Scholarly article on topic 'Combination of Chitosan and Bentonite as Coagulant Agents in Dissolved Air Flotation'

Combination of Chitosan and Bentonite as Coagulant Agents in Dissolved Air Flotation Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — M.A.Z. Mohd Remy Rozainy, M. Hasif, Syafalny, P. Puganeshwary, A. Afifi

Abstract The experiment was carried out to study the dissolved air flotation (DAF) process in a tank involving mainly velocity distribution and turbidity removal. Chitosan and Bentonite were known as coagulant agents thus were used in the study. Measurements were carried out on four cases with different inlet velocities of 0.3m/s, 0.6m/s, 0.9m/s and 1.2m/s. Laboratory tests were conducted to test the water quality based on turbidity values and basic drinking water parameters. From the test results, it was found that the inlet velocity gave impacts on the distribution of flow in the tank and thus affected the efficiency of the flotation process. Chitosan and Bentonite can be applied to the flotation tank resulting in an average of 97% turbidity removal. This study successfully proved the effectiveness of the combination of Chitosan and Bentonite as a coagulating agent in the DAF tank for raw water treatment process.

Academic research paper on topic "Combination of Chitosan and Bentonite as Coagulant Agents in Dissolved Air Flotation"

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APCBEE Procedia 10 (2014) 229 - 234

ICESD 2014: February 19-21, Singapore

Combination of Chitosan and Bentonite as Coagulant Agents in

Dissolved Air Flotation

Mohd Remy Rozainy M. A. Z.a'*, Hasif M.a, Syafalnyb, Puganeshwary P.a and Afifi

aSchool of Civil Engineering, Universiti Sains Malaysia, Nibong Tebal, Penang 14300, Malaysia bCivil Engineering Department, Bina Nusantara University, Palmerah, Jakarta 11480, Indonesia

Abstract

The experiment was carried out to study the dissolved air flotation (DAF) process in a tank involving mainly velocity distribution and turbidity removal. Chitosan and Bentonite were known as coagulant agents thus were used in the study. Measurements were carried out on four cases with different inlet velocities of 0.3m/s, 0.6m/s, 0.9m/s and 1.2m/s. Laboratory tests were conducted to test the water quality based on turbidity values and basic drinking water parameters. From the test results, it was found that the inlet velocity gave impacts on the distribution of flow in the tank and thus affected the efficiency of the flotation process. Chitosan and Bentonite can be applied to the flotation tank resulting in an average of 97% turbidity removal. This study successfully proved the effectiveness of the combination of Chitosan and Bentonite as a coagulating agent in the DAF tank for raw water treatment process.

© 2014TheAuthors. PublishedbyElsevierB.V.This isanopenaccessarticleunder the CCBY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Keywords: Chitosan, Bentonite, Dissolved air flotation (DAF)

1. Intoduction

In typical terms of particle size, shape and density as well as particle charge, all of them are controlled to some appropriate condition by the coagulation and the flocculation process [1]. The process is simple and that process is a vital stage in most water treatment systems. The agglomeration of fine particles or colloids

* Corresponding author. Tel.: +6045996231; fax: +6045941009. E-mail address: ceremy@eng.usm.my; remyrozainy@yahoo.com.

2212-6708 © 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi: 10.1016/j.apcbee.2014.10.044

into large particles can be considered as a well-established approach for removing turbidity, natural organic matters and other soluble organic and inorganic pollutants [2]. In water treatment capacity, coagulation can be defined as the process whereby particles in water are destabilized by dosing the certain chemical additives i.e coagulant and causing rapid formation of small agglomerates or known as 'flocs'. Flocculation is then the process of destabilization of particles and small agglomerates, whereby, they are encouraged to collide with each other (agitated) to form flocs [1]. Actually, to eradicate these particles from water, it is required to neutralize the negative charge. In fact, there are quite numbers of mechanisms for destabilizing these particles, but most suitable for water treatment is through the addition of a chemical coagulant [1]. There are a number of coagulation mechanisms including double layer compression, charge neutralization, sweep flocculation and inter particle bridging, however the coagulant selected, its dose and water quality determine the mechanism. The coagulation process is generally optimized for a particular system in terms of coagulant dose and pH, achieved through a series of bench scale jar test [2].

