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A STUDY ON CACTUS OPUNTIA AS NATURAL COAGULANT IN TURBID

WATER TREATMENT

By:

Yin Chun Yang1, *, Suhaimi Abdul-Talib

2, Lim Ying Pei

1, Mohd Safirun Nizan Ismail

1,

Siti Nor Aisah Abd-Razak1 and Ahmad Mahyuddin Mohd-Mohtar

1

1Faculty of Chemical Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, 2Faculty of Civil Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor,

*Corresponding author. Phone: +603-5543 6348, Fax: +603-5543 6300

Email: yinyang@salam.uitm.edu.my; yinyang@streamyx.com

Abstract

Coagulation is an important wastewater treatment process used to reduce water turbidity and

normally precedes the more complex secondary and tertiary water treatment processes. In this

study, the effectiveness of a natural macromolecular coagulant derived from a cactus species for

turbidity removal from estuarine and river waters were evaluated using jar test. Initial turbidity

values measured at 499 NTU and 547 NTU for estuarine and river waters respectively were

reduced by as much as 98% (estuarine) and 70% (river). Other parameters such as pH as well as

alkalinity were also studied. It was indicated that the coagulant did not have a considerable effect

on final pH of the waters. The amount of cactus added was well correlated with the final turbidity

and alkalinity of the waters. High turbidity removal determined in this study indicates that cactus

opuntia has the potential to be utilized for surface water treatment applications.

Keywords: Natural Macromolecular Coagulant, Turbidity, Alkalinity, pH, Estuarine and River

Waters

1. Introduction

Coagulation is an essential process in the treatment of both turbid surface and industrial

wastewaters. Examples of chemical-based coagulants that are available commercially include

lime, alum, ferric chloride and polyaluminium chloride. While the effectiveness of these

chemicals as coagulants are well noted (Edzwald, 1993; Kang et al., 2003), there are, nonetheless,

disadvantages linked with usage of these coagulants such as comparatively high costs, harmful

effects on human health as well as the fact that they appreciably affect pH of treated waters. As

such, it is desirable to substitute these chemical coagulants with cost-effective natural coagulants

to offset the aforesaid disadvantages. Research on natural coagulants have been focused on

Moringa oleifera seeds (Olsen, 1987; Muyibi and Evison, 1995; Ndabigengesere et al., 1995) for

the past 20 years but more researchers are studying application of other natural coagulants such as

long bean extract and cactus opuntia. It was determined, via two separate studies, that standalone

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long bean extract (Liew et al., 2004) was ineffective in removing turbidity while cactus opuntia

(Zhang et al., 2006) exhibited high turbidity removal efficiency. Hence, the positive outcome of

the latter study justifies further research on cactus opuntia as a natural macromolecular coagulant.

2. Objectives of Study

The objectives of this study were to evaluate the efficiency of natural coagulant derived from

cactus opuntia for turbidity removal from surface waters (estuarine and river) using jar test and

determine the effect of dosage of cactus powder on turbidity, pH and alkalinity of the waters.

3. Methodology

3.1 Preparation and Characterization of Cactus Powder

Cactus opuntia used in the study was collected from a nursery in Sg Buloh, Selangor. The cactus

was washed with tap water and subsequently sliced into small pieces to facilitate drying. The

sliced cactus was then dried in oven for 8 hours at 80°C. The dried cactus was ground into fine

powders using pestle and mortar and subsequently sieved to sizes 53 – 106 µm. Elemental

analysis of the cactus powder to determine its carbon, hydrogen and nitrogen contents was carried

out using Thermo Electron Flash EA 1112 Elemental Analyzer. The pH of cactus powder was

determined by mixing the powder in distilled water at dosages of 13, 53, 213 and 853 mg/L and

stirred at 130 rpm for 3 minutes prior to measurement.

3.2 Collection of Surface Water Samples

Estuarine water samples were collected from the estuary of Klang river at Port Klang, Selangor. It

was observed that the samples were turbid and brown-yellowish in color. It was presumed that the

samples were contaminated with oil and grease that originated from spent diesel spilled from

boats in addition to other turbid-causing substances such as silt and plankton within the estuary.

