Comparative study on biosorption of Zn(II), Cu(II) and Cr(VI) from textile dye effluent using activated rice husk and activated coconut fibre
K Gopalakrishnan* & T Jeyadoss
Department of Chemistry and Biosciences, SRC Campus, SASTRA University, Kumbakonam 612 001, India Received 13 July 2009; accepted 30 March 2010
This paper reports the results of the study on the performance of the low cost adsorbents such as activated rice husk (ARH) and activated coconut fibre (ACF) in removing the heavy metals such as Zn(II), Cu(II) and Cr(VI) from textile dye effluent. Biosorption studies are carried out through various parameters such as adsorbent dosage, pH and contact time.
Removal of heavy metal ions from the textile dye effluent increases with increase in adsorbent dosage. In ARH, at 50 g/L the maximum of 62%, 68% and 65% removal of Zn(II), Cu(II) and Cr(VI) are obtained respectively, whereas, in ACF, at 50 g/L the maximum of 64%, 67% and 72% removal of Zn(II), Cu(II) and Cr(VI) are obtained respectively. In the effect of pH, the maximum removal of metal ions occurs at pH 1-3 for both the adsorbents. In contact time, the maximum removal of heavy metal ions is observed at optimum time of 300 min. The maximum removal of heavy metal ions from the textile dye effluent using ARH and ACF is evaluated successfully through the percentage of seed germination of Vigna mungo L with the treated adsorbents. On comparison, ACF is good adsorbent when compared with ARH.
Keywords: Biosorption, Zinc, Copper, Chromium, Textile dye effluent
Dyes are widely used in industries such as textile, rubber, paper, plastics and cosmetics to colour their products. These dyes are invariably left in the industrial waste. Dyes even in low concentration affect the aquatic life and food web, due to the large degree of heavy metals present in the modern dyes.
The discharge of heavy metals such as lead, chromium, mercury, uranium, selenium, zinc, arsenic, cadmium, copper, nickel, etc., into aquatic ecosystems constitute severe health hazards mainly due to their non-degradability and toxicity1. Due to their mobility in natural water ecosystems and their toxicity to higher life forms, heavy metals in surface and groundwater supplies have been prioritized as major inorganic contaminants in the environment. Even if they are present in dilute, undetectable quantities, their recalcitrance and consequent persistence in water bodies imply that through natural process such as biomagnifications, concentration may become elevated to such an extent that they begin exhibiting toxic characteristics2.
During recent years, many researchers have focused their interest on heavy metals due to their known toxicity and carcinogenicity3. The removal of the toxic metal ions from water is a very difficult task
due to the high cost of treatment methods. Various methods exist for the removal of toxic metal ions from dye effluent is reverse osmosis, ion exchange, and electro dialysis. These techniques are not only expensive but also suffer with incomplete removal, high reagent and energy requirements and generation of toxic sludge4.
In recent years, biosorption has been suggested as being cheaper and more effective than chemical or physical technologies5. The major advantage of biosorption over conventional treatment methods include low cost, high efficiency, minimization of chemical and biological sludge. Moreover, regeneration of biosorbents and metal recovery is also possible6. Natural materials that are available in large quantities or certain waste products from agricultural operation may have the potential as inexpensive sorbents. Due to their low cost, after these materials have been expended, they can be disposed of without expensive regeneration7. The mechanism of binding of metal ions by adsorbents may depend on the chemical nature of metal ions (species size and ionic charge), the type of biomass, environmental conditions (pH, temperature, ionic strength) and existence of competing organic or inorganic metal chelators8.
In Tamil Nadu, the rice husk and the coconut fibre are abundantly available and cheap, because of large scale
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*Corresponding author (E-mail: kgk_1985@yahoo.co.in )
cultivation of rice and coconut. Moreover, on activation, both have the capability to remove heavy metal ions to the maximum extent from the textile dye effluent.
