Desalination: Mohd Nordin Adlan, Puganeshwary Palaniandy, Hamidi Abdul Aziz
Desalination: Mohd Nordin Adlan, Puganeshwary Palaniandy, Hamidi Abdul Aziz
Desalination: Mohd Nordin Adlan, Puganeshwary Palaniandy, Hamidi Abdul Aziz
Desalination
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
a r t i c l e i n f o a b s t r a c t
Article history: FeCl3 coagulation and dissolved air flotation (DAF) were combined to assess the success of these techniques
Received 14 December 2010 for the treatment of semiaerobic landfill leachate. Treatment parameters (i.e.; flow rate, coagulant dosage, pH
Received in revised form 30 March 2011 and injection time) were optimized via response surface methodology (RSM) using central composite design
Accepted 1 April 2011
(CCD) to yield the maximum removal of turbidity, chemical oxygen demand (COD), color and ammonia
Available online 4 May 2011
nitrogen (NH3-N). Model-determined optimum conditions were tested to confirm the predicted results.
Keywords:
Initial concentrations of turbidity (259 FAU), COD (2010 mg/L), color (4000 PtCo) and NH3-N (1975 mg/L)
Dissolved air flotation were reduced by 50%, 75%, 93% and 41%, respectively. These experimental results were consistent with those
Coagulation predicted by the model. The optimum operating conditions for coagulation and DAF were 599.22 mg/L of
Ferric chloride FeCl3 at pH 4.76 followed with saturator pressure of 600 kPa, flow rate 6 L/min and injection time of 101 s.
Landfill leachate © 2011 Elsevier B.V. All rights reserved.
Response surface methodology
0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.desal.2011.04.006
M.N. Adlan et al. / Desalination 277 (2011) 74–82 75
2.3. Experimental set-up and procedure preliminary experiments [27]. Another factor that was concern in this
study is the injection time. The maximum value for the injection time was
The coagulation and DAF processes were performed as follows: set at 120 s in order to reduce the dilution effect in the batch study. The
(i) the pH of the leachate (4 L) was adjusted according to the experiment injection times were varied from 30 up to 120 s. However, increasing of
and the sample was added to the flotation cell, (ii) FeCl3 was added to the injection time will also increase the number of bubbles in the flotation
cell according to the design of experiment (iii) the leachate and FeCl3 cell, which simultaneously promotes more bubble particle attachment
were rapidly mixed (470 rpm for 5 min), (iv) water saturated with air and thus more particles will be floated. The values of pressure and flow
was injected from the saturator into the flotation cell for 2 min, and rate were set based on the research work conducted by Edzwald et al. [28]
(v) flotation was allowed to occur for 20 min and samples were collected in order to produce microbubbles in the flotation cell. This has been
from the sampling point. Treated leachate samples were analyzed using proved by Al-Shamrani et al. [14] in her study on treating oily wastewater.
the standard method [24]. COD was measured according to Method Four main parameters were chosen to evaluate the effectiveness of
5220D [24], (closed reflux, colorimetric method). Colors were reported the coagulation/DAF process, including turbidity (Y1), COD (Y2), color
as true color (filtered using 0.45 μm filter paper) and were determined (Y3) and NH3-N (Y4).
using a DR 2010 HACH spectrophotometer, as in Method 2120C [24]. Generally, the CCD consists of a 2k factorial with nF factorial runs
Turbidity was determined using a DR2010 HACH spectrophotometer. (points with all possible combination of the minimum and maximum
NH3-N was measured according to the Nessler method and using a DR values of the control parameters), 2k axial or star runs (one of the
2010 HACH spectrophotometer as in Method 4500C. Alkalinities were parameters has the minimum or maximum value and all other
measured using 2320B titration methods [24] and are reported as mg/L parameters have their nominal value), and nC center runs (all control
of calcium carbonate. SS were determined using a DR 2010 HACH parameters are set to their nominal values). In this study, a total of 50
spectrophotometer, similar to Method 2540D [24]. The pH and DO were experiments were performed to assess the five experimental factors,
measured using a W-100 Witeg pH meter and WTW multi-parameter according to the equation CCD = 2k + 2 k + 8, where k is the number
340i, respectively. of factors. Forty-two experiments were improved with eight replica-
tions at the design center to evaluate the pure error, [26]. Eq. (2)
2.4. Calculations shows the quadratic model used to estimate the optimal point:
Table 4
Results of the central composite design.
