INTRODUCTION:

Coagulation/flocculation has remained the most widely used method for the removal of particled and organic matter in wastewater treatment⁽¹⁾. In this case, a coagulant agent is employed that usually reacts with water and forms hydrophobic hydroxide and polymeric compounds with different charges, depending on the solution’s pH. Coagulant agents interact with colloidal materials by charging either neutralization or adsorption, leading towards coagulation/flocculation, usually followed by sedimentation ⁽²⁾. Conventional coagulants in wastewater treatment are alum [Al₂(SO₄)₃.14H₂O], ferric chloride [FeCl₃.6H₂O], sodium aluminate, aluminum chloride and ferric sulfate. Conventional coagulants are basically salts of a strong acid (e.g. HCl or H₂SO₄) and a weak base (e.g. Al₂(OH)₃ or Fe(OH)₃); thus they are a mixture of a cation (from a base) and an anion (from an acid).

However, recent studies have detected several serious drawbacks, such as the onset of Alzheimer’s disease, when aluminum salts are used. There is also the problem of alum reaction to natural alkalinity present in the water which leads to pH reduction. In this context, an environmental friendly coagulant presents a viable alternative for the treatment of wastewater ⁽³⁾. The use of natural coagulants (tannin, chitosan etc) in the coagulation could provide a more suitable sludge for fertilization purposes as these natural coagulants are biodegradable ^{(4) .}

Chitosan is a type of natural polyaminosaccharide, synthesized from the deacetylation of chitin, which is a polysaccharide consisting predominantly of unbranched chains of (1→4)-2-acetoamido-2-deoxy-d-glucose. Chitin is the second most abundant polymer in nature after cellulose. It can be extracted from crustacean shell such as prawns, crabs, fungi, insects and other crustaceans⁽⁵⁾. Widely available biopolymers are also being used for adsorption mainly because they are a cheap resource or a freely available resource⁽⁶⁾. The structure of chitosan is presented schematically in Figure 1.

Figure 1 : Structure of Chitosan

To improve chitosan’s performance as an adsorbent, cross-linking reagents such as glyoxal, formaldehyde, glutaraldehyde, epichlorohydrin, ethylene glycon diglycidyl ether and isocyanates have been used ⁽⁷⁾. Cross-linking agents do not only stabilize chitosan in acid solutions so that it becomes insoluble but also enhance its mechanical properties ⁽⁸⁾. Chitosan derivatives have been extensively investigated as adsorbents ⁽⁹⁾. Different kinds of substances have been used to form composite with chitosan such as montmorillonite ⁽¹⁰⁾, polyurethane ⁽¹¹⁾, activated clay ⁽¹²⁾, bentonite ⁽¹³⁾, poly vinyl alcohol, poly vinyl chloride, kaolinite ⁽¹⁴⁾, oil palm ash ⁽¹⁵⁾and perlite ⁽¹⁶⁾.

The high effeciency of this natural polymer results in novel binding properties for bentonite in wastewater. Chitosan has been used for about three decades in water purification processes. ⁽¹⁷⁾. It has an amine functional group which is strongly reactive with metal ions ⁽¹⁸⁾. Tannins are high molecular weight polycyclic aromatic compounds widely distributed through the plant kingdom. Tannins can be classified into two groups ⁽¹⁹⁾, the proanthocyanidins (or condensed tannins) and the polyesters of gallic acid and (or) hexahydroxydiphenic acid (hydrolysable tannins, respectively, gallo- and ellagitannins). The co-occurrence of both kinds of tannins in the same plant or plant tissue is often observed. Tannins are found in the leaves, fruits, barks, roots and wood of trees ⁽²⁰⁾. The structure of tannin is presented schematically in Figure 2 . Complex polysaccharide tannin derivatives have been used extensively in potable water, wastewater and industrial effluent treatment applications ⁽²¹⁾. In addition tannin helps the filtration process ⁽²²⁾ . The various studies that have been conducted on water treatment using the tannins as a coagulant have revealed that the effectiveness of tannins depends mainly on the chemical structure of tannins that have been extracted from thet plant and the degree of tannin modification ⁽²³⁾.

