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Cactus Opuntia as natural flocculant for urban wastewater treatment Raouen Rachdi, Feyda Srarfi and Najet Slim Shimi
ABSTRACT The cactus tree, species Opuntia ficus-indica, is a primary material of many products in various domains such as cosmetics, medicine and nutrition. In the present work, we assess its potential as a flocculant. We tried a technique which adopts three sequential treatments that used coagulation, flocculation and sedimentation processes under certain operating conditions. For this purpose, we used the aluminum sulfate (AS) as coagulant and fresh cladodes juice (FCJ) as bioflocculant. All tests were carried out on high turbid urban wastewater collected from the Metlaoui’s Wastewater Treatment Plant (MWTP) (in Gafsa in southwest Tunisia). Experiments with this couple AS/FCJ show very interesting results: a high-removal of turbidity (TUR), suspended solids (SS) and chemical oxygen demand (COD). The percentages of abatement of these parameters are respectively 93.65%, 82.75% and 64.30%. The experimental results of the present study prove that the turbidity, SS and COD
Raouen Rachdi (corresponding author) Feyda Srarfi Najet Slim Shimi Palaeo-Environment Geomaterials and Geological Threats, Faculty of Sciences of Tunis, A campus university 2092, El Manar Tunis, Tunisia E-mail: [email protected] Feyda Srarfi Najet Slim Shimi Faculty of Sciences of Tunis, Department of Geology, University Campus El Manar Tunis 2092 El Manar Tunis, Tunisia
removal efficiency of new technique is superior to that of conventional process (with only AS). By this technique, we save 50% in AS dose. Moreover, flocs formed by the treatment using AS/FCJ are coarse and readily settleable. Key words
| bio-flocculation, COD, Opuntia ficus-indica, suspended solids, turbidity
INTRODUCTION Urbanization, industrialization and extensive agricultural production are responsible for generating polluted effluents which need to be treated. The principal objective of wastewater treatment is generally to allow human and industrial effluents to be disposed into the hydrographic network without danger to human health or unacceptable damage to the natural environment. Various treatment methods have been applied for the removal of pollutants from wastewater such as ion exchange, membrane filtration, activated carbon and coagulation/flocculation processes (Muralimohan et al. ). The coagulation/flocculation processes have remained the most widely practiced techniques in wastewater treatment for removing particulate, organic matter, color, and heavy metal (Verma et al. ). They are used whenever the natural settling rate of suspended material is too slow to provide a very effective clarification. They allow to improve the aesthetic appearance of turbid water. This technique aims to remove suspended particles by destabilization and the formation of larger and heavier flocs which facilitate their sedimentation. doi: 10.2166/wst.2017.370
This technique offers various advantages for the treatment of different kinds of wastewaters (industrial, urban, etc.) such as easy operation and lower sensitivity to toxic loadings, etc. However, it is well-recognized that the use of metal salts in this process has numerous disadvantages such as: relatively high procurement costs for many developing countries, the typical high quantities of chemicals needed, production of large sludge volumes and the significant change in pH of treated water. But with these chemical products, there is always the concern about residuals in the treated water. However, several studies demonstrate that chemicals (coagulants or flocculants) remain in the water after treatment may cause many detrimental effects on human health and on the environment. Because of the drawbacks of these technologies, it is therefore desirable to substitute these chemical products with natural compounds derived from plant material to produce the coagulation/flocculation process (Theodoro et al. ). The use of flocculants of vegetable origin to treat aqueous solutions is a relatively new process that has proven very interesting results in the removal of contaminants
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from wastewater (Chopra & Ruhi ). Historically, natural coagulants and bioflocculants based plant were used in water and wastewater treatment before the advent of synthetic chemicals. But their use has been discouraged in developed countries under the pretext that they have never been subjected to rigorous scientific evaluation. The previous studies have not determined whether such natural coagulants are economically and environmentally more acceptable than chemical products (Theodoro et al. ). Recently, there has been more interest in the subject of natural products. It shows a bright future and starts to motivate many researchers because it has several advantages like abundance and it is presumed to be safe for human health (Muralimohan et al. ; Rebah & Siddeeg ). In addition, it produces a readily biodegradable and less voluminous sludge (Jadhav & Mahajan ). In the last few decades, cactus (Opuntia ficus-indica (OFI)) has attracted attention in nutrition (El-Mostafa et al. ), cosmetics (Schmid et al. ; RamírezMoreno et al. ), medical (Abdel-Hameed et al. ; Monrroy et al. ) and industrial domains (Mannai et al. ). However, the application of this plant for water treatment is quite new in comparison with other natural coagulants like Moringa oleifera and Nirmali (Theodoro et al. ). A few studies have examined the use of the cactus as a natural biodegradable flocculant instead of those chemicals in the coagulation/flocculation process.
Figure 1
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In Tunisia, the cactus plant is abundant (600,000 hectares were planted). In the arid and semi-arid zones of the country, it is used as forage for bovine. But, despite its widespread, it has poor commercial value due to lack of knowledge about its properties (Nefzaoui & Ben Salem ). Hence, the objective of the present study is to study the effect of the successive use of aluminum sulfate (AS) as a coagulant and fresh cladodes juice (FCJ) used as a natural flocculant to treat urban wastewater. This paper reports the results obtained: the optimal dosages, condition of agitation and analysis of clear water which was recovered at the end of treatments. The efficiency of this treatment is evaluated based on the turbidity, suspended solids (SS) and chemical oxygen demand (COD) removal. Conductivity and pH are also studied.
MATERIALS AND METHODS Urban wastewater sampling The samples were obtained from the Metlaoui’s Wastewater Treatment Plant (MWTP) (Figure 1). This city is the most important mining town (south west of Tunisia). This treatment plant was designed some years ago (in 2006) to receive municipal wastewater. The sources of contamination are especially of domestic origin. It is advisable to keep
Map of Metlaoui’s Wastewater Treatment Plant (MWTP). (a) MWTP; (b) a mechanical bar screen, a grit chamber, an oil separator; (c) two aeration basins; (d) two secondary clarifiers; (e) a pumping sludge; (f) 38 drying beds.
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W
samples at a temperature of 4 C until use in order to minimize the changes in their characteristics and to slow down bacterial activity.
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homogenized by stirring. The initial pH in the cactus juice was adjusted to a desired value with NaOH. In fact, from the bibliography, the flocculating activity of FCJ is best at a basic pH.
