Scholarly article on topic 'Coagulation Flocculation Test of Keddara's Water Dam Using Chitosan and Sulfate Aluminium'

Coagulation Flocculation Test of Keddara's Water Dam Using Chitosan and Sulfate Aluminium Academic research paper on "Chemical sciences"

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Abstract of research paper on Chemical sciences, author of scientific article — Hassiba Zemmouri, Madani Drouiche, Amna Sayeh, Hakim Lounici, Nabil Mameri

Abstract Chitosan is a natural polymer prepared from crab, shrimp and lobster shells. It has been used as coagulant in water treatment to avoid the human health problems caused by the residual aluminum and chemical polymers in water. In this study, the raw water from Keddara dam characterized by low turbidity was treated using chitosan as primary flocculant and as coagulant aid with aluminum sulfate. The result shows that chitosan was not too efficient as alum, if it is used as primary coagulant for treating Keddara raw water. However, when chitosan was applied as coagulation aid agent with aluminum sulfate, highest turbidity removal (97%) was carried out with 0.2 mgl-1of chitosan after 45minutes of settling time. The organic carbon contribution on the coagulation flocculation performance is negligible because chitosan is used in small doses. Hence, chitosan could be used as natural coagulant aid for drinking water treatment with lowest risks of organic release.

Academic research paper on topic "Coagulation Flocculation Test of Keddara's Water Dam Using Chitosan and Sulfate Aluminium"

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Procedía Engineering 33 (2012) 254 - 260

Procedía Engineering

www.elsevier.com/Iocate/procedia

ISWEE 11

Coagulation Flocculation Test of Keddara's Water Dam Using Chitosan and Sulfate Aluminium

Hassiba Zemmouria' b*, Madani Drouichea, Amna Sayeh a, Hakim Lounici a, Nabil Mameri a

aLaboratoire de Biotechnologie Environnementale et Génie des Procédés, BIOGEP, Ecole Nationale Polytechnique 10, Avenue Hacène Badi, B.P. 182, El-Harrach, Alger bCentre de Développement des Energie Renouvelables BP. 62 Route de l'Observatoire Bouzaréah - Alger, Algérie

Abstract

Chitosan is a natural polymer prepared from crab, shrimp and lobster shells. It has been used as coagulant in water treatment to avoid the human health problems caused by the residual aluminum and chemical polymers in water. In this study, the raw water from Keddara dam characterized by low turbidity was treated using chitosan as primary flocculant and as coagulant aid with aluminum sulfate.

The result shows that chitosan was not too efficient as alum, if it is used as primary coagulant for treating Keddara raw water. However, when chitosan was applied as coagulation aid agent with aluminum sulfate, highest turbidity removal (97 %) was carried out with 0.2 mgl-1of chitosan after 45 minutes of settling time. The organic carbon contribution on the coagulation flocculation performance is negligible because chitosan is used in small doses. Hence, chitosan could be used as natural coagulant aid for drinking water treatment with lowest risks of organic release.

© 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ISWEE'11

Keywords: Coagulation Flocculation, Turbidity, Chitosan, Aluminium Sulfate

1. Introduction

The drinking water treatment aims to produce water biologically and chemically safe for human consumption and aesthetically pleasing in terms of odor, appearance and taste. Turbidity is one of the most important parameters in controlling drinking water quality. It is caused by impurities or colloidal and suspended particles.

This turbidity can be caused by many substances like silt, minerals dissolution (as iron), fine organic and inorganic matter, algae (phytoplankton), and other microscopic organisms (virus, bacteria, etc). Turbidity can change the organoleptic properties of water. It can also provide food and shelter for pathogens in the distribution system leading to waterborne diseases [1]. To purify potable water, a combination of chemical and physical processes is used. It consists of coagulation/flocculation followed by settling, filtration and/or flotation.

* Corresponding author. Tel.: +213 21 90 15 03; fax: +213 21 90 15 60

1877-7058 © 2012 Published by Elsevier Ltd. doi:10.1016/j.proeng.2012.01.1202

The coagulation flocculation is considered the most important process in water surface treatment. Coagulation allows by the injection and the scattering of chemical (coagulants) during relatively intense mixing to destabilize naturally occurring particles and macromolecules and/or to precipitate additional particles [1]. Flocculation permits, by the addition of synthetic or natural polymers in slant of slow mixture, to promote the aggregation and bind together the micro-flocs of destabilized particles into larger flocks that can be removed subsequently by sedimentation and/or filtration. However, the use of these chemicals, particularly aluminum, may have several environmental consequences: (a) human health implications such as Alzheimer and other diseases with carcinogenic properties [2]; (b) production of big volumes of sludges [3]. Use of synthetic organic polymer coagulants such as polyacrylamides and polyamines are also problematic since they may be toxic under certain circumstances [4].

