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Biosorption of Chromium(VI) From Aqueous solutions by green algae spirogyra species
PII: S0043-1354(01)00138-5
Wat. Res. Vol. 35, No. 17, pp. 4079–4085, 2001 # 2001 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/01/$ - see front matter
BIOSORPTION OF CHROMIUM(VI) FROM AQUEOUS SOLUTIONS BY GREEN ALGAE SPIROGYRA SPECIES V. K. GUPTA1*, A. K. SHRIVASTAVA2 and NEERAJ JAIN2 1
Department of Chemistry, University of Roorkee, Roorkee 247 667, India and 2 Department of Civil Engineering, University of Roorkee, Roorkee 247 667, India (First received 1 September 1999; accepted in revised form 1 March 2001)
Abstract}Biosorption of heavy metals is an effective technology for the treatment of industrial wastewaters. Results are presented showing the sorption of Cr(VI) from solutions by biomass of filamentous algae Spirogyra species. Batch experiments were conducted to determine the adsorption properties of the biomass and it was observed that the adsorption capacity of the biomass strongly depends on equilibrium pH. Equilibrium isotherms were also obtained and maximum removal of Cr(VI) was around 14.7 103 mg metal/kg of dry weight biomass at a pH of 2.0 in 120 min with 5 mg/l of initial concentration. The results indicated that the biomass of Spirogyra species is suitable for the development of efficient biosorbent for the removal and recovery of Cr(VI) from wastewater. # 2001 Elsevier Science Ltd. All rights reserved Key words}biosorption, adsorption, biosorbent, algae, wastewater
INTRODUCTION
The presence of heavy metal ions in surface water continues to be the most pervasive environmental issues of present time (Hotton and Symon, 1986; Nriagu, 1988). Chromium is one of the contaminants, which exists in hexavalent and trivalent forms. Hexavalent form is more toxic (Smith and Lec, 1972) than trivalent and requires more concern. Strong exposure of Cr(VI) causes cancer in digestive tract and lungs (Kaufman, 1970) and may cause epigastric pain, nausea, vomiting, severe diarrhea and hemorrhage (Browning, 1969). It is therefore, essential to remove Cr(VI) from wastewater before disposal. The main sources of chromium(VI) are tannery, paint, ink, dye, and aluminium manufacturing industries etc. Chemical precipitation with lime or caustic soda is one of the common conventional treatments, where recovery of metals or water is not a consideration. However, to effectively decrease metals to acceptable levels by this treatment requires a large excess of chemicals, which generates volumetric sludge and increases the costs of treatment (Spearot and Peck, 1984). Other available treatments such as ion exchange, electrolysis and reverse osmosis require high capital investment and running costs. The process of adsorption is by far the most versatile and widely used technique for the removal
*Author to whom all correspondence should be addressed. Tel.: +91-1332-85801; fax: +91-1332-73560; e-mail: [email protected]
of metal ions. Activated carbon has been the water industrys’ standard adsorbent for the reclamation of municipal and industrial wastewater for potable use for almost three decades (Fornwalt and Hutchins, 1966). Despite its prolific use in the water and waste industries, activated carbon remains an expensive material. In recent years, research interest into the production of low-cost alternatives to activated carbon has grown. It has been demonstrated that biosorption is a potential alternative to traditional treatment processes of metal ions removal (Volesky, 1990). The phenomenon of biosorption has been described in a wide range of non-living biomass like bark (Alves et al., 1993); lignin (Srivastava et al., 1994); and peanut hulls (Periasamy and Namasivayam, 1994) as well as of living biomass like fungi (Lewis and Kriff, 1988; Matheickal et al., 1991; Fourest et al., 1994), bacteria (Scott and Palmer, 1990; Grappelli et al., 1992; Churchill et al., 1995; Chang et al., 1997), yeast (Huang et al., 1990; Volesky et al., 1993), moss (Lee and Low 1989; Low and Lee 1991), aquatic plants (Srivastav et al., 1994) and algae (Xue et al., 1988; Yu et al., 1999). Biosorption utilizes the ability of biological materials to accumulate heavy metals from waste streams by either metabolically mediated, or purely physico-chemical pathways of uptake (Fourest and Roux, 1992). A survey of literature indicated that not much work has been done so far on living biomass for heavy metal removal. Efforts made to use the algae and aquatic plants, moss and fern for heavy metals
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include the use of silica-immobilized algae Chlorella pyrenoidosa at low pH for Cr(VI) (Greene et al., 1987); Chlaymydomonas rheinhardii for Cu(II) and Cd(II) (Xue et al., 1988); pretreated biomass of nine common species of marine macro algae for lead(II), copper(II) and cadmium(II) (Yu et al., 1999); marine alga Durvillaea potatorum for cadmium(II) (Matheickal et al., 1999); Sphagnum moss peat for Cr(VI) (Sharma and Forster, 1993); Azolla pinnta R. Br. and Lemna minor L. for Pb(II) and Zn(II) (Jain et al., 1990); Azollla filiculoides for Cr(VI) and Zn(II) (Zhao et al., 1997a,b; 1999); Salvinia and Spirodela for chromium and nickel (Srivastav et al., 1994); Sargassum fluitans for Cu(II) in column operation (Kratochvil et al., 1997); water hyacinth (Ipomea aquatica) for Cu, Co and Ni (Low and Lee, 1991); Eichhornia crassipes for As, Cd, Pb and Hg (Chigbo et al., 1982); Eichhornia crassipes for Zn, Cr and Cd (Delgado et al., 1993); Eichhornia maxima for Cu, Ni and Cd from single and mixed metal ion solutions (Williams et al., 1998); and so forth. The purpose of the present study is to evaluate the biosorption capacity of the algae Spirogyra species for Cr(VI) from aqueous solutions. The material is green filamentous algae belonging to the family Chlorophyceae and is available in abundance. Further, no report is available on the use of this material for the adsorption of any metal ion. The adsorption capacities were evaluated from equilibrium adsorption isotherms and the results indicated that the alga is a suitable material for the development of high capacity biosorbent for Cr(VI) removal.