Coagulation/flocculation tests with AS Coagulation-flocculation tests with the couple (AS/FCJ) To approach the optimal concentration a variable dose of the coagulant ‘AS’ are added (ranging from 0.3 to 2 g L1). Each dose is added into the beakers and is mixed at a high speed of 100 rpm for 2 min. The mixing speed is then reduced to 50 rpm and kept for another 8 min. After 30 min, this is performed on water decanted to all measures of water quality. Harvesting and preparation of fresh cladodes juice The cladodes of OFI used in this study were collected locally from El-Sened (in Gafsa in southern Tunisia). The pads were first collected and transported to the laboratory. They are cleaned by removing thorns and brown spots. Then they are cut into small pieces, and they were ground with a grinder. The liquid extract obtained is filtered using a gauze compress. We obtained a viscous liquid with green color, with a range of pH of (3–4) and miscible with water. Its density is equal to 1,014 kg/L. The FCJ can maintain its flocculation capacity for several days at room temperature, which is proved also by Abid et al. (). The filtrate collected is diluted to 10% in distilled water and
Figure 2
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Coagulation/flocculation test by the couple (AS/FCJ).
In order to decrease residual AS concentration in treated water, juice of cladodes of cactus is used as a natural flocculant in conjunction with AS. After performing a series of experiments, the following operating conditions are established. During this study, the coagulation with AS is added into the beakers and are mixed at a high speed of 100 rpm for 2 min. This high speed is important after adding the AS to obtain a uniform dispersion of the coagulant. The speed is then reduced to 50 rpm (large floc forming rate) for a period of 4 min. Under the same stirring, we add the bioflocculant for duration of 1 min. This agitation decreases thereafter up to 10 rpm for 3 min. In this stage, the flocs formed are larger and heavier. This step is followed by decantation phase of 30 min (Figure 2). Analytical methods The physico-chemical analyses of water examined as part of this work are: turbidity, SS, COD pH and conductivity. SS and COD are measured in laboratories according to the methods given in the series of standard methods for the
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examination of water and wastewater (Rodier ). Turbidity is determined using a turbidity meter (DR/2010 HACH). The pH is measured using a pH meter (Hach brand, model ION1 direction). The electrical conductivity was determined using an electrical conductivity meter (ORIEN brand). Each experiment is carried out in triplicate and the average results are presented herein.
RESULTS AND DISCUSSION Characterization of wastewater The wastewater collected from MWTP is examined for various parameters, in which turbidity, SS, and COD are in superior limits and in demand of elimination. The sample shows those mean values for pH 7.54, turbidity 296.33 NTU, COD 223.15 mg O2 L1 and SS 120 mg L1. Although their average loads of conductivity were 3,562.5 μs cm1. This pollutant load is due to the urban origin of wastes. Those wastewaters need to be suitably treated in order to avoid environmental problems. If compared with other wastewater data found in the literature (ArslanAlaton et al. ) our working water has nearly similar pollutant charge. Determination of the optimum dosage of the AS Clarified samples with AS are collected from the top of the beakers, and all measures of water quality are measured taken and tabulated (Table 1). Six glass beakers are filled with samples of wastewater obtained from the MWTP. Table 1 shows that the addition of AS caused a pH decreases. It is 7.22 ± 0.43; 7.18 ± 0.24; 6.68 ± 0.20; 5.66 ± 0.09; 4.69 ± 0.16 for respectively 0.3; 0.5; 1; 1.5 and 2 g L1 of AS. This pH decrease can be explained by the fact that the addition of aluminum salts causes water
Table 1
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liberation of Hþ ions. The value noted in the optimum dose (1 g L1) is always located in the Tunisian standard, thus requiring no adjustment of the pH of the effluent. The efficient removal of the turbidity is 93.09%, but the obtained water is still considered slightly cloudy water. The removal of the SS is 65.55%. The COD removal is 47.36%. These values exceed the standards according to the Tunisian standard. Higher dosages (1.5 g L1, 2 g L1) are not economical and did not significantly increase pollutant removal. This may be due to the inefficient of aluminum towards very fine particles (Sharma et al. ). In addition, residual aluminum in treated water may cause many secondary effects in the water. It is considered harmful to the environment and toxic to human’s fauna and flora (Bina et al. ; Jadhav & Mahajan ; Elsheikh et al. ). In order to decrease the residual Alþ3 concentration in treated water, cactus juice as natural flocculant in conjunction with aluminum may be used. Physico-chemical characteristics of the water treated by the couple AS/FCJ An approach to reduce the concentration of residual aluminum in finished water is to use a natural flocculant (FCJ) with primary coagulant (AS). At the beginning of this work, we tried to optimize the treatment of these kind of samples (with high turbidity) by the use of the fresh cactus juice alone, without the intervention of chemicals. But the results are not satisfactory. This, maybe, depends on what kind of effluent is being treated. It can be explained by the fact that this type of sample is highly charged by different types of pollutants. So in this step, our concern is to use the least amount of coagulant, for both economic and health reasons. So, the feasibility in the treatment of MWTP wastewater using AS and FCJ has been taken for investigation. Optimum dosage for maximum removal percentage in turbidity, the SS and
Coagulation/flocculation performance using AS: turbidity removal; SS removal and COD removal; pH and conductivity variations The added concentration of aluminium sulfate (g L1)
Parameters
Treated water
0.3
0.5
1.0
1.5
2.0
pH
7.54 ± 0.34
7.22 ± 0.43
7.18 ± 0.24
6.68 ± 0.20
5.66 ± 0.09
4.69 ± 0.16
TUR (NTU)
296.75 ± 48.19
59.25 ± 18.51
36.75 ± 5.85
20.5 ± 3.87
50 ± 14.49
75.5 ± 10.08
SS (mg L1)
120 ± 12.46
60 ± 9.17
55.5 ± 9.31
41.33 ± 11.21
60.08 ± 23.07
104.75 ± 22.59
COD (mg O2 L1)
274.25 ± 61.43
186.12 ± 13.64
164.37 ± 10.27
144.35 ± 10.22
151.49 ± 17.63
199.38 ± 26.34
Conductivity (μs/cm)
3562.5 ± 134
3700 ± 137.35
3962.5 ± 154.35
4000 ± 178.32
4047.5 ± 130.73
4153.33 ± 164.38
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COD use the couple AS/FCJ is found to be 0.5 g L1 of AS/ 5 mL L1 of the FCJ dosage ratio. This dosage ratio is the most viable and reduces 93.65% of turbidity and 82.75% of SS and 64.30% of COD. It is observed that this couple has more potential for the removal of concern pollutants in wastewater. Cactus significantly reduces the required dosage of aluminum of by 50%, thereby reducing costs of treatment and also negative effects on health and the environment. So, this combination is the optimum used in this work to get better results abatement of pollutants, spending a lower dosage of AS. Hence, it is recommended to add the FCJ after the addition of aluminum. Poor performance is obtained when FCJ and AS are added simultaneously. This is in agreement with a study done by the use of alum with another natural polyelectrolyte (Chitosan) (Bina et al. ). Indeed, in this part we need to test the effect of adding an FCJ on suspensions destabilized by coagulation with AS. The results obtained are detailed in Figures 3–7.