2. Combination of Chitosan and Bentonite

The most favourable concentration weight ratio of the natural polymer to natural clay of bentonite is in between 1:5 to 1:20 [1]. In order to remove particles and colour from drinking water, natural cationic polymer coagulant and clay mineral in an adequate amount are believed to be effective to coagulate suspended particles in the raw water [1][3][4]. In order to to achieve a good removal, the effective or optimum dose needs to be investigated. The optimal dosage denotes to be a dose that is sufficient to produce the desired effect of removing particles in maximum while taking into consideration of cost and efficiency. The term 'primary coagulant' refers to the main coagulant which is typically a metal salt (conventionally alum) added alone or being added together with the secondary coagulant or 'coagulant aid'. The term 'coagulant aid' referring to a polymer substance typically a cationic, synthetic organic polymer, when added with a primary coagulant, will enhance the adherence of the particles [1]. In fact, an anionic or nonionic polymer which generally consists of high molecular weight is added after flocculation is initiated. The polymer will act as a flocculent aid by the mean of aggregation of the flocs [3].

Anionic particles of Bentonite are electrostatically attracted by the protonated amino groups of Chitosan [5]. This reaction facilitates the neutralization of the anionic charges which can bind together and settle rapidly by the effect of gravity. The total turbidity reduction is reached, when the number of protonated amino groups neutralizes all anionic charges [6]. Murcott et al., (1996) [3] in their experiment use Chitosan as a primary coagulant in combination with Bentonite as coagulant aids. As a result particles had removed from raw water as well or better than either Chitosan alone. It is reported that the combination of both natural coagulants, is better than the conventional chemical coagulant typically the metal salts (aluminum sulfate with or without a synthetic polymer). The natural coagulant currently is very famous and being used in most water treatment plants worldwide. It is proven that low doses of the natural polymer of Chitosan together with the coagulant aid of Bentonite are able to perform better than alum with a synthetic polymer in the removal of particulate matter and color from raw water [3].

3. Jar Test

The purpose of the jar tests was to determine the effectiveness of the combination of Chitosan with coagulant aid Bentonite as an alternate coagulant in terms of dose, coagulant mixture ratio, pH and mixing time [3]. A jar test is vital in most water treatment plant systems. The minimal coagulant dosage and concentration to optimally remove the residual turbidity of the water are determined by the jar test technique [4]. It can be said that many factors will influence coagulation beside there are complex reactions involved, it

is not feasible to calculate directly the coagulant dosage required for coagulation of particular water. With a varying raw water quality, the jar test may need to be carried out in quite of numbers to ensure that optimum flocculation conditions are maintained in water treatment plant [5].

In this study, the jar tests (six beakers) were filled with 500ml raw water from Kerian River. Then, Bentonite and Chitosan were added simultaneously and mixed at 100 rpm for 2 minutes. Mixing speed is reduced to 30 rpm for 30 minutes. The mixer is turned off and flocs are allowed to settle for 30 minutes [7]. In practice, it is very important to determine the optimum dosage of coagulant and to establish optimum chemical conditions as pH value. For this purpose, the well-known jar test procedure is very widely used in water treatment laboratories. Samples of water are dosed with varying amounts of coagulant under standard rapid mix conditions, in order to distribute the additive evenly. The samples are then used to optimize mix time, during which flocs may form. A certain period of sedimentation is then allowed. The samples of water are then withdrawn for turbidity measurement. The residual turbidity of settled samples gives a good indication of the degree of clarification obtained and can be used to locate the optimum flocculation condition. The tests normally conducted in a purpose-built apparatus with multiple stirrers, so that a number of samples can be tested simultaneously [2].

The effect of different Bentonite-Chitosan dosage on the turbidity removal was analyzed. The experiments were conducted at various different dosages of combination Bentonite-Chitosan were carried out at original pH and temperature of 30°C. The pH was controlled by adding either strong acid (H2SO4) or strong base (NaOH).

4. Results and Discussion

The study was conducted on the effect of mixing time to the coagulation and flocculation occurrence. The effect of mixing time was analyzed with concentration of 1000 mg/L with the initial raw water pH of 7.3. A preferred concentration weight ratio of Chitosan-Bentonite is 1:5 [3]. The Jar test was conducted with 100 rpm of mixing rate for 2 minutes and 30 rpm for a range of mixing time which varies from 10 to 60 minutes and finally settling time of 30 minutes. It was observed that the turbidity removals for all readings are in the range of 88% to 97%. The large different percentage of reduction in particular mixing time is recorded at 30 minutes when comparing with the shorter mixing time (10 minutes) and longer mixing time (60 minutes). By analyzing every point in the Fig 1(a) and turbidity reductions respectively, it is clearly stated that the mixing time of raw water has an influence on coagulation and fluctuation to be occurred. Furthermore, Fig 1(a) demonstrates 97% of turbidity reduction achieved in 30 minutes. From the experiment, it can be said that the optimum mixing time condition of the treatment system is 30 minutes. Mixing period is very essential for polymeric flocculent for their performance in flocculation.