1 2 3 4 1 2 3 4
1 500 5 812.5 5 75 43.2 71.6 91.7 37.5 2.74 32.37 50.21 10.88
2 600 4 125 4 30 − 4.8 36.5 54.9 9.5 2.74 36.70 55.62 10.88
3 500 5 812.5 5 120 54.0 74.6 95.1 39.3 2.74 30.20 50.21 10.88
4 600 4 125 6 30 − 6.4 28.7 34.9 3.0 2.74 34.53 55.62 10.88
5 600 4 1500 6 30 −80.8 50.5 78.5 6.7 − 31.38 53.44 65.84 19.43
6 400 4 125 4 30 −12.1 32.3 51.6 8.0 − 31.38 57.77 71.26 19.43
7 400 6 125 4 30 − 4.0 30.7 51.9 11.9 − 31.38 55.61 65.84 19.43
8 400 5 812.5 5 75 29.9 68.8 93.8 33.5 − 31.38 59.94 71.26 19.43
9 500 6 812.5 5 75 7.8 70.8 90.8 38.1 − 24.21 26.46 35.65 10.88
10 600 6 125 6 30 − 0.3 32.0 37.8 2.8 − 24.21 30.79 41.07 10.88
11 600 4 1500 4 120 −37.2 74.3 89.6 49.5 − 24.21 24.29 35.65 10.88
12 600 4 125 6 120 26.7 57.9 60.8 40.0 − 24.21 28.62 41.07 10.88
13 500 5 812.5 5 30 46.7 64.4 94.1 9.3 − 58.33 47.52 71.25 19.43
14 600 6 125 4 30 0.4 33.4 53.6 16.6 − 58.33 51.85 76.66 19.43
15 500 5 812.5 5 75 45.2 72.3 95.7 27.1 − 58.33 49.69 71.25 19.43
16 600 5 812.5 5 75 16.6 77.5 93.8 41.5 − 58.33 54.02 76.66 19.43
17 500 5 1500 5 75 15.5 71.0 89.4 38.3 32.63 55.89 64.98 40.54
18 600 4 125 4 120 30.1 59.4 74.6 48.6 32.63 60.22 70.40 40.54
19 400 6 1500 6 30 −48.5 54.4 80.6 18.2 32.63 53.72 64.98 40.54
20 500 5 125 5 75 15.8 46.9 56.5 29.7 32.63 58.05 70.40 40.54
21 500 5 812.5 5 75 44.9 72.6 91.8 34.6 − 1.48 67.97 80.62 49.08
22 600 6 1500 6 30 − 104.6 53.5 80.1 30.6 − 1.48 72.30 86.03 49.08
23 500 5 812.5 6 75 − 48.3 53.3 70.0 36.1 − 1.48 70.14 80.62 49.08
24 500 5 812.5 5 75 46.5 72.8 94.9 31.0 − 1.48 74.47 86.03 49.08
25 400 4 1500 6 120 − 63.1 63.8 79.4 47.9 5.68 49.98 50.43 40.54
26 400 4 125 6 30 − 20.6 27.7 55.6 12.2 5.68 54.31 55.84 40.54
27 500 4 812.5 5 75 48.8 72.2 89.0 36.9 5.68 47.81 50.43 40.54
28 500 5 812.5 4 75 − 11.5 65.5 80.9 39.2 5.68 52.14 55.84 40.54
29 400 6 125 4 120 26.4 54.3 64.8 42.6 − 28.44 62.06 86.03 49.08
30 400 4 1500 4 30 − 52.8 57.7 53.4 28.1 − 28.44 66.39 91.44 49.08
31 400 6 125 6 30 − 12.5 22.9 19.6 11.9 − 28.44 64.23 86.03 49.08
32 400 4 125 6 120 19.1 51.2 54.4 41.2 − 28.44 68.56 91.44 49.08
33 600 6 125 6 120 39.3 53.7 48.7 49.8 35.85 68.94 88.21 35.53
34 400 4 125 4 120 30.2 54.2 64.0 42.8 35.85 73.27 93.63 35.53