MATERIALS AND METHODS
Materials
Kinetics studies Sorption studies were conducted in 500 ml conical flasks at natural solution pH (5.85). Dry Spirogyra species biomass (1, 1.5, 3, 5, 10, and 15 g/l) were thoroughly mixed individually with 300 ml of chromium solution (25 mg/l) and the suspensions were shaken at room temperature (188C). Samples of 5 ml were collected from the duplicate flasks at required time intervals viz. 30, 60, 90, 120, 150 and 180 min and were filtered through Whattman No. 1 filter paper. The filtrates were analysed for residual chromium concentration in the solution. Similarly, varying initial chromium concentrations (1, 5 and, 15 mg/l) were taken for different algal doses with same interval of contact time as above. As the sorption studies have been carried out using adsorption technique, the following mathematical relation between contact time and percent removal has been used to find out adsorption kinetics constant for algae R ¼ a ðtÞb
where, R is percent removal of Chromium, a and b are the constants and t is the contact time in minutes. The linearized relationship of the equation (1) can be expressed as log R ¼ log a þ b log t
pH measurements were made using a pH meter (model CT No. CL46, Toshniwal, India). The chromium was determined after acid digestion (HNO3–HClO4) and was analysed using an Instrumentation Laboratory, atomic absorption spectrophotometer model Z-7000 (Hitachi, Japan) at a wavelength of 359.3 nm.
ð2Þ
Adsorption isotherms Batch sorption experiments were carried out in 250 ml conical flask at 188C on a rotary shaker for 120 min. The dry biomass (5, 10 and 15 g/l) was thoroughly mixed with 100 ml of chromium solutions. The isotherm studies were performed by varying the initial chromium concentrations from 1 to 25 mg/l at a pH of 1.0, 2.0, 3.0, 4.0 and 5.0, respectively. The pH values were adjusted using 0.1 M HCl or NaOH before addition of biomass and were maintained throughout the experiment. After shaking the flasks for 120 min, the reaction mixture was analysed for residual chromium concentration. The Langmuir sorption model was adopted for the estimation of maximum chromium uptake (Xm ) where they could not be reached in the experiment (Gosset et al., 1986; Holan et al., 1993).
All reagents used were of AR grade either from Merck, Germany or s:d.Fine-CHEM Ltd., India. Equipment
ð1Þ
1=qe ¼ 1=ðXm bCe Þ þ 1=Xm
ð3Þ
where Xm and b are Langmuir constants, indicative of maximum adsorption capacity and a measure of adsorption energy, respectively. qe is the metal adsorption in mg/g of dryweight biomass and Ce is the equilibrium chromium concentration (mg/l).
RESULTS AND DISCUSSION
Kinetic studies Biomass Fresh algal biomass of Spirogyra species was collected from the concrete curing tanks in the premises of Civil Engineering Department, University of Roorkee, Roorkee, India. Before use, it was washed with distilled water to remove dirt and was kept on a filter paper to reduce the water content. After this, the biomass was sun dried for 6 h and milled to a gritty consistency. The biomass was sieved to select particles between 2–3 mm in size for use. Preparation of synthetic sample A stock solution of hexavalent chromium (50 mg/l) was prepared in distilled water with potassium dichromate. All working solutions of varying concentrations were obtained by diluting the stock solution with distilled water.
The results of percent chromium adsorption as a function of time at different algal doses have been shown plotted in Figs 1–4. All the figures show that the sorption of Cr(VI) increases (at varying initial concentrations with various algal doses of 1–15 g/l) with time from 0 to 120 min and after that becomes almost constant up to the end of the experiment (180 min). The removal of Cr(VI) ranges from 12% to 30% at 120 min with various algal doses. It can be concluded that the rate of Cr(VI) binding with algal biomass is more at initial stages, which gradually decreases and remains almost constant after an optimum period of 120 min.
