The PONILIT GT-2 anionic polyelectrolyte was tested as flocculant into chemical wastewater treatment. The modeling of laboratory wastewater treatment ...
“Gh.Asachi” TECHNICAL UNIVERSITY OF IASI FACULTY OF CHEMICAL ENGINEERING, DEPARTMENT OF ENVIRONMENTAL ENGINEERING AND MANAGEMENT, 71A D.Mangeron Bvd., 700050 IASI, ROMANIA
INDUSTRIAL WASTEWATER REUSE. WASTEWATER CHEMICAL TREATMENT WITH PONILIT GT-2 ANIONIC POLYELECTROLYTE Carmen ZAHARIA, Mioara SURPĂŢEANU and Matei MACOVEANU • Wastewater reuse into the technological process becomes a demand for process efficiency improvement and, also, for minimization or reduction of environment pollution. In this context, chemical wastewater treatment (e.g., coagulation-flocculation followed by sedimentation and/or filtration) before wastewater recycling into the technological process is an opportunity to remove some important pollutants as solid particles, organic compounds expressed through chemical oxygen demand (COD), total organic carbon (TOC) or biochemical oxygen demand (BOD), heavy metals or other toxic pollutants1-10.
• Moreover, the European Union elaborated the Directive on Integrated Pollution Prevention and Control (IPPC) that provides emission limits, as well as recommendations for futher reduction in water use. The recent developed purification technologies and anticipated technologies show that there is potential to produce a high water quality by internal treatments of process water. Consequently, there is a better chance to reuse the industrial wastewater effluent into the technological process as fresh water, progressing toward “zero liquid effluent” (ZLE) concept. Lab and practical experiments on ceramic manufacturing shown that a multi-component removal system consisting of coagulant / flocculant / microparticles (bentonite, other clays) can be an effective way to optimize the wastewater treatment and reduce the process water loading.
• The PONILIT GT-2 anionic polyelectrolyte was tested as flocculant into chemical wastewater treatment. The modeling of laboratory wastewater treatment considering as independent variables the temperature, polyelectrolyte dose, mixing time and as modeling function or optimization criteria the turbidity and color removal efficiency, was performed using a third order rotatable design 23 type3,10.
The experiments were performed on synthetic wastewaters with different composition (e.g., turbidity of 100-500 FTU, suspended solids of 250-1000 mg/L, COD of 52-72 mg O2/L, pH of 6.5-7, conductivity of 250-270 µS/cm, total hardness of 14-15°G, chloride of 75 mg/L etc.), temperatures, mixing times, and flocculant doses. As flocculation agent was used an anionic polyelectrolyte solution of 0.5 % (w/v) named PONILIT GT-211. All experiments were performed at laboratory scale set-up. Water treatment efficiency It was expressed by turbidity, color and/or chemical oxygen demand (COD) removals using Eq.(1).
R% =
C0 − C ⋅ 100 C0
(1) where: C0 and C are initial and final turbidity, color or COD.
Preparation of synthetic waters
Flocculation agent
Synthetic wastewaters were prepared with drinking water, organic substances (e.g., additives, conditioning agent etc.), and bentonite which was previously dried at 105°C for 2 hours. The turbidity, suspended solids, chlorides (Table 1) were directly measured with DRELL DR 2000 spectrophotometer, HACH company. The wastewater color was expressed in Hazen units, after determination of absorbance at 456 nm (50 HU corresponds to an absorbance of 0.069). pH was directly measured using a digital HACH pH-meter. Conductivity was measured with a RADELKIS OK-102/1 conductometer. For chemical oxygen demand (COD) was used the dichromate spectrophotometrical method12. The titrimetric method with Complexon III and ErioT was used for total wastewater hardness12.
It was used an anionic polyelectrolyte containing the sodium salt of a copolymer based on maleic acid and vinyl acetate (PONILIT GT-2), as 0.5 % (w/v) solution. The principal characteristics of this polyelectrolyte are: a yellow-amber color, a content of active product varying between 33-36 % (w/w), a density at 20 0C of 1.18 g/cm3, pH which varies between 6.5 – 8 and average molecular mass of 2.106 11. The polyelectrolyte dose was varied between 0.1 - 100 mg/L.
