European Journal of Scientific Research ISSN 1450-216X / 1450-202X Vol. 148 No 1 December, 2017, pp. 143-154 http://www. europeanjournalofscientificresearch.com
Rheological Properties of Waste water from the ceramic tile Industry Treated with Different Coagulants El-Shimaa M. El-Zahed Chemical Engineering Department Higher Technological Institute, 10th of Ramadan City Sh.K. Amin Corresponding Author, Associate Professor Chemical Engineering and Pilot Plant Department Engineering Research Division, National Research Centre (NRC) 33 El Bohouth St. (Former El Tahrir St.), Dokki, Giza, Egypt PO box 12622, Dokki, Giza, Egypt Affiliation ID: 60014618 Tel: 202 33335494; Fax: 202 33370931 E–mail:
[email protected] or
[email protected] N.F. Abdel Salam Chemical Engineering Department Faculty of Engineering, Cairo University F.I. Barakat Chemical Engineering Department Faculty of Engineering, Cairo University M.F. Abadir Chemical Engineering Department Faculty of Engineering, Cairo University Abstract The rheological properties of wastewater sludge emanating from a ceramic tiles factory were investigated using a Brookfield type rheometer. Three coagulants were used in different proportions, namely, carboxy-methyl cellulose(CMC), alum, and poly-acrylamide(PAM). The effect of the coagulant type and percent addition on the non – Newtonian behavior of the suspension was disclosed. Results revealed that adding 0.6% alum (by weight) yielded the lowest viscosity among chosen coagulants which reflects positively on the power required to pump the waste sludge and move it to the filtration or sedimentation units.
Keywords: Wastewater treatment, Tile industry, Coagulant, rheology 1. Introduction Ceramic Tile manufacturing industry is one of the most popular industries around the world. It involves several operations and processes such ascrushing, grinding, wet mixing, drying, glazing,
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El-Shimaa M. El-Zahed, Sh.K. Amin, N.F. Abdel Salam, F.I. Barakat and M.F. Abadir
firing, and selection-packing [Bhalodiya et al., 2016]. As water is a major raw material in the manufacturing of tiles, itsusage varies greatly between sectors and processes [Ibáñez-Forés et al., 2013].Large amounts of waste water are produced throughout the wet grinding and forming processes [Huang et al., 2013]. The composition of these wastewaters effluent includes fine suspended particles of clays minerals or glazes resulting in colored wastewater with high concentrations ofturbidity and suspended solids. Also, insoluble silicates, electrolytes, anions such as sulfate(100-500 mg/L), chloride (100-700mg/L), suspended and dissolved heavy metals such as lead and zinc, COD (150- 1000 mg/L) and BOD (50-400 mg/L) can be found among its components [Enrique et al., 2000; Ibáñez-Forés et al., 2013; Bhalodiya et al., 2016]. The presence of appropriate wastewater treatment systems prevents the contamination of waterresources and environment and provides a new source of water for reuse [Aghakhani et al., 2010]. Two main techniques are used in that respect, namely, sedimentation in settling tanks and filtration. In both cases, chemicalcoagulants are often added to the industrial effluents to remove the substances producing turbidity before discharge or recycle [Bhalodiya et al., 2016]. Coagulants are metallic salts or polymers that assist in agglomerating fine particles into flocs that are easier to remove [Abadi et al., 2016].In general the use of any specific coagulant has to take into consideration, the technical, economic, social and environmental impacts of its usage. Khan et al.[2003] used aluminum sulphate (Alum) and iron sulphateto flocculate fine particles in the sugar industry,whileParmar et al.[2011] used that salt to treat dairy waste water.Also, the use of aluminum chloride was investigated by Kumar et al. [2011] in the pulp and paper industry, while ferric chloride was used by Ghaly et al. [2006] to treatgrease waste water. Besides aluminum sulphate, Poly aluminum chloride (PAC) is a polymer that has been successfully used in many industries such as textile industry [Sabur et al., 2012] and effluent oil industry [Ahmad et al., 2006]. Other polymeric materials have been also used although to lesser extentsuch as Poly ferric chlorides (PFCs) [Yu-li et al., 2006] and lanthanide salts [Sahu and Chaudhari, 2013]. On the other hand, the investigation of fluids rheology has been a major contributor in assessing the flow pattern of that fluid and predicts the power required for its transportation and pumping. In the present case, collected waste water has to be routed to either settling tanks or filters to separate its solid component. Several rheological studies have been conducted on different types of sludge in particular sewage sludge [Aranowskiet al., 2010; Novarino et al., 2010; Sahu and Chaudhari, 2013] and industrial sludge [Mortadi et al., 2017]. In the present study,the rheological behavior of ceramic sludge suspension was investigated in presence of three different coagulants (carboxy-methyl cellulose, CMC, Poly-acryl-amide, PAM, and Alum).
