Entrapment of fungus Rhizomucor tauricus, removal of Zn (II) from aqueous solution and spectroscopic characterization PROF A V N SWAMY, JNTUA College of Engg Anantapur A.P. India

Removal of zinc (II) was investigated using an industrial waste fungus Rhizomucor tauricus dead mycelia biomass powder and also live biomass entrapped into alginate gel liquid curing method in the presence of Ca (II) ions.

The effect of initial zinc concentration, pH and temperature on zinc removal has been investigated. The maximum experimental biosorption capacities for entrapped live and dead powdered fungal of Rhizomucor tauricus were found to be ± 4.7 mg Zn (II) g -1 and ± 3.8 mg Zn (II) g -1 respectively.

The kinetics of zinc biosorption was slow; approximately 75% of biosorption takes place in 3 ½ hours and the equilibrium time was noted as 4 for immobilized 3 hrs for dead powdered biomass. The biosorption equilibrium data were well described by Langmuir and Freundlich adsorption isotherms.

The responsible functional groups were aromatic –OH and –NH2 in the biosorption process Since binding capacities were relatively high for both immobilized live and dead powdered fungus forms, those fungal forms could be considered as suitable biosorbents for the removal of Zn (II) in wastewater treatment.

Materials and methods Rhizomucor tauricus MTCC PDA medicum for culture The concentrations of unadsorbed zinc ions in the supernetant liquid was measured by AAS Perkin Elmer AA200 with air acetylene flame with wave number 232 Cs= V(CT-C)/M Metal % removal = (CT-CA)/CT x 100

FTIR The powdered biomass before and after adsorption was air dried at 60C and was analyzed in FTIR ( Perkin Elmer make serial no by potassium bromide pellet method. Wave number 400 to 4000

Biosorption The increase in biosorption of Zn II at high pH is due to ionization of functional groups at cell surface. The adsorption of Zn(II) by immobilized R. tauricus biomass was studied at different metal ion concentrations ranging from 25 to 100 mg L -1 The percent adsorption increased with increasing initial Zn(II) ion concentration.

The temperature also affected the adsorption capacity. Various temperatures from 10 to 50 C studied to know the adsorption on cell surface. With L/s ratio of 10. The adsorption of zn II did not increase with the increase of temperature above 30 C on immobilized Rhizomucor tauricus. The percentage adsorption was little changed from 30 to 50C

adsorption The phenomena of increase in adsorption with increase in temperature may be attributed to increase in active site or decrease in thickness of boundary layer of adsorbent.

Effect of temperature on the adsorption of Zn(II) at pH 6

Temperature effect The temperature of the process also influenced the adsorption capacity. The temperature range, 10 to 50  C (10, 30, and 50  C), was studied with the L/S ratio of 10, while other variables were kept constant. Increased the percent adsorption of Zn(II) on immobilized R. tauricus biomass was observed with increasing temperature from 10 ± 1  C to 50 ± 1  C.

Contd..tempeature effect Increases in percent adsorption with temperature may (Fig. 5) be attributed to either an increase in the number of active surface sites available for adsorption on the adsorbent. The similiar results were drawn in the case of Penicillium simplicissimum (Ting et al. 2008) and R. oligosporus (Duygu et al. 2008);

Increase I binding sites that is the increase in metal uptake at increased temperature is due to either higher affinity of sites for the metal or an increase in binding sites on relevant biomass.

Effect of biomass dosage on the adsorption of Zn(II) at pH 6

Biomass loading The biomass loading was studied with Zn(II) from 100 to 500 mg, while other variables were kept constant. The weight of biomass beads significantly influenced the extent of Zn(II) biosorption; increase in the biomass quantity decreased the metal uptake. Variation of metal concentration in the immobilized beads with aqueous metal concentration at different pH values is shown plotted in Fig. at 30  C.

Fig.6 Fig. 6 shows that all the curves have the same trend, i.e. an initial quick decrease followed by a final stability, with the increasing of biomass dose. This was due to the interference between binding sites and higher biomass dose or insufficiency of metal ions in solution with respect to available binding sites (Rome and Gadd, 1987).

