*6.3.2. Bacteria as biosorbents*

THE cell surface structure plays a vital role in biosorption. The cell wall of bacteria is primarily made up of peptidoglycan. Different species of bacteria can be classified based on cell wall composition. Two major types of bacteria are present. Gram-positive bacteria contain thick peptidoglycans bridged by amino acids. The teichoic acids present in the cell wall are linked with the lipids of the cytoplasmic membrane by forming lipoteichioc acids which are responsible for strong bonding with the membrane. The presence of phospodiester bonds between the teichoic acid monomers gives an overall negative charge and hence are involved in the biosorption of divalent cations (metal ions). Gram-negative bacteria have a thin cell wall containing a less amount of peptidoglycan. However, the presence of an additional outer layer composed of phospholipids and lipopolysaccharides confers an overall negative charge facilitating metal binding [104]. Most bacteria develop many resistance mechanisms and efficient systems for the removal of metal ions for their survival. Some bacteria produce slime or a capsule-like layer on the surface of cell wall. These are mostly composed of polysaccharides which are charged and help to detoxify metal ions from wastewaters [105]. Because of their high surface to volume ratio and high content of potential active sorption sites, bacteria make excellent biosorbents for sequestering metal ions form industrial effluents. *Enterococcus faecium*, a lactic acid bacterium, was able to biosorb Cu (II) ions from aqueous solutions with the maximum biosorption capacity of 106.4 mg per gram of dry biomass and showed better fit with the Freundlich isotherm model [106]. The dead cells of *Bacillus subtilis* biosorb Cu (II), Fe (II), and Zn (II) from its solutions by 25.86, 21.30, and 26.83%, respectively [107]. **Table 6** summarizes some more examples of bacteria as biosorbents.

## *6.3.3. Fungi as biosorbents*

Fungi are also considered as economic and ecofriendly biosorbents because of characteristic features, that is, easy to grow, high yield of biomass, and ease of modification (chemically and genetically) [120]. The cell wall of fungi shows excellent binding properties because of distinguishing features like chitin, lipids, polyphosphates, and proteins among different species of fungi [121]. The cell wall of fungi is rich in polysaccharides and glycoproteins which contain various metal-binding groups like amines, phosphates, carboxyls, and hydroxyls. The fungal organisms are used in a wide variety of fermentation processes. Hence, they can be easily produced at the industrial level for biosorption of metal ions from a large volume of contaminated water resources. Besides, the biomass can be easily and cheaply obtained from inexpensive growth media or even as byproducts from many fermentation industries. Further, fungi are less sensitive to the variations in nutrients and other process parameters like pH, temperature, and aeration [122]. Because of their filamentous nature, they are easy to separate by means of simple techniques like filtration.

Yeasts are unicellular. Most of the yeast biomass either biosorb a wide range of metals or strictly are specific to a single metal ion. *Saccharomyces cerevisiae* biomass has been widely studied as a yeast biosorbent, with high biosorption capacity [123, 124]. Yeast is also reported to have high bioaccumulation capacity and hence can be used as a suitable biosorbent for the removal of metal ions by growing them in metal-laden solutions. Many works reported that ion exchange was the key mechanism for fungi metal biosorption experiments. When *Saccharomyces cerevisiae* is grown in the media containing zinc in the concentration of 1.4372 g/L, the maximum amount of zinc found in the yeast cell was 1699 g/g of the biomass [125]. The filamentous industrial fungus *Rhizopus cohnii* was used as a biosorbent for the removal of cadmium from wastewater with the maximum biosorption capacity of 40.5 mg/g and the functional groups

**Biosorbent type Metal** 

*Lactobacillus delbruckii bulgaricus, streptococcus thermophilus*

*Bacillus thuringiensis*

*Pseudomonas putida*

*Bacillus licheniformis*

a

*Bacillus thioparans* Cu (II),

*Rhizobium spp* Cd (II),

experiments at laboratory scale.