Biosorption of chromium (VI) from aqueous solutions by Spirogyra Sps.
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Fig. 1. Effect of contact time on the sorption of Cr(VI) by Spirogyra at natural pH.
Fig. 3. Effect of contact time on the sorption of Cr(VI) by Spirogyra at natural pH.
Fig. 2. Effect of contact time on the sorption of Cr(VI) by Spirogyra at natural pH.
Fig. 4. Effect of contact time on the sorption of Cr(VI) by Spirogyra at natural pH.
All the figures shows that a linear relationship exist in percent removal of Cr(VI) and contact time. Hence equation (1) was fitted in the experimental data and constants ‘a’ and ‘b’ were calculated and values are shown in Table 1. The values of ‘a’ ranges from 4.36 to 12.02. It is clear from the table that with decrease in algal dose for same initial Cr(VI) concentration, value of ‘a’ decreases, which suggests that with the decrease in algal dose, adsorption capacity also decreases. The value of ‘a’ is highest at Cr(VI) concentration of 5 mg/l with an algal dose of 5 g/l, suggesting these as optimum condition for the adsorbent as well as adsorbate. The value of ‘b’ ranges from 0.303 to 0.61. The low values of ‘b’ suggest that with
increase in time, rate of percentage removal decreases. Effect of pH Earlier studies have indicated that solution pH is an important parameter affecting biosorption of heavy metal ions (Matheikal et al., 1991; Fourest et al., 1994; and Matheikal and Yu, 1996). Cr(VI) removal was studied as a function of pH at various algal doses and the results are shown in Figs 5–12. It is clear from these figures that the percent adsorption of Cr(VI) increases with increase in pH from pH 1.0 to 2.0 and thereafter decreases with further increase in pH. It is important to mention that the
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V. K. Gupta et al. Table 1. Values of adsorption kinetic constant
Cr(VI) (mg/l)
Algal dose (g/l)
Log a
a
b
25
15 10 5
0.86 0.81 0.64
7.24 6.52 4.36
0.50 0.51 0.61
15
10 5 3
1.03 0.92 0.80
10.72 8.32 6.31
0.45 0.57 0.47
5
5 3 1.5
1.08 1.04 0.80
12.02 10.96 6.31
0.47 0.30 0.35
1
3 1.5 1
0.96 0.77 0.68
9.12 5.89 4.79
0.43 0.41 0.45
Fig. 5. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 7. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 6. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 8. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Biosorption of chromium (VI) from aqueous solutions by Spirogyra Sps.
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Fig. 9. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 11. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 10. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 12. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
maximum adsorption at all the concentrations takes place at pH 2.0. Further, these figures also show that maximum adsorption (96%) takes place at an algal dose of 5 g/l as well as with 5 mg/l of initial Cr(VI) concentration. This behavior can be explained considering the nature of the biosorbent at different pH in metal adsorption. The cell wall of Spirogyra species contains a large number of surface functional groups. The pH dependence of metal adsorption can largely be related to type and ionic state of these functional groups and also on the metal chemistry in solution (Matheickal et al., 1999). Adsorption of Cr(VI) below pH 3.0 (maximum at pH 2.0) suggests that the negatively charged chromium species (chromate/
dichromate in the sample solution) bind through electrostatic attraction to positively charged functional groups on the surface of algal cell wall because at this pH more functional groups carrying positive charges would be exposed. But at pH above 3.0, it seems that algal cell wall possesses more functional groups carrying a net negative charge which tends to repulse the anions. However, there is removal above pH 3.0 also, as is indicated by the Figs 5–12, but the rate of removal is considerably reduced. Hence, it could be said that above pH 3.0, other mechanism like physical adsorption on the surface of sorbent could have taken an important role in sorbing Cr(VI) and exchange mechanism might have reduced (Greene et al., 1987).
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V. K. Gupta et al. Table 2. Langmuir parameters for adsorption isotherms
pH
Xm (mg metal/kg of dry weight biomass 103 l/kg)
b ( 102 l/mg)
Bio-concentration factor ( 103 l/kg)
7.6 14.70 12.35 5.46 3.38
15.56 19.61 18.83 13.84 6.24
12.16 70.00 41.86 4.96 1.35
1 2 3 4 5
Adsorption Isotherms The chromium sorption isotherms followed the Langmuir model (equation (3)) well, as shown by high values of the correlation coefficient (r2 ) given in Table 2 alongwith the Langmuir constants. Since solution pH has a significant effect on adsorption equilibrium, the Cr(VI) removal was evaluated by adsorption isotherms obtained at a number of different equilibrium solution pH values at an optimum algal dose of 5 g/l. The maximum Cr(VI) adsorption at an optimum pH of 2.0 is 14.7 103 mg metal/kg of dry weight biomass (Table 2), which is much higher than those of most other types of sorbent reported earlier and comparable to commercial ion exchange resin capacities. The Langmuir constant b can serve as an indicator of isotherm rise in the region of lower residual metal concentrations, which reflects the strength or affinity of the sorbent for the solute (Holan et al., 1993). It was found to decrease with increase in pH from 2.0 to 5.0, which implies that the removal of Cr(VI) at lower pH could be more complete than that at a high pH. The values of bioconcentration factor are also calculated and given in Table 2. The value of this factor under optimum conditions is 70 103 l/kg. This value further confirms the affinity of the biosorbent for Cr(VI).
