194

13 Biosorption of Heavy Metals and Metal-Complexed Dyes Under the Influence

biosorption capacity of about 41.84 mg/g of inactive cell at pH 6. Microalgae also

have the ability to resist zinc ions which is mainly due to the properties of their cell

wall and their ability for phytochelatin production.

13.5.3

Removal of Toxic Heavy Metals by Fungi

Fungal biomass has also revealed a significant potential to remove heavy metals

and radio-nuclides from the polluted water system. The Streptomyces, Rhizopus,

Aspergillus, Penicillium, and Mucor are the different genera of fungi used by various

researchers for the bioremediation of heavy metals [25]. It [26] was reported that

the use of Aspergillus niger for zinc biosorption resulted in a maximum zinc removal

in the pH range of 3–6.5. A dead biomass of Streptomyces rimosus was collected

from the antibiotic fermentation industry, and it was used in the biosorption studies

of zinc and the efficiency of the biosorption was found to be improved after the

modification of the surface of the fungi using 1 mol/l NaOH [25]. Nongrowing

Penicillium spinulosum showed sixfold higher zinc biosorption compared to the

growing cells. The time taken by the nongrowing mycelia for biosorption process

was found to be 60–120 minutes, while, in the case of living cells, the accumulation

of heavy metals depends on the age of the cells. The amount of zinc biosorbed was

high during the lag phase, and the rate of adsorption was decreased at early stages

of growth as well as in stationary phase [1]. The fungal species such as A. niger and

Trichoderma viride also found a similar way of uptake analogy. The biosorption

capability of Penicillium, Rhizopus, and Aspergillus toward different metal ions can

be represented as Fe > Cu > Zn, Ni > Cd, Pb > UO, UO2 > Pb > CD > Zn > Cu and

Fe²⁺ > UO > Cu > Zn.

13.5.4

Biosorption of Heavy Metals Using Yeast

The yeast Saccharomyces cerevisiae attracts more attention among the researchers

for the bioremediation of heavy metals due to its distinctive nature despite of

its average capability of metal uptake. The yeast biomass, which was collected

from the fermentation industries, could bioaccumulate various metal ions such as

Ag⁺, Cd²⁺, Cr³⁺, Cs⁺, Cu²⁺, Ni²⁺, Pb²⁺, Sr²⁺, and Zn²⁺ at different pH [2]. More-

over, the yeast biomass can be easily and quickly parted from processed effluent

because of its self-aggregation properties. Several yeast species such as Candida,

Clavispora, Pichia, Rhodosporidium, Rhodotorula, Sporidiobolus, Debaryomyces,

Leucosporidium, Sporobolomyces, Saccharomyces, Stephanoascus, Trichosporon, and

Yarrowia are found to have higher capability to biodegrade organic contaminants

and bioremediate heavy metals. The S. cerevisiae is used as a model system to study

about mechanisms involved in the interactions between the metal and microbe

at the molecular level. The S. cerevisiae is found to be an excellent biosorbent to

remediate toxic heavy metals such as Zn, Pb, Cu, and Cd [10]. It was observed by

Mapelelo et al. that a maximum biosorption of multi-metal system comprising

Cu²⁺, Cr³⁺, Pb²⁺, Cd²⁺, and Zn²⁺ by S. cerevisiae was occurred at pH 5.