**ion**

Fe (II), Zn (II)

Pb (II)

Cr (VI), Fe (II), Cu (II)

Co (II)

Indicates the dry weight of the biosorbent; <sup>b</sup>

**Table 6.** Bacterial biomass used for biosorption of metals.

*E. coli* Ni (II) 6.9 mg/gb\* Redlich-

**Biosorption capacity/efficiency (mg/g or %)**

*Trametes versicolor* Cu (II) 140.9 mg/ga\* Langmuir –NH<sup>2</sup>

*Bacillus cereus* Zn (II) 66.6 mg/ga\* Langmuir

**Isotherm model**

and Freundlich

*Bacillus pumilus* Pb (II) 28.06 mg/ga\* Langmuir [109]

100%, 90%a\* Carboxyl

*Bacillus coagulans* Cr (II) 39.9 mg/g\* [112]

Peterson

*Arthrobacter sp* Cu (II) 32.64 mg/ga\* Langmuir [117]

**Functional groups involved**

Application of Biosorption for Removal of Heavy Metals from Wastewater

Amino, carboxyl, hydroxyl, carbonyl

–C=O

and hydroxyl

27.3, 210.1 mg/g\* Langmuir [114]

95%, 52%, 32%b\* [118]

135.3, 167.5 mg/ga\* Langmuir [119]

Indicates the wet weight of the biosorbent; \*

Ni (II) 15.7%a\* Langmuir [113]

Zn 17.7 mg/ga\* [116]

, –OH,

**Mechanism Reference**

http://dx.doi.org/10.5772/intechopen.77315

chemisorption [110]

[108]

83

[111]

Indicates batch biosorption

Physic-chemical adsorption and ion exchange

C–H Ion exchange [115]


a Indicates the dry weight of the biosorbent; <sup>b</sup> Indicates the wet weight of the biosorbent; \* Indicates batch biosorption experiments at laboratory scale.

**Table 6.** Bacterial biomass used for biosorption of metals.

for Pb (II) and Cu (II), respectively. The biosorption process showed the better fit with the Langmuir model, and the mechanism involved for biosorption is physical or ion exchange [95]. A marine algae *Sargassum filipendula* was used as a biosorbent for Cu (II) and Ni (II) ions with biosorption capacity of 1.324 and 1.070 mmol/g. An ion exchange mechanism was involved in biosorption with the Langmuir isotherm model showing the better fit [96]. **Table 5** summarizes

THE cell surface structure plays a vital role in biosorption. The cell wall of bacteria is primarily made up of peptidoglycan. Different species of bacteria can be classified based on cell wall composition. Two major types of bacteria are present. Gram-positive bacteria contain thick peptidoglycans bridged by amino acids. The teichoic acids present in the cell wall are linked with the lipids of the cytoplasmic membrane by forming lipoteichioc acids which are responsible for strong bonding with the membrane. The presence of phospodiester bonds between the teichoic acid monomers gives an overall negative charge and hence are involved in the biosorption of divalent cations (metal ions). Gram-negative bacteria have a thin cell wall containing a less amount of peptidoglycan. However, the presence of an additional outer layer composed of phospholipids and lipopolysaccharides confers an overall negative charge facilitating metal binding [104]. Most bacteria develop many resistance mechanisms and efficient systems for the removal of metal ions for their survival. Some bacteria produce slime or a capsule-like layer on the surface of cell wall. These are mostly composed of polysaccharides which are charged and help to detoxify metal ions from wastewaters [105]. Because of their high surface to volume ratio and high content of potential active sorption sites, bacteria make excellent biosorbents for sequestering metal ions form industrial effluents. *Enterococcus faecium*, a lactic acid bacterium, was able to biosorb Cu (II) ions from aqueous solutions with the maximum biosorption capacity of 106.4 mg per gram of dry biomass and showed better fit with the Freundlich isotherm model [106]. The dead cells of *Bacillus subtilis* biosorb Cu (II), Fe (II), and Zn (II) from its solutions by 25.86, 21.30, and 26.83%,

respectively [107]. **Table 6** summarizes some more examples of bacteria as biosorbents.

Fungi are also considered as economic and ecofriendly biosorbents because of characteristic features, that is, easy to grow, high yield of biomass, and ease of modification (chemically and genetically) [120]. The cell wall of fungi shows excellent binding properties because of distinguishing features like chitin, lipids, polyphosphates, and proteins among different species of fungi [121]. The cell wall of fungi is rich in polysaccharides and glycoproteins which contain various metal-binding groups like amines, phosphates, carboxyls, and hydroxyls. The fungal organisms are used in a wide variety of fermentation processes. Hence, they can be easily produced at the industrial level for biosorption of metal ions from a large volume of contaminated water resources. Besides, the biomass can be easily and cheaply obtained from inexpensive growth media or even as byproducts from many fermentation industries. Further, fungi are less sensitive to the variations in nutrients and other process parameters like pH, temperature, and aeration [122]. Because of their filamentous nature, they are easy to

some more examples of algae as biosorbents.