CONCLUSIONS
The data from batch studies on the biosorption of Cr(VI) on algae Spirogyra species provided fundamental information in terms of optimum pH, optimum algal dose for maximum removal of chromium from the solution. The maximum chromium removal was found to be 14.7 103 mg metal/ kg of dry weight biomass at a pH of 2.0 in 120 min with 5 mg/l of initial concentration. The decreased affinity of the biomass for metals at high pH can be used as a procedure for biomass regeneration and metal ions recovery. The study also indicated that spirogyra species biomass can be used to develop high capacity biosorbent materials for the removal and recovery of heavy metal ions from the dilute industrial wastewater streams. Further studies are needed in understanding the interaction behavior between the activated biomass and heavy metal ions in batch and column.
r2 0.96 0.99 0.98 0.90 0.90
Acknowledgements}Authors are thankful to Council of Scientific & Industrial research, New Delhi, India for supporting this work.
REFERENCES
Alves M. M., Ceca C. G. G., Carvalho R. G. De, Castanheira J. M., Periera M. C. S. and Vasconcelos L. A. T. (1993) Chromium removal in tannery wastewaters polishing by Pinus sylvestris bark. Water Res. 27, 1333– 1338. Browning E. (1969) Toxicity of Industrial Metals, Chapter 12, 2nd ed. Butterworths, London, UK. Chang J. S., Law R. and Chang C. C. (1997) Biosorption of lead, copper and cadmium by biomass of Pseudomonas aeruginosa PU21. Water Res. 31, 1651–1658. Chigbo F., Smith R. W. and Shore F. L. (1982) Uptake of arsenic, cadmium, lead and mercury from polluted waters by the water hyacinth (Eichhornia crassipes). Water. Sci. Tech. 19, 123–128. Churchill S. A., Walters J. V., Member ASCE and Churchill P. F. (1995) Sorption of heavy metals by prepared bacterial cell surfaces. J. Environ. Eng. ASCE 121, 706– 711. Delgado M., Bigeriego M. and Duardiola E. (1993) Uptake of Zn, Cr and Cd by water hyacinths. Water Res. 27, 269– 272. Fornwalt H. J. and Hutchins R. A. (1966) Purifying liquids with activated carbon. Chemical Engng. 73, 179–184. Fourest E., Canal C. and Roux J. C. (1994) Improvement of heavy metal biosorption by mycelial dead biomasses (Rhizopus arrhizus, Muchor miehei, and Pencillium chrysogenum): pH control, and cationic activation. FEMS Microbiol. Rev. 14, 325–332. Fourest E. and Roux J. C. (1992) Heavy metal biosorption by fungal mycelial by-products: mechanisms and influence of pH. Appl. Microbiol. Biotechnol. 37, 399–403. Gosset T., Transcart J. L. and Thevnot D. R. (1986) Batch metal removal by peat: kinetics and thermodynamics. Water Res. 20, 21–26. Grappeli A., Campanella L., Cardarelli E., Mazzei F., Cordatore M. and Pietrosanti W. (1992) Metals removal and recovery by Arthrbacter sp. biomass. Water Sci. Tech. 26, 2149–2152. Greene B., McPherson R., and Darnall D. (1987) Algal sorbents for selective metal ion recovery. In Metals Speciation, Separation and Recovery, Lewis Publishers Inc., Chelsea, MI, USA. Holan Z. R., Volesky B. and Prasetyo I. (1993) Biosorption of cadmium by biomass of marine algae. Biotechnol Bioeng. 41, 819–825. Hotton M. and Symon C. (1986) Quantities of cadmium, lead, mercury and arsenic entering the environment from human activities. Sci. Total Environ. 57, 129–150. Huang C. P., Huang C. P. and Moreheart A. L. (1990) The removal of Cu(II) from dilute aqueous solutions by Saccharomyces cereviceae. Water Res. 24, 433–439. Jain S. K., Vasudevan P. and Jha N. K. (1990) Azolla pinnata R. Br. and Lemna minor L. for removal of lead and zinc from polluted water. Water Res. 24, 177–183.