Effect of AS/FCJ on the pH variation For this study, the initial pH of the preparation of FCJ is adjusted in 8.5. In fact, from the bibliography, the flocculating activity of FCJ is best at a basic pH (Taa et al. ). In this study with a pH 8.5 we illustrate better turbidity, SS and COD removal. According to several tests, pH values below or above this value cause side effects such as flotation particle, foam formation and training black layers above the beakers.
Figure 3
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Change in pH depending on the type of treatment.
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The pH of the cactus solution, previously adjusted with sodium hydroxide at the beginning of the treatment has no effect on final pH of the treated water. The coagulation/flocculation by the pair (AS/FCJ) lowers the pH to 6.95 ± 0.35 (Figure 3). This is similar to the observed flocculation activities described previously for Aloe Vera leaf gel as a natural flocculant (Nougbodé et al. ). They found that there was a slight decrease in pH after water treatment by a natural flocculant. He explains this decrease by the acid characteristic of the plant. Therefore, the pH should not be neutralized before discharging the treated wastewater in the wadi. It is a neutral pH, which guarantees respect for Tunisian standards in effect for this parameter.
Effect of AS/FCJ on the removal of turbidity, SS and COD The entire process of coagulation/flocculation by the combination AS/FCJ, allows increasing significantly the rate of elimination of the turbidity (Figure 4), of SS (Figure 5) and COD (Figure 6). These three parameters are therefore taken into account in evaluating the efficiency of this couple in the treatment of this kind of wastewater. The mechanism can be explained as follows: when the AS is dissolved in water it generates highly charged cations that destabilize negatively charged particles and allow them to come into closer contact. The addition of fresh cactus juice allows the destabilized particles by the AS to attach to their long chains of polymers. Mannai et al. () notes that the chemical composition of the Tunisian OFI showed that it was rich with polymers.
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Figure 4
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Figure 5
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Change in turbidity depending on the type of treatment.
Change in SS depending on the type of treatment. Values correspond to the mean of three measurements ± standard deviation (SD). *p 0.05 compared to treated wastewater with the optimal dose of AS (1 g/L).
The use of the bioflocculant (FCJ) previously adjusted to 8.5 might confer positive charges on the particle surface (a positive zeta potential) allowing redispersion of the particles as reported for polyelectrolytes. With 50% saving in AS dose and 5 mL of FCJ, the best percentages of removal of turbidity are obtained, SS and COD are respectively 93.65%, 82.75% and 64.30%. Consequently, these results showed a high effectiveness in wastewater clarification, and they therefore conclude that this couple is suitable for use to process coagulation/
flocculation to better clarify the samples. Study by Jadhav & Mahajan indicates that the concurrence of polyelectrolyte with a metal coagulant improves clarification of water by accelerating the process of coagulation/flocculation. The presence of natural flocculant reduces the necessity of alum and improves the physical characteristics of flocs (Jadhav & Mahajan ). It is important to note that, in this study, there is an improvement in the floc size when a cactus is used as a flocculant in conjunction with AS as compared to either cactus or AS alone.
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Change in COD depending on the type of treatment. Values correspond to the mean of three measurements ± standard deviation (SD). *p 0.05 compared to treated wastewater with the optimal dose of AS (1 g/L).
The flocculant capacity of cactus may be attributed to the presence of mucilage which is a viscous and complex carbohydrate stored in cactus racket (Pichler et al. ). Turbidity is the best indicator of the effectiveness of these treatments. With reducing optimum dose of aluminum to 1/2 and optimum dose of the natural flocculant (FCJ), Figure 4 shows that the addition of FCJ produces an appreciable removal of turbidity. Initially, the turbidity of the raw
Figure 7
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samples in the plant of Metlaoui is high (296.33 ± 35.11 NTU). Upon the application of coagulation/flocculation treatment by the pair AS/FCJ the value of this parameter decreases again (18.66 ± 3.51 NTU). It is obvious that the reduction of the initial turbidity is accompanied by a reduction in SS and COD. Jadhav & Mahajan () note that with the combination of alum and cactus Opuntia, there is a percentage greater than 90% in turbidity removal
Change in conductivity depending on the type of treatment. Values correspond to the mean of three measurements ± standard deviation (SD). *p 0.05 compared to treated wastewater with the optimal dose of AS (1 g/L).
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efficiency for high turbidity level (314.4 NTU) of synthetic turbid water prepared from local clays. In 2009, Abid et al. have found that for pH below 9, the combination treatment (iron chloride/cactus juice) in the presence of NaOH is very advantageous. This treatment has a high efficiency in the clarification of liquid effluents charged with copper, zinc and SS (all tests were carried out on pseudo-industrial samples prepared in the laboratory and on the other ones stemmed from a surface treated unit). In this study, cactus OFI shows a high-capacity power of flocculation. It reduces the use of synthetic and expensive technologies frequently employed for the removal of toxic pollutants from contaminated water. Also, the use of OFI in this coagulation/flocculation process may reduce the negative impact on the environment often affected by these chemical products. This strategy is more economical and eco-friendly. It is necessary to note that naturally occurring products are biodegradable and are presumed safe for human health (Chopra & Ruhi ). This finding was also confirmed by Taa et al. in . The coagulation performance of cactus acts as a natural macromolecular coagulant is also studied by Zhang and his collaborators in 2006 (Zhang et al. ). They recommend also that when the cactus was used with AlCl3-6H2O to treat the synthetic water, the removal efficiency of turbidity and COD were higher than that of the cactus or AlCl3-6H2O when it was used solely. They reported that this treatment achieves comparatively high COD and turbidity removal efficiency, and water with turbidity less than 5 NTU could be obtained with initial turbidities from 20 to 200 NTU. As it was recommended by Nougbodé and his collaborators in , they found that the successive addition of the aqueous Opuntia solution and the lime gave a better elimination of turbidity and SS which exceed 95%. In another study, when the M. oliefera was used with alum in a combination 50:50 dosage ratio and gave good results, it has more potential for the removal of concern pollutants in textile wastewater. This dosage ratio was the most viable for maximum removal percentage in turbidity, TDS, TSS, BOD and COD. The percentage removals were 61.6%, 60.4%, 54.15%, 80.67% and 66.73%, respectively. All these studies reinforce the results obtained after treatment with AS/FCJ. The performance of this couple was found to be good as compared to AS with the advantages of the biodegradability. A natural polymer in conjunction with a metal coagulant improves coagulation by accelerating the process of coagulation. This bioflocculant reduces the requirement of alum and improves the physical characteristic of flocs, which results in better quality of treated water (Muralimohan et al. ).
