The Application of Cluster-Surfactant Flocculants in the Advanced Treatment of Coking Industrial Wastewater

Reclamation

Guanghua Wang1,2*, kun Chen1,2, Wenbing Li1,2*, Wenmin Liu1,2, Tiejun Liu1,2, Zhaoyang Wu1,2, Zhu Zhang 3，Hongbing Chang4, Xiangyong Liu4

1. College of Chemical Engineering and Technology, Wuhan University of Science and Technology, Wuhan 430081,China 2. Hubei Key Laboratory of Coal Conversion and New Carbon Materials, Wuhan 430081,China

3. The Lingxiang Iron Ore Plant of Wuhan Iron and Steel (Group) Corp, Daye 435121, China

4. The Coking Plant of Wuhan Iron and Steel (Group) Corp, Wuhan 430083, China

* Correspondence author: wghuah@21 cn.com;liwenbing@126.com

Abstract: Coking wastewater from the process of coking, coal gas purification and the coking products refine, whose ingredients are complicated and inconstant, is hard to meet the standard of reclaimed water used for industrial water by secondary treatment. In view of this situation, the advanced treatment technique of coking wastewater was desired. The innovatory flocculation treatment was used to regenerate coking wastewater with the help of surfactant (the number of the Chinese patent is: CN200910063253.2). The synergistic effects of the surfactant (named K) could improve the traditional flocculation treatment process. The results showed that in the combination of IPF(Inorganic polymer flocculants)+OPF(Organic polymer flocculants) + Surfactant(K), surfactant (K) can incur obvious synergistic effects within the flocculants system. The COD and chromaticity less than 50mg/l and 30° respectively under the optimum condition, the water quality of the treatment of coking industrial wastewater can meet the water quality standard for industrial uses. So this synergistic treatment technology by fine chemicals and flocculants can be effective for industrial wastewater regeneration.

Keywords: coking wastewater; cluster-surfactant flocculants; synergistic effects; regeneration

1 Introduction

Coking wastewater is generated from coal coking, coal

gas purification and by-product recovery processes of

coking[1]. It contains complex inorganic and organic

pollutants, such as ammonium, sulfate, cyanide,

thiocyanate, phenolic compounds, polynuclear aromatic

hydrocarbons and polycyclic nitrogen-containing acyclic

compounds, most of which are refractory, toxic,

mutagenic and carcinogenic [2-5]. It will produce severe,

long-term environmental and ecological impacts [6,7] if

it is discharged directly into the receiving river. The

untreated of coking wastewater is a serious problem all

over the world, especially in China, where coal is treated

as the main energy sources.

Currently, the methods of coking wastewater treatment

mainly contain: Biological treatment, such as anoxic-oxic

(A-O), anaerobic-anoxic-oxic (A-A-O)，sequencing batch

reactor(SBR) and HSBEMBM○R , are usually used to

treat coking wastewater [8-12]. The water quality of

effluent can merely achieve effluent demand partly by

biological treatment, and be hard to the water quality

standard of reclaimed water for industrial water;

Physical-chemical process, such as adsorption technique,

advanced oxidation [13-15] and coagulation used to

advanced treatment of coking wastewater, have been

investigated. However, the former two methods are either

economically unfavorable or technically complicated,

which make them difficult to be used in practice.

Coagulation is widely used for advanced treatment

wastewater due to the high ability of chemical

compounds separation and convenient operation. Various

coagulant have been developed to treat wastewater

including inorganic coagulants, organic coagulants and

inorganic–organic dual-coagulants in recent years[16-21].

Because the coking wastewater composition are very

complicated, current coagulation treatment processes are

often not sufficient enough to meet the requirements of

wastewater reuse for the national stringent regulations,

especially in COD and chromaticity of the wastewater.

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Since entering the 21st century, the technology and

usage of recycled water can increasingly catch

government’s attention. Due to less of economic, the

utilization rate of recycled waste water is only about 15%,

while the amount of waste recycled is less than 5%.

In recent years, the research of industrial Wastewater

reclamation was focused on the improvement of

regeneration technology, recycling rate and low-carbon

operation mode. This article focuses on cluster-surfactant

flocculants: fine chemicals was introduced to the

traditional flocculation process, through the synergistic

effects by fine chemicals and flocculants, make effluent

achieve the water quality standard of reclaimed water for

industrial water.