Biosorption of chromium (VI) from aqueous solutions by Spirogyra Sps. Kaufaman D. B. (1970) Acute potassium dichromate poisoning in man. Am. J. Diseases Children 119, 374–379. Kratochvil D., Volesky B. and Demopoulos G. (1997) Optimizing Cu removal/recovery in a biosorption column. Water Res. 31, 2327–2339. Lee C. K. and Low K. S. (1989) Removal of copper from solution using moss. Environ. Tech. Letts. 10, 395–404. Lewis D. and Kriff R. J. (1988) The removal of heavy metals from aqueous effluents by immobilized fungal biomass. Environ. Tech. Lett. 9, 991–998. Low K. S. and Lee C. K. (1991) Cadmium uptake by the moss Calymperes delessertii. Bioresour. Tech. 38, 1–6. Matheickal J. T., Yu Q. and Woodburn G. M. (1999) Biosorption of cadmium from aqueous solutions by pretreated biomass of marine alga Durvillaea potatorum. Water Res. 33, 335–342. Matheickal J. T., Iyengar L. and Venkobachar C. (1991) Sorption and desorption of Cu(II) by Ganoderma lucidum. Wat. Poll. Res. J. Canada. 26, 187–200. Matheickal J. T. and Yu Q. (1996) Biosorption of lead from aqueous solutions by marine alga Ecklonia radiata. Water Sci. Tech. 34, 1–7. Nriagu J. O. (1988) A silent epidemic of environmental metal poisoning. Environ. Pollution 50, 139–161. Periasamy K. and Namasivayam C. (1994) Process development for removal and recovery of cadmium from wastewater by a low cost adsorbent: adsorption rate and equilibrium studies. Ind. Eng. Chem. Res. 33, 317–322. Scott J. A. and Palmer S. J. (1990) Sites of cadmium uptake in bacteria used for biosorption. Appl. Microbiol. Biotechnol. 33, 221–225. Sharma D. C. and Forster C. F. (1993) Removal of hexavalent chromium using Shagnum moss peat. Water Res. 27, 1201–1208. Srivastav R. K., Gupta S. K., Nigam K. D. P. and Vasudevan P. (1994) Treatment of chromium and nickel in wastewater by using aquatic plants. Water Res. 28, 1631–1638.
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Srivastava S. K., Tyagi R., Pant N. and Pal N. (1994) Studies on the uptake of lead and zinc by lignin obtained from black liquor}a paper industry waste material. Environ. Tech. 15, 353–361. Smith R. G. and Lec D. H. K. (1972) Chromium in Metallic Contaminants and Human Health. Academic Press, New York. Spearot R. M. and Peck J. R. (1984) Recovery process for complexed copper-bearing rinse waters. Environ. Prog. 3, 124–129. Volesky B. (1990) Biosorption and biosorbents. In Biosorption of Heavy Metals, ed. B. Volesky. CRC Press Inc., Boca Raton. Volesky B., May H. and Holan Z. (1993) Cadmium biosorption by S. cerevisiae. Biotechnol. Bioeng. 41, 826–829. Williams C. J., Aderhold D. and Edyvean R. G. J. (1998) Comparison between biosorbents for the removal of metal ions from aqueous solutions. Water Res. 32, 216– 224. Xue H. B., Stumm W. and Stagg L. (1988) The binding of heavy metals to algal surfaces. Wat. Res. 22, 917–926. Yu Q., Matheickal J. T., Yin P. and Kaewsarn P. (1999) Heavy metal uptake capacities of common marine macro algal Biomass. Water Res. 33, 1534–1537. Zhao M. and Duncan J. R. (1997a) Batch removal of hexavalent chromium by Azolla filiculoides. Appl. Biochem. Biotechnol. 26, 179–183. Zhao, M. and Duncan J. R. (1997b) Column studies on the accumulation and desorption of hexavalent chromium by Azolla filiculoides. Resource Environ. Biotechnol. 26, 51–64. Zhao M., Duncan J. R. and Hille R. P. V. (1999) Removal and recovery of zinc from solution and electroplating effluent using Azolla filiculoides. Water Res. 33, 1516– 1522.