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Prickly pear nopals of OFI are mostly composed by polysaccharides. These latter revealed a good stability of viscosity of the solutions to added salts. This property can be viewed as a consequence of the low charge density of the polymer backbone (Majdoub et al. ). Effect of AS/FCJ on the conductivity Figure 7 shows the variation of conductivity of the treated water as a function of type of treatment. This parameter reaches higher values when using 0.5 g/L of AS only with respect to raw sample. The coagulation/flocculation with AS/FCJ increases the values of the conductivity with respect to those obtained by using 0.5 g/L and 1 g/L of AS (Figure 7). This can be explained by a significant mineralization of the sample and confirms the presence of several types of charge carriers: the cations (Al3þ and Naþ) and anions (SO2 4 and OH).
CONCLUSION In summary, the use of AS as a coagulant and FCJ as a natural biodegradable flocculant to improve the quality of treated urban wastewater, seems to be an interesting solution. These results show that we can value the cactus (OFI) of the Gafsa region (southern Tunisia) in the treatment of urban wastewater. This study investigates the effect of the use of the couple (AS/FCJ) in the treatment of wastewater in terms of turbidity and SS removals and the extent of residual COD in the treated water. The treatment conducted by AS followed by cactus juice had significantly better turbidity removal efficiency (93.65%) with the lower residual COD (64.30%) and SS (82.75%) in the treated water. Also, it offers certain advantages such as availability, cost, and strength of the flocs formed, etc., and thus makes their uses more reasonable. It concludes that this couple was found to be especially effective in reducing the parameters turbidity, SS and COD. The experimental results conducted for this study encourage the use of cactus in other forms and for other types of wastewater treatment purpose.
ACKNOWLEDGEMENTS This work is done in the Laboratory of ONAS of Gafsa City; This research is also supported by the Tunisian Ministry of Higher Education and Scientific Research via the
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Department of Geology and Faculty of Sciences of Gafsa. The authors wish to thank all the staff of these two institutions.
REFERENCES Abdel-Hameed, E. S. S., Nagaty, M. A., Salman, M. S. & Bazaid, S. A. Phytochemicals, nutritionals and antioxidant properties of two prickly pear cactus cultivars (Opuntia ficus-indica Mill.) growing in Taif, KSA. Food Chem. 160, 31–38. Abid, A., Zouhri, A., Ider, A. & Kholtei, S., Valorisation d’un nouveau biofloculant (extrait de cactus) dans le traitement physico-chimique des rejets liquides chargés en cuivre, en zinc et en matière en suspension. Revue des Energies Renouvelables 12, 321–330. Arslan-Alaton, I., Tanik, A., Ovez, S., Iskender, G., Gurel, M. & Orhon, D. Reuse potential of urban wastewater treatment plan effluents in Turkey: a case study on selected plants. Desalination 215, 159–165. Ben Rebah, F. & Siddeeg, S. M. Cactus an eco-friendly material for wastewater treatment: a review. Journal of Materials and Environmental Sciences 8 (5), 1770–1782. Bina, B., Mehdinejad, M. H., Nikaeen, M. & Movahedian Attar, H. Effectiveness of chitosan as natural coagulant aid in treating turbid waters. Iranian Journal of Environmental Health Science and Engineering 6 (4), 247–252. Chopra, H. & Ruhi, G. Eco friendly chitosan: an efficient material for water purification. The Pharma Innovation Journal 5 (1), 92–95. El-Mostafa, K., El Kharrassi, Y., Badreddine, A., Andreoletti, P., Vamecq, J., El Kebbaj, M. S., Latruffe, N., Lizard, G., Nasser, B. & Cherkaoui-Malki, M. Nopal cactus (Opuntia ficus-indica) as a source of bioactive compounds for nutrition, health and disease. Molecules 19 (9), 14879–14901. Elsheikh, R., Abo-ELfadl, M. M. S., Ali, M. E. A. & Khader, K. Impact of sludge produced from drinking water plants on groundwater and its treatment by a natural polymer. Journal of American Science 13 (2), 95–105. Jadhav, M. V. & Mahajan, Y. S. A comparative study of natural coagulants in flocculation of local clay suspensions of varied turbidity. International Journal of Civil and Environmental Engineering 35, 1701–8285. Majdoub, H., Roudesli, S., Picton, L., Le Cerf, D., Muller, G. & Grisel, M. Prickly pear nopals pectin from Opuntia ficus indica physico-chemical study in dilute and semi-dilute solutions. Carbohydrate Polymers 46, 69–79. Mannai, F., Ammar, M., Yanez, J. G., Elaloui, E. & Moussaoui, Y. Cellulose fiber from Tunisian Barbary Fig ‘Opuntia ficus-indica’ for papermaking. Cellulose 23 (3), 2061–2072. Monrroy, M., García, E., Ríos, K. & García, J. R. Extraction and physicochemical characterization of mucilage from
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Opuntia cochenillifera (L.) Miller. Journal of Chemistry 2017, 1–9. Muralimohan, N., Palanisamy, T. & Vimaladevi, M. N. Experimental study on removal efficiency of blended coagulants in textile wastewater treatment. International Journal of Research in Engineering & Technology 2 (2), 15–20. Nefzaoui, A. & Ben Salem, H. Opuntia: a strategic fodder and efficient tool to combat desertification in the WANA Region, Rapport FAO/CACTUSNET NEWSLETT, The use of opuntia as forage, FAO, Rome, Italy. Nougbodé, Y. A. E. I., Agbangnan, C. P., Koudoro, A. Y., Dèdjiho, C. A., Aïna, M. P., Mama, D. & Sohounhloué, D. C. K. Evaluation of the Opuntia dillenii as natural coagulant in water clarification: case of treatment of highly turbid surface water. Journal of Water Resource and Protection 5 (12), 1242–1246. Nougbodé, Y. A. E. I., Sessou, P., Alassane, A., Youssao, A. K. A., Agbangnan, C. P., Mama, D. & Sohounhloue, K. C. D. Evaluation of aloe vera leaf gel as a natural flocculant: phytochemical screening and turbidity removal trials of water by coagulation flocculation. Research Journal of Recent Sciences 5 (1), 9–15. Pichler, T. K., Young, K. & Alcantar, N. Eliminating turbidity in drinking water using the mucilage of a common cactus. Water Science & Technology: Water Supply 12 (2), 179–186. Ramírez-Moreno, E., Cariño-Cortés, R., Cruz-Cansino, N. S., Delgado-Olivares, L., Ariza-Ortega, J. A., MontañezIzquierdo, V. Y., Hernández-Herrero, M. M. & FilardoKerstupp, T. Antioxidant and antimicrobial properties of cactus pear (Opuntia) seed oils. Journal of Food Quality 2017, 1–8. Rodier, J. L’analyse de l’eau – eaux naturelles, eaux résiduaires, eau de mer, 9ème édition, Paris, Dunod, 1475 p. Schmid, D., Suter, F. & Zülli, F. Soothing factor from Opuntia cactus for sensitive skin. SöFW Journal 131 (11), 14–18. Sharma, B. R., Dhuldhoya, N. C. & Merchant, U. C. Flocculants an ecofriendly approach. Journal of Polymers and the Environment 14 (2), 195–202. Taa, N., Benyahya, M. & Chaouch, M. Using a bio-flocculent in the process of coagulation flocculation for optimizing the chromium removal from the polluted water. Journal of Materials and Environmental Science 7 (5), 1581–1588. Theodoro, J. D. P., Lenz, G. F., Zara, R. F. & Bergamasco, R. Coagulants and natural polymers: perspectives for the treatment of water. Plastic and Polymer Technology 2 (3), 55–62. Verma, A. K., Dash, R. R. & Bhunia, P. A review on chemical coagulation/flocculation technologies for removal of colour from textile wastewaters. Journal of Environmental Management 93 (1), 154–168. Zhang, J., Zhang, F., Luo, Y. & Yang, H. A preliminary study on cactus as coagulant in water treatment. ProcessBiochem 41, 730–733.
