studies on the removal of hexavalent chromium from ...

ISSN: 1579-4377

STUDIES ON THE REMOVAL OF HEXAVALENT CHROMIUM FROM INDUSTRIAL WASTEWATER BY USING BIOMATERIALS. Malairajan Singanan* and Alemayehu Abebaw Vinodhini Singanan Dept.of Applied Chemistry, Ambo College – Jimma University, P.O.Box.No. 19. Ambo Town, Western Shoa, Ethiopia. Dept. of Pharmacy, Hayome Medical College, Ambo Town, Western Shoa, Ethiopia. Email: [email protected]

ABSTRACT Chromium (VI) is one of the highly toxic ions released into the environment through leather processing and chrome plating industries. There are a number of methods available for the removal of Cr (VI) from industrial wastewater. In recent years, cyanobacteria were used as bioadsorbent for the removal of certain heavy metals. However, most of the conventional methods generate secondary effluent impacts on the recipient environment. The aim of the present investigation is to develop a suitable phytoremediation technology for the procumbens removal of Cr (VI) in industrial wastewater. In the present research work, a novel biomaterial, Tridax (Asteraceae), a medicinal plant was used as a bioadsorbent. The optimum pH of the experimental solution was 2.5 and batch experiments were performed. The efficiency of the activated carbon of the biomaterials for Cr (VI) removal was evaluated by studying the contact time, quantity of adsorbent and concentration of Cr (VI). The result of the present study showed that, 97 percent Cr (VI) removal in synthetic wastewater sample was achieved when 5g of the bioadsorbent was used. This method is also applied to the removal of Cr (VI) from tannery industry wastewater.. Hence, it is recommended that, this bioremediation technology is a cleaner and useful methodology for the removal of Cr (VI) from the industrial wastewater. KEYWORDS Phytoremediation technology, hexavalent chromium, biomaterials and Industrial wastewater.

Singanan et al. EJEAFChe, 6 (11), 2007. [2557-2564]

INTRODUCTION Water is one of the most important natural resources, essential for all forms of life. This natural resource is being contaminated every day by various anthropogenic activities such as rapid growth of populations, urbanization and industrialization that ultimately make the environment polluted. Since recent years, sewage waters have been used for irrigation purposes [1]. There are greater concerns about heavy metal contamination [2, 3] in the receiving water system and land. The occurrence of toxic heavy metals in the soil is of geogenic or anthropogenic origin. Heavy metals from the point of origin and other sources can be transported to distant environments [4, 5]. High levels of heavy metals can damage soil fertility and may affect productivity [6, 7]. Heavy metals in the environment may also change plant diversity and affect aquatic life. Chromium in trace concentration is an essential element in the diet, because it regulates the glucose metabolism in the human body. Excess amounts of chromium uptake are very dangerous due to its carcinogenic effect. Chromium in soils affects plant growth [8], it is non-essential for microorganisms and other life forms and when in excess amounts it exerts toxic effect on them after cellular uptake. Cr (VI) is more toxic than Cr (III). Leather and chromium plating industries are the major causes for environmental influx of chromium [9, 10]. The movement of chromium and its bioavailability poses a potential threat to the environment. In this context, it is important to note that, large numbers of leather industries are engaged in chrome tanning processes in Ethiopia. There is a possibility of chromium contamination in soils and waters around industrial sites. Cleaning up of the chromium-contaminated sites is a challenging task because removal of Cr (VI) in aqueous solution is very difficult. Hence, proper treatment of tannery wastewater is essential before releasing into the recipient environment. There are a number of methods employed [11 – 15] for removal of hexavalent chromium from industrial wastewater such as the use of various types of adsorbents. In recent years, cyanobacteria were used as bioadsorbent for the removal of certain heavy metals from heavy metal polluted water [16]. However, most of the conventional methods generate secondary effluent impacts on the recipient environment; mainly microbial bioadsorbent methods are economically not feasible. In this context, the phytoremediation technology is an emerging technology, which is considered for the removal of chromium in contaminated systems because of its cost effectiveness, aesthetic advantages and long-term applicability. The aim of the present research work was to test the applicability of plant material for the removal of Cr (VI) in the industrial wastewater. In our previous research, work [17], it was reported that, the color removal efficiency of the raw plant leaf powder from industrial wastewater was found to be 92 percent. In the present investigation, the removal of Cr (VI) by using the activated carbon of the bioadsorbent (ACBA) was carried out and the analytical results are presented here. MATERIALS AND METHODS In the present research work, synthetic wastewater samples were prepared by using analytical grade potassium dichromate. The concentration of the solution was 0.1M. The test 2558


