13.5 Microbial Species Used for the Removal of Metals and Metal-Complexed Dyes

193

more than the nonliving cells under the tested conditions. It was found that live cells

actively accumulate 40–50% of zinc and copper with the remaining metal ions being

passively bound onto the bacterium. Similarly, the desorption efficiency achieved

by the living cells was also found to be less than the nonliving cells mainly due to

the enhancement of intracellular accumulation of Cu(II) and Zn(II) by the live cells.

The Cu, Zn, and Cd metals present in the water waste were treated by immobilized

autochthonous microorganism P. veronii 2E [17]. The toxic heavy metal ions are

retained by beads, and the entrapment of bacterial cells in calcium alginate is

futile to progress the heavy metal holding [18]. The performance of biosorption

of zinc by Botrytis cinerea was improved by treating the bacterial cells with heat,

sodium hydroxide, detergent, and acetic acid. The gram-negative microbial species

Pseudomonas aeruginosa secluded from the petroleum site was found to have more

tolerance to the toxic heavy metals such as trivalent chromium, divalent copper,

zinc, and manganese and also it can adapt to higher concentrations (300, 150, 100,

and 320 mg/l, respectively) [19]. In addition to that, the efficacy of biosorption of

zinc by P. aeruginosa AT18 was found to be very effective in single metal system

than multi-metal solution mixture containing Cr³⁺, Cu²⁺, Mn²⁺, and Zn²⁺. It was

reported that the Bacillus thuringiensis could achieve a maximum biosorption of

Zn(II) at pH 6 [20].

13.5.2

Biosorption of Heavy Metals by Algae

Algae play a significant role in the biosorption of toxic heavy metals in aqueous

systems. Different types of brown, green, and red algae have the capability for the

removal of heavy metal effectively. The algal cell wall is mainly composed of cellu-

losic compounds, glycoproteins, amino acids, and polysaccharides [21]. The removal

of copper, zinc, iron, and manganese was investigated using the dead biomass of

Cyanobacterium and Phormidium laminosum, and it was found that the removal

process is very rapid for a single metal at an optimum pH of 7. The biosorbents

modified by dilute acids showed a better performance compared to those treated

with NaOH, NaCl, CaCl2, and ultrapure water. Likewise, the effect of macro algae,

Chaetomorphalinum, on the removal of zinc ion was studied [22] and found that

maximum biosorption of zinc could be achieved at pH 5. Beyond pH 5, biosorp-

tion of zinc sharply declined and attributed to the formation of an anionic form of

zinc hydroxide complexes which restrict the interaction of metals with active sites.

It [20] was reported that maximum biosorption of zinc happens with six types of

algae namely Codium vermilaria, Chondrus crispus, Spirogyra insignis, Asparagop-

sis armata, Ascophyllum nodosum, and Fucus spiralis at pH 5 and 6. Also, there is

the biosorption of zinc by the various algal species such as Chlorella vulgaris, L. tay-

lorii, L. tayloriiphos, Ankistrodesmus densus, and Dunaliella bioculata occurs. The

zinc biosorption studies using Sargassum muticum, Laminaria hyperborea, Bifur-

caria bifurcata, and F. spiralis showed a maximum zinc uptake of 18–32 mg/g at

pH 5 at an initial zinc concentration of about 75 ppm [23]. The biosorption capa-

bility of other algal species such as Sargassum filipendula, Caulepra lentilliferra, and

Codium vermilara was also reported [24]. The S. filipendula showed maximum zinc