First received 6 March 2017; accepted in revised form 7 June 2017. Available online 20 June 2017
© IWA Publishing 2017 Water Science & Technology
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Cactus Opuntia as natural flocculant for urban wastewater treatment Raouen Rachdi, Feyda Srarfi and Najet Slim Shimi
ABSTRACT The cactus tree, species Opuntia ficus-indica, is a primary material of many products in various domains such as cosmetics, medicine and nutrition. In the present work, we assess its potential as a flocculant. We tried a technique which adopts three sequential treatments that used coagulation, flocculation and sedimentation processes under certain operating conditions. For this purpose, we used the aluminum sulfate (AS) as coagulant and fresh cladodes juice (FCJ) as bioflocculant. All tests were carried out on high turbid urban wastewater collected from the Metlaoui’s Wastewater Treatment Plant (MWTP) (in Gafsa in southwest Tunisia). Experiments with this couple AS/FCJ show very interesting results: a high-removal of turbidity (TUR), suspended solids (SS) and chemical oxygen demand (COD). The percentages of abatement of these parameters are respectively 93.65%, 82.75% and 64.30%. The experimental results of the present study prove that the turbidity, SS and COD
Raouen Rachdi (corresponding author) Feyda Srarfi Najet Slim Shimi Palaeo-Environment Geomaterials and Geological Threats, Faculty of Sciences of Tunis, A campus university 2092, El Manar Tunis, Tunisia E-mail: [email protected] Feyda Srarfi Najet Slim Shimi Faculty of Sciences of Tunis, Department of Geology, University Campus El Manar Tunis 2092 El Manar Tunis, Tunisia
removal efficiency of new technique is superior to that of conventional process (with only AS). By this technique, we save 50% in AS dose. Moreover, flocs formed by the treatment using AS/FCJ are coarse and readily settleable. Key words
| bio-flocculation, COD, Opuntia ficus-indica, suspended solids, turbidity
INTRODUCTION Urbanization, industrialization and extensive agricultural production are responsible for generating polluted effluents which need to be treated. The principal objective of wastewater treatment is generally to allow human and industrial effluents to be disposed into the hydrographic network without danger to human health or unacceptable damage to the natural environment. Various treatment methods have been applied for the removal of pollutants from wastewater such as ion exchange, membrane filtration, activated carbon and coagulation/flocculation processes (Muralimohan et al. ). The coagulation/flocculation processes have remained the most widely practiced techniques in wastewater treatment for removing particulate, organic matter, color, and heavy metal (Verma et al. ). They are used whenever the natural settling rate of suspended material is too slow to provide a very effective clarification. They allow to improve the aesthetic appearance of turbid water. This technique aims to remove suspended particles by destabilization and the formation of larger and heavier flocs which facilitate their sedimentation. doi: 10.2166/wst.2017.370
This technique offers various advantages for the treatment of different kinds of wastewaters (industrial, urban, etc.) such as easy operation and lower sensitivity to toxic loadings, etc. However, it is well-recognized that the use of metal salts in this process has numerous disadvantages such as: relatively high procurement costs for many developing countries, the typical high quantities of chemicals needed, production of large sludge volumes and the significant change in pH of treated water. But with these chemical products, there is always the concern about residuals in the treated water. However, several studies demonstrate that chemicals (coagulants or flocculants) remain in the water after treatment may cause many detrimental effects on human health and on the environment. Because of the drawbacks of these technologies, it is therefore desirable to substitute these chemical products with natural compounds derived from plant material to produce the coagulation/flocculation process (Theodoro et al. ). The use of flocculants of vegetable origin to treat aqueous solutions is a relatively new process that has proven very interesting results in the removal of contaminants
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from wastewater (Chopra & Ruhi ). Historically, natural coagulants and bioflocculants based plant were used in water and wastewater treatment before the advent of synthetic chemicals. But their use has been discouraged in developed countries under the pretext that they have never been subjected to rigorous scientific evaluation. The previous studies have not determined whether such natural coagulants are economically and environmentally more acceptable than chemical products (Theodoro et al. ). Recently, there has been more interest in the subject of natural products. It shows a bright future and starts to motivate many researchers because it has several advantages like abundance and it is presumed to be safe for human health (Muralimohan et al. ; Rebah & Siddeeg ). In addition, it produces a readily biodegradable and less voluminous sludge (Jadhav & Mahajan ). In the last few decades, cactus (Opuntia ficus-indica (OFI)) has attracted attention in nutrition (El-Mostafa et al. ), cosmetics (Schmid et al. ; RamírezMoreno et al. ), medical (Abdel-Hameed et al. ; Monrroy et al. ) and industrial domains (Mannai et al. ). However, the application of this plant for water treatment is quite new in comparison with other natural coagulants like Moringa oleifera and Nirmali (Theodoro et al. ). A few studies have examined the use of the cactus as a natural biodegradable flocculant instead of those chemicals in the coagulation/flocculation process.
Figure 1
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In Tunisia, the cactus plant is abundant (600,000 hectares were planted). In the arid and semi-arid zones of the country, it is used as forage for bovine. But, despite its widespread, it has poor commercial value due to lack of knowledge about its properties (Nefzaoui & Ben Salem ). Hence, the objective of the present study is to study the effect of the successive use of aluminum sulfate (AS) as a coagulant and fresh cladodes juice (FCJ) used as a natural flocculant to treat urban wastewater. This paper reports the results obtained: the optimal dosages, condition of agitation and analysis of clear water which was recovered at the end of treatments. The efficiency of this treatment is evaluated based on the turbidity, suspended solids (SS) and chemical oxygen demand (COD) removal. Conductivity and pH are also studied.