Figure 2 : Structure of Tannin

The aim of this study is to investigate the bentonite turbidity removing from wastewater by adsorption and to evaluate factors affecting on the removal of bentonite turbidity using as a bio-adsorption material

MATERIALS AND METHODS:

Materials:

All reagents in this work were of analytical grade and were used as received without further purification and then tested and prepared in order to be suitable for real experiments. The prepared reagent consist of: (1) reagent for isolation of chitosan, i.e. 45% (w/v) NaOH and 1 M HCl (2) reagents for preparation of chitosan – tannin polymer beads, i.e 1% acetic acid , HCl and buteraldehyde (3)Stock solution of 500 NTU from bentonite (4) standard solutions for preparing 10, 20, 50, 100, 200, 300 NTU for the determination of turbidities using Turbidity meter( LP2000 HANNA).

METHODS:

Isolation of Chitosan:

The shrimp shells which were used for chitosan isolation was purchased from local seafood processing industry . Chitin, isolated from shrimp shell, was ground to powder form.This powdered chitin was then deacetylated with NaOH (45% w/w) in 100°C water bath for 60 min and the reaction was terminated by an ice bath. Following that, the product was cleaned several times with deionized water until the pH of the suspension reached 7. The suspended particles were collected with a membrane filter and dried at 80°C for 48 h. The chitosan powder was modified with a novel method different from the previous one to achieve better performance.

Isolation of Tannin:

The Laurus nobilis leaves were cut into pieces and powdered using grinding machine. The powdered sample was sieved through a pair of 40 and 60 mesh sieve. In order to obtain maximum quantity of tannin, extraction was carried out at elevated temperature. The extraction of 50 gram of sample was carried out with water-ethanol mixture (1:1) in soxhlet apparatus. The tannin extract obtained from different cycles of reflux was collected in a flask and its volume was reduced in rotary evaporator. The concentrated tannin extract was dried at 50°C. The dried tannin extract which contains 64-67% tannin was ground in a morter with a pestle. The powdered sample was sieved (60 mesh) and stored in sample bottle.

Chitosan- Tannin Polymer Synthesis :

A 250 mL 2-necked round-bottom flask containing 1% acetic acid, 2 gm of chitosan were added and a magnetic stirring bar and mixed at 100 rpm for 60 min or until dissolved to make. After that an aqueous solution of 2 gm tannin in 25 ml distilled water were added, and then 0.5 ml of buteraldehyde was added into the reactor by controlling the dropping speed. The reaction was continued for 3hrs at room temperature (25°C). Adjusted the pH to 2 by HCl, the chitosan - tannin was obtained. The structure of chitosan-tannin polymer is presented schematically in Figure 3.

Figure 3: Chitosan - Tannin polymer structure.

Characterization techniques and instruments

Six methods were used for the characterization of the chitosan , tannin and chitosan – tannin polymer:

The UV-visible spectra were recorded over the range of 200–700 nm using the T60 U PG Instrument Limited UV-visible spectrophotometer (UK). Fourier transform infrared (FTIR) spectra were obtained with a FTIR- RX1 spectrometer (Perkim Elmer, USA) with samples incorporated into KBr discs in the range of 400 to 4000 cm^-1. Gas chromatography-mass spectrometry (GC-MS) were performed using an Agilent Technologies 7890 GC with 5975 MSD1µL of reconstituted sample was injected through a 7683B Series Injector using a split mode of 50%. The GC separation was done using a DB5 column at a flow rate of 1mL/min He 99.999%. The oven temperature was programmed as follows: 50 °C (hold 1 min), 25°C/min to 150°C, 20°C/min to 170°C and 80°C/min to 250°C for 3 min. (The total run time was 10 min). Products were detected using a 5975C VLMSD with Triple Axis Detector (m/z 50-250). Differential scanning calorimetry (DSC) experiments were carried out using a TA Instruments DSC 30 (Mettler Toledo, Switzerland) Differential Scanning Calorimeter. Samples (5–10 mg) were loaded into standard aluminium pans and run using a heat/cool/heat cycle with a heating rate of 10 °C min^-1 and a cooling rate of 5 °C min^-1.