The developments that had been illustrated in Fig 1(a) showed that the longer or shorter agitation time which is beyond the optimum, would result in less performance of coagulant to form a binding with the particle. At the lower agitation time for example 10 minutes, the collisions between the coagulant and suspended particles are low and will lead to the lower flocculation rate as there are not much contact time [4]. Instead, if the mixing time is too long, the flocculation chains tend to halt and limiting the size of the flocs formed. The small size flocs are not dense to settle down in raw water and thus, indirectly cause the sample to be turbid again [4].

From the various mixture ratios of Chitosan-Bentonite, the result (Fig 1(b)) shows that 30:70 is the optimum ratio with highest turbidity removal efficiency of 97.03%. Therefore, effective coagulation was achieved with much lower doses of Chitosan than would be required for complete neutralization of Bentonite's charge, and this process was guided by the combined effects of electrostatic patch and bridging mechanisms [8].This means, Bentonite is more likely to have less positive charge than the Chitosan, so it

needs less natural coagulant to neutralize the Bentonite. Analogously, three particles of Chitosan are enough to attract and bind seven particles of Bentonite to perform as the best coagulant agent and remove almost 97% of suspended particles in the raw water. Chitosan alone performed unwell by 93.3% of turbidity remova

1(a) Effect of Mixing Time with Removal Percentage

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30 40 Mixing Time (min)

1(b) Effect of Mixture Ratio with Removal Percentage

0:100 10:90 20:80 30:70 40:60 50:50 60:40 70:30 80:20 90:10 100:0 Chitosan:Bentonite Ratio

1(c) 120

S" — 100 re

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Effect of pH with Removal Percentage

1(d) Effect of Concentration with Removal Percentage

— 100 re

200 400 600 800 1000 1200 1400 1600 Coagulant Concentration (mg/l)

Fig. 1. (a) Effect of mixing time with turbidity removal percentage; (b) effect of mixture ratios with turbidity removal percentage (c) effect of pH with Turbidity Removal Percentage and (d) effect of concentration with turbidity removal percentage

compare to others (Fig (1b)). However in combination with Bentonite, Chitosan shows improved results. However, overdosing of Chitosan beyond the optimal state causes the slightly decreased in removal efficiencies, as shown in the figure. This could be due to reversal of surface charge as well as their stabilization of coagulated particles. Once the Chitosan dosage exceeds the saturation of polymer bridging, surplus Chitosan has a tendency to destroy the polymer bridging between particles thereby exhibiting an increase in residual [9].

The experiment was conducted by adjusting the pH from two to twelve, using the dosage of 1000mg/l with 30 minutes of mixing time. Shellshear, (2008) in his experiment had a two minute rapid mixing phase at 100 RPM, followed by flocculation at 30RPM for 30 minutes and finally settling time of 30 minutes to check for the optimum coagulation. The turbidity removals for Chitosan-Bentonite coagulation at different pH are shown in Fig 1(c). Although the differences in pH two to eight are not very much, but that pH range provides the optimum turbidity removal compare to other pH with 97% turbidity removal. The coagulants demonstrated the best result of turbidity removal when the condition is acidic and or slightly basic. The best turbidity removal is at the initial pH of raw water with 97% efficiency. In the other hand, the turbidity removal is sharply decreased or distorted when the pH is over 8. This could be due to the alkaline condition in which the positive charges on the Chitosan-Bentonite surface significantly decrease as solution pH increased, so this will contribute to the decreasing charge of both Chitosan and Bentonite to attract the negatively

charged suspended particle. By observing every pH point with the removal efficiencies of turbidity, it can be said that the pH has a significant influence to the coagulation and flocculation process. This was supported by the literature, stating that the sorption capacity of the Chitosan was best at acidic or neutral condition based on the impurities that needs to be treated [4].

Dosage was one of the most important parameters that must be considered to determine the optimum condition for the performance of Chitosan-Bentonite in coagulation and flocculation process. Basically, insufficient dosage or overdosing would result in poorer performance in flocculation. Therefore, it was critical to determine the optimum dosage in order to minimize the dosing cost and obtain the optimum performance in treatment [4]. From Fig 1(d), the results show that the increased of coagulant dosage lead to better coagulant performance from 200mg/l to 800mg/l. Under the optimal dosage condition the percentage of removals of those concentrations increased slightly. The 1000mg/l concentration of coagulant shows the best efficiency with 97.23% of turbidity removal. Conversely, it can also be seen that from 1200mg/l to I600mg/l, the turbidity removal reduced very slightly. These could be explained based on the density of the charge. Chitosan has a high charge density compared to the other coagulants. That is why, even with higher concentrations, the Chitosan can still attract the impurities even the turbidity of water itself is caused by the overdosing. Moreover, polymer adsorption increased as the charge density of the polymer increased [9]. The effect of the concentration of colloidal particles in water is important because they serve as cores to the coagulation. If the concentration of colloids in the water is low, there are too few particles to ensure good flocculation, even though they are neutralized. Another inconvenience of waters that contain few colloids comes because it is easy to add coagulant and to reverse the load of the particles finally instead of neutralizing it [6].