35 400 6 1500 4 120 −11.7 69.7 78.9 41.4 35.85 71.11 90.92 35.53
36 400 6 125 6 120 −41.2 49.2 59.8 41.5 35.85 71.11 90.92 35.53
37 600 4 1500 4 30 8.7 59.6 82.1 23.2 52.91 51.76 64.33 31.26
38 500 5 812.5 5 75 35.3 70.5 86.6 43.2 18.79 70.51 89.95 39.80
39 600 6 1500 6 120 43.6 73.5 93.2 50.8 0.63 64.56 81.90 35.53
40 400 4 1500 6 30 −80.4 41.8 66.3 13.9 − 26.32 58.64 77.33 35.53
41 400 4 1500 4 120 − 4.2 68.9 81.3 55.0 20.90 61.60 83.53 15.16
42 600 6 125 4 120 30.8 56.8 69.4 34.6 50.79 80.62 98.31 44.81
43 600 4 1500 6 120 − 21.2 61.2 89.7 46.6 35.85 71.11 90.92 35.53
44 500 5 812.5 5 75 50.3 71.8 89.6 33.9 35.85 71.11 90.92 35.53
45 600 6 1500 4 30 − 27.3 54.9 66.5 29.8 35.85 71.11 90.92 35.53
46 400 6 1500 6 120 − 48.5 61.8 84.9 42.4 35.85 71.11 90.92 35.53
47 500 5 812.5 5 75 25.2 70.9 86.5 30.6 35.85 71.11 90.92 35.53
48 500 5 812.5 5 75 48.0 69.2 88.0 37.5 35.85 71.11 90.92 35.53
49 400 6 1500 4 30 6.8 55.0 65.1 22.0 35.85 71.11 90.92 35.53
50 600 6 1500 4 120 42.8 74.7 89.3 47.8 35.85 71.11 90.92 35.53
previous reports [14]. COD was reduced by 22.9 to 77.5%, color by 19.6 concentration of 1975 mg/L, was achieved at pH 4, 400 kPa, 4 L/min flow
to 95.7%, and NH3-N by 2.8 to 55% (Table 4). COD was reduced by a rate, and 120 s injection time, and FeCl3 dose of 1500 mg/L.
maximum of 78%, from an initial concentration of 2610 mg/L, using
the following treatment conditions: pressure, 600 kPa; flow rate, 5 L/ 3.1. Regression model equation and analysis of variance (ANOVA)
min; FeCl3 dose, 812.5 mg/L; pH 5; and injection time, 75 s. Using a
coagulation/flocculation treatment, Tatsi and co-workers [33] dem- Based on the sequential model sum of squares, the models for
onstrated a reduction in COD by 80% with a FeCl3 dosage of 1500 mg/L turbidity, COD, color and NH3-N percentages removal were selected based
and flotation time of 20–30 min [7]. The coagulation/DAF treatment on the highest order polynomials where the additional terms were
used in the current study required only 5–10 min and also reduced significant and the models were not aliased. The models were coded as Y1,
the amount of sludge produced after treatment. Y2, Y3 and Y4 for turbidity, COD, color and NH3-N, respectively.