2. Raw Materials and Experimental Techniques 2.1. Raw Materials 2.1.1. Sludge Samples The sludge samples employed for theexperiments were kindly supplied by a ceramic tile plantlocated in Al–SharkiaGovernorate, Lower Egypt. 2.1.2. Coagulants All coagulants used in this study were diluted in distilled water before using as rheology control additives. Table (1) summarizes the properties of the three coagulants as for their formula and molecular weight. Table 1:
Coagulants characteristics
Rheological Properties of Waste Water from the Ceramic Tile Industry Treated with Different Coagulants
Coagulant (CMC) (PAM) Alum
Chemical Carboxy-Methyl Cellulose Poly Acrylamide, Poly (2-Propenamide) Aluminum Sulfate
Formula C₈H₁₆O₈ (C3H5NO)n Al2(SO4)3
145 Mol. Weight, (g.mol-1) 3.9304 × 105 4.1486 × 104 342
2.2. Rheological Behavior The apparatus used in following up the rheological behavior is the Brookfield DV-III Ultra Rheometerthat simultaneously measures viscosity (cP or Pa.s), shear rate (s-1) and shear stress (Pa).All experiments were performed at 25oC (± 1). To study the effect of additive concentration a series of experiments was performed using different concentrations and different spindle speeds from 5 to 250 rpm. Alum and CMC were diluted in concentrationsranging from 0.1 to 1% of ceramic sludge waste, whilePAM was diluted in concentrationsranging from 0.2 to 0.6 % of waste sludge.
3. Results and Discussion 3.1. Rheology of Pure Waste Sludge Fig(1) shows the results obtained for pure sludge to which no additions were made. This plot clearly illustrates the Bingham nature of that suspension. The constitutional equation of that suspension is: ߬ = 0.0026 ߛሶ + 0.097 (1) Accordingly, the limiting viscosity of that suspension (at infinite shear rate) = 0.0026 Pa.s (2.6cP) and its yield stress = 0.097 Pa. Figure 1: Shear stress – shear rate plot for pure sludge suspension
This is emphasized by the viscosity plot shown in Fig(2) which points out to reaching a limiting value for apparent viscosity. This is expected since on dividing the two sides of equation (1) byߛሶ , we obtain the following expression for apparent viscosity: .ଽ (2) ߤ = 0.0026 + ఊሶ
As ߛሶ → ∞, μ → 0.0026
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El-Shimaa M. El-Zahed, Sh.K. Amin, N.F. Abdel Salam, F.I. Barakat and M.F. Abadir Figure 2: Apparent viscosity – shear rate plot for pure sludge suspension
3.2. Effect of Addition of CMC On the other hand, Fig(3) shows the shear stress – shear rate relations in case of CMC addition to different levels. Figure 3: Shear stress – shear rate plot for CMC doped sludge suspensions
Actually the previous plot points out to pure Newtonian behavior with straight lines passing through origin. The slopes of the lines represent the suspension viscosities. These are seen to increase with increased addition level. The increase in viscosity following CMC addition is exponential in nature. The following expression was obtained to relate viscosityto the percentage of CMC added (x). ߤ = 0.0026 ݁ ଷ௫ (3) With a determination coefficient (R2) = 0.98 (Fig. 4)
Figure 4: Effect of CMC addition on apparent viscosity of sludge suspensions
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On the other hand, it is clear from Fig(3) that the values of shear stress steadily increase with CMC addition. The following expression was obtained correlating shear stress to both shear rate (ߛሶ ) and percent CMC addition by weight (x): ln ߬ = −4.98 + 0.827 ln ߛሶ + 2.027 ݔ (4) 2 With a determination coefficient (R ) = 0.964 Finally, the relative dependence of shear stress on both shear rate and percent CMC addition is illustrated in Table (2) which represents the values of correlation coefficient between these variables. Table 2:
Correlation coefficients for CMC addition Shear rate 1 0 0.5047
Shear rate % CMC Shear stress
% CMC
Shear stress
1 0.7825
1
This table points out to the fact that shear stress dependence on CMC addition is higher than its dependence on shear rate. 3.3. Effect of Addition of Alum Fig (5) displays the shear stress – shear rate relations obtained as function of percent alum addition. As can be observed from that figure, all curves are actually straight lines with intercepts that nearly increase on increasing alum addition. This suggests Bingham behavior with more or less constant limiting apparent viscosities asevidenced by the almost parallel character of the lines. Figure 5: Shear stress – shear rate plot for alum doped sludge suspensions