Table 1 Wastewater characteristics Indicators
Series I
Series II
Series III
pH Conductivity, µS/cm Suspended solids (SS), mg/L Turbidity, FTU COD, mg O2/L Temporary hardness, °G Total hardness, °G Chlorides, mg/L
6.5 250 250 100 72 3.07 14.25 75
6.83 265 500 250 63.9 3.27 14.53 75.1
7.0 270 1000 500 52.7 3.7 14.76 75.1
Table 2 Experimental data of flocculation-sedimentation using PONILIT GT-2 polyelectrolyte Color , HU
Color removal, %
COD, mg O2/L
COD removal, %
0.647
234.42
32.44
42.93
18.53
86.15
0.147
53.26
85.72
29.60
43.83
34
88.23
0.122
44.20
88.12
28.59
45.27
15
28
90.31
0.10
36.23
90.29
28.66
45.27
The experimental results after flocculation and sedimentation of synthetic wastewater samples treated with PONILIT GT-2 polyelectrolyte are presented in Table 2.
20
29
89.96
0.099
35.86
90.38
29.5
44.02
25
37
87.19
0.135
48.91
86.89
34.06
35.37
30
25
91.34
0.097
35.14
90.58
34.27
34.98
The removal efficiency after a supplementary step of wastewater treatment, filtration under pressure, is no more than 2.42 % higher for turbidity than the values performed after sedimentation (for COD removals, the values are similar).
50
154
46.71
0.53
197.03
48.54
35.80
24.49
100
84
70.93
0.30
108.70
70.87
34.67
34.22
0
97
40.85
0.297
107.63
47.89
45.60
28.63
5
79
49.68
0.285
103.26
48.64
50.54
20.9
10
45
71.33
0.162
58.69
70.81
50.54
20.9
15
24
84.71
0.090
32.61
83.78
53.36
16.48
20
31
80.25
0.112
40.58
79.82
52.59
17.71
25
43
72.61
0.152
55.07
72.61
52.58
17.71
30
35
77.70
0.124
44.93
77.65
52.96
50
50
68.15
0.177
61.13
69.66
100
99
36.94
0.355
128.62
0
75
21.05
0.271
5
21
75.58
10
27
15
SS, mg/L
When no polyelectrolyte is added, the removal degrees are low as follows: 36.33 % turbidity, 32.44 % color and 20.45 % COD.
It can be appreciated the chemical wastewater treatment by flocculation with PONILIT GT-2 anionic polyelectrolyte followed by solid/liquid separation using sedimentation and/or filtration leads to higher removal degrees for turbidity, color (e.g., > 80 %) and, partially, COD (e.g., < 45 mg O2/L).
1000
500
The matrix with the experimental modeling design is presented into Table 4. The proposed model is described by the following two equations: 2+
Y1 = 62.603 + 17.424 X1 - 4.012 X2 + 1.375 X3 + 1.312 X1 1.365 X22 + 1.012 X32 + 0.556 X1X2 - 0.394 X1X3 - 0.169 X2X3
(4)
2
Y2 = 69.36 + 16.396 X1 + 3.913 X2 + 1.472 X3 + 0.538 X1 + 1.475 X22 + 0.468 X32 + 0.288 X1X2 - 0.088 X1X3 - 0.688 X2X3 (5) The correlation coefficients have the following values: RY1X1X2X3 = 0.986 for Y1 and RY2X1X2X3 = 0.983 for Y2, values close to unity. The Fisher test values were found to be: F1calc = 186.49 for Y1 and F2calc = 152.87 for Y2. Comparing them with Ftab = 6.59, resulted values higher than the value from the statistical table. It demonstrates that the independent variables have a significant influence on the dependent variable. For Y1 function, the local maximum point is X1* = 1.682, X2* = 0 and X3* = 0 corresponding to a turbidity removal of 95.6 %. For Y2 function, the local maximum point is: X1* = 0, X2* = 1, X3* = 1 corresponding to a color removal of 93.135 %. The average deviation is of 2.86 % for Y1, and of 2.57 % for Y2. Transposed to real variables, these optimal values correspond to a temperature of 23.41°C, a polyelectrolyte dose of 10 mg/L PONILIT GT-2 and a mixing time of 20 minutes for turbidity removal and, respectively, a temperature of 20°C, a dose of 15 mg/L polyelectrolyte and a mixing time of 30 minutes for color removal.
