Biosorption of mercury from aqueous solution by Ulva lactuca biomass

Short Communication

Biosorption of mercury from aqueous solution by Ulva lactuca biomass

Youssef Zeroual

, Adnane Moutaouakkil

, Fatima Zohra Dzairi

, Mohamed Talbi

, Park Ung Chung

, Kangmin Lee

, Mohamed Blaghen

aLaboratory of Microbiology, Biotechnology and Environment, Faculty of Sciences A€ıın chock, University Hassan II-A€ıın chock, Km 8 Route d’El Jadida, B.P. 5366 M^aaarif, Casablanca, Morocco

bLaboratory of Analytical Chemistry, University Hassan II-Mohammedia, Faculty of Sciences Ben Msik, Casablanca, Morocco

cLaboratory of Biochemistry, Chonbuk National University, Chonju 561-576, South Korea

dLaboratory of Enzyme Technology, Chonbuk National University, Chonju 561-576, South Korea Received 25 December 2002; received in revised form 22 March 2003; accepted 26 March 2003

Abstract

The mercury biosorption onto non-living protonated biomass of

from aqueous solutions, was investigated. Batch equilibrium tests showed that at pH 3.5, 5.5 and 7 the maxima of mercury uptake values, according to Langmuir adsorption isotherm, were 27.24, 84.74 and 149.25 mg/g, respectively. The ability of

biomass to adsorb mercury in fixed-bed column, was investigated as well. The influence of column bed height, flow rate and effluent initial concentration of metal was studied. The adsorbed metal ions were easily desorbed from the algal biomass with 0.3 N H

SO

solution. After acid desorption and regeneration with distilled water, the biomass could be reused for other biosorption assays with similar performances.

Ó

2003 Elsevier Ltd. All rights reserved.

Keywords:Biosorption; Mercury removal;Ulva lactuca; Fixed-bed column

1. Introduction

Mercury is one of the most toxic heavy metals re- leased in the environment (Shaolin and David, 1997;

Zilloux et al., 1993). The use of inexpensive biological materials, such as bacteria, fungi and algae, for remov- ing and recovering heavy metals from contaminated industrial effluents has emerged as a potential alternative method to conventional techniques, which may be ex- pensive and ineffective (Chang and Hong, 1994; Kra- tochvil et al., 1997).

Marine algae, a renewable natural biomass prolifer- ate ubiquitously and abundantly in the littoral zones of world oceans often posing environmental nuisance.

These biomasses have attracted the attention of many

investigators as organisms to be tested and used as new supports to concentrate and adsorb metal ions (Hamdy, 2000; Valdman et al., 2001).

Biosorption of metals consists in an adsorptive bind- ing of metals to inactive dead biomass, using purely physicochemical pathways of uptake (Tsezos and Vole- sky, 1981). The implied mechanisms in biosorption differ qualitatively and quantitatively according to the type of biomass, its origin and its processing (Volesky and Kuyucak, 1988).

This work aimed to perform an experimental study on mercury removal from synthetic mercurial water using Ulva lactuca as biosorbent biomass. In this work, basic parameters of mercury biosorption equilibrium were determined in batch stirred reactor and the bio- sorption–desorption in a flow-through fixed-bed column was examined; the experiments were carried out to en- hance the effect of important design parameters such as column bed height, flow rate and initial concentration of mercurial solution.

*Corresponding author.

E-mail address:blaghen@hotmail.com(M. Blaghen).

0960-8524/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.

doi:10.1016/S0960-8524(03)00122-6

Bioresource Technology 90 (2003) 349–351

2. Methods

2.1. Biosorbent preparation

Ulva lactuca, fresh seaweed biomass was collected from Moroccan Atlantic coast at Casablanca region.

The algal samples were washed to remove salts and ex- traneous matters. The washed algae were then air-dried.

Protonated biomass was prepared by washing the algae with 0.3 N H

SO

, after 3 h of acid contact the biomass was rinsed many times with distilled water. The pre- treated biomass was then dried overnight at 50 °C.

2.2. Equilibrium sorption experiments

Solutions of Hg

in distilled water were prepared using HgCl

. One hundred mg of dried biomass was combined with 100 ml of metal solution in 250 ml Erlenmeyer flasks. The flasks were placed on a shaker with constant speed of 100 rpm and left to equilibrate for 2 h at 25 °C. Mercury uptakes were determined by calculating the difference of metal concentration in ini- tial and final solutions. The solution pH before and during the sorption tests was adjusted with 1 mM NaOH and 1 mM H

SO

solutions.