Wat. Res. Vol. 35, No. 17, pp. 4079–4085, 2001 # 2001 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/01/$ - see front matter
BIOSORPTION OF CHROMIUM(VI) FROM AQUEOUS SOLUTIONS BY GREEN ALGAE SPIROGYRA SPECIES V. K. GUPTA1*, A. K. SHRIVASTAVA2 and NEERAJ JAIN2 1
Department of Chemistry, University of Roorkee, Roorkee 247 667, India and 2 Department of Civil Engineering, University of Roorkee, Roorkee 247 667, India (First received 1 September 1999; accepted in revised form 1 March 2001)
Abstract}Biosorption of heavy metals is an effective technology for the treatment of industrial wastewaters. Results are presented showing the sorption of Cr(VI) from solutions by biomass of filamentous algae Spirogyra species. Batch experiments were conducted to determine the adsorption properties of the biomass and it was observed that the adsorption capacity of the biomass strongly depends on equilibrium pH. Equilibrium isotherms were also obtained and maximum removal of Cr(VI) was around 14.7 103 mg metal/kg of dry weight biomass at a pH of 2.0 in 120 min with 5 mg/l of initial concentration. The results indicated that the biomass of Spirogyra species is suitable for the development of efficient biosorbent for the removal and recovery of Cr(VI) from wastewater. # 2001 Elsevier Science Ltd. All rights reserved Key words}biosorption, adsorption, biosorbent, algae, wastewater
INTRODUCTION
The presence of heavy metal ions in surface water continues to be the most pervasive environmental issues of present time (Hotton and Symon, 1986; Nriagu, 1988). Chromium is one of the contaminants, which exists in hexavalent and trivalent forms. Hexavalent form is more toxic (Smith and Lec, 1972) than trivalent and requires more concern. Strong exposure of Cr(VI) causes cancer in digestive tract and lungs (Kaufman, 1970) and may cause epigastric pain, nausea, vomiting, severe diarrhea and hemorrhage (Browning, 1969). It is therefore, essential to remove Cr(VI) from wastewater before disposal. The main sources of chromium(VI) are tannery, paint, ink, dye, and aluminium manufacturing industries etc. Chemical precipitation with lime or caustic soda is one of the common conventional treatments, where recovery of metals or water is not a consideration. However, to effectively decrease metals to acceptable levels by this treatment requires a large excess of chemicals, which generates volumetric sludge and increases the costs of treatment (Spearot and Peck, 1984). Other available treatments such as ion exchange, electrolysis and reverse osmosis require high capital investment and running costs. The process of adsorption is by far the most versatile and widely used technique for the removal
*Author to whom all correspondence should be addressed. Tel.: +91-1332-85801; fax: +91-1332-73560; e-mail: [email protected]
of metal ions. Activated carbon has been the water industrys’ standard adsorbent for the reclamation of municipal and industrial wastewater for potable use for almost three decades (Fornwalt and Hutchins, 1966). Despite its prolific use in the water and waste industries, activated carbon remains an expensive material. In recent years, research interest into the production of low-cost alternatives to activated carbon has grown. It has been demonstrated that biosorption is a potential alternative to traditional treatment processes of metal ions removal (Volesky, 1990). The phenomenon of biosorption has been described in a wide range of non-living biomass like bark (Alves et al., 1993); lignin (Srivastava et al., 1994); and peanut hulls (Periasamy and Namasivayam, 1994) as well as of living biomass like fungi (Lewis and Kriff, 1988; Matheickal et al., 1991; Fourest et al., 1994), bacteria (Scott and Palmer, 1990; Grappelli et al., 1992; Churchill et al., 1995; Chang et al., 1997), yeast (Huang et al., 1990; Volesky et al., 1993), moss (Lee and Low 1989; Low and Lee 1991), aquatic plants (Srivastav et al., 1994) and algae (Xue et al., 1988; Yu et al., 1999). Biosorption utilizes the ability of biological materials to accumulate heavy metals from waste streams by either metabolically mediated, or purely physico-chemical pathways of uptake (Fourest and Roux, 1992). A survey of literature indicated that not much work has been done so far on living biomass for heavy metal removal. Efforts made to use the algae and aquatic plants, moss and fern for heavy metals
4079
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V. K. Gupta et al.
include the use of silica-immobilized algae Chlorella pyrenoidosa at low pH for Cr(VI) (Greene et al., 1987); Chlaymydomonas rheinhardii for Cu(II) and Cd(II) (Xue et al., 1988); pretreated biomass of nine common species of marine macro algae for lead(II), copper(II) and cadmium(II) (Yu et al., 1999); marine alga Durvillaea potatorum for cadmium(II) (Matheickal et al., 1999); Sphagnum moss peat for Cr(VI) (Sharma and Forster, 1993); Azolla pinnta R. Br. and Lemna minor L. for Pb(II) and Zn(II) (Jain et al., 1990); Azollla filiculoides for Cr(VI) and Zn(II) (Zhao et al., 1997a,b; 1999); Salvinia and Spirodela for chromium and nickel (Srivastav et al., 1994); Sargassum fluitans for Cu(II) in column operation (Kratochvil et al., 1997); water hyacinth (Ipomea aquatica) for Cu, Co and Ni (Low and Lee, 1991); Eichhornia crassipes for As, Cd, Pb and Hg (Chigbo et al., 1982); Eichhornia crassipes for Zn, Cr and Cd (Delgado et al., 1993); Eichhornia maxima for Cu, Ni and Cd from single and mixed metal ion solutions (Williams et al., 1998); and so forth. The purpose of the present study is to evaluate the biosorption capacity of the algae Spirogyra species for Cr(VI) from aqueous solutions. The material is green filamentous algae belonging to the family Chlorophyceae and is available in abundance. Further, no report is available on the use of this material for the adsorption of any metal ion. The adsorption capacities were evaluated from equilibrium adsorption isotherms and the results indicated that the alga is a suitable material for the development of high capacity biosorbent for Cr(VI) removal.