Reduction in color was considerably high, with the highest removal of The quadratic model for all four terms, Y1, Y2, Y3 and Y4, were selected
96%, from an initial measurement of 4000 PtCo units. This was achieved as suggested by the software and are shown in Eqs. (3)–(6). The
using 812.5 mg/L FeCl3 with pH 5, at 500 kPa, 5 L/min flow rate and 75 s independent variables in the models were pressure, flow rate, dosage, pH
injection time. The maximum removal of NH3-N (55%), from an initial and injection time and were coded as A, B, C, D, and E respectively. The
78 M.N. Adlan et al. / Desalination 277 (2011) 74–82
final empirical models used to generate coded factors for each variable determination (R2) for each empirical equation from Eq. (3)–Eq. (6),
are as follows: were 0.65, 0.97, 0.89 and 0.86 respectively. Three out of four models
(Y2, Y3 and Y4) show a good agreement between the experimental and
2
Y1 = 35:85−17:06 C−13:48D + 14:95E−48:70D ð3Þ model-predicted values. The standard deviations for the models were
24.58, 2.89, 6.50, and 5.44 for Y1, Y2, Y3 and Y4 respectively. Here, for
2 2 turbidity removal, the coefficient of determination was considerably
Y2 = 71:11 + 2:16A + 9:37C−2:96D + 9:51E–9:97C –9:51D ð4Þ
low and the standard deviation model was fairly high compared to
+ 1:09BC–2:25CE
other models. As shown in Table 5, 65%, 97%, 89% and 86% of the total
2 2
variability in turbidity, COD, color and NH3-N removal percentages
Y3 = 90:92 + 2:71A + 12:81C−2:29D + 7:39E−13:78C −11:31D ð5Þ were accredited to the empirical model, respectively. The ANOVA
+ 4:99CD (Table 5) revealed that all independent variables were significant
(p b 0.05) for determining turbidity, COD, color, and NH3-N.
2
Y4 = 35:53 + 4:27 C + 14:83E–5:55E : ð6Þ
3.2. Effect of factors on turbidity, COD, color, and NH3-N removal
The quality of the model was evaluated based on the coefficient of
determination in addition to the ANOVA statistical analysis. The Perturbation plots were analyzed in order to further identify the
ANOVA results for the quadratic model for turbidity, COD, color and most sensitive factors for leachate treatment (Fig. 2). Coagulant dose,
NH3-N percentage removal are shown in Table 5. The coefficients of pH, and injection time appeared to be the most influential for
reducing turbidity (Fig. 2a). COD and color removals were affected by
Table 5
pressure, flow rate, coagulant dosage, pH, and injection time (Fig. 2b
ANOVA of quadratic model for turbidity (Y1), COD (Y2), color (Y3) and NH-N3 (Y4) and c). However, only injection time and coagulation dose were
percentage removal with the operating parameters. (pressure (A), flow rate (B), dosage important for NH3-N removal (Fig. 2d).