The objective of this study was to investigate the feasibility of using activated rice husk and activated coconut fibre as natural biosorbents for the removal of heavy metals from the textile dye effluent. The success of the study is confirmed by conducting the percentage of seed germination on black gram (Vigna mungo L) before and after treatment of textile dye effluent with activated rice husk and activated coconut fibre.
Materials and Methods
Textile dye effluent
The textile dye effluent was taken from textile dyeing industry located in and around Thirupur, Tamilnadu. India. The collected textile dye effluent was kept in the closed air tight container.
Biosorbent collection and activation
Rice husk was obtained from local rice mill and it was washed with distilled water for three times to remove the dust like impurities and dried under sunlight. The activation of rice husk9 was done at the temperature of 400 K for 1 h.
Coconut fibre was collected from coir industry located in Thanjavur, Tamilnadu. The raw material was washed thoroughly with tap water to remove earthly matter and dried under sunlight; activated coconut fibre was prepared by thermal pyrolysis of coconut fibre at 823 K for 2 h10.
Analysis of metal ions
Heavy metals of Textile dye effluent were quantitatively assessed using AAS Model no. A2 Solar, Series no. 978142F. This method quantitatively determines the concentration of Zinc, Copper, Chromium, Iron, Magnesium, Mercury, etc. utilizing a nitric acid/hydrogen peroxide microwave digestion and determination by AAS. The methodology utilizes a pressure digestion/dissolution of the sample and is incomplete relative to the total oxidation of organic carbon11.
Seed Germination seeds
For the germination test, 25 seeds of black gram (Vigna mungo L) were placed in sterilized glass petri dishes of uniform size lined with two filter paper discs. These filter discs were then moistened with 5 mL of distilled water for control and with the same quantity of untreated dye effluent and treated dye
effluent. There were three replications for each treatment. The seeds that germinated were counted and removed from the petri dishes at the time of first count on each day until there is no further germination. The criterion of germination which we took was the visible protrusion of radicle through seed coat and it was expressed in percentage12.
Results and Discussion
Characterization of textile dye effluent
The physicochemical characteristics like pH, electrical conductivity, carbonate, bicarbonate, chloride, sodium, potassium, zinc, copper and chromium of textile dye effluent were determined and given in Table 1. The values reveal that the effluent is highly contaminated. Both cations and anions in the textile dye effluent are found to be above the permissible limit. The heavy metals like zinc, copper and chromium are present in high concentration in the textile dye effluent. This high concentration of heavy metals leads to various environmental problems. The permissible value for zinc, copper and chromium in the textile dye effluent is 0.5 mg/L, 0.05 mg/L and 0.05 mg/L respectively. But the values of zinc, copper and chromium are 4.56 mg/L, 2.69 mg/L and 2.49 mg/L respectively.
Characterization of biosorbents
The physicochemical characteristics like moisture content, particle density, ash content, acid extractable components and water soluble components of adsorbents such as activated rice husk and activated coconut fibre were determined and given in Table 2.
The bulk density and particle density affect the adsorption of metal ions. The decrease in the bulk density enhances the adsorption of metal ions. Finer the size of the adsorbent, greater will be the
Table 1―Physiochemical analysis of textile dye effluent
Parameters Value
pH 10.58
Electrical Conductivity (dsm-1) 39.0
Carbonate (mg/L) 1224
Bicarbonate (mg/L) 6100
Chloride (mg/L) 10656
Sulphate (mg/L) 4032
Calcium (mg/L) 2400
Magnesium (mg/L) 960
Sodium (mg/L) 7176
Potassium (mg/L) 312
Zinc (mg/L) 4.56
Copper (mg/L) 2.69
Chromium (mg/L) 2.49
adsorption. The bulk density value less than 1.2 indicates the adsorbent materials are fine nature.
When this value falls within the range 1.2-2 the materials are medium and the value more than 2 indicates that the materials are coarse in nature. The particle density value is less than 2.2, which indicates the materials are finer, the value between 2.2-4 are medium and more than 4 indicates materials are coarse in nature. In the present study, the bulk density and particle density values obtained are closer to fine in nature.