2 Materials and methods

2.1 Raw wastewater and materials

The raw wastewater used in the experiments was

collected from the outlet after A-A-O and HSBEMBM○R

biological treatment. Table 1 showed some special

chemical parameters of the wastewater sample1 and

sample2.

Table 1 Characteristics of raw wastewater Parameter Unit sample1 Sample2

pH 7.7 ± 0.3 7.4± 0.2

Temperature (in situ) ℃ 30 ± 2 28 ± 2

Conductivity μS/cm 3300 ± 20 2000± 20

COD mg/L 350 ± 20 150± 20

chromaticity ° 800~1000 400~600

Main materials: silver sulfate, potassium bichromate,

mercuric sulfate, ammonium ferrous sulfate, potassium

chloroplatinate, cobalt chloride, All reagents above

mentioned are analytical reagent . Polyaluminium

Chloride(PAC), Polyferric Sulfate(PFS), polymeric

aluminum ferric chloride (PAFC) and Polyacrylamide

(PAM) are Tech Technical grade.

Main instruments: electronic analytical balance, JJ-4

Jar-test Apparatus, surface tensiometer, acidometer.

2.2 Experimental method

Coagulation experiments were preformed in 250ml

beakers using a conventional Jar-test apparatus with six

paddles (JJ-4 Jar-test Apparatus). The measured amount

of coagulant was pipetted into the wastewater sample

(200mL). The pH of wastewater was adjusted with

HCl(1mol/L) or NaOH (1mol/L). The wastewater

samples were mixed rapidly at 150rpm for 2 min after

dosing, followed by slow stirring at 50rpm for 5 min and

sedimentation for 25 min. After flocculation, a

supernatant sample was withdrawn from about 20mm

below the wastewater surface for analyzing of chemical

oxygen demand (COD) and chromaticity removal

efficiency. The COD of the samples was determined by

the Chinese state standards GB11914-89. The

chromaticity of the samples was determined by the

Chinese state standards GB11903-89.

2.3 Experimental procedure

(1)The Screening of flocculants and synergistic effects

with surfactant.

(2)The comparison between cluster-surfactant flocculants

and traditional flocculation process.

(3)Regeneration of coking industrial wastewater by

cluster-surfactant flocculants.

3 Results and discussion

3.1 The Screening of flocculants and synergistic

effects with surfactant

Screening of flocculants is through check the removal

rate of COD and chromaticity of sample 1 by coagulant

dosage and pH.

3.1.1 Effect of coagulant dosage on COD and

chromaticity removal

In order to determine the optimum dosage of the three

coagulants for the removal of COD and chromaticity,

different dosages of PFS, PAFS and PAC were used in

the experiments. Fig.1 presents the experimental data for

the removal of COD and chromaticity.

As shown in Fig.1, with the increases dosage of three

kind of IPF, the rate of COD removal all increases

considerably till a loading. After this loading, the rate of

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COD removal started to decrease. Among three kind of

IPF, 70% COD reduction for optimum loading of

1500mg/l PFS, 68% COD reduction for optimum loading

of 1500mg/l PAFS, and 57% COD reduction for

optimum loading of 2000mg/l PAC. Under the same

dosage of flocculants, it was observed that the COD

removal rate by PFS was obvious higher than others.

500 1000 1500 2000 2500 300038

40

42

44

46

48

50

52

54

56

58

60

62

64

66

68

70

the

rem

ovin

g ra

te o

f C

OD

/%

the dosage of flocculant/mg/l

PAC PAFC PFS

Fig.1. Effect of coagulant dosage on the COD removal rate.

500 1000 1500 2000 2500 300050

52

54

56

58

60

62

64

66

68

70

72

74

76

78

80

the

rem

ovin

g ra

te o

f ch

rom

atic

ity/

%

the dosage of flocculant/mg/l

PAC PAFC PFS

Fig. 2. Effect of coagulant dosage on the chromaticity removal rate

As shown in Fig.2, with the increases dosage of three

kind of IPF, the rate of chromaticity removal all increases

till a loading and started to decrease. Among three kind

of IPF, 76% chromaticity reduction for optimum

loading of 1500mg/l PFS, 73% chromaticity reduction

for optimum loading of 1500mg/l PAFS, and 68%

chromaticity reduction for optimum loading of 2500mg/l

PAC. Under the same dosage of flocculants, the

chromaticity removal rate by PFS was obvious higher

than the others.