Thermogravimetric analysis (TGA) measurements were performed using a TA Instruments TGA (Mettler Toledo, Switzerland) Thermogravimetric Analyzer. Samples (8–14 mg) were weighed out on platinum pans and heated to 600°C at 10°C min^-1under a nitrogen atmosphere. All thermal analysis employed duplicate runs for each sample. Working temperature range was 25–800°C with a efficiency of 10°C min⁻¹. Air was used as environmental medium at100 ml min⁻¹flux. The crystallinity of materials in powder form was studied by X-ray diffraction method (Empyrean series 2) PAN analytical (Netherland) using Cu Kα radiation generated at 40 kV and 40 mA at scanning speed of 0.3 2⍬/ min within a range of 10°to 60°.

Study of Coagulation Adsorption Experiment by Synthesized Chitosan – Tannin Polymer:

Bentonite has been chosen for this study for its abundance and availability. To prepare water with turbidities (10, 20, 50, 100, 200, and 300) NTU, bentonite was ground and sieved. The sieve fraction below 200 μm was maintained for all the tests. The initial suspensions were mixed with deionized water at 500 rpm for 5 minutes. The suspensions were left thereafter, settling in for 20 minutes. This operation is followed by filtration of the supernatant to remove the large particles not suspended.

A convential jar test apparatus was used for the coagulation experiments. In all the experiments before the best slow stirring velocity and time were determined. The pH of the suspension was adjusted by adding 0.1 M NaOH or 0.1 M HCl. The reactor, which contains turbid water or synthetic water having different pH and turbidity values, was set at 100 rpm paddle speed. Once the polymer was added, then water was fast mixed for 1 min at 200 rpm followed by 15 min of slow mixing (at 15 rpm). The supernatant was the withdrawn for turbidity measurement using pipette with the open end placed 3 cm below the surface of the liquid. The sensitivity of the instrument permits the detection of turbidity as low as 0.02 NTU (Nephlometric Turbidity Units).

RESULTS AND DISCUSSION:

Ultraviolete –visible study of the Compounds:

Ultraviolet/visible (UV-Vis) spectroscopy is useful as an analytical technique for two reasons. Firstly, it can be used to identify certain functional groups in molecules, and secondly, it can be used for assaying. UV-Vis spectroscopy involves the absorption of electromagnetic radiation from the 200–800 nm range and the subsequent excitation of electrons to higher energy states. The absorption of ultraviolet/visible light by organic molecules is restricted to certain functional groups (chromophores) that contain valence electrons of low excitation energy. The UV of the studied compounds: chitosan and tannin was carried out in double beam UV-visible photometer, using dilute solution (3.5×10^-3). UV-Vis spectra of chitosan are usually recorded in aqueous acetic acid solutions in a 1.0 cm quartz cell at ambient temperature. Chitosan include various ratios of two far-UV chromophoric groups, N-acetylglucosamine (GlcNAc) and glucosamine (GlcN); as a result, their extinction coefficients for wavelengths shorter than approximately 225 nm is non-zero. Because GlcNAc and GlcN residues show no evidence of interacting within the chitin/chitosan chain, the monomer units contribute in a simple, additive way to the total absorbance of this polymer at a particular wavelength. The UV spectra of chitosan were shown in Figure 4 and the λmax is 201 nm in 0.1 M HAc solution. The U.V. spectra for tannin, show an intense bands at λmax 270 nm for π→ π* transition due to the high conjugation between the π electrons of the benzene ring and the carbonyl group through the carbon-carbon double bond.