River water samples were collected from a river located with Shah Alam, Selangor. These

samples were also turbid possibly due to high concentrations of silt along the river. Both the

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estuarine and river water samples were collected via grab sampling and stored in plastic

containers prior to immediate experimentation.

3.3 Jar test

Jar test was used to determine the effectiveness of using cactus powder as coagulant. The test was

conducted via jar test apparatus (Chemix Floc-Tester – CL6) using 300 mL-capacity jars (Figure

1). Raw water samples of 300 mL each were stirred at 130 rpm for 3 minutes in which cactus

powder was added during this time. Cactus powder of dosages of 13, 53, 213 and 853 mg/L for

each water samples were tested. This was the mixing stage. After 3 minutes, the coagulation stage

commenced where the samples were stirred again at 80 rpm for 30 minutes. After the coagulation

stage, the samples were allowed to stand for 30 minutes after which treatment was completed

(settling stage). Turbidity, pH and alkalinity of samples before and after jar test were measured

and tabulated. Turbidity values were determined via 2100P HACH Turbiditimeter while pH

values were determined via Mettler-Toledo Delta 320 pH meter. Alkalinity values were

determined by using HACH basic laboratory test kit via Method 8203.

Figure 1. Jar test

4. Results and Discussion

4.1 Characterization of cactus opuntia

Elemental analysis (Table 1) was carried out to provide a preliminary comparison between the

elemental compositions of the cactus with that of a conventional natural coagulant, Moringa

oleifera as determined by Ndabigengesere et al. (1995). In this study, it was determined that

cactus opuntia contained 2.3% nitrogen, 29.4% carbon and 1.7% hydrogen. From Table 1, it was

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evident that the carbon percentage of both the shelled and non-shelled Moringa were almost twice

the carbon percentage of cactus. This was perhaps attributed to the composition of Moringa

which consisted of more organic matter as compared to cactus. Table 2 shows the pH of the

natural coagulants mixed in distilled water (cactus) and tap water (Moringa). The latter was

determined by Ndabigengesere and Narasiah (1999). Both coagulants were slightly acidic in the

presence of water. It was observed that increased cactus dosages correlated with decreased pH.

Table 1. Elemental analysis of natural coagulants Cactus opuntia Shelled Moringa seeds

a Non-shelled Moringa seeds

a

N (%) 2.3 6.1 5.0

C (%) 29.4 54.8 53.3

H (%) 1.7 8.5 7.7 aAs determined by Ndabigengesere et al. (1995)

Table 2. pH of natural coagulants Cactus opuntia Shelled Moringa seeds

b Non-shelled Moringa seeds

b

Water only 7.00 7.30 7.30

13 mg/L 6.88 - -

53 mg/L 6.50 - -

213 mg/L 6.21 - -

853 mg/L 6.00 - -

50,000 mg/L - 6.40 5.8 bAs determined by Ndabigengesere and Narasiah (1999)

4.2 Effect of Cactus Dosage on Turbidity Removal

It was observed that the powdered cactus formed large flocs with impurities in the sample which

facilitated settling and as a result, clear supernatant was produced. Similar observation was also

noted for treated river water. Figure 1 shows the effect of dosage of cactus powder on turbidity of

the waters. Initial turbidity values measured were 499 and 547 NTU for estuarine and river

waters respectively. Turbidity removal efficiencies after treatment at various dosages range from

93.1 – 98.2% (estuarine) and 49.9 – 69.7% (river). From Figure 2, the optimum dosage for both

waters was approximately 13 mg/L which incidentally, was the smallest dosage used in the study.

This was compared with the finding of a study conducted by Zhang et al (2006) where the

optimum dosage of cactus opuntia used for turbidity removal of seawater (980 NTU) was 60

mg/L. In that study, the highest removal efficiency reached 99% which was comparatively similar

to the highest removal efficiency obtained for treated estuarine water (98.2%) in this study.