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On the other hand, Fig (6) illustrates the effect of alum addition and shear rate on the apparent viscosities of sludge suspensions. Since a Bingham behavior seems to prevail, a constant limiting viscosity is reached in each case. Figure 6: Apparent viscosity – shear rate plots for alum doped suspensions
The effect of percent alum addition on the yield stress of the different suspensions is illustrated in Fig(7), while its effect on limiting viscosity is shown in Fig (8). In both figures, a peculiar behavior can be observed for the suspension upon alum additions exceeding about 0.8%. Figure 7: Effect of alum addition on yield stress
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Figure 8: Effect of alum addition on apparentviscosity
In all previous figures the Bingham relation τ = kߛሶ + τ0 holds. Hence the shear stress (τ0) and the limiting viscosity (k) can be obtained respectively from the intercept and the slope of the straight lines obtained in Fig (5). The previous figures display respectively a maximum yield stress and a minimum apparent viscosity at 0.8% alum addition. Actually, this result is of practical importance since this percentage would correspond to a minimum circulating power owing to the minimum viscosity obtained. The elevated value of yield stress only affects the initial movement of the fluid and does not affect its steady state flow. The relative dependence of shear stress on both shear rate and percent alum addition is illustrated in Table (3). In the present case, the effect of alum addition is slightly less pronounced than that of shear rate. Table 3:
Correlation coefficients for alum addition
Shear rate % alum Shear stress
Shear rate 1 0 0.7055
% alum
Shear stress
1 0.5859
1
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El-Shimaa M. El-Zahed, Sh.K. Amin, N.F. Abdel Salam, F.I. Barakat and M.F. Abadir
3.4. Effect of Addition of PAM The effect of PAM addition on the rheological properties of ceramic sludge is illustrated in Fig(9) illustrating the shear rate – shear stress curves obtained. Figure 9: Shear stress – shear rate plot for PAM doped sludge suspensions
The shapes of the curves point out to a real plastic behavior as expressed by the Hershel – Buckley equation: (5) ߬ = ݇ߛሶ + ߬ ሺ݊ < 1ሻ This equation upon rearranging and linearization becomes: lnሺ߬ − ߬ ሻ = ln ݇ + ݊ ln ߛሶ (6) Those linearized curves are shown in Fig(10)depicting the relation between ln (τ– τ0) and ln ߛሶ . Figure 10: Linear plots between ln (τ – τ0) and ln ࢽሶ
The value of the yield stress was obtained by extrapolation to zero shear rate. This assumed value of τ0 is then substituted in the above equation and the determination coefficient of the relation
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between ln (τ – τ0) and ln ߛሶ obtained. Using the “Solver” facility of the EXCEL program the value of τ0 corresponding to a maximum value of R2 was chosen each time. The values of yield stress obtained by the previous method are shown in Table (4). In that table are also shown the values of the flow index (n) and the consistency factor (k). Table 4:
Effect of PAM addition on yield stress 0 0.097 1 0.097
% PAM τ0 (Pa) n k
0.2 0.52 0.651 0.1
0.3 1.64 0.677 0.083
0.5 1.8 0.924 0.0384
0.6 5.11 0.961 0.031
Except for pure sludge which behaves as Bingham fluid, the shear thinning character of the suspension seems to decrease upon adding more PAM as evidenced by the increasing values of flow index. Also the consistency factor tends to decrease on adding more PAM. It is worth mentioning that it was possible to correlate the shear stress not only to strain rate but also to the percent PAM added (x). This was done by correlating the values of τ0, n and k to x than substituting in equation (5). The following expression was obtained: ߬ = 0.137 ݁ .ସ ௫ + ሺ0.136 − 0.183 ݔሻߛሶ .଼ ௫ + 0.456 (7) It appears from equation (5) that upon rearrangement, one can obtain the following expression for apparent viscosity: ఛ ߤ = భష + బ (8) ఊሶ
ఊሶ
This form implies that as ߛሶ → ∞, μ will approach a zero value and not a terminal asymptotic viscosity as is the case with Bingham fluids. Fig(11) illustrates the effect of PAM addition of the apparent viscosity – shear rate behavior of different sludge suspensions. The vertical axis was drawn in logarithmic scale since the variations in viscosity were appreciable from one case to the other. Figure 11: Apparent viscosity – shear rate plots for APM doped suspensions
3.5. Comparison between Different Additions Since the rheological properties are essential in predicting different power requirements during storage and transportation of the sludge it was thought necessary to establish a brief comparison between the different additives used.