250
Polyeel. dose, mg/L
Turbidity, FTU
Turbidity removal, %
A456
0
184
36.33
5
40
10
Operational regime The wastewater samples were firstly mixed for 3 minutes with 160 rpm, and then slowly for 30 minutes with 50 rpm. In the next interval of 60 minutes, the agitation was interrupted, in order to allow the generated flocs to settle at the bottom of reaction reactor (a batch experimental system was used). Moreover, the supernatant was filtrated under pressure, and the filtrate was analyzed in terms of turbidity, color and COD. Experimental modeling and design The main factors that influence the synthetic wastewater treatment were considered to be: temperature (z1), polyelectrolyte dose (z2) and mixing time at 50 rpm (z3) (Table 3). As modeling function or optimization criteria were considered the removal degree (Y,%) concerning the turbidity (Y1) and color (Y2). The mathematical model of a “n” variable central composite design is presented by Eq.(2): n
Y = b0 + ∑ bi X i + i =1
n
∑b j ,i =1
ji
(2) where: Y – response function; Xi, Xj – coded
Xi X j
variable, b0, bi, bj, bij – model coefficients.
Table 3 Codification of independent variables Variable/value
Real variable
Coded variable
Real basic value, zi0
Variation step, ∆zi
Temperature, °C
z1
X1
15
5
Polyelectrolyte dose, mg/L
z2
X2
10
5
Mixing time, min
z3
X3
20
10
The coded value of zi, denoted as Xi, is determined with Eq.(3) 3:
xi =
zi − zi 0 ∆zi
(3)
Table 4 The experimental matrix of the wastewater treatment Exp no
Z1
Z2
Z3
X1
X2
X3
Y1
Y2
1
10
5
10
-1
-1
-1
44.3
50.7
2
20
5
10
1
-1
-1
81.6
84.2
17.11
3
10
15
10
-1
1
-1
52.3
59.3
53.66
16.01
4
20
15
10
1
1
-1
89.9
93.8
36.03
55.33
13.40
5
10
5
30
-1
-1
1
49.4
56.3
98.19
19.34
57.28
20.45
6
20
5
30
1
-1
1
83.2
89.3
0.079
28.62
75.50
53.23
22.56
7
10
15
30
-1
1
1
54.8
62.0
68.60
0.091
32.97
77.82
55.65
22.70
8
20
15
30
1
1
1
92.7
96.3
19
77.90
0.074
26.81
77.09
59.70
17.08
9
6.59
10
20
-1.682
0
0
36.0
41.5
20
28
67.44
0.103
37.32
68.11
58.95
18.13
10
23.41
10
20
1.682
0
0
90.3
94.2
25
24
72.09
0.078
28.26
75.85
62.24
13.56
11
15
1.59
20
0
-1.682
0
56.3
63.8
30
14
83.72
0.055
19.93
82.97
61.52
14.55
50
21
75.58
0.076
27.54
76.47
63.17
12.26
12
15
18.41
20
0
1.682
0
70.3
77.2
100
29
66.27
0.105
38.04
67.49
63.55
11.74
13
15
10
3.18
0
0
-1.682
60.3
66.4
14
15
10
36.82
0
0
1.682
64.3
68.9
15
15
10
20
0
0
0
62.0
69.3
16
15
10
20
0
0
0
62.9
69.7
17
15
10
20
0
0
0
63.1
70.1
18
15
10
20
0
0
0
62.8
69.6
19
15
10
20
0
0
0
63.2
68.8
20
15
10
20
0
0
0
62.7
69.7
1.50 1.00 0.50 0.00 -0.50 -1.00 -1.50 -1.50
-1.00
-0.50
0.00
0.50
1.00
1.50
Figure 1 Dependence of Y1 (turbidity) on X2 and X3 (X1=0). a: Y1=Y(0,x2,X3) ; b: isoline 1.50 1.00
1.
0.50 0.00 -0.50
• A study of chemical wastewater treatment using PONILIT GT-2 anionic polyelectrolyte for removal of turbidity, color and COD was performed. Reuse of treated industrial wastewater into the technological process (after flocculation, sedimentation and/or filtration) is a demand for implementation of European directives in order to achieve “zero liquid effluent” emission. • The testing of PONILIT GT-2 anionic polyelectrolyte as flocculant into the lab wastewater treatment leads to high removal degree of turbidity and color (e.g., >80 %) and, partially, of COD (e.g.,