Fig(4): UV-Vissible Spectra of chitosan and Tannin Gas Chromatography- Mass Spectrmetry

Mass spectrometry (MS) is a destructive analytical technique used for measuring the characteristics of individual molecules. The basic information obtained from mass spectrometric analysis is the molecular mass of a compound, which is determined by measuring the mass to charge ratio (m/z) of its ion. With the ionization method, full particulars about a molecule’s chemical structure can be found.

MS can analyze chemicals with wide mass range–from small molecules to complicated biomolecules such as carbohydrates, proteins, peptides or nucleic acids. The GC-MS analysis detected all organic species quantitatively. Each peak area in the chromatogram was propotional to the amount of the organic compounds forming that peak. GC-MS spectra of chitosan is shown in Fig.5, from the mass spectra it is possible to identify volatile compounds obtained from chitosan. The peaks at m/z 537.9 with retention times under our chromatography conditions around ~15 mins are derived from glucosamine. The molecular weight of the obtained chitosan was 2561.1. Conditions could be found for tannin that giving peaks at 647.2 m/z with retention times under our chromatography conditions around ~15 mins as shown in Fig. 6. Tannin consists of a ratio of gallic acid to glucose units of approximately 12:13. Therefore this tannin could be considered a hydrolysable tannin. The molecular weight of the obtained lignin was 2836.7

Forier Transformer Spectroscopy(FTIR):

Fourier transform infrared spectroscopy (FTIR) was used to determine the vibration frequency of the functional groups in the three different polymers. The spectra were measured by an FTIR spectrometer within the range of 400–4000 cm−1 wave number. The dry amount of polymers (about 0.1 g) was thoroughly mixed with KBr and pressed into a pellet and the FTIR spectrum was then recorded.

FTIR of Chitosan:

The characteristic IR absorption peaks of chitosan were observed (Fig. 7), which include a broad and strong band ranging from 3200-3700 cm ^-1 (stretching vibration of O-H and extension vibration of N-H). The peaks located at 2920 and 2881 cm^-1 can be assigned to asymmetric and symmetric –CH₂ groups. The peak located at 1642 cm^-1 is characterstic of amine deformation. The prominent peak at observed at 1383 cm^-1 represents C-N stretching. The peak at 1164 cm^-1 can be attributed to the C-O-C stretching. The peak at 1022 cm^-1 is characteristic of C-O stretching vibration. The absorption band at 896 cm ^-1, corresponds to the characteristic absorption of β-D- glucose unit.

FTIR of Tannin:

The poly phenolic tannin compound has many characteristics bands at certain frequencies. Its FT-IR spectrum is shown in Fig.(7) broad peak at 3412 cm-1 is attributed to polymeric O-H group, the frequency at 2935 cm-1 corresponds to C-H stretching frequency and the peak at 1614 cm-1 has been assigned to C=O , and the wideness of the 1709 cm-1 band can be related to the presence of conjugated carbonyl groups . The presence of the functional group C-O-C in tannin is confirmed from the band at 1207 cm-1, C-H bending frequency is noted at 1340 cm-1. A notable band at 1031 cm-1 can be assigned to C-O stretching. At 759 cm-1 shows the result distortion vibration of C=C in benzene rings. Around 1449 cm-1 stretching vibrations of C-C aromatic groups appear in spectrum. The absorption band at 869 cm-1, corresponds to the characteristic absorption of β-D- glucose unit Table 3.2 shows the important main bands of tannin.