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Upon storage and before conveying the suspension to filters or to sedimentation tanks, it is necessary to keep the suspension in a stable sate to avoid settling of solids in the storage tank. This is usually performed by installing a central impeller that rotates at relatively low speeds (30 – 90 rpm) corresponding to relatively low values of shear rate in the 101 – 102 s-1 range. On the other hand the suspension pipe flow occurs at velocities in the 5 – 10 m.s-1 range. The shear rate is related to velocity by the expression: ଼௩ ߛሶ = (9) -1 3 Then, for a velocity of 5 m.s in a 1” pipe (0.0254 m) the shear rate will be in the 10 range, which practically represents the case of limiting viscosities. In the following table are compared the viscosities of the sludge at a shear rate of 85 s-1 and their values at a shear rate of 103 s-1. In case of adding CMC, as the behavior was essentially Newtonian there was no effect of shear rate on viscosity. In case of adding alum, the limiting viscosity deduced was used for the shear rate of 103 s-1. Finally, in case of adding PAM, the expressions deduced were used in calculating the viscosity at the high shear rate. Table 5:
Comparison of viscosities of suspensions (cP)
% Addition CMC
ࢽሶ s-1
0 3.8 85 3.8 Alum 103 3.8 85 3.8 PAM 103 3.8 * Extrapolated values are totally out of range.
0.1 3.9 2.38 1.8 13.2 15
0.35 9.43 2.76 1.5 17.5 22.7
0.5 13.9 3.03 1.4 50 28.7
0.75 22 3.6 1.3 141 120
1 50 3.66 2.1 n.d.* n.d.*
It appears from that table that the values of viscosity are lowest in case of adding alum a whether at low or high speeds and highest in case of adding PAM particularly under conditions of low shear rate. The addition of CMC gave reasonable viscosities especially at low levels of addition. However, the decisive factor in choosing any of the above additions is not only the ease of mixing or pumping but also the settling properties of the solids upon making any of these additions. This effect is to be discussed in a forthcoming paper.
4. Conclusion The following conclusions could be drawn from the present research: 1) Pure waste sludge behaved as Bingham fluid with a limiting viscosity of 2.6 cP and a yield stress of 0.097 Pa. 2) The addition of CMC at doses ranging from 0.1 to 1% produced Newtonian suspensions the viscosity of which increased exponentially with the level of addition. 3) On adding alum at doses ranging from 0.1 to 1%, the behavior of the suspension followed that of a Bingham fluid with limiting viscosities reaching a minimum value at 0.6% addition. This level of addition would correspond to minimum pumping and transportation power. 4) When PAM was added to waste water sludge in levels ranging from 0.2% to 0.6%, the suspensions followed a shear thinning behavior with initial yield stress (Hershel – Buckely equation). This yield stress increased exponentially with the addition level. The values of viscosities at different shear rates were way higher than those obtained on adding alum. 5) It could be concluded that adding alum at 0.5% level minimizes pumping and transportation cost of the flocculated suspension. However, the settling properties of suspensions need to be further followed up to decide about the most appropriate addition.
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LIST OF SYMBOLS Symbol
Variable
Unit
D
Pipe diameter
m
k
Consistency factor
Pa.sn
n
Flow index
---
v
Average velocity in pipe
m.s-1
x
Percent addition (by weight)
---
μ
Apparent viscosity
Pa.s
τ
Shear stress
Pa
τ0
Yield stress
Pa
ߛሶ
Shear rate
s-1
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