3.1.2 Effect of pH on coagulation

The pH of water samples is one of the important factor

affecting flocculation, determined the optimum pH value

of flocculation and treatment effect by experiments, the

results shown in Fig.3

4 5 6 7 8 9

42

44

46

48

50

52

54

56

58

60

62

64

66

68

70

72

the

rem

ovin

g ra

te o

f ch

rom

atic

ity/

%

pH

PAC PAFC PFS

Fig. 3. Effect of pH on the COD removal rate.

As shown in Fig.3, among three kinds of inorganic

polymer flocculants, compared with PAFC and PAC, PFS

reagent worked efficiently in a pH range from 5 to 9 and

significantly better than others. The best performance

was observed at pH 8. It was more than evident that at

pH 4 the performance was markedly dropped down to an

unsatisfactory level. The results showed that PFS not

only gave a good coagulation performance among the

three IPF, but also had a broader adaptability of pH in the

advanced treatment of coking wastewater.

After screening, PFS was determined as the

flocculants for cluster-surfactant flocculants.

3.1.3 Synergistic effects of coagulant and surfactant

(1) Surfactant synergistic test

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This experiment tests with four factors and three levels,

i.e., the dosage of PFS(mg/l) (A), the dosage of

PAM(mg/l) (B), the dosage of Surfactant K(mg/l) (C) and

pH (D), the percentage of COD and chromaticity removal

were the target in this experiments. The design and results

of experiment were as follow in Table 2.

Table 2 The result and analysis of orthogonal experiment

Factors NO

A B C D

Color Remov

al /%

COD Remova

l /%

1 1000 1.5 25 4 15 72.4

2 1000 2.5 37.5 7 77 72.4

3 1000 3.5 50 10 72 67.7

4 1500 1.5 37.5 10 77 68.8

5 1500 2.5 50 4 10 73.8

6 1500 3.5 25 7 85 76.0

7 2000 1.5 50 7 72 62.5

8 2000 2.5 25 10 80 74.6

9 2000 3.5 37.5 4 35 74.6

color K1

54.667 54.667 60.000 20.000 － －

color K2

57.333 55.667 63.000 78.000 － －

color K3

62.333 64.000 51.333 76.333 － －

color R

7.666 9.333 11.667 58.000 － －

COD K1

70.833 67.900 74.333 73.600 － －

COD K2

72.867 73.600 71.933 70.300 － －

COD K3

70.567 72.767 68.000 70.367 － －

COD R

2.300 5.700 6.333 3.300 － －

The result of orthogonal test shown that the sequence

of affect factors impacting the removal rate of COD as

follow: dosage of Surfactant (K)>the dosage of

PAM>pH>the dosage of PFS; the sequence of affect

factors impacting the removing rate of chromaticity as

follow: pH>dosage of Surfactant (K)>the dosage of

PAM> the dosage of PFS.

The best combination was A2B3C1D2: the dosage of

PFS was 1500mg/L, the dosage of PAM was 3.5mg/L, the

dosage of Surfactant (K) was 25 mg/L and pH=7 .

Through the analysis of the single factors test, the

optimum condition after correcting as follow: the dosage

of PFS was 1500mg/L, the dosage of PAM was 2.5mg/L,

the dosage of Surfactant (K) was 25 mg/L and pH=8.

Under this condition, the removal rate of COD and

chromaticity reached to 79% and 90.0% respectively, and

increased 9% and 14% respectively. As showed in Fig.1

and Fig.2, the synergistic effect was obviously.

(2) Analysis of synergistic effects

When the surfactant was added to the solution, the

surface tension would have change, the Fig.4 showed the

relationship of surface tension and the COD removal

rate.