FTIR of Chitosan – Tannin Polymer:

Some functional groups of tannin were also present in chitosan. Therefore, the same vibrations were observed but with different intensities(Fig.7). The absorption intensity of –NH₂ group and –OH group (peak 3200 – 3700 cm^-1) from chitosan – tannin polymer is obviously lower than that of –NH₂ group and –OH group from chitosan, which indicates a cross-linked reaction occurred between chitosan and tannin. Moreover, the reduction in the intensities at 1450 cm^-1 peak (primary amino group, -NH₂) showed that most of the primary amino groups were involved in the cross – linking process

Fig.(7): FTIR of Chitosan, Tannin and Chitosan-Tannin polymer

The Thermal Stability Study of the compounds:

In the present study the thermal stability characteristics of the compounds was investigated by TG and DTG technique. TG is one of the familiar techniques for systematic assessment of polymers thermal stability. It is very useful tool and help to indicate the relative order of stability of various polymers. TG is defined as a continuous measurement of sample weight as a function of time or temperature at a programmed rate of heating. The resulting weight change v.s. temperature (or time) curve gives information about the thermal stability and decomposition of the materials.

The thermogravimetric analysis traces obtained for the polymers heated at a rate of 10°C/ min, which show the dependence of the mass loss of the sample expressed as a percentage of the initial mass and temperature. Also the first derivative is below of them. From thermogram of weight loss vs. temperature one suggest a mechanism for the degradation of chitosan in the review of the decomposition temperature.

Fig.(8) shows the dynamic thermogravimetric analysis of chitosan which showed wt.% loss of 3.15% at 100°C, which can be related to the loss of water molecule from the backbone chain of chitosan. The second loss peak of about 47.3% at 260°C correspond to the cleavage of the NH₂ and OH bond of chitosan moiety forming (NH₃, H₂O) molecules and the loss of this groups for each repeating unit .The third loss peak found in thermogram is propotional to 11.62% wt. loss at 480°C which are attributed to the cleavage of polymer and gaseous products leaving the carbon residue about 37.8% wt.

This method encompasses several spectroscopic techniques for determining the electronic and geometric structures of materials using X-ray excitation: X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES), X-ray photoelectron spectroscopy (XPS) and X-ray Auger spectroscopy. Which type of X-ray spectroscopy is employed depends on whether the target information is electronic, geometric or refers to oxidation states. X-ray spectroscopy is thus a powerful and flexible tool and an excellent complement to many structural analysis techniques. The properties of polymers depended mostly on the molecular weight, polydispersity and crystallinity. XRD Commonly used to measure crystallinity, the crystallinity index (CI) can be calculated on the basis of X-ray diffractograms. Postulating the following equation for determining the crystallinity index (CI):

CI (%) = [(Im - Iam)/I110] × 100

Where: Im (arbitrary units) is the maximum intensity of the crystalline peak at around 2θ = 51°, and Iam (arbitrary units) is the amorphous diffraction at 2θ = 15°. In most cases, CI provides information about the crystal state. crystallinity could also be assigned from an X-ray diffractogram by dividing the area of the crystalline peaks by the total area under the curve (background area). In these calculations, the crystallinity percentage supplied information on relative crystallinity. The typical chitosan diffraction pattern, given in angle form. Fig.12, showed strong reflections at 2θ around 42° and 2θ of 51°, However, differently indexed crystalline peaks (90%), the chains form hydrogen-bonded sheets linked by C=O...H–N bonds approximately parallel to the a axis, and each chain is stabilized by an C(3’)O–H····OC(5) intramolecular hydrogen bond, as in cellulose. These data also indicated that a statistical mixture of CH₂OH orientations was present, equivalent to half an oxygen on each residue, each forming inter and intramolecular hydrogen bonds.

Figure (11) shows the X-ray diffraction patterns of the tannin sample showed strong reflections at 2θ around 42° and 2θ of 51°. The crystallizations of tannin were 50%. Tannin have crystalline region and non-crystalline region. Compared to chitosan, the X-ray diffraction patterns of the chitosan-tannin polymer showed that the bands at 2θ = 42° and 51°, the crystallization decreasing of chitosan-tannin polymer (86%) indicates that the interaction force of polymer molecular chains has become weaker and the degree of regularity is decreased. The molecular flexibility of chitosan-tannin polymer is higher than that of chitosan and lower than tannin. It was therefore concluded that the crystallizations is influenced by components, reaction condition and so on.