MATERIALS AND METHODS Urban wastewater sampling The samples were obtained from the Metlaoui’s Wastewater Treatment Plant (MWTP) (Figure 1). This city is the most important mining town (south west of Tunisia). This treatment plant was designed some years ago (in 2006) to receive municipal wastewater. The sources of contamination are especially of domestic origin. It is advisable to keep
Map of Metlaoui’s Wastewater Treatment Plant (MWTP). (a) MWTP; (b) a mechanical bar screen, a grit chamber, an oil separator; (c) two aeration basins; (d) two secondary clarifiers; (e) a pumping sludge; (f) 38 drying beds.
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W
samples at a temperature of 4 C until use in order to minimize the changes in their characteristics and to slow down bacterial activity.
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homogenized by stirring. The initial pH in the cactus juice was adjusted to a desired value with NaOH. In fact, from the bibliography, the flocculating activity of FCJ is best at a basic pH.
Coagulation/flocculation tests with AS Coagulation-flocculation tests with the couple (AS/FCJ) To approach the optimal concentration a variable dose of the coagulant ‘AS’ are added (ranging from 0.3 to 2 g L1). Each dose is added into the beakers and is mixed at a high speed of 100 rpm for 2 min. The mixing speed is then reduced to 50 rpm and kept for another 8 min. After 30 min, this is performed on water decanted to all measures of water quality. Harvesting and preparation of fresh cladodes juice The cladodes of OFI used in this study were collected locally from El-Sened (in Gafsa in southern Tunisia). The pads were first collected and transported to the laboratory. They are cleaned by removing thorns and brown spots. Then they are cut into small pieces, and they were ground with a grinder. The liquid extract obtained is filtered using a gauze compress. We obtained a viscous liquid with green color, with a range of pH of (3–4) and miscible with water. Its density is equal to 1,014 kg/L. The FCJ can maintain its flocculation capacity for several days at room temperature, which is proved also by Abid et al. (). The filtrate collected is diluted to 10% in distilled water and
Figure 2
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Coagulation/flocculation test by the couple (AS/FCJ).
In order to decrease residual AS concentration in treated water, juice of cladodes of cactus is used as a natural flocculant in conjunction with AS. After performing a series of experiments, the following operating conditions are established. During this study, the coagulation with AS is added into the beakers and are mixed at a high speed of 100 rpm for 2 min. This high speed is important after adding the AS to obtain a uniform dispersion of the coagulant. The speed is then reduced to 50 rpm (large floc forming rate) for a period of 4 min. Under the same stirring, we add the bioflocculant for duration of 1 min. This agitation decreases thereafter up to 10 rpm for 3 min. In this stage, the flocs formed are larger and heavier. This step is followed by decantation phase of 30 min (Figure 2). Analytical methods The physico-chemical analyses of water examined as part of this work are: turbidity, SS, COD pH and conductivity. SS and COD are measured in laboratories according to the methods given in the series of standard methods for the
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examination of water and wastewater (Rodier ). Turbidity is determined using a turbidity meter (DR/2010 HACH). The pH is measured using a pH meter (Hach brand, model ION1 direction). The electrical conductivity was determined using an electrical conductivity meter (ORIEN brand). Each experiment is carried out in triplicate and the average results are presented herein.
RESULTS AND DISCUSSION Characterization of wastewater The wastewater collected from MWTP is examined for various parameters, in which turbidity, SS, and COD are in superior limits and in demand of elimination. The sample shows those mean values for pH 7.54, turbidity 296.33 NTU, COD 223.15 mg O2 L1 and SS 120 mg L1. Although their average loads of conductivity were 3,562.5 μs cm1. This pollutant load is due to the urban origin of wastes. Those wastewaters need to be suitably treated in order to avoid environmental problems. If compared with other wastewater data found in the literature (ArslanAlaton et al. ) our working water has nearly similar pollutant charge. Determination of the optimum dosage of the AS Clarified samples with AS are collected from the top of the beakers, and all measures of water quality are measured taken and tabulated (Table 1). Six glass beakers are filled with samples of wastewater obtained from the MWTP. Table 1 shows that the addition of AS caused a pH decreases. It is 7.22 ± 0.43; 7.18 ± 0.24; 6.68 ± 0.20; 5.66 ± 0.09; 4.69 ± 0.16 for respectively 0.3; 0.5; 1; 1.5 and 2 g L1 of AS. This pH decrease can be explained by the fact that the addition of aluminum salts causes water
Table 1
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liberation of Hþ ions. The value noted in the optimum dose (1 g L1) is always located in the Tunisian standard, thus requiring no adjustment of the pH of the effluent. The efficient removal of the turbidity is 93.09%, but the obtained water is still considered slightly cloudy water. The removal of the SS is 65.55%. The COD removal is 47.36%. These values exceed the standards according to the Tunisian standard. Higher dosages (1.5 g L1, 2 g L1) are not economical and did not significantly increase pollutant removal. This may be due to the inefficient of aluminum towards very fine particles (Sharma et al. ). In addition, residual aluminum in treated water may cause many secondary effects in the water. It is considered harmful to the environment and toxic to human’s fauna and flora (Bina et al. ; Jadhav & Mahajan ; Elsheikh et al. ). In order to decrease the residual Alþ3 concentration in treated water, cactus juice as natural flocculant in conjunction with aluminum may be used. Physico-chemical characteristics of the water treated by the couple AS/FCJ An approach to reduce the concentration of residual aluminum in finished water is to use a natural flocculant (FCJ) with primary coagulant (AS). At the beginning of this work, we tried to optimize the treatment of these kind of samples (with high turbidity) by the use of the fresh cactus juice alone, without the intervention of chemicals. But the results are not satisfactory. This, maybe, depends on what kind of effluent is being treated. It can be explained by the fact that this type of sample is highly charged by different types of pollutants. So in this step, our concern is to use the least amount of coagulant, for both economic and health reasons. So, the feasibility in the treatment of MWTP wastewater using AS and FCJ has been taken for investigation. Optimum dosage for maximum removal percentage in turbidity, the SS and
Coagulation/flocculation performance using AS: turbidity removal; SS removal and COD removal; pH and conductivity variations The added concentration of aluminium sulfate (g L1)
Parameters
Treated water
0.3
0.5
1.0
1.5
2.0
pH
7.54 ± 0.34
7.22 ± 0.43
7.18 ± 0.24
6.68 ± 0.20
5.66 ± 0.09
4.69 ± 0.16
TUR (NTU)
296.75 ± 48.19
59.25 ± 18.51
36.75 ± 5.85
20.5 ± 3.87
50 ± 14.49
75.5 ± 10.08
SS (mg L1)
120 ± 12.46
60 ± 9.17
55.5 ± 9.31
41.33 ± 11.21
60.08 ± 23.07
104.75 ± 22.59
COD (mg O2 L1)
274.25 ± 61.43
186.12 ± 13.64
164.37 ± 10.27
144.35 ± 10.22
151.49 ± 17.63
199.38 ± 26.34
Conductivity (μs/cm)
3562.5 ± 134
3700 ± 137.35
3962.5 ± 154.35
4000 ± 178.32
4047.5 ± 130.73
4153.33 ± 164.38
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COD use the couple AS/FCJ is found to be 0.5 g L1 of AS/ 5 mL L1 of the FCJ dosage ratio. This dosage ratio is the most viable and reduces 93.65% of turbidity and 82.75% of SS and 64.30% of COD. It is observed that this couple has more potential for the removal of concern pollutants in wastewater. Cactus significantly reduces the required dosage of aluminum of by 50%, thereby reducing costs of treatment and also negative effects on health and the environment. So, this combination is the optimum used in this work to get better results abatement of pollutants, spending a lower dosage of AS. Hence, it is recommended to add the FCJ after the addition of aluminum. Poor performance is obtained when FCJ and AS are added simultaneously. This is in agreement with a study done by the use of alum with another natural polyelectrolyte (Chitosan) (Bina et al. ). Indeed, in this part we need to test the effect of adding an FCJ on suspensions destabilized by coagulation with AS. The results obtained are detailed in Figures 3–7.