0.0 12.5 25.0 37.5 50.0 62.5 75.015

20

25

30

35

40

45

50

55

60

65

70

75

60

65

70

75

80

the

rem

ovin

g ra

te o

f C

OD

/%

surf

ace

tens

ion/

(mN

/m)

the dosage of Surfactant(K)/mg/l

surface tension

the removing rate of COD

Fig. 4. The relationship between surface tension and the COD removal rate

We could see from Fig.4, at first, with the increase of

Surfactant (K), the surface tension of solution had a

sharp decline until the dosage of Surfactant (K) reached

25 mg/l and smoothed mainly after this point, meanwhile,

the COD removal rate reached to the peak point. Because

surfactant (K) changed the permeability, conductivity

and surface tension of the solution, physical properties

had changed when the concentration reached to CMC

(critical micelle concentration).

3.2 The comparison of cluster-surfactant

flocculants and traditional flocculation process

The Fig.5 showed the comparison of coagulation

performance of cluster-surfactant flocculants (PFS+PAM

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+Surfacant (k)) with inorganic coagulants (PFS) and

inorganic–organic dual-coagulants(PFS+PAM).

1 2 3 4 5 6serial number

PFS+PAM PFS+PAM+Surfactant(K)

Fig. 5. Effect of different flocculation combinations on the COD removal rate

As shown in Fig.5, when the Surfactant (K) was

charged into the traditional flocculation treatment

processing, the effect of flocculant strengthen observably.

Surfactant (K) could exert obvious synergistic effects

within the flocculants system. The removal rate of COD

reached to 79% under the optimum condition, improved

9% and 8% respectively when compare with PFS and

PFS+PAM, and cluster-surfactant flocculants had a better

precipitation effect.

3.3 Regeneration of coking industrial wastewater

by cluster-surfactant flocculants

In order to verify cluster-surfactant flocculants was

feasible to make the water can achieve the water quality

standards for the reclaimed wastewater, coking

wastewater sample 2 that outlet after A-A-O and

HSBEMBM○R biological treatment was investigated as

the object of study in this experiment. Table 1 showed

some special chemical parameters of sample 2 and Fig.6

presented the experimental data for the removal of COD

and chromaticity.

As shown in Fig.6 and Fig.7, Surfactant(K) could exert

obvious synergistic effects within the flocculants system,

when the Surfactant(K) was charged into the flocculation

treatment processing, The removal rate of COD could be

increased to 70% from 49% and the removal rate of

chromaticity may be increased to 93% from 85%. The

COD and chromaticity of effluent was less than 50 mg/L

and 30°respectively, so cluster-surfactant flocculants

make the coking industrial wastewater met the water

quality standard of reclaimed water.

1 2 3 4 5 6

20

25

30

35

40

45

50

55

60

65

70

the

rem

ovin

g ra

te o

f C

OD

/%

serial number

PFS PFS+PAM PFS+PAM+Surfactant(K)

Fig. 6. Effect of different flocculation combinations on the COD removal rate

1 2 3 4 5 6

55

60

65

70

75

80

85

90

95

the

rem

ovin

g ra

te o

f ch

rom

atic

ity/

%

serial number

PFS PFS+PAM PFS+PAM+Surfactant(K)

Fig. 7. Effect of different flocculation combinations on the

chromaticity removal rate

4 Conclusions

(1) Through studying the removal rate of COD and

chromaticity of sample 1 by coagulant dosage and pH，

PFS was determined as the flocculants for cluster

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-surfactant flocculants.

(2) Surfactant(K) can enhance the removal rate of

COD and chromaticity greatly, through synergistic test

and single factors correcting test we can draw that the

best condition of sample 1 was: the dosage of PFS was

1500mg/L, the dosage of PAM was 2.5mg/L ,the dosage

of Surfactant(K) was 25 mg/L and pH=8. Under this

condition, the removal rate of COD and chromaticity

improved 9% and 14% respectively when compared with

the traditional flocculation process, the synergistic effects

was obviously because Surfactant (K) changed the

physical properties of the solution.

(3) Cluster-surfactant flocculants make the COD and

chromaticity of coking industrial wastewater less than 50

mg/L and 30°respectively that meet the water quality

standard of reclaimed water. Therefore, the synergistic

treatment technology by fine chemicals and flocculants

can be effective for industrial wastewater recycling.

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