Aliquots were collected at pre-defined time intervals, centrifuged and the amount of mercury in the superna- tant was determined by flameless atomic absorption spectrophotometer MAS 50 (Mercury Analyzer System, Bacharach, USA).

2.3. Sorption and desorption in fixed-bed column reactor The biosorption process was carried out in a fixed- bed column reactor with an internal diameter of 3 cm and 45 cm in length. Mercurial synthetic aqueous solu- tions were percolated along the adsorbent stationary bed of U. lactuca biomass. The flow rate was regulated with a variable peristaltic pump. Samples were taken from downstream of the column at different time inter- vals by a fraction collector and analyzed by atomic ab- sorption. The experiments were pursued until column saturation. The mercury loaded biosorbent was regen- erated with 0.3 N H

SO

. After the column regenera- tion, the adsorption studies were carried out, this cycle of adsorption–desorption was repeated at least five times to check biosorbent adsorption capacity.

3. Results and discussion

The kinetic of mercury biosorption by native and protonated biomass of U. lactuca was investigated. The sorption rate could be divided into two stages: a fast initial rate followed by a much slower sorption rate. The fast initial metal sorption rate was attributed to the

surface binding by natural particles and the following slower sorption was attributed to the interior penetra- tion (Khummongol et al., 1982; Lodi et al., 1998). More than 90% of the mercury uptake occurred within 20 min and equilibrium was reached in 40 min. The use of protonated biomass gives sorption rates more important than those obtained with native biomass. This can be explained by the fact that the acid treatment of algal biomass allows the elimination of the impurities that can occupy the binding sites of mercury such as Ca

, Mg

, Na

, . . .

Mercury adsorption by protonated biomass of U.

lactuca as a function of solution pH was studied. The mercury biosorption rate on U. lactuca biomass was strongly influenced by the sorption system pH value.

Contrary to the results obtained by Darnall et al. (1986) and Greene et al. (1987) who reported that biosorption of Hg

, Ag

, Au

on Chlorella vulgaris biomass was pH independent in the range between 2 and 7. At higher pH values, the mercury concentration decreased at shorter contact time. The pH dependence of heavy metal uptake could be largely related to the various functional groups on the algal cell surface and the metal solution chemistry (Kuyucak and Volesky, 1988; Fourest and Roux, 1992; Pinghe et al., 1999).

The maximum uptake capacity q

and the equilib- rium constants b in Langmuir model as well as k and n in Freundlich model, were regressed from experimental data at various pH values and are listed in Table 1. The adsorption capacity at pH 7 was fivefold higher than that at pH 3.5 which dropped from 149.25 to 27.24 mg/g when pH decreased from pH 7 to 3.5.

Biosorption of mercury on protonated U. lactuca was also studied in a packed biomass column. Adsorption breakthrough curves obtained at different flow rates, represented in Fig. 1, indicated that this parameter af- fects directly the efficiency of the treatment and the treated effluent volume. This latter decreases when the flow rate increases. The time required for detection of mercury breakthrough point is 2.7 h at flow rate of 12 ml/min and passes to 1.18 h at a flow rate of 20 ml/min.

This behavior is due to the low quantity of metal ions passing through the column and to the short residence time of the solute in column (Aksu and Kutsal, 1998;

Zulfadhly et al., 2001).

Table 1

Regressed Langmuir and Freundlich sorption isotherm model para- meters

Langmuir parameters Freundlich parameters qmax

(mg/g)

b(mg/L)¹ r² K n¹ r²

pH 3.5 27.247 1.395 0.89 63.09 0.29 0.91 pH 5.5 84.74 1.044 0.98 38.64 0.38 0.93

pH 7 149.25 0.788 0.99 13.57 0.37 0.94

350 Y. Zeroual et al. / Bioresource Technology 90 (2003) 349–351

The effect of bed height on the biosorption of mer- curic ion on U. lactuca biomass was also studied. The uptake capacity of mercury and the breakthrough time increases with the increase of the bed height which leads to an increase in the surface area of adsorbent (Zulfadhly et al., 2001). However different results were obtained when the effect of initial concentration of mercurial solution was investigated. The uptake of mercury decreased with the increase in initial concen- tration of mercurial solution and the biosorbent gets saturated early at high concentration (data not shown).