Effect of AS/FCJ on the pH variation For this study, the initial pH of the preparation of FCJ is adjusted in 8.5. In fact, from the bibliography, the flocculating activity of FCJ is best at a basic pH (Taa et al. ). In this study with a pH 8.5 we illustrate better turbidity, SS and COD removal. According to several tests, pH values below or above this value cause side effects such as flotation particle, foam formation and training black layers above the beakers.
Figure 3
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Change in pH depending on the type of treatment.
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The pH of the cactus solution, previously adjusted with sodium hydroxide at the beginning of the treatment has no effect on final pH of the treated water. The coagulation/flocculation by the pair (AS/FCJ) lowers the pH to 6.95 ± 0.35 (Figure 3). This is similar to the observed flocculation activities described previously for Aloe Vera leaf gel as a natural flocculant (Nougbodé et al. ). They found that there was a slight decrease in pH after water treatment by a natural flocculant. He explains this decrease by the acid characteristic of the plant. Therefore, the pH should not be neutralized before discharging the treated wastewater in the wadi. It is a neutral pH, which guarantees respect for Tunisian standards in effect for this parameter.
Effect of AS/FCJ on the removal of turbidity, SS and COD The entire process of coagulation/flocculation by the combination AS/FCJ, allows increasing significantly the rate of elimination of the turbidity (Figure 4), of SS (Figure 5) and COD (Figure 6). These three parameters are therefore taken into account in evaluating the efficiency of this couple in the treatment of this kind of wastewater. The mechanism can be explained as follows: when the AS is dissolved in water it generates highly charged cations that destabilize negatively charged particles and allow them to come into closer contact. The addition of fresh cactus juice allows the destabilized particles by the AS to attach to their long chains of polymers. Mannai et al. () notes that the chemical composition of the Tunisian OFI showed that it was rich with polymers.
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Figure 4
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Figure 5
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Change in turbidity depending on the type of treatment.
Change in SS depending on the type of treatment. Values correspond to the mean of three measurements ± standard deviation (SD). *p 0.05 compared to treated wastewater with the optimal dose of AS (1 g/L).
The use of the bioflocculant (FCJ) previously adjusted to 8.5 might confer positive charges on the particle surface (a positive zeta potential) allowing redispersion of the particles as reported for polyelectrolytes. With 50% saving in AS dose and 5 mL of FCJ, the best percentages of removal of turbidity are obtained, SS and COD are respectively 93.65%, 82.75% and 64.30%. Consequently, these results showed a high effectiveness in wastewater clarification, and they therefore conclude that this couple is suitable for use to process coagulation/
flocculation to better clarify the samples. Study by Jadhav & Mahajan indicates that the concurrence of polyelectrolyte with a metal coagulant improves clarification of water by accelerating the process of coagulation/flocculation. The presence of natural flocculant reduces the necessity of alum and improves the physical characteristics of flocs (Jadhav & Mahajan ). It is important to note that, in this study, there is an improvement in the floc size when a cactus is used as a flocculant in conjunction with AS as compared to either cactus or AS alone.
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Figure 6
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Change in COD depending on the type of treatment. Values correspond to the mean of three measurements ± standard deviation (SD). *p 0.05 compared to treated wastewater with the optimal dose of AS (1 g/L).
The flocculant capacity of cactus may be attributed to the presence of mucilage which is a viscous and complex carbohydrate stored in cactus racket (Pichler et al. ). Turbidity is the best indicator of the effectiveness of these treatments. With reducing optimum dose of aluminum to 1/2 and optimum dose of the natural flocculant (FCJ), Figure 4 shows that the addition of FCJ produces an appreciable removal of turbidity. Initially, the turbidity of the raw
Figure 7
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samples in the plant of Metlaoui is high (296.33 ± 35.11 NTU). Upon the application of coagulation/flocculation treatment by the pair AS/FCJ the value of this parameter decreases again (18.66 ± 3.51 NTU). It is obvious that the reduction of the initial turbidity is accompanied by a reduction in SS and COD. Jadhav & Mahajan () note that with the combination of alum and cactus Opuntia, there is a percentage greater than 90% in turbidity removal
Change in conductivity depending on the type of treatment. Values correspond to the mean of three measurements ± standard deviation (SD). *p 0.05 compared to treated wastewater with the optimal dose of AS (1 g/L).