Recently, the use of environmentally friendly coagulants is widened. They can be proposed as an important alternative for water treatment. Natural organic polymers named biopolymers are naturally produced or extracted from animals, plant tissues or microorganisms. These biopolymers are no toxic for human health and are biodegradable. Their use as coagulants is advantageous because they are efficient in low dosage and therefore permit the reduction of sludge volume while their impact on pH and alkalinity is insignificant [3].

Chitin and chitosan are two natural biopolymers. They have interesting properties as part of a strategy for water treatment and environmental protection. Chitin: a Poly (N-acetyl-D-glucosamin) is the second most abundant polymer in nature after cellulose. It is present in the exoskeleton of crustaceans in the marine arthropods, in some seaweed and yeasts [5]. Chitosan is a continuum of different copolymers of N-acetyl-D-glucosamine and glucosamine units. It differs from chitin by amine groups -NH2. In acidic medium, chitosan has more than one reactive centers, through its functions and amino alcohol. Due to its biodegradability and no residual toxicity, its polyelectrolytic nature and its tendency to flocculation, chitosan is able to overcome the nuisances of traditional coagulants. According to its excellent properties, chitosan is recommended as a suitable flocculant in many applications such as: solids suspensions from various food processing wastes [6], Silt River [7], latex particles [8], microorganisms [9], and the treatment of dyes in effluents [10]. Several studies [7, 11 - 15] have treated the effect of chitosan on removing turbidity from turbid waters, but only a few have studied the effectiveness of chitosan as a coagulant for drinking water treatment. This research studies the efficiency of chitosan as a biomaterial for drinking water treatment by coagulation flocculation process. Initially the chitosan will be used as a primary coagulant, then as a coagulation aid agent with aluminum sulfate. For this study, coagulation-flocculation-sedimentation tests were conducted in the laboratory using a conventional Jar Test. Water samples are collected from Keddara dam at about 30 km east of Algiers. This dam supplies the great Algiers region with drinking water. The performance of the coagulation flocculation was assessed by measuring the supernatant residual turbidity of the aqueous solution for various parameters, namely, chitosan and aluminium sulfate doses, and pH. The evolution of the organic material was also analyzed through the measurement of specific UV absorbance at 254 of the treated solution.

2. Materials and methods

2.1 Description of Drinking water treatment plant

Before 1987, the drinking water of greater Algiers was provided by the Mazafran, Baraki, and Hamiz well-drills. The amount of groundwater could no longer meet requirements. To address the shortage of drinking water in the region of Algiers, a new supply system was put into service from 1987, the utilization of surface water of Isser River.

The treatment plant is located 8 km from the dam Keddara, between Boudouaou city and Ouled Moussa. It occupies an area of 17 hectares. It is part of the production system Keddara-Isser, treating water from dams Beni Amrane, Keddara and Hamiz, and covers the water needs of a population of around 4.000.000 inhabitants. Its processing capacity is 540.000 m3 and presents a storage capacity of 100,000 m3.

Keddara's raw water flowing in Boudouaou station undergoes a series of processing operations before distribution to the consumer. These operations are: a) The raw water aeration is supplied by four valves permitting adequate oxygenation; b) The pH adjustment with sulfuric acid in order to achieve a good coagulation flocculation; c) The pre-chlorination by means of chlorine gas injection in the form of chlorinated water.

It also aims to destruct the existing microorganisms which are likely to grow in the treatment devices sludge bed, to oxidatize the organic matter and the reducing elements (iron, manganese, etc); d) Coagulation flocculation is taking place with the injection of alum as a coagulant and polyelectrolyte (anionic) as flocculant; e) The slop is a step of settling flocs obtained during coagulation flocculation clarifier to form a sludge bed; f) The filter is a solid liquid separation technique. It is provided by type filters AQU AZUR "V"; g) The neutralization of pH is used to obtain the calco-carbonic balance. It is performed by injecting lime; h) Finally, the treated water is stored in two tanks with capacity of 50.000 m3.

2.2 Raw w/ter sample

Table 1 presents the characteristic properties of the Keddara raw water collected from the Boudouaou treatment plant. Samples were analyzed with minimal delay just after collection. No pretreatment was performed on any collected water sample, except for pH adjustment.