solution was acidified with concentrated sulphuric acid. The stock solution was prepared by dilution with double distilled water, which contains 100 ppm of Cr (VI). The color of the sample was reddish yellow. The biomaterial, Tridax procumbens (Asteraceae – Compositae) was collected from the agricultural field, air-dried and powdered. The homogeneous powder was selected for the experiments. Activated carbon of the biomaterial was prepared by treating with the concentrated sulphuric acid (Sp. gr.1.84) in a weight ratio of 1:1.8 (biomaterial: acid). The resulting black product was kept in an air-free oven maintained at 160 ± 5 oC for 6 hours followed by washing with distilled water until free of excess acid dried at 105 ± 5 oC. The activated carbon obtained from biomaterial was ground and the portion retained between 90 and 125 µm sieves was used for metal adsorption experiments [18]. The result of characterization of activated carbon of biomaterial was presented in table-1. Batch experiments were conducted by varying amounts of Cr (VI) in ten 250 ml conical flask. All the samples were mechanically agitated at 100 rpm. Table – 1. Characteristics of the Activated carbon derived from Biomaterial. Sl.No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Parameters Bulk density (g/mL) Moisture (%) Ash (%) Solubility in water (%) Solubility in acid (%) pH Decolorizing power (mg/g) Phenol number Surface area (m2/g) Iron (%)

Value 0.75 0.50 0.70 0.45 1.0 7.55 0.55 35.65 320 0.75

From a South Indian tannery industry, composite wastewater sample was collected and diluted to 10 times by using double distilled water. The results of characterization of tannery wastewater samples were presented in table-2. Adsorption of Cr (VI) on the activated carbon of the bioadsorbent in tannery wastewater sample was carried out in similar way of synthetic water samples. The amount of Cr (VI) adsorbed on the activated carbon of the bioadsorbent (ACBA) in both cases was determined at 635 nm by Systronics UV – Visible spectrophotometer. The percent removal of Cr (VI) on the adsorbents was calculated as % removal =

Co – Cf ----------- x 100 Co

Where Co is the initial concentration of Cr (VI) and Cf is the final concentration of Cr (VI) in ppm.

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Table – 2. Characteristics of Tannery industry wastewater. Sl.No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Parameters pH Electrical conductivity (µmhos/cm) Total dissolved solids (mg/L) Turbidity (NTU) COD (mg/L) BOD (mg/L) Chloride (mg/L) Sulphate (mg/L) Chromium (VI) (mg/L) Calcium (mg/L) Sodium (mg/L) Potassium (mg/L)

Value 8.7 4842.50 7450 9.25 6590 40 640 1450 2050 350 275 58

RESULTS AND DISCUSSION Effect of contact time on adsorption Kinetic experiments were carried out to evaluate the potential of the adsorbents for the commercial applications. In order to estimate the adsorption capacity of the adsorbent accurately, it is very much important to allow significant time for the experimental solution to attain equilibrium. The amount of Cr (VI) adsorbed at different contact time with different adsorbent dose for an initial concentration of 100 ppm are shown in Figure 1.The kinetics of Cr (VI) removal by the adsorbents were observed to be gradually increasing when the contact time increases up to 180 minutes. A reaction time of 3 hours was employed for all the subsequent equilibrium studies.

