The ability and efficiency of dead and live biomass of five fungal species namely: Aspergillus niger, Penicillium austurianum, Saccharomyces cerevisiae, Mucor arcindloides and Trichoderma reesi to sorb lead ion from aqueous solution were evaluated using batch process. The effect of pH on sorption efficiency was studied at pH of 2, 4, 6 and 7. Modification of the fungal biomass with the least sorption capacity was carried out using a four-step procedure. Three different modifying agents under the optimized experimental conditions were used. The percentage uptake of lead ion by fungi species ranged from: Aspergillus niger: 6.71-64.95% and 66.91-95.27%; Penicillium austurianum: 44.47-98.85% and 75.57-94.21%; Saccharomyces cerevisiae: 52.61-88.68% and 61.20-89.95%; Mucor arcindloides: 83.78-93.13% and 62.91-97.65% and Trichoderma reesi: 52.52-80.70% and 35.31-88.13% for dead and live biomass respectively. Optimal adsorption was observed at pH 7 which decreased in the order pH 7 > 2 > 6 > 4 with the exception of Mucor (pH 7 > 2 > 4 > 6). Modified biomass of Aspergillus niger with oxalic acid, malic acid and ethylenediamine tetraacetic acid (EDTA) recorded 92.84%, 48.11% and 39.83% uptake of Pb respectively which correspond to 69.65%, 41.23% and 29.25% increase when compared to 28.18% of the unmodified biomass. These quantitative adsorptions demonstrate the potential application of modified biomass for the removal of Pb ion from aqueous solution.

All reagents used were of analytical grades. 1000 mg l^-1 of lead standard stock solution (AAS grade) was prepared from reagent grade Pb(NO₃)₂ purchased from Heyns Laboratory; Fonteinbleau, South Africa. Working standard solutions were prepared by dilution of the stock. Deionised water from Millipore Instrument Corporation was used throughout the study. Portable hand-held combo (HI 98830) from Hanna Inc. was used for pH measurements. A Perkin Elmer AA 3030 Flame Atomic Absorption Spectrometer (FAAS) equipped with automatic background corrector was used for all trace metal determinations.

Five different species of fungi namely: Aspergillus niger (TUTC 120), Penicillium sp (TUTC 077), Saccharomyces cerevisiae (TUTC 112), Mucor circinelloides f. circinelloides (CBS 106.18) and Trichoderma reesi (TUTC 101) were used in this study. They were cultivated on Malt Extract Agar (MEA) and the fungal biomasses harvested and incubated with metal ions using 100 ml of 100 mg l^-1 of lead standard in glass stopper 250 ml Erlenmeyer flask. The solution pH in the range of 2, 4, 6 and 7 were evaluated for their influence on metal adsorption. 0.3 g of the powdered biomass was added to the flask and the cell suspension was adequately mixed by incubating and agitating at 150 rpm for 24 hrs at 25ºC. All experiments were carried out in triplicate. Fungal suspension was filtered using 0.45 µm membrane filter and the remaining non-adsorbed lead ion in cell-free filtrate was determined using FAAS. Good linearity of the calibration standards was obtained and triplicate analysis of each sample was carried out together with blank analysis. The amount of metal taken up by the biomass was calculated as the difference between the initial and final concentration of the metal in the aqueous solution.

Modification of the biomass of Aspergillus niger was carried out using oxalic acid, malic acid and ethylenediamine tetraacetic acid (EDTA). About 1 g of powdered biomass were separately placed in three clean 10 ml beakers and slightly moistened with demonized water. 7 ml of 0.05 M solution of EDTA, 0.1 M solution of oxalic and malic acids were separately added to each of the three beakers respectively. The acid/slurry was dried in the oven at 50ºC overnight. The modified dried biomasses were then washed with 20 ml of distilled water to remove unreacted acid until the pH of the filtrate was near neutral. The modified biomass were again dried at 50ºC for 6 hrs, allowed to cool and then gently stirred with glass rod to return them to powdery form. 0.3 g of the modified biomasses was taken through metal adsorption and determination protocols at pH 7 as described earlier.

All reagents used were of analytical grades. 1000 mg l^-1 of lead standard stock solution (AAS grade) was prepared from reagent grade Pb(NO₃)₂ purchased from Heyns Laboratory; Fonteinbleau, South Africa. Working standard solutions were prepared by dilution of the stock. Deionised water from Millipore Instrument Corporation was used throughout the study. Portable hand-held combo (HI 98830) from Hanna Inc. was used for pH measurements. A Perkin Elmer AA 3030 Flame Atomic Absorption Spectrometer (FAAS) equipped with automatic background corrector was used for all trace metal determinations.