5. Water Quality Test

The water quality test for raw water and treated water are reported in Table 1. The water quality test for this experiment is mainly focused on the removal of turbidity in raw water. The basic drinking water parameters were analysed for any potential improvement. From the table, it is clear that DAF is very efficient in removing turbidity for low velocity of water. 0.3m/s of inlet velocity reported the highest which is 97% of removal efficiency compared to other inlet velocities with treated turbidity of 1.82 NTU from the raw water turbidity of 52.3 NTU. Also, for Dissolved Oxygen (DO) reading, it shows the significant decrease with the higher inlet velocity. This is due to, slower the inlet velocity, the more contact time, the more water can be oxygenized.

Table 1. Water Quality Test for before and after DAF treatment with different inlet velocity

Parameters Before After Treatment

Inlet Velocity

0.3m/s 0.6m/s 0.9m/s 1.2m/s

Turbidity (NTU) 52.3 1.82 2.14 3.96 7.89

DO (mg/l) 2.22 3.77 3.72 3.3 2.81

Conductivity (us/cm) 84.50 92.3 90.3 92.3 89.1

TDS (mg/l) 58.3 50.3 50.3 49.8 51.2

pH 7.3 7.3 7.3 7.3 7.3

Salinity 0.03 0.04 0.04 0.03 0.03

6. Conclusion

This study successfully proved the effectiveness of the combination of Chitosan and Bentonite as a

coagulating agent in a DAF tank for raw water treatment process. The optimal conditions were determined on the basis of turbidity removal. In addition, the principal factors affecting coagulation were determined throughout the study, including optimal coagulant dosage, mixing time, pH and mixture ratio of primary coagulant and coagulant aid in the treatment of raw water. Coagulation with Chitosan-Bentonite had successfully removed the turbidity with the efficiency of 97%. The coagulants performed well (97% removal of turbidity) when Chitosan-Bentonite ratio of 30:70, concentration of 1000mg/l (300mg:700mg in 1 Liter of raw water), optimal pH of 7.3 and 30 minutes of mixing time during flocculation.

Acknowledgements

This research was carried out with financial support from the School of Civil Engineering, Universiti Sains Malaysia and Short Term Grant (304/P AW AM/60313007). Also thanks to Prof Nordin Adlan for giving advices and supports throughout this study.

References

[1] Syafalni, Abustan, Farhana. Raw water treatment using Bentonite-Chitosan as coagulant, Water Science & Technolgy: Water Supply, 2012; 480-487.

[2] Parsons, S. A. & Jefferson, B. Clarification Process: Introduction to potable water treatment process, Blackwell Publisher, School of Water Science, Cranfield University, UK, 2009.

[3] Murcott S. E, Donald R. Herleman F. Method of drinking water treatment with natural cationic polymers, Massachusetts Institute of Technology, Cambridge, 1996.

[4] Hassan M. A., Tan P. L., Zainura Z. N. Coagulation and flocculation treatment of wastewater in textile industry using chitosan, Faculty of Chemical and Natural Resources Engineering, UTM, 2008.

[5] Pan, J. R., Chih P., Huang, S. C., Chen, Ying C. Evaluation of modified chitosan biopolymer for coagulation of colloidal particals. Colloids and Surfaces A: Physicochemical and Engineering Aspects 1999;147: 359-364.

[6] Zemmouri H., Majda A. A., Rachid B., Hakim L. Use of chitosan in coagulation flocculation of raw water of keddara and beni amrane dams, Centre of Development of Renewable Energies, Algeria, 2008.

[7] Shellshear, M. S. Urban stormwater treatment using chitosan. B. Eng. In civil Engineering Thesis, Faculty of Engineering and Surveying, University of Southern Queensland, 2008.

[8] Chatterjee T., Chatterjee S., Seung Han Woo. Enhanced coagulation of bentonite particles in water by a modified chitosan biopolymer, Department of Chemical Engineering , Hanbat National University, Korea, 2009.

[9] Noor Z. Z., Hassan M. A, Lim S. H., Zaini U. Removal of boron from industrial wastewater by chemical precipitation using chitosan, Faculty of Chemical and Natural Resources Engineering, UTM, 2008.