100

% Removal

ACBA -1g

80

ACBA -2g

60

ACBA -3g ACBA -4g

40 ACBA -5g

20

0 0

30

60

90

120

150

180

Time (M in)

Fig. 1. Percent removal of Cr (VI) ions.

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210


Effect of quantity of adsorbent The effective removal of Cr (VI) from the synthetic samples varied with respect to the amount of the ACBA used. The adsorption of Cr (VI) on the adsorbent linearly increased as the amount of adsorbent increased from 1 – 5g. The analytical results were presented in the Figure 2.

% Removal of Cr (VI)

100 1g

80

2g

60

3g 4g

40

5g

20 0 0

1

2

3

4

5

Amount of ACBA (gm)

Fig. 2. Effect of ACBA on adsorption.

The increase can be attributed to the increase in the availability of adsorption sites. Navinchandra et al. [19] have observed similar trend in the case of removal of lead ions in the aqueous solutions on talc surface. In our present research work, when 5g of ACBA was used, after 180 minutes, the removal of Cr (VI) remained constant. Hence, it is possible that, further increase in the amount of adsorbent can remove Cr (VI) completely. Effect of concentration of Cr (VI) ions In the present study, in dilute solutions (25 ppm), the percentage removal of Cr (VI) was only about 65 percent. However, in higher concentrations (50 ppm), the percent removal was 80 after 150 minutes. This observation clearly indicates that, the removal of high concentration of Cr (VI) is easily accomplished which will indicate that, this method is recommended for highly contaminated wastewater. The analytical results are shown in Figure 3. Effect of temperature and pH In the present study, all batch experiments were conducted in room temperature (30oC) only. Literature survey reveals that [18], when the experimental temperature increases, the rate of

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adsorption on the adsorbent also increases. This is due to the enlargement of pore sizes of the adsorbents [20]. In these experiments, the optimum pH value of solution was maintained at 2.5 only to reduce the operational time.

25 ppm

50 ppm

100

% Removal

80 60 40 20 0 0

30

60

90

120

150

180

210

Time (min) Fig. 3. Effect of concentration of Cr (VI) ions.

Treatment of tannery wastewater The suitability of the bioadsorbent materials for the removal of Cr (VI) was tested with the tannery industry wastewater. The composite sample pH value was maintained at 2.5. The effect of contact time with the adsorbent dose of 5 g on Cr (VI) removal is shown in Figure 4. It has been found that increase in contact time increased the percentage adsorption. The data reveals that the treatment of Cr (VI) in industrial wastewater is significantly good. Almost complete removal of Cr (VI) from 100 ppm wastewater was possible with 5g of the selected bioadsorbent. Thus, the results are in good agreement with the results obtained from the batch experiments conducted for the Cr (VI) removal in synthetic wastewater samples. This demonstrates that the selected bioadsorbent can be successfully used for the removal of Cr (VI) from tannery industry wastewaters.

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ACBA -5g

100

% Removal

80 60 40 20 0 0

30

60

90

120

150

180

210

Time (Min)

Fig. 4. Treatment of tannery wastewater.

CONCLUSION The removal of Cr (VI) in synthetic wastewater and tannery wastewater by using bioremediation technology was studied in batch experimental systems. The heavy metal removal efficiency of the activated carbon of the biomaterial is excellent. The percent removal of Cr (VI) in synthetic wastewater is 97 with the effective dose of 5g of bioadsorbent. The percent removal of Cr (VI) in tannery wastewater is 98. The method can be recommended for the removal of high concentration of Cr (VI) from industrial wastewater. The experimental conditions are very simple and operational cost is low. The handling of the biomaterial is very easy and harmless. The proposed bioremediation technology is economically feasible and eco-friendly in nature. This process can be effectively used for the removal of Cr (VI) and other heavy metals from industrial wastewater. Preliminary treatment such as suspended solid removal of the industrial wastewater is essential before applying this methodology. REFERENCES 1. 2. 3. 4. 5. 6. 7.

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