*6.3.2. Bacteria as biosorbents*

82 Biosorption

*6.3.3. Fungi as biosorbents*

separate by means of simple techniques like filtration.

Yeasts are unicellular. Most of the yeast biomass either biosorb a wide range of metals or strictly are specific to a single metal ion. *Saccharomyces cerevisiae* biomass has been widely studied as a yeast biosorbent, with high biosorption capacity [123, 124]. Yeast is also reported to have high bioaccumulation capacity and hence can be used as a suitable biosorbent for the removal of metal ions by growing them in metal-laden solutions. Many works reported that ion exchange was the key mechanism for fungi metal biosorption experiments. When *Saccharomyces cerevisiae* is grown in the media containing zinc in the concentration of 1.4372 g/L, the maximum amount of zinc found in the yeast cell was 1699 g/g of the biomass [125]. The filamentous industrial fungus *Rhizopus cohnii* was used as a biosorbent for the removal of cadmium from wastewater with the maximum biosorption capacity of 40.5 mg/g and the functional groups


biosorbents are amenable for modification in order to increase the available binding sites and enhance the biosorption capacity leaving low residual metal concentration. A number of methods have been employed for surface modification of microbial biomass. The physical methods of pretreatment include heating, autoclaving, freeze drying, thawing, and lyophilization. Various chemical methods used for the pretreatment include acid or alkali treatment, washing with detergents, treatment with organic chemicals such as formaldehyde, sodium hydroxide, dimethyl sulfoxide, and cross-linking with organic solvents [3]. Physical- or chemical-treated microbial biomass show altered properties of metal biosorption compared to the original biomass. If the biomass is large in size, they are grounded into fine granules and are treated further for efficient biosorption [8]. The characteristic feature of pretreatment is to modify the surface groups either by removing or masking or by exposing the greater number of binding sites [3]. It is also observed that the longer duration of pretreatment can

**Type of biosorbent**

*Bacillus subtilis*

*Penicillium lanosa coeruleum*

*Termitomyces clypeatus*

*Aspergillus niger*

*Aspergillus versicolor*

*Pencillium chrysogenum*

*Anabaena variabilis*

a

*Saccharomyces cerevisiae*

**Type of treatment**

Supercritical CO2, autoclaving

Heat, NaOH, detergent Gulteraldehyde

*Mucor rouxii* 0.5 N NaOH Pb (II).

**Metal ions**

Pb (II)

Pb (II), Cu (II) Ni

Cd (II), Ni (II), Zn (II)

0.5 N NaOH Pb (II), Ni

Alkali Cr (III),

Indicates the dry weight of the biosorbent, \*

(II)

Ni (II), Zn (II)

Acetic acid Cr, Ni 84.60%,

Acid and alkali Cr 100%a\* Langmuir

DMSO Pb (II) 30.6 mg/ga\* Redlich-

**Table 8.** Use of chemically modified (treated) biosorbents for the biosorption of metals.

Ni (II) 98.54%,

Ethanol Cd (II),

**Biosorption capacity/ efficiency (mg/g or %)**

15.63 and 17.5 mg/ga\*

99.2%a\*

127%, 106%, 95%, 162% 72%a\*

66%, 76%, 189%, 120%a\*

27.2, 19.2, 24.5 mg/ga\*

83.10%a\*

and Freundlich

Peterson

**Isotherm model**

**Functional groups involved**

Application of Biosorption for Removal of Heavy Metals from Wastewater

http://dx.doi.org/10.5772/intechopen.77315

85

Carboxyl, phosphate amino, hydroxyl

Amino, carboxyl, phosphate, hydroxyl, carbonyl

80%, 60%a\* [145]

Amino, carboxyl, hydroxyl

Indicates batch biosorption experiments at laboratory scale.

N–H, C–H, C=O, COO– Physical adsorption, ion exchange, complexation, electrostatic attraction

Ion exchange [146]

Langmuir [140]

**Mechanism Reference**

[141]

[142]

[143]

[144]

[147]

[148]

a Indicates the dry weight of the biosorbent; <sup>b</sup> Indicates the wet weight of the biosorbent; \* Indicates batch biosorption experiments at laboratory scale.

**Table 7.** Fungal biomass used for biosorption of metals.

involved in biosorption was carboxyl, amino, and hydroxyl groups. The Langmuir isotherm model showed the better fit with an ion exchange mechanism for biosorption [89]. **Table 7** summarizes some more examples of fungi as biosorbents.