After saturation, the biomass was eluted using 0.3 N of H

SO

. The obtained results showed that the adsor- bent metal ions can be completely and easily desorbed from the bed in the column. The regenerated biosorbent was reused for up to five adsorption–desorption cycles without loss in the biosorption capacity.

4. Conclusion

This study shows that U. lactuca was found to be an effective biosorbent for mercury removal. The mechanism and kinetics of mercury biosorption on algal biomass depends on the experimental conditions particularly medium pH and mercury concentration.

The present work demonstrates that mercury can be very effectively removed from the mercurial solution by continuous biosorption process. The biosorbent can be conveniently eluted from the sorption column with a small volume of sulfuric acid. The high efficiency of biosorption and elution, low biomass damage and sta- bility over prolonged operation time make this process

an economical effective alternative technique for mer- cury pollution monitoring.

References

Aksu, Z., Kutsal, T., 1998. Determination of kinetic parameters in the biosorption of copper(II) on Cladophora sp., in a packed bed column reactor. Proc. Biochem. 33 (1), 7–13.

Chang, J.S., Hong, J., 1994. Biosorption of mercury by the inactivated cells of Pseudomonas aeruginosa PU 21 (Rip 64). Biotechnol.

Bioeng. 44, 999–1006.

Darnall, D.W., Greene, B., Henzl, M.T., Hosea, J.M., McPherson, R.A., Sneddon, J., Alexander, M.D., 1986. Selective recovery of gold and other ions from an algal biomass. Environ. Sci. Technol.

20, 206–208.

Fourest, E., Roux, J., 1992. Heavy metal biosorption by fungal mycelial by product: mechanisms and influence of pH. Appl.

Microbiol. Biotechnol. 37, 399–403.

Greene, B., McPherson, R.A., Darnall, D.W., 1987. Algal sorbents for selective metal ion recovery. In: Patterson, J., Pasino, R. (Eds.), Metals Speciation, Separation and Recovery. Lewis, Chelsea, MI.

Hamdy, A.A., 2000. Biosorption of heavy metals by marine algae.

Curr. Microbiol. 41, 232–238.

Khummongol, D., Canterford, G.S., Fryer, C., 1982. Accumulation of heavy metals in unicellular algae. Biotech. Bioeng. 25, 2643–2660.

Kratochvil, D., Volesky, B., Demopoulos, G., 1997. Optimizing Cu removal/recovery in a biosorption column. Water Res. 31 (9), 2327–2339.

Kuyucak, N., Volesky, B., 1988. Biosorbent for recovery of metals from industrial solutions. Biotechnol. Lett. 10, 137–142.

Lodi, A., Solisio, C., Converti, A., Del Borghi, M., 1998. Cadmium, zinc, copper, silver and chromium(III) removal from wastewaters by Sphaerotilus natans. Bioproc. Eng. 19, 197–203.

Pinghe, Y., Qiming, Y., Bo, J., Zhao, L., 1999. Biosorption removal of cadmium from aqueous solution by using pretreated fungal biomass cultured from starch wastewater. Water Res. 33, 1960–

1963.

Shaolin, C., David, B.W., 1997. Construction and characterization of genetically engineered for bioremediation of Hg^2þ contaminated environments. Appl. Environ. Microbiol. 63, 2442–2445.

Tsezos, M., Volesky, B., 1981. Biosorption of uranium and thorium.

Biotechnol. Bioeng. 23, 583–604.

Valdman, E., Erijman, L., Pessoa, F.L.P., Leite, S.G.F., 2001.

Continuous biosorption of Cu and Zn by immobilized waste biomassSargassumsp. Process Biochem. 36, 869–873.

Volesky, B., Kuyucak, N., 1988. Biosorbent for gold. US Patent No.

4,769,233.

Zilloux, E.J., Porcella, D.B., Benott, J.M., 1993. Mercury cycling and effects in freshwater wetland ecosystems. Environ. Toxicol. Chem.

12, 2245–2264.

Zulfadhly, Z., Mashitah, M.D., Bhatia, S., 2001. Heavy metals removal in fixed-bed column by the macro fungus Pycnoporus sanguineus. Environ. Pollut. 112, 463–470.

Fig. 1. Effect of flow rate on the breakthrough profiles for adsorption of mercuryC0¼250 mg/l, pH¼4.5, biomass weight¼15 g (dry).

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