Table 1. Water quality collected from Boudouaou drinking water treatment plant

Parameters Average values

Temperature (°C) 15.2

pH 8.1

Turbidity (NTU) 7.81

MES (mg l-1) 4

Conductivity (^S/cm) 931

UV (abs/254) 0.12

TH (°F) 35.53

TAC (°F) 14.9

Ammonia (mg l-1) < 0.008

Nitrite (mg l-1) < 0.002

Phosphate (PO43- mg l-1) < 0.06

Fe2+ (mg l-1) <0.02

Mn2+ (mg l-1) < 0.05

Total Coliform (CFU ml-1) 86.76

Fecal Coliform (CFU ml-1) 83.7

2.3. Preparation of chitosan solution

Chitosan, purchased from Sigma® was used in this study. It comes from a chitin shell crab and was characterized by a deacetylation degree (DD) of 85%. 100 mg of chitosan were dissolved in 1 ml of acetic acid (85% w/w) under agitation and subsequently hydrated overnight in 99 ml of demineralised water. The final polymer solution was maintained at pH 4. All agents used in the experiment were of laboratory grade.

2.4 Coagulation flocculation experiments (Jar Tests)

Performance of chitosan used alone and as a coagulation aid with aluminum sulfate was evaluated through jar tests. Conventional Jar Test (Janke and Hunkeler) was used in this study having 5 agitators with variable speed, and five trains equipped each one with llitre beaker.

As soon as the flocculant was added to beakers, the solution was strongly mixed at 200 rpm for 3 minutes. This step is followed by a slow mixing (40 rpm) for 20 minutes. Thereafter, the solution was settled for 45 minutes to assess analytically the coagulation-flocculation effectiveness; the supernatant of the solution was removed from the top by siphoning. Turbidity was analyzed using a turbidity meter (HACH Model 2100P). Turbidity is expressed in terms of the standard nephelometry method. UV254 absorption was determined in 3 replicates at a wavelength of 254 nm using a quartz cell and a Shimadzu spectrophotometer model 2100. The pH of the solution was adjusted by the addition of solutions of 0,1N HCl or 0,1N NaOH.

The coagulation-flocculation tests performed were as follows: a) first, a specific amount of chitosan (as a natural primary coagulant) was added alone to form a floc in the drinking water, b) second, chitosan was used as a coagulant aid with aluminium sulfate. The main factors studied within this study are the dosage of the coagulant, the pH, the alkalinity, the residual aluminium in treated water.

3. Experimental results and discussion

3.1. Chitosan solubilization

Chitosan solubility is a very difficult parameter to control [17]. The importance of this parameter must be taken into account in order to study the chitosan efficiency. Chitosan is a hydrophilic copolymer; therefore it can dissolve in dilute organic or inorganic acid solutions.

In this study, acetic acid (AcOH), a common solvent, was chosen for this bioflocculant. After dissolution, the obtained solution was very clear; chitosan was completely soluble. The acid medium is used to solubilize and favour the ionization of amine groups in C2 of D-glucosamine residues [16, 17]. Their pKa is about 6.3 [17]. At pH below 4, chitosan acquired a high charge density [12]. Note that chitosan solubilization depends on the deacetylation degree. It is estimated that 85% of deacetylation allows a complete dissolution [18].

3.2. Coagulation flocculation test

First, Jar test ware conducted to study the chitosan performance alone on turbidity removal of Keddara dams raw water. Chitosan was added with a dosage of 0,1, 0,2, 0,3,....until 10 mg l-1, respectively. Other tests were conducted with 10, 20, 30, 40, 40, 50, and 60 mg l-1.

Chitosan doses (mgl-1)

Fig. 1. Effect of various chitosan dosages on turbidity removal from Keddara raw water (5 NTU) at actual pH and 45 minutes of settling time.

Figure 1 shows the efficiency of turbidity removal by the chitosan alone. A lowest turbidity reduction, with 5% (4 NTU) after 45 minutes of settling for all chitosan doses applied (0.1 - 60 mg l-1), was recorded. Chitosan alone performed poorly in terms of turbidity removal. No flocs were observed for all chitosan doses. This could be attributed to the low turbidity and the presence of colloids in the collected water. Indeed, the effect of the colloidal particles concentration in water is important because they serve as cores to the coagulation [14]. If the concentration of colloids is low, there are few particles to ensure good flocculation, regardless their neutralization.

Another inconvenience of the waters containing few colloids is the ease of adding coagulant and the reverse of the particles load instead of their neutralization. Results obtained indicate that chitosan effectiveness in removing turbidity of raw water is highly dependent on initial turbidity.