Coagulation Study:

Polymers have been utilized in coagulation/ flocculation processes for water purification for more than three decades. Organic polymers may be used as coagulants as well as in the more traditional flocculation step of binding already formed small flocs into larger particles in water treatment. Coagulation with organic polymers followed by sedimentation can clean up industrial effluent when the flocs formed are dense enough. A major use of organic polymers in water treatment is as a coagulant aid to bridge the coagulated particles formed. The large aggregates formed then settle more rapidly. The mixture of fine particles of bentonite in water induces a detachment of them due to their strong hydration. The dispersion of bentonite releases very fine colloidal particles. They remain in a state of suspension and cannot be removed from the dispersion by sedimentation or ultracentrifugation. The two mechanisms (strong hydration and dispersion), believed to play an important role in the detachment of bentonite colloidal particles; increase the solubility and the stabilization of colloidal system. After the coagulant was added to the jars, which contained turbid water, rapid mixing was done for 1 min at 200 rpm and slow stirring for 15 min at 15 rpm. Fifteen minutes were allowed for the settling of the flocs. The turbidity of the supernatant, withdrawn using pipette from a 3 cm depth, was measured by using a Turbidimeter. The sensitivity of the instrument permits the detection of turbidity as low as 0.02 NTU (Nephleometric turbidity units). The removal efficiency of the studied parameters in these experiments was calculated by applying the following formula:

Removal efficiency

Where, TO(NTU) is the initial turbidity of solution, Ti (NTU) is the final turbidity of solution.

Effect of pH on Turbidity Removal Effeciency:

A series of jar tests was conducted to study the coagulation effectiveness of chitosan with turbidities of 10, 20, 50, 100, 200 and 300 NTU under various pH conditions for each turbidity value with pH values of : 2, 3, 4, 5, 6, 7, 8 and 9, respectively. The obtained results in Fig.(13) shows that the removal efficiency of bentonite decreasing with increasing pH. Therefore, the optimal pH was 3 in which high removal efficiency of bentonite was observed, the effect of pH on synthesized polymer was insignificant in terms of bentonite removal in the range pH 5-9. This can attribute to an increase in the number of protonated amine groups in polymer at lower pH. The destabilization of particles was enhanced by the increased number of charged groups followed by charge neutralization. The use of chitosan-tannin polymer in water treatment as coagulant is hardly ever preferred.

Fig (13) :Turbidity removal efficiency of Chitosan-Tannin polymer as a function of pH .

Effect of the chitosan-Tannin Polymer Dosage on Turbidity Removal Effeciency:

To determine the effect of polymer dosage, the jar test experiments with chitosan-tannin polymer using synthetic water with turbidities of 10, 20, 50, 100, 200 and 300 NTU on turbidity removal at pH 3, were run. We initially conducted tests to determine the optimal dosage of polymer (0.1-1) gm. The results obtained are shown in Figure (14) indicate that the optimum coagulation dosage were 0.1 gm for 10, 20 and 50 NTU turbidities respectively, and it was 0.2 gm for 100, 200 and 300 NTU turbidities. The obtained curves are typical of coagulation flocculation process controlled by the neutralization of charges. Anionic particles of bentonite are electrostatically attracted by the protonated amino groups of chitosan-tannin polymer. This reaction facilitates the neutralization of the anionic charges which can bind together and settle rapidly by the effect of gravity. If the increase of the polymer amount added to the solution is in excess, the protonated amino groups (cationic charges) cause a further stabilization of the suspension and reduce the process efficiency.

Fig. (14): Turbidity removal efficiency as a function of Chitosan-Tannin polymer dosage (gm).

Effect of Flocculation time on Turbidity Removal Efficiency:

The effect of flocculation time on turbidity removal effeciency was studied by varying the flocculation time from 10 to 60 min, at optimum pH, dose, for 10, 20, 50, 100, 200 and 300 NTU turbidities. The results obtained are shown in Figure (15), the optimum flocculation time for chitosan-tannin polymer is 30 min. The obtained results show an increase in residual turbidity with flocculation times. This could be due to the redispersion and restabilization of flocs at higher flocculation time. The efficiencies of turbidity removal at the optimum conditions were 99%, 97%, 95%, 98%, 99% and 99.5% for 10, 20, 50, 100, 200 and 300 NTU turbidities, respectively.