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efficiency for high turbidity level (314.4 NTU) of synthetic turbid water prepared from local clays. In 2009, Abid et al. have found that for pH below 9, the combination treatment (iron chloride/cactus juice) in the presence of NaOH is very advantageous. This treatment has a high efficiency in the clarification of liquid effluents charged with copper, zinc and SS (all tests were carried out on pseudo-industrial samples prepared in the laboratory and on the other ones stemmed from a surface treated unit). In this study, cactus OFI shows a high-capacity power of flocculation. It reduces the use of synthetic and expensive technologies frequently employed for the removal of toxic pollutants from contaminated water. Also, the use of OFI in this coagulation/flocculation process may reduce the negative impact on the environment often affected by these chemical products. This strategy is more economical and eco-friendly. It is necessary to note that naturally occurring products are biodegradable and are presumed safe for human health (Chopra & Ruhi ). This finding was also confirmed by Taa et al. in . The coagulation performance of cactus acts as a natural macromolecular coagulant is also studied by Zhang and his collaborators in 2006 (Zhang et al. ). They recommend also that when the cactus was used with AlCl3-6H2O to treat the synthetic water, the removal efficiency of turbidity and COD were higher than that of the cactus or AlCl3-6H2O when it was used solely. They reported that this treatment achieves comparatively high COD and turbidity removal efficiency, and water with turbidity less than 5 NTU could be obtained with initial turbidities from 20 to 200 NTU. As it was recommended by Nougbodé and his collaborators in , they found that the successive addition of the aqueous Opuntia solution and the lime gave a better elimination of turbidity and SS which exceed 95%. In another study, when the M. oliefera was used with alum in a combination 50:50 dosage ratio and gave good results, it has more potential for the removal of concern pollutants in textile wastewater. This dosage ratio was the most viable for maximum removal percentage in turbidity, TDS, TSS, BOD and COD. The percentage removals were 61.6%, 60.4%, 54.15%, 80.67% and 66.73%, respectively. All these studies reinforce the results obtained after treatment with AS/FCJ. The performance of this couple was found to be good as compared to AS with the advantages of the biodegradability. A natural polymer in conjunction with a metal coagulant improves coagulation by accelerating the process of coagulation. This bioflocculant reduces the requirement of alum and improves the physical characteristic of flocs, which results in better quality of treated water (Muralimohan et al. ).
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Prickly pear nopals of OFI are mostly composed by polysaccharides. These latter revealed a good stability of viscosity of the solutions to added salts. This property can be viewed as a consequence of the low charge density of the polymer backbone (Majdoub et al. ). Effect of AS/FCJ on the conductivity Figure 7 shows the variation of conductivity of the treated water as a function of type of treatment. This parameter reaches higher values when using 0.5 g/L of AS only with respect to raw sample. The coagulation/flocculation with AS/FCJ increases the values of the conductivity with respect to those obtained by using 0.5 g/L and 1 g/L of AS (Figure 7). This can be explained by a significant mineralization of the sample and confirms the presence of several types of charge carriers: the cations (Al3þ and Naþ) and anions (SO2 4 and OH).
CONCLUSION In summary, the use of AS as a coagulant and FCJ as a natural biodegradable flocculant to improve the quality of treated urban wastewater, seems to be an interesting solution. These results show that we can value the cactus (OFI) of the Gafsa region (southern Tunisia) in the treatment of urban wastewater. This study investigates the effect of the use of the couple (AS/FCJ) in the treatment of wastewater in terms of turbidity and SS removals and the extent of residual COD in the treated water. The treatment conducted by AS followed by cactus juice had significantly better turbidity removal efficiency (93.65%) with the lower residual COD (64.30%) and SS (82.75%) in the treated water. Also, it offers certain advantages such as availability, cost, and strength of the flocs formed, etc., and thus makes their uses more reasonable. It concludes that this couple was found to be especially effective in reducing the parameters turbidity, SS and COD. The experimental results conducted for this study encourage the use of cactus in other forms and for other types of wastewater treatment purpose.
ACKNOWLEDGEMENTS This work is done in the Laboratory of ONAS of Gafsa City; This research is also supported by the Tunisian Ministry of Higher Education and Scientific Research via the
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Department of Geology and Faculty of Sciences of Gafsa. The authors wish to thank all the staff of these two institutions.
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Opuntia cochenillifera (L.) Miller. Journal of Chemistry 2017, 1–9. Muralimohan, N., Palanisamy, T. & Vimaladevi, M. N. Experimental study on removal efficiency of blended coagulants in textile wastewater treatment. International Journal of Research in Engineering & Technology 2 (2), 15–20. Nefzaoui, A. & Ben Salem, H. Opuntia: a strategic fodder and efficient tool to combat desertification in the WANA Region, Rapport FAO/CACTUSNET NEWSLETT, The use of opuntia as forage, FAO, Rome, Italy. Nougbodé, Y. A. E. I., Agbangnan, C. P., Koudoro, A. Y., Dèdjiho, C. A., Aïna, M. P., Mama, D. & Sohounhloué, D. C. K. Evaluation of the Opuntia dillenii as natural coagulant in water clarification: case of treatment of highly turbid surface water. Journal of Water Resource and Protection 5 (12), 1242–1246. Nougbodé, Y. A. E. I., Sessou, P., Alassane, A., Youssao, A. K. A., Agbangnan, C. P., Mama, D. & Sohounhloue, K. C. D. Evaluation of aloe vera leaf gel as a natural flocculant: phytochemical screening and turbidity removal trials of water by coagulation flocculation. Research Journal of Recent Sciences 5 (1), 9–15. Pichler, T. K., Young, K. & Alcantar, N. Eliminating turbidity in drinking water using the mucilage of a common cactus. Water Science & Technology: Water Supply 12 (2), 179–186. Ramírez-Moreno, E., Cariño-Cortés, R., Cruz-Cansino, N. S., Delgado-Olivares, L., Ariza-Ortega, J. A., MontañezIzquierdo, V. Y., Hernández-Herrero, M. M. & FilardoKerstupp, T. Antioxidant and antimicrobial properties of cactus pear (Opuntia) seed oils. Journal of Food Quality 2017, 1–8. Rodier, J. L’analyse de l’eau – eaux naturelles, eaux résiduaires, eau de mer, 9ème édition, Paris, Dunod, 1475 p. Schmid, D., Suter, F. & Zülli, F. Soothing factor from Opuntia cactus for sensitive skin. SöFW Journal 131 (11), 14–18. Sharma, B. R., Dhuldhoya, N. C. & Merchant, U. C. Flocculants an ecofriendly approach. Journal of Polymers and the Environment 14 (2), 195–202. Taa, N., Benyahya, M. & Chaouch, M. Using a bio-flocculent in the process of coagulation flocculation for optimizing the chromium removal from the polluted water. Journal of Materials and Environmental Science 7 (5), 1581–1588. Theodoro, J. D. P., Lenz, G. F., Zara, R. F. & Bergamasco, R. Coagulants and natural polymers: perspectives for the treatment of water. Plastic and Polymer Technology 2 (3), 55–62. Verma, A. K., Dash, R. R. & Bhunia, P. A review on chemical coagulation/flocculation technologies for removal of colour from textile wastewaters. Journal of Environmental Management 93 (1), 154–168. Zhang, J., Zhang, F., Luo, Y. & Yang, H. A preliminary study on cactus as coagulant in water treatment. ProcessBiochem 41, 730–733.
First received 6 March 2017; accepted in revised form 7 June 2017. Available online 20 June 2017