0 10 20 30 4 0 50 60 70

Aluminium sulphate doses (mgl-1)

Fig. 2. Effect of various Aluminum sulfate dosages on turbidity removal from Keddara water (5 NTU) at actual pH and 30 minutes of settling time

At the second phase, the raw water of Keddara was treated by aluminum sulfate alone as primary coagulant for turbidity removal. We have chosen 45 minutes of settling time in order to evaluate the metal ions performance. Fig. 2 shows the results concerning the effect the dose of aluminum sulfate (ranged from 10 to 60 mgl-1) on the evolution of residual turbidity. It can be seen that an increase in aluminum sulfate concentration results to a decreased turbidity. The better turbidity removal occurs when the dose of aluminum sulfate solution is 40 mgl-1 for a residual turbidity reaching 2.1 NTU. Above this dosage, the suspensions showed a tendency to re-stabilize. The residual aluminum for this optimal dose is found 0.5 mgl-1. The aluminum sulfate when used alone proves to be slightly efficient at removing turbidity. No visible floc formation occurred at a dosage of 40 mgl-1, which it is reflected in the low values for suspended solids.

Chitosan doses (mgl-1)

Chitosan doses (mgl-1) (b)

Fig. 3. Effect of various amounts of Aluminium sulfate and chitosan on: a) turbidity removal of Keddara raw water b) UV absorbance at 254 nm abatements

Relying on previous results showing the chitosan inefficiency when used as a primary coagulant for the treatment of raw water of low turbidity, a set of coagulation-flocculation experiments were conducted for testing the chitosan performance as an aid coagulant. It was tested in a concentration range from 0.05 to 0,3 mgl-1. Alum sulfate (40 mgl-1) was used as coagulant for this experiment. Optimal dose was determined on the basis of both turbidity removal and UV absorbance at 254 nm abatements.

Fig. 3 illustrates the turbidity and the UV absorbance at 254 nm as a function of the chitosan dose. According to Fig. 3 the residual turbidity reduces as the chitosan dosage increases. After the optimum point corresponding to the lowest value of the residual turbidity, a slight increase in turbidity values is observed when adding more chitosan.

The use of chitosan in combination with Alum sulfate leads to an increase in the flocculation efficiency (97% after 45 minutes of settling) and to the formation of denser flocs at lower chitosan concentrations. The major turbidity decrease occurred in the above experiments carried out with 0.2 mgl-1 of chitosan. At the same value, UV absorbance at 254 nm decreases reaching the lowest value (absorbance density 0,02). It is noted also, that beyond the optimal point, the values of the residual turbidity increase; this means that suspension tends to re-stabilize. For this value we analyzed the supernatant residual aluminum and found a value of 0,2 mgl-1 Al3+. These results concord with that found by Bina and al. [19] who reported a decrease in the residual Al3+ in treated water when using chitosan as an aid coagulant in the coagulation-flocculation process.

No change in pH was observed. According to the flocculation and sedimentation processes, the formation of flocs after the addition of the chitosan was observed. They are bigger than those obtained with the chitosan used as primary coagulant. They were of rounded shapes, glued one to the other, forming in the middle of the backer a big ball. They settled well in less than 10 minutes. The final solution became very clear and very limpid. These results are in agreement with those found by Guibal [20]. Indeed, according to Roussy et al. [14], the ionic sulfate compounds have a significant effect on the chitosan's sorption, despite the fact that chitosan has a higher molecular weight in the presence of sulfates [20]. Van Duin and Hermans [21] justified their hypothesis with the fact that chitosan forms large aggregates which can easily precipitate in the presence of sulfate. They also reported that taking into account the low dosage of chitosan in these experiments (less than 1 mgl-1), the amount of residual organic carbon introduced to the system was low enough (less than 0,8 mgl-1) to make its contribution negligible for the coagulation-flocculation performance. Thus, chitosan could be used as natural aid coagulant for drinking water treatment with the lowest risks of organic release

4. Conclusion

Experiments were conducted to determine the chitosan ability as natural flocculant for drinking water treatment of raw water. The experimental work showed that chitosan when used as a primary coagulant is no effective for Keddara raw water. This behavior is related to the very low initial turbidity of the Keddara raw water. On the contrary, chitosan is more effective (turbidity removal 97 %) in removing turbidity when used as an aid coagulant to the aluminium sulphate as the main coagulant. The chitosan efficiency is highly dependent on the initial turbidity and on chitosan dosage. The organic carbon contribution on the coagulation-flocculation performance is negligible because chitosan is used in small doses. Hence, chitosan could be used as natural aid coagulant for drinking water treatment with the lowest risks of organic release.

5. References

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