Fig.(15) : Turbidity removal efficiency of Chitosan-Tannin polymer as a function of flocculation time.

Desorption study for Chitosan-Tannin Polymer Polymers:

For the batch desorption experiments of bentonite from Chitosan-Tannin polymer were performed by suspending 0.1 gm for 10, 20 and 50 NTU turbidities respectively, and 0.2 gm for 100, 200 and 300 NTU turbidities respectively of synthesized polymer in 10 ml of 3 M HCl and shaking on shaker at 200 rpm at 25°C . After constant time intervals (0.5-24 hrs) the samples were filtered (Whatman filter paper No. 42) and the filterate was analyzed by Turbidimeter for the turbidity contents. The recovery percentage of bentonite from Chitosan-Tannin polymer at different contact time are shown in Figs.(16). The present results show that recovery percentage of bentonite increased initially with the increasing of the contact time. After six hours, maximum recovery of bentonite were observed.

Fig(16): Effect of contact time on the recovery percentage of bentonite from

Chitosan-Tannin Polymer with (3 M HCl) Treatment of Raw Water Samples by the Chitosan-Tannin Polymer:

Jar tests were conducted again to test the polymers flocculation ability on initial turbidity for raw water sample near paper production factory with high initial turbidity 155 NTU. The raw water sample was treated with the optimum amount of the polymers for 50 ml from raw water samples and pH, polymer dosage and flocculation time as discussed previously. Fig.(17) shows the water turbidity removal efficiency of the synthesized polymer. A large removal efficiency of polymer has been observed. It was recorded a good removing of turbidity of approximately 98% at 2 mg of Chitosan-Tannin polymer. At this dose, the settling rate was very fast. These results shows that the synthsized polymer are effective for the turbidity reduction of raw water near the paper production factory with a high initial turbidity (155 NTU), It was observed during the second phase (slow agitation) of coagulation flocculation process that flocs appear rapidly with large size. They were fibrous forming cobwebs. This could be attributed to high concentration of colloidal particles, the effect of the concentration of colloidal particles in water is important because they serve as cores to the coagulation. If the concentration of colloids in the water is low, there are too few particles to ensure good flocculation, even though they are neutralized. Another inconvenience of waters that contain few colloids comes because it is easy to add coagulant and to reverse the load of the particles finally instead of neutralizing it. Results obtained indicate the Chitosan-Tannin polymers are effectiveness in removing of turbidity of raw water which is highly dependent on initial turbidity and on flocculant dose.

Fig.(17) : Effect of Chitosan-Tannin polymer on residual turbidity of supernatant of paper production factory (at 155 NTU) raw water at optimum conditions.

ACKNOWLEDGMENT:

The authors gratefully acknowledge the contributions of Prof Dr.S.Archibald in the University of Hull, UK for his benefic contribution of this study.

CONCLUSION:

Natural polymer “Chitosan-Tannin polymer” provides axcellant method for bentonite removing. The characterization of material gives information about molecular weight, crystallinity, good chemical and thermal stability which revels applicability towards turbidity removing. This low-cost adsorbents are effective for the removal of bentonite from aqueous solutions. The batch method was employed parameters such as pH, polymer dose and agitation time was studied at an ambient temperature 25^oC. The optimum pH corresponding to the maximum adsorption of bentonite removing was pH 6. Bentonite was adsorbed onto the adsorbents very rapidly within the 0.3 gm of polymer for 4 hrs.

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Received on 22.01.2015 Modified on 20.02.2015

Asian J. Research Chem 8(4): April 2015; Page 241-252

DOI: 10.5958/0974-4150.2015.00042.5