Moisture content, though does not affect the adsorption power, dilutes the adsorbents and therefore necessitates the use of additional weight of adsorbents to provide the required weight. Ash content generally gives an idea about inorganic constituents associated with carbon. In any case, the actual amount of individual inorganic constituents will vary from one type to another as they are mainly derived from different source of material. The values of matter soluble in water and acid are more informative for designing the adsorption process10.
Effect of adsorbent dosage
To study the influence of the adsorbent dosage on the removal of heavy metal ions, different values have been taken by varying the adsorbent concentration ranging from 10 to 50 g/L by keeping the volume of the effluent solution constant under optimum condition temperature (T) 296 K and time (t) 60 min.
Figure 1 shows the effect of adsorbent dosage on the removal of Zn(II), Cu(II) and Cr(VI) by activated rice husk at optimum temperature (T) 296 K and time (t) 60 min. Removal of 9% Zn(II) was obtained at initial dosage of adsorbent 10 g/L, which increased with the increase of adsorbent dosage reaching the maximum of 62% removal of Zn(II) was obtained at 50 g/L. 25% removal of Cu(II) was obtained at initial dosage of adsorbent 10 g/L, which increased with the
increase of adsorbent dosage reaching the maximum of 68% removal of Cu(II) was obtained at 50 g/L.
19% removal of Cr(VI) was obtained at initial dosage of adsorbent 10 g/L, which increased with the increase of adsorbent dosage reaching the maximum of 65% removal of Cr(VI) was obtained at 50 g/L.
Likewise, Fig. 2 shows the effect of adsorbent dosage on the removal of Zn(II), Cu(II) and Cr(VI) by activated coconut fibre at optimum temperature (T) 296 K and time (t) 60 min. Removal of 15% Zn(II) was obtained at initial dosage of adsorbent 10 g/L, which increased with the increase of adsorbent dosage reaching the maximum of 64% removal of Zn(II) was obtained at 50 g/L. 24% removal of Cu(II) was obtained at initial dosage of adsorbent 10 g/L, which increased with the increase of adsorbent dosage reaching the maximum of 67% removal of Cu(II) was obtained at 50 g/L. 20% removal of Cr(VI) was obtained at initial dosage of adsorbent 10 g/L, which increased with the increase of adsorbent dosage reaching the maximum of 72% removal of Cr(VI) was obtained at 50 g/L.
Removal of heavy metal ions from the textile dye effluent increases with increase in adsorbent dosage.
This can be explained by the availability of the
Table 2―Physiochemical analysis of Biosorbents Parameters Activated rice
husk
Activated coconut fibre
pH 5.81 5.83
Bulk density (g/cc) 0.94 0.87
Particle density (g/cc) 1.30 1.22
Moisture (%) 4.56 6.29
Organic carbon (%) 4.29 3.42
Water holding capacity (%) 67.62 87.64 Matter soluble in water (%) 0.54 0.64 Matter soluble in acid (%) 99.46 99.31
Ash (%) 12.48 12.57
Fig. 1―Effect of adsorbent dosage on the removal of Zn(II), Cu(II) and Cr(VI) by activated rice husk (Condition: T = 296 K and t = 60 min)
Fig. 2―Effect of adsorbent dosage on the removal of Zn(II), Cu(II) and Cr(VI) by activated coconut fibre (Condition: T = 296 K and t = 60 min)
exchangeable sites or surface area on the adsorbents.
In the minimum adsorbent dosage level (10 g/L) there will be a low availability of exchangeable sites, ultimately the removal of metal ions at low adsorbent dosage is also minimum. But at the maximum adsorbent dosage level (50 g/L) there will be a greater availability of exchangeable sites or surface area, hence, the removal of metal ions at maximum adsorbent dosage is also maximum13.
Success of removal of heavy metal ions with the effect of adsorbent dosage has been evaluated through the study of the percentage of seed germination of black gram (Vigna mungo L) before and after treatment, which is given in Table 3.