MATERIALS AND METHODS
Materials
Kinetics studies Sorption studies were conducted in 500 ml conical flasks at natural solution pH (5.85). Dry Spirogyra species biomass (1, 1.5, 3, 5, 10, and 15 g/l) were thoroughly mixed individually with 300 ml of chromium solution (25 mg/l) and the suspensions were shaken at room temperature (188C). Samples of 5 ml were collected from the duplicate flasks at required time intervals viz. 30, 60, 90, 120, 150 and 180 min and were filtered through Whattman No. 1 filter paper. The filtrates were analysed for residual chromium concentration in the solution. Similarly, varying initial chromium concentrations (1, 5 and, 15 mg/l) were taken for different algal doses with same interval of contact time as above. As the sorption studies have been carried out using adsorption technique, the following mathematical relation between contact time and percent removal has been used to find out adsorption kinetics constant for algae R ¼ a ðtÞb
where, R is percent removal of Chromium, a and b are the constants and t is the contact time in minutes. The linearized relationship of the equation (1) can be expressed as log R ¼ log a þ b log t
pH measurements were made using a pH meter (model CT No. CL46, Toshniwal, India). The chromium was determined after acid digestion (HNO3–HClO4) and was analysed using an Instrumentation Laboratory, atomic absorption spectrophotometer model Z-7000 (Hitachi, Japan) at a wavelength of 359.3 nm.
ð2Þ
Adsorption isotherms Batch sorption experiments were carried out in 250 ml conical flask at 188C on a rotary shaker for 120 min. The dry biomass (5, 10 and 15 g/l) was thoroughly mixed with 100 ml of chromium solutions. The isotherm studies were performed by varying the initial chromium concentrations from 1 to 25 mg/l at a pH of 1.0, 2.0, 3.0, 4.0 and 5.0, respectively. The pH values were adjusted using 0.1 M HCl or NaOH before addition of biomass and were maintained throughout the experiment. After shaking the flasks for 120 min, the reaction mixture was analysed for residual chromium concentration. The Langmuir sorption model was adopted for the estimation of maximum chromium uptake (Xm ) where they could not be reached in the experiment (Gosset et al., 1986; Holan et al., 1993).
All reagents used were of AR grade either from Merck, Germany or s:d.Fine-CHEM Ltd., India. Equipment
ð1Þ
1=qe ¼ 1=ðXm bCe Þ þ 1=Xm
ð3Þ
where Xm and b are Langmuir constants, indicative of maximum adsorption capacity and a measure of adsorption energy, respectively. qe is the metal adsorption in mg/g of dryweight biomass and Ce is the equilibrium chromium concentration (mg/l).
RESULTS AND DISCUSSION
Kinetic studies Biomass Fresh algal biomass of Spirogyra species was collected from the concrete curing tanks in the premises of Civil Engineering Department, University of Roorkee, Roorkee, India. Before use, it was washed with distilled water to remove dirt and was kept on a filter paper to reduce the water content. After this, the biomass was sun dried for 6 h and milled to a gritty consistency. The biomass was sieved to select particles between 2–3 mm in size for use. Preparation of synthetic sample A stock solution of hexavalent chromium (50 mg/l) was prepared in distilled water with potassium dichromate. All working solutions of varying concentrations were obtained by diluting the stock solution with distilled water.
The results of percent chromium adsorption as a function of time at different algal doses have been shown plotted in Figs 1–4. All the figures show that the sorption of Cr(VI) increases (at varying initial concentrations with various algal doses of 1–15 g/l) with time from 0 to 120 min and after that becomes almost constant up to the end of the experiment (180 min). The removal of Cr(VI) ranges from 12% to 30% at 120 min with various algal doses. It can be concluded that the rate of Cr(VI) binding with algal biomass is more at initial stages, which gradually decreases and remains almost constant after an optimum period of 120 min.
Biosorption of chromium (VI) from aqueous solutions by Spirogyra Sps.
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Fig. 1. Effect of contact time on the sorption of Cr(VI) by Spirogyra at natural pH.
Fig. 3. Effect of contact time on the sorption of Cr(VI) by Spirogyra at natural pH.
Fig. 2. Effect of contact time on the sorption of Cr(VI) by Spirogyra at natural pH.
Fig. 4. Effect of contact time on the sorption of Cr(VI) by Spirogyra at natural pH.
