage, and then decreasing significantly as dosage further increased. Different changing trend was observed for the floc aggregation parameters obtained by EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g): increasing with dosage, and then remaining almost unchanged after the maximum was reached. In the treatment of EPI–DMA (g = 1000 mPa s and s = 4.83 mmol/ g) and EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/g), the variance of floc size was large, indicating that floc size was in a wide range. This may result from the existence of different flocculation mechanisms for the removal of Direct Violet N dye. For these two flocculants, all the floc aggregation rate, sedimentation rate and floc size decreased with dosage further increasing. This is associated with the change of main flocculation mechanism. Floc size and aggregation rate increased at the initial stage of flocculation because of the strong adsorption bridging and charge neutralization of EPI–DMA with a long molecular chain and high cationicity. With dosage further increasing, the charge on the floc surface increased and switched from negative to positive at certain dosage. The repulsion between flocs increased, and particle restabilization occurred. Therefore, floc size and growth rate decreased. In the treatment of EPI–DMA with the lowest g and s, both slope and R values were the lowest with dosage lower than 20 mg/L, but increased to the highest above 20 mg/L of dosage compared to those of the other two flocculants. Whereas the sedimentation slope and RV values of flocs formed by EPI–DMA (g = 120 mPa s and s = 4.25 mmol/g) were the lowest than those of the other two flocculants. The lowest and relatively constant variance suggested the

Table 2 Relationship between zeta potential and dosage during the flocculation process of Direct Violet N dyeing wastewater. EPI–DMA flocculant

Equation

Correlation coefficient

Dosage at IEP (mg/L)

120 mPa s, 4.25 mmol/g 1000 mPa s, 4.83 mmol/g 3200 mPa s, 5.36 mmol/g

y = 23.7 + 0.4x

0.99

56

y = 22.1 + 0.6x

0.97

32

y = 24.1 + 0.8x

0.97

28

mentation rate, floc size and variance with dosage further increasing may be due to the change of main flocculation mechanism, switching from adsorption bridging to charge neutralization. This is in agreement with the results shown in Fig. 2. Compared with EPI–DMA (g = 3200 mPa s and s = 5.36 mmol/ g), similar flocculation dynamic process was observed by EPI– DMA (g = 1000 mPa s and s = 4.83 mmol/g), but the flocs formed were smaller, less dense and in a wider size range. In the treatment of EPI–DMA (g = 120 mPa s and s = 4.25 mmol/ g), floc increased slowly with the lowest grow rate, and then settled with the lowest sedimentation rate, indicating that small and loose flocs were produced. The lowest RV indicated the narrowest range of floc size. The reason may be that only one flocculation mechanism performed during the flocculation process. 3.5. Floc aggregation properties of EPI–DMA for Direct Violet N dye Floc aggregation during the flocculation process of Direct Violet N dye was online monitored, and the results were presented in Fig. 5. It was found that different EPI–DMA flocculants produced

(a)

0.030

(b)

5

0.025 4 3

0.015

R

Slope

0.020

2

0.010 0.005

1

120 mPa.s 1000 mPa.s 3200 mPa.s

0.000 5

10

15

20

25

30

35

120 mPa.s 1000 mPa.s 3200 mPa.s

0

40

45

5

10

Dosage (mg/L)

30

(c)

25

30

35

40

(d)

120 mPa.s 1000mPa.s 3200 mPa.s

27 24

0.025

RV (%)

Sedimentation slope

0.030

20

Dosage (mg/L)

120 mPa.s 1000 mPa.s 3200 mPa.s

0.035

15

0.020 0.015

21 18

0.010

15

0.005

12

0.000

9 5

10

15

20

25

30

Dosage (mg/L)

35

40

45

10

15

20

25

30

35

Dosage (mg/L)

Fig. 4. Parameters of floc aggregation for Acid Cyanine 5R dyeing wastewater.

40

45

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3.0

(a)

0.030

2.7

0.025

2.4 R

Slope

0.035

0.020 0.015

1.5

120 mPa.s 1000 mPa.s 3200 mPa.s

0.005 0

10

120 mPa.s 1000 mPa.s 3200 mPa.s

1.2

20 30 40 Dosage (mg/L)

50

60

0

(c)

0.020

10

20 30 40 Dosage (mg/L)

50

60

(d)

27 24

0.016

RV (%)

Sedimentation slope

2.1 1.8

0.010

0.000

(b)

0.012

21 18

0.008

0.000

15

120 mPa.s 1000 mPa.s 3200 mPa.s

0.004

0

10

20

30

40

120 mPa.s 1000 mPa.s 3200 mPa.s

12 50

60

0

Dosage (mg/L)

10

20 30 40 Dosage (mg/L)

50

60

Fig. 5. Parameters of floc aggregation for Direct Violet N dyeing wastewater.

narrowest range of floc size. The results are consistent with the changing trend of the decolorization efficiency presented in Fig. 3(a).

4. Conclusions The tested dyes were effectively removed by EPI–DMA. Both viscosity and cationicity were the factor influencing color removal. Adsorption bridging was responsible for removing acid dye, and charge neutralization was stronger with dosage. Direct dye was more easily removed by adsorption bridging and charge neutralization. Chemical interaction occurred between R4N+ of EPI–DMA and —SO 3 of dye. For acid dyeing wastewater, EPI–DMA with the highest g and s produced the largest and dense flocs with the fastest aggregation rate. However, for direct dyeing wastewater, EPI–DMA with the lowest g and s produced the largest flocs with the fastest aggregation rate.

Acknowledgements This research was supported by National Natural Science Foundation of China (50578089), National Natural Science Foundation of China (21077066), The Scientific Technology Research and Development Program of Shandong of China (2009GG10006003; 2010GZX20605) and Natural Science Foundation of Shandong Province of China (ZR2010BM014).

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