of coagulant (C), pH (D) and injection time (E)). Coagulant dosage is the only factor that exhibited a significant
Source/operating Sum of Degree of Mean F Value Prob N F effect for all parameters. For example, turbidity is removed with
parameters squares freedom square increasing FeCl3 concentration up to a threshold level (above 813 g/L
Model (Y1) 49461.46 4 12365.37 20.47 b0.0001 based on Table 4), after which higher dosages produced bigger and
C 9893.44 1 9893.44 16.38 0.0002 heavier flocs. This result was likely due to high concentrations of
D 6174.92 1 6174.92 10.22 0.0025 humic acids in the leachate [34], which are able to react with the
E 7594.30 1 7594.30 12.57 0.0009 metal coagulant and form complex substances that produce sludge
2
D 25798.81 1 25798.81 42.70 b0.0001
Residual 27187.12 45 604.16
[35]. This sludge cannot be removed by DAF, thus increasing turbidity
Lack of Fit 26714.91 38 703.02 10.42 0.0017 and impeding leachate treatment [14]. COD and color exhibited a
Pure error 472.20 7 67.46 similar response to coagulant dosage (Fig. 2b and c). These results
Std. Dev. = 24.58 PRESS = 34,356.53 C.V. = 898.97 R-squared = 0.6453 suggest that similar components of the leachate contribute to both
Adj R-squared = 0.6138 Adeq precision = 14.311
COD and color [3,36]. Color was steadily removed with increasing
Model (Y2) 10469.67 8 1308.71 156.92 b0.0001 FeCl3 dose until it reached a maximum removal percentage (~96%;
A 159.37 1 159.37 19.11 b0.0001 Fig. 2c). The color of the treated leachate then increased with higher
C 2986.03 1 2986.03 358.03 b0.0001 coagulant dosage due to the excess ferric chloride in the treated
D 297.54 1 297.54 35.68 b0.0001 sample. NH3-N was also removed with increasing coagulant dosage
E 3077.06 1 3077.06 368.94 b0.0001
C2 361.33 1 361.33 43.32 b0.0001
(Fig. 2d). According to Dempsey [37], charged NH3-N particles are
D2 328.42 1 328.42 39.38 b0.0001 neutralized during coagulation and subsequently adsorbed onto floc
BC 37.69 1 37.69 4.52 0.0396 surfaces. The sludge that is generated is then removed by DAF.
CE 161.69 1 161.69 19.39 b0.0001 As shown in Fig. 2(a), (b) and (c), pH strongly influenced turbidity,
Residual 341.95 41 8.34
COD and color removals. Coagulation induced by FeCl3 was most
Lack of Fit 331.49 34 9.75 6.52 0.0076
Pure Error 10.46 7 1.49 effective under acidic conditions. This finding is consistent with
Std. Dev. = 2.89 PRESS = 543.48 C.V. = 4.99 R-squared = 0.9684 previous leachate treatment studies that used coagulation/flocculation
Adj R-squared = 0.9622 Adeq precision = 45.980 strategies [6,10,33]. This is likely due to the adsorption of negatively
charged organic matter [21] onto the positively charged coagulant ions
Model (Y3) 14882.44 7 2126.06 50.37 b0.0001
A 249.43 1 249.43 5.91 0.0194
(e.g., Fe3+, Fe(OH)+2 , and Fe(OH)
2+
) under acid conditions [38]. The
C 5577.22 1 5577.2 132.14 b0.0001 ideal pH for leachate treatment thus lies in the slightly acidic region
D 177.80 1 177.80 4.21 0.0464 (pH = 4.76). On the other hand, pH did not appear to influence NH3-N
E 1856.22 1 1856.22 43.98 b0.0001 removal (Fig. 2d). At pH 4 to 7, the majority of ions will exist as NH+4
2
C 689.87 1 689.87 16.34 0.0002
[39], thus the pH range (4 to 6) considered for this study did not alter
D2 464.33 1 464.33 11.00 0.0019
CD 797.30 1 797.30 18.89 b0.0001 conditions enough to affect NH3-N adsorption.
Residual 1772.73 42 42.21 Injection time also influenced turbidity, COD, color and NH3-N
Lack of Fit 1684.84 35 48.14 3.83 0.0350 reduction, as all variables were significantly reduced with increasing
Pure Error 87.89 7 12.56 injection time (Fig. 2(a), (b), (c) and (d)). This may be due to the
Std. Dev. = 6.50 PRESS = 2627.93 C.V. = 8.80 R-squared = 0.8936
Adj R-squared = 0.8758 Adeq precision = 24.112
dilution effect resulting from the sustained injection of the air-
saturated water.
Model (Y4) 8429.14 3 2809.71 94.90 b0.0001 Overall, pressure and flow rate did not appear to be as important as
C 620.60 1 620.60 20.96 b0.0001 other factors. Fig. 2b and c indicate that slight increases in these
E 7473.73 1 7473.73 252.44 b0.0001
parameters resulted in slightly enhanced removal of COD and color.