After the treatment of textile dye effluent with various absorbents such as activated rice husk and activated coconut fibre at maximum adsorbent dosage level (50 g/L) the percentage of seed germination was 74.6+1.8 and 81.3+1.8. However, before the treatment of textile dye effluent with various adsorbents the percentage of seed germination was 20+3.2. The control value was 97.3+1.8. These values show that the percentage of seed germination of Vigna mungo L was increased after the treatment of textile dye effluent with the various adsorbents when compared to untreated textile dye effluent.
Effect of pH
The influence of pH on the removal of heavy metal ions was studied by varying the pH ranging from 1 to 7 and keeping the volume of the effluent solution constant under optimum condition temperature (T) 296 K and time (t) 60 min. Figures 3 and 4 show that the optimum pH for the removal of Zn(II) ion by activated rice husk was pH 1.0. At this pH the maximum of 60% removal of Zn(II) was obtained, whereas the maximum of 61.5% of Zn(II) was obtained at the pH 1.0 with activated coconut fibre respectively. Likewise, Figs 3 and 4 show that the optimum pH for the removal of Cu(II) ion by activated rice husk was pH 1.0. At this pH the maximum of 70% removal of Cu(II) was obtained,
whereas the maximum of 77.5% of Cu(II) was obtained at the pH 1.0 with activated coconut fibre respectively. Similarly, Figs 3 and 4 show that the optimum pH for the removal of Cr(VI) ion by activated rice husk was pH 1.0. At this pH the maximum of 63.5% removal of Cr(VI) was obtained, whereas the maximum of 67% of Cr(VI) was obtained at the pH 1.0 with activated coconut fibre respectively.
It is quite obvious from the results (Figs 3 and 4) that the pH plays an important role in the adsorption process. Removal of heavy metal ions such as Zn(II), Cu(II) and Cr(VI) from the textile dye effluent increases at acidic pH. Adsorption of Zn(II) increases at high acidic pH because Zinc ion exists as Zn(OH)+ which is favorable species for adsorption of trace zinc ions.
Adsorption of Cu(II) increases at high acidic pH because of ionic interaction between the metal and the adsorbent increases. Adsorption of Cr(VI) is also increases at high acidic pH because of redox reaction between the sorbent surface groups and sorbate. Higher H+ ion concentration could strengthen the redox reaction and enable the carbon to adsorb more Cr(VI)7.
Success of removal of heavy metal ions with the effect of pH has been evaluated through the study of
Table 3―Effect of adsorbent dosage on percentage of seed germination of Vigna mungo L
Name of the Sample Percentage of seed germination
Water 97.3 + 1.8
Untreated textile dye effluent 20 + 3.2 Activated rice husk (50 g/L)
treated textile dye effluent
74.6 + 1.8 Activated coconut fibre (50
g/L)treated textile dye effluent
81.3 + 1.8
Fig. 3―Effect of pH on the removal of Zn(II), Cu(II) and Cr(VI) by activated coconut fibre (Condition: T = 296 K and t = 60 min)
Fig. 4―Effect of pH on the removal of Zn(II), Cu(II) and Cr(VI) by activated rice husk (Condition: T = 296 K and t = 60 min)
the percentage of seed germination of black gram (Vigna mungo L) before and after treatment, which is given in Table 4.
After the treatment of textile dye effluent with various adsorbents such as activated rice husk and activated coconut fibre at acidic pH (1.0) the percentage of seed germination was 46.6 + 1.8 and 53.3 + 1.8. However, before the treatment of textile dye effluent with various adsorbents the percentage of seed germination was 20 + 3.2. The control value was 97.3 + 1.8. These values show that the percentage of seed germination of Vigna mungo L is increased after the treatment of textile dye effluent with the various adsorbents when compared to untreated textile dye effluent.
Effect of contact time
The influence of the contact time on the removal of heavy metal ions at different time intervals ranging from 60 min to 300 min while keeping the volume of the effluent solution constant under optimum temperature (T) 296 K and adsorbent dosage 50 g/L was studied.