All the figures shows that a linear relationship exist in percent removal of Cr(VI) and contact time. Hence equation (1) was fitted in the experimental data and constants ‘a’ and ‘b’ were calculated and values are shown in Table 1. The values of ‘a’ ranges from 4.36 to 12.02. It is clear from the table that with decrease in algal dose for same initial Cr(VI) concentration, value of ‘a’ decreases, which suggests that with the decrease in algal dose, adsorption capacity also decreases. The value of ‘a’ is highest at Cr(VI) concentration of 5 mg/l with an algal dose of 5 g/l, suggesting these as optimum condition for the adsorbent as well as adsorbate. The value of ‘b’ ranges from 0.303 to 0.61. The low values of ‘b’ suggest that with
increase in time, rate of percentage removal decreases. Effect of pH Earlier studies have indicated that solution pH is an important parameter affecting biosorption of heavy metal ions (Matheikal et al., 1991; Fourest et al., 1994; and Matheikal and Yu, 1996). Cr(VI) removal was studied as a function of pH at various algal doses and the results are shown in Figs 5–12. It is clear from these figures that the percent adsorption of Cr(VI) increases with increase in pH from pH 1.0 to 2.0 and thereafter decreases with further increase in pH. It is important to mention that the
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V. K. Gupta et al. Table 1. Values of adsorption kinetic constant
Cr(VI) (mg/l)
Algal dose (g/l)
Log a
a
b
25
15 10 5
0.86 0.81 0.64
7.24 6.52 4.36
0.50 0.51 0.61
15
10 5 3
1.03 0.92 0.80
10.72 8.32 6.31
0.45 0.57 0.47
5
5 3 1.5
1.08 1.04 0.80
12.02 10.96 6.31
0.47 0.30 0.35
1
3 1.5 1
0.96 0.77 0.68
9.12 5.89 4.79
0.43 0.41 0.45
Fig. 5. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 7. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 6. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 8. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Biosorption of chromium (VI) from aqueous solutions by Spirogyra Sps.
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Fig. 9. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 11. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 10. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
Fig. 12. Effect of pH on sorption of Cr(VI) by Spirogyra after 120 min of contact time.
maximum adsorption at all the concentrations takes place at pH 2.0. Further, these figures also show that maximum adsorption (96%) takes place at an algal dose of 5 g/l as well as with 5 mg/l of initial Cr(VI) concentration. This behavior can be explained considering the nature of the biosorbent at different pH in metal adsorption. The cell wall of Spirogyra species contains a large number of surface functional groups. The pH dependence of metal adsorption can largely be related to type and ionic state of these functional groups and also on the metal chemistry in solution (Matheickal et al., 1999). Adsorption of Cr(VI) below pH 3.0 (maximum at pH 2.0) suggests that the negatively charged chromium species (chromate/
dichromate in the sample solution) bind through electrostatic attraction to positively charged functional groups on the surface of algal cell wall because at this pH more functional groups carrying positive charges would be exposed. But at pH above 3.0, it seems that algal cell wall possesses more functional groups carrying a net negative charge which tends to repulse the anions. However, there is removal above pH 3.0 also, as is indicated by the Figs 5–12, but the rate of removal is considerably reduced. Hence, it could be said that above pH 3.0, other mechanism like physical adsorption on the surface of sorbent could have taken an important role in sorbing Cr(VI) and exchange mechanism might have reduced (Greene et al., 1987).
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V. K. Gupta et al. Table 2. Langmuir parameters for adsorption isotherms
pH
Xm (mg metal/kg of dry weight biomass 103 l/kg)
b ( 102 l/mg)
Bio-concentration factor ( 103 l/kg)
7.6 14.70 12.35 5.46 3.38
15.56 19.61 18.83 13.84 6.24
12.16 70.00 41.86 4.96 1.35
1 2 3 4 5
Adsorption Isotherms The chromium sorption isotherms followed the Langmuir model (equation (3)) well, as shown by high values of the correlation coefficient (r2 ) given in Table 2 alongwith the Langmuir constants. Since solution pH has a significant effect on adsorption equilibrium, the Cr(VI) removal was evaluated by adsorption isotherms obtained at a number of different equilibrium solution pH values at an optimum algal dose of 5 g/l. The maximum Cr(VI) adsorption at an optimum pH of 2.0 is 14.7 103 mg metal/kg of dry weight biomass (Table 2), which is much higher than those of most other types of sorbent reported earlier and comparable to commercial ion exchange resin capacities. The Langmuir constant b can serve as an indicator of isotherm rise in the region of lower residual metal concentrations, which reflects the strength or affinity of the sorbent for the solute (Holan et al., 1993). It was found to decrease with increase in pH from 2.0 to 5.0, which implies that the removal of Cr(VI) at lower pH could be more complete than that at a high pH. The values of bioconcentration factor are also calculated and given in Table 2. The value of this factor under optimum conditions is 70 103 l/kg. This value further confirms the affinity of the biosorbent for Cr(VI).
CONCLUSIONS
The data from batch studies on the biosorption of Cr(VI) on algae Spirogyra species provided fundamental information in terms of optimum pH, optimum algal dose for maximum removal of chromium from the solution. The maximum chromium removal was found to be 14.7 103 mg metal/ kg of dry weight biomass at a pH of 2.0 in 120 min with 5 mg/l of initial concentration. The decreased affinity of the biomass for metals at high pH can be used as a procedure for biomass regeneration and metal ions recovery. The study also indicated that spirogyra species biomass can be used to develop high capacity biosorbent materials for the removal and recovery of heavy metal ions from the dilute industrial wastewater streams. Further studies are needed in understanding the interaction behavior between the activated biomass and heavy metal ions in batch and column.
r2 0.96 0.99 0.98 0.90 0.90
Acknowledgements}Authors are thankful to Council of Scientific & Industrial research, New Delhi, India for supporting this work.
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