Five different species of fungi namely: Aspergillus niger (TUTC 120), Penicillium sp (TUTC 077), Saccharomyces cerevisiae (TUTC 112), Mucor circinelloides f. circinelloides (CBS 106.18) and Trichoderma reesi (TUTC 101) were used in this study. They were cultivated on Malt Extract Agar (MEA) and the fungal biomasses harvested and incubated with metal ions using 100 ml of 100 mg l^-1 of lead standard in glass stopper 250 ml Erlenmeyer flask. The solution pH in the range of 2, 4, 6 and 7 were evaluated for their influence on metal adsorption. 0.3 g of the powdered biomass was added to the flask and the cell suspension was adequately mixed by incubating and agitating at 150 rpm for 24 hrs at 25ºC. All experiments were carried out in triplicate. Fungal suspension was filtered using 0.45 µm membrane filter and the remaining non-adsorbed lead ion in cell-free filtrate was determined using FAAS. Good linearity of the calibration standards was obtained and triplicate analysis of each sample was carried out together with blank analysis. The amount of metal taken up by the biomass was calculated as the difference between the initial and final concentration of the metal in the aqueous solution.

Modification of the biomass of Aspergillus niger was carried out using oxalic acid, malic acid and ethylenediamine tetraacetic acid (EDTA). About 1 g of powdered biomass were separately placed in three clean 10 ml beakers and slightly moistened with demonized water. 7 ml of 0.05 M solution of EDTA, 0.1 M solution of oxalic and malic acids were separately added to each of the three beakers respectively. The acid/slurry was dried in the oven at 50ºC overnight. The modified dried biomasses were then washed with 20 ml of distilled water to remove unreacted acid until the pH of the filtrate was near neutral. The modified biomass were again dried at 50ºC for 6 hrs, allowed to cool and then gently stirred with glass rod to return them to powdery form. 0.3 g of the modified biomasses was taken through metal adsorption and determination protocols at pH 7 as described earlier.

Batch experimental systems were used in the optimization of metal sorption by fungal biomasses with respect to pH. Results of sorption efficiency by both live and dead biomass of each of the evaluated fungi species: Aspergillus niger; Penicillium austurianum; Saccharomyces cerevisiae; Mucor arcindloides and Trichoderma reesi were in the range of 6.71-64.95% and 66.91-95.27%; 44.47-98.85% and 75.57-94.21%; 52.61-88.68% and 61.20-89.95%; 83.78-93.13% and 62.91-97.65% and 52.52-80.70% and 35.31-88.13% for the dead and live biomass respectively across optimized pH of 2, 4, 6 and 7. Quantitative adsorption of lead ion by both live and dead biomass of fungal species was obtained with the exception of dead biomass of Aspergillus niger (6.71). Optimal sorption of lead ion was recorded at pH 7 hence, further optimization of the modified biomass of Aspergillus niger was carried out at this pH. Results of the percentage uptake of Pb ion by unmodified and modified biomass of dead Aspergillus niger using oxalic acid, malic acid and EDTA as modifying agents is presented in Table 1. Modified biomass of Aspergillus niger with oxalic acid, malic acid and ethylenediamine tetraacetic acid (EDTA) recorded 92.84%, 48.11% and 39.83% uptake of Pb respectively which correspond to 69.65%, 41.23% and 29.25% increase when compared to 28.18% of the unmodified biomass. The four-step modification protocol (addition of modifying agent to biomass, drying of biomass at 50ºC for 12 hrs, washing of biomass using distilled water and final drying of biomass at 50ºC for 3-4 hrs) was found to be simple, fast, economical and environmental friendly.

The ability of fungi species to sorb lead ion from aqueous solution through batch experiments was demonstrated. Quantitative adsorption of lead ion by both live and dead biomass of fungal species was obtained with the exception of dead biomass of Aspergillus niger (6.71%) at pH 2. A regular pattern of sorption efficiency among the dead fungi species with respect to pH was observed and the % adsorption decreased in the order pH 7 > 2 > 6 > 4 with the exception of Mucor (pH 7 > 2 > 4 > 6). A new approach to biomass modification protocol was developed which was found to be simple, fast and efficient with respect to sorption of lead ions from aqueous system.

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