Contd.. The similiar results were reported for Zn(II) on Penicillium simplicissimum (Ting et al. 2008). These results may be explained that the initial metal concentration provides a driving force to overcome all mass transfer resistances between the biosorbent and biosorption medium.

Freundlich isotherm The Freundlich adsorption isotherm was proposed by Boedecker and was later modified by Freundlich (1926). The Freundlich adsorption equation can be written as: (3)

Taking the logarithm on both sides, one obtains

Contd.. where q e is equilibrium adsorption capacity (mg g -1 ), C e is the equilibrium concentration of the adsorbate in solution, and K f and n f are constants related to the adsorption process such as adsorption capacity and intensity, respectively.

Fig. 7. Freundlich plot for Zn(II) on Rhizomucor tauricus beads at different pH values

Fig.7 Figure 7 shows that the data were well fitted to the Freundlich equation. The constant n is found to be independent of pH, while the constant K f varies with pH. This is also suggestive that the metal ion under study could well be separated from its aqueous solution with high adsorption capacity.

Contd.. The most widely used isotherm equation for modeling equilibrium is the Langmuir equation, which is valid for monolayer sorption onto a surface with a finite number of identical sites. A basic assumption of the Langmuir theory is that sorption takes place at specific homogeneous sites within the adsorbent.

Langmuir This model can be written in non-linear form (Langmuir 1918), and it is represented by the equation,

Contd.. where q m is the maximum amount of the metal ion per unit weight of adsorbent to form a complete monolayer on the surface bound at high C A (mg/g), and b is a constant that accounts for the affinity of the binding sites (L/mg). q m represents the limiting adsorption capacity when the surface is fully covered with metal ions and helps in the evaluation of adsorption performance, particularly in cases where the sorbent did not reach its full saturation during contact.

Contd.. From the plots between (C e /q e ) and C e, the slope (1/q m ) and the intercept (1/b) can be calculated.

Contd. langmuir The Langmuir adsorption constants evaluated from the isotherms at different temperatures with correlation coefficients are presented in Table 1. From the Langmuir isotherm for cadmium, the biosorption affinity constants b and maximum capacity (q m ) to form a complete monolayer on to the surface of the R. tauricus biomass at 30  C were estimated as (L mg -1 ) and mg g -1, respectively, with R indicating the present sorption data could be best represented by the Langmuir model.

Constants at different pH values S. No.IsothermParameterpH 3pH 5pH 6pH 7 1Experimentalq max (mg g -1 )94 2FreundlichN K f (mg g −1 ) R2R Langmuirq max (mg g −1 ) b (mg −1 ) R2R Table 1. The Constants Obtained From the Isotherm Models at Different Initial pH Values

FTIR analysis The FTIR spectroscopic analysis of the biomass, dead powder of Rhizomucor tauricus before adsorption of heavy metal ions (Fig. 9) indicated broad adsorption band at Cm -1, representing –OH and -NH stretching, Cm -1 and Cm -1 represented –CH stretching. The absorption band at Cm -1 could be attributed to C=O group of carboxylic acid and absorption band at Cm -1 representing carboxylate group. Further at Cm -1 indicating –OH group of sugars and Cm -1 and Cm -1 are representing amide C-N stretching and –P=O stretching respectively.

Fig. FTIR spectra of R.tauricus (a) before loading (b) after loading of Zn(II) ions

Contd.. Fungus, Rhizomucor tauricus after adsorption of Zn(II) heavy metal ions revealed that the main functional groups –COOH, -COO-, -NH and –OH were involved in metal complexation.

CONCLUSIONS The maximum experimental biosorption capacities for entrapped live and dead powdered fungal of Rhizomucor tauricus were found to be ± 4.7 mg Zn (II) g -1 and ± 3.8 mg Zn (II) g -1 respectively. The kinetics of zinc biosorption was slow; approximately 75% of biosorption takes place in 3 ½ hrs and equilibrium was time 4 hrs and 3 hrs for immobilized biomass and dead powdered biomass respectively. The biosorption equilibrium data were well described by Langmuir and Freundlich adsorption isotherms. The responsible functional groups were aromatic –OH and – NH 2 in the biosorption process.