E2 334.81 1 334.81 11.31 0.0016
Residual 1361.89 46 29.61 However, saturator pressure and flow rate are very important in order
Lack of Fit 1185.24 39 30.39 1.20 0.4314 to obtain higher saturator efficiency and bubble volume concentration
Pure error 176.66 7 25.24 as well as smaller bubble size [16]. These features are important for
Std. Dev. = 5.44 PRESS = 1617.29 C.V. = 17.13 R-squared = 0.8609 designing and operating of DAF as a solid–liquid separation process
Adj R-squared = 0.8518 Adeq precision = 24.819
[18].
M.N. Adlan et al. / Desalination 277 (2011) 74–82 79
Fig. 2. Perturbation plot for (a) turbidity, (b) color, (c) COD, and (d) NH3-N removal. Coded values are shown for each factor and refer to actual values listed in Table 3 (Note: A =
pressure, B = flow rate, C = dosage, D = pH and E = injection time).
In order to study the interactive relationship between independent shows that at constant pH 5, the turbidity removal has reduced with an
variable and responses, 3D surface response and counter plots of the increase in coagulant dosage.
quadratic model were drawn using Design Expert software. Fig. 3(a), Based on Fig. 3(b), the COD removal was optimum at higher dosage
(b), (c) and (d), show the 3D surface response and counter plots, where of 812.5 to 1156.25 mg/L FeCl3, with pH between 4.5 and 5.5. At this
two variables were varied within the experimental range while others condition, the percentage removal of COD was 73%. In this figure, the
were kept constant. The constant variables were chosen based on the dosage and the pH values were varied, while other factors (pressure,
level of sensitivity of the variables toward the responses, (based on flow rate and injection time) were kept constant at higher values due to
Fig. 2). the same reason as for the turbidity removal as shown in Fig. 3(b).
Fig. 3(a), shows the pH and dosages of coagulant were varied. Other However, for COD removal pressure and flow rate were observed given
factors pressure, flow rate and injection time were kept constant at the less significant effect compared to Fig. 2(a).
maximum values. This is because, based on the perturbation plots, only As for color removal, Fig. 3(c) indicated that the maximum removal
three factors (pH, coagulant dosage and injection time) had contributed was at coagulant dosage of 812.5 mg/L with pH value between 4.5 and 5.
significant effect toward the percentage removal of turbidity. As Again in this 3D response surface, the coagulant dosage and pH were
mentioned above, highest injection time, flow rate and pressure offer varied. This is because, the perturbation plot in Fig. 2(c), suggested that
a favorable condition. Due to that, these three conditions were kept coagulant dosage and pH had significant effect toward the color removal.
constant at highest value (120 s, 6 L/min and 600 kPa respectively). In terms of ammonia nitrogen removal Fig. 3(d) indicates that, the
Based on Fig. 3(a), the optimum condition was at pH 5, with coagulant dosage and the injection time were varied based on the significance in
dosage 125 mg/L, and the removal of turbidity was 70%. Fig. 3(a) also the perturbation plot (Fig. 2(d)). Other factors (pressure, flow rate
80 M.N. Adlan et al. / Desalination 277 (2011) 74–82
Fig. 3. 3D response surface for (a) turbidity, (b) COD, (c) color and (d) ammonia nitrogen removal.
and pH) were kept constant. The highest removal was obtained at the Acknowledgments
highest dosage with highest injection time. At this condition, the
ammonia nitrogen removal was 49%. This study was funded by the Ministry of Science, Technology
and Environment of Malaysia (Grant no. 6013309) and Universiti
Sains Malaysia USM-RU-PGRS (Grant no. 1001/PAWAM/8042021).
3.3. Optimization of experimental conditions The author also wishes to acknowledge cooperation provided by the
Majlis Perbandaran Seberang Perai, Penang and the contractor Idaman
Graphical optimization was used to determine the optimum process Bersih Sdn. Bhd., Penang
parameters for maximum removal of turbidity, COD, color, and NH3-N
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