Figure 5 shows that with activated rice husk, the optimum time was obtained at 300 minutes for Zn(II), Cu(II) and Cr(VI) respectively. At this time the maximum removal of Zn(II) was 51%, whereas 65%of Cu(II) and 60.5% of Cr(VI) were obtained under optimum conditions. Likewise, Fig. 6 shows that with activated coconut fibre, the optimum time was obtained at 300 min for Zn(II), Cu(II) and Cr(VI) respectively. At this time the maximum removal of Zn(II) was 55.5%, whereas 67% of
Cu(II) and 64.5% of Cr(VI) were obtained under optimum conditions.
Contact time is an important parameter in all transfer phenomena including adsorption. Consequently it is important to study its effect on the capacity of removal of heavy metal ions by low cost adsorbents.
Removal efficiency increased with an increase in contact time and this can be explained by the affinity of the adsorbents towards metal ions13.
Success of removal of heavy metal ions with the effect of contact time has been evaluated through the study of the percentage of seed germination of black gram (Vigna mungo L) before and after treatment, which is given in Table 5.
After the treatment of textile dye effluent with various absorbents such as activated rice husk and activated coconut fibre at maximum contact time (300 min) the percentage of seed germination was 76 + 1.8 and 84 + 1.8. However, before the treatment of textile dye effluent with various adsorbents the percentage of seed germination was 20+3.2. The control value was 97.3+1.8. These values show that the percentage of seed germination of Vigna mungo L
Table 4―Effect of pH on percentage of seed germination of Vigna mungo L
Name of the sample Percentage of seed germination
Water 97.3 + 1.8
Untreated textile dye effluent 20 + 3.2 Activated rice husk (pH 1.0)
treated textile dye effluent
46.6 + 1.8 Activated coconut fibre (pH 1.0)
treated textile dye effluent
53.3 + 1.8 Table 5―Effect of contact time on percentage of seed
germination of Vigna mungo L
Name of the sample Percentage of seed germination
Water 97.3 + 1.8
Untreated textile dye effluent 20 + 3.2 Activated rice husk (300 min)
treated textile dye effluent
76.0 + 1.8 Activated coconut fibre (300
min) treated textile dye effluent
84.0 + 1.8
Fig. 5―Effect of contact time on the removal of Zn(II), Cu(II) and Cr(VI) by activated coconut fibre (Condition: T = 296 K and adsorbent dosage = 50 g/L)
Fig. 6―Effect of contact time on the removal of Zn(II), Cu(II) and Cr(VI) by activated coconut fibre (Condition: T = 296 K and adsorbent dosage = 50 g/L)
is increased after the treatment of textile dye effluent with the various adsorbents, when compared to untreated textile dye effluent.
Conclusions
The present study clearly shows that activated rice husk and activated coconut fibre can be used as an effective adsorbents for removal of Zn(II), Cu(II) and Cr(VI) from textile dye effluent. This adsorption process is also dependent on numerous factors such as adsorbent dosage, pH and contact time. The increase in adsorbent dosage also increases the removal of metal ions from textile dye effluent. In activated rice husk, at 50 g/L the maximum of 62%, 68% and 65%
removal of Zn(II), Cu(II) and Cr(VI) were obtained respectively, whereas, in activated coconut fibre, at 50 g/L the maximum of 64%, 67% and 72% removal of Zn(II), Cu(II) and Cr(VI) were obtained respectively.
In the effect of pH, the maximum removal of metal ions occurs at pH 1.0 for both the adsorbents. The study of pH effects has confirmed that ion exchange is the major mechanism of removal of metal ions using activated rice husk and activated coconut fibre. In contact time, the maximum removal of heavy metal ions was observed at optimum time of 300 min. At this time the maximum removal of Zn(II), Cu(II) and Cr(VI) were observed under optimum condition using activated rice husk and activated coconut fibre. It is
also quite interesting to observe that the percentage of seed germination of Vigna mungo L increases with treated dye effluent. Thus, among the two biosorbents, coconut fibre as an agro-industrial waste has negligible cost and has also been proved to be an efficient biosorbent when it was activated.
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