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0

100

200

300

400

500

600

0 100 200 300 400 500 600 700 800 900

Cactus powder (mg/L)

Turbidity of water (NTU)

Estuarine water

River water

Figure 2. Effect of dosage of cactus powder on turbidity of estuarine and river waters

4.3 Effect of Cactus Dosage on pH and Alkalinity of Samples

Initial pH of cactus powder mixed in distilled water was 6.50 (slightly acidic). Figure 3 shows the

effect of dosage of cactus powder on final alkalinity and pH of the waters. It appeared that

increased cactus dosages from 13 to 853 mg/L had a marginal effect on final pH of the waters

with values ranged from 7.25 to 7.69 (estuarine) and 7.83 to 8.49 (river). This result implied that

even though the dosages were substantially increased, final pH values of the waters were

relatively unaffected as compared to usage of chemical-based coagulants. This notion was

reinforced by study conducted by Fatoki and Ogunfowokan (2002) involving coagulation of

turbid river water by means of alum and ferric chloride showed that dosage of 10 mg/L either

chemical constituted pH increase by at least 0.4. It was therefore, anticipated that further increase

in dosage of the chemicals would substantially increase the pH of treated water. It can be seen

that the amount of cactus added was well correlated with the final alkalinity to pH 5.1, albeit at

contrasting trend for the two waters. For estuarine water, increase of cactus dosage from 0 to 853

mg/L represented decrease of alkalinity values from 71.2 to 64.8 mg CaCO3/L. For river water,

initial dosage at 13 mg/L decrease alkalinity values from 104.8 to 91.2 while further increase of

dosages increased alkalinity values from 98.8 mg CaCO3/L (dosage 53mg/L) to 105.6 mg

CaCO3/L (dosage 853mg/L).

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0

20

40

60

80

100

120

140

160

0 13 53 213 853Dosage of cactus powder (mg/L)

Final alkalinity to pH 5.1

(mg CaCO3/L)

1

2

3

4

5

6

7

8

9

Final pH

Alkalinity of estuarine water Alkalinity of river water

pH of estuarine water pH of river water

Figure 3. Effect of dosage of cactus powder on final alkalinity and pH of estuarine and river

waters

5. Conclusions

It was shown that powdered and dried cactus opuntia was very effective in removing turbidity

from both estuarine and river waters as evident by the high removal efficiencies. It was also

proven that the cactus powder did not have a significant effect on final pH of the waters as

compared to chemical-based coagulants. Increased cactus dosages correlated with decreased pH

of surface water. It can be concluded that cactus opuntia has the potential to be utilized for

surface water treatment applications.

References

Edzwald, J.K. (1993). “Coagulation in drinking water treatment: particles, organics and

coagulants.” Water Science Technology, 27(11), 21 – 35.

Fatoki, O.S. and Ogunfowokan, A.O. (2002). Effect of coagulant treatment on the metal

composition of raw water.” Water SA, 28(3), 293 – 298.

Kang, M., Kamei, T. and Magara, Y. (2003). “Comparing polyaluminium chloride and ferric

chloride for antimony removal.” Water Research, 37(17), 4171 – 4179.

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Liew, A.G., Noor, M.J.M.M. and Ng, Y.M. (2004). “Coagulation of turbid waters using

extraction of long bean.” Malaysian Journal of Science, 23, 185 - 191.

Ndabigengesere, A., Narasiah, K.S. and Talbot, B.G. (1995). “Active agents and mechanism of

coagulation of turbid waters using Moringa oleifera.” Water Research, 29(2), 703 - 710.

Ndabigengesere, A. and Narasiah K.S. (1998). “Quality of water treated by coagulation using

Moringa oleifera seeds” Water Research, 32(3) 781 – 791.

Muyibi, S.A. and Evison, L.M. (1995). “Optimizing physical parameters affecting coagulation of

turbid water with Moringa oleifera seeds.” Water Research, 29(12), 2689 - 2695.

Olsen, A. (1987). “Low technology water purification by bentonite clay and Moringa oleifera

seeds flocculation as performed in sudanese villages: effects on Schistosoma Mansoni

cericariae.” Water Research, 21(5), 81 - 92.

Zhang, J., Fang, Z., Luo, Y. and Yang, H. (2006). “A preliminary study on cactus as coagulant in

water treatment.” Process Biochemistry, 41(3), 730 – 733.