**4. Time course of Cr (VI) decrease and Cr (III) production**

The ability of the *L. chinensis* Sonn shell to decrease the initial Cr (VI) of 1.0 g/L and Cr (III) production in solution are analyzed. Figure 5 shows that the shell exhibited a remarkable efficiency to diminish Cr (VI) level with the concomitant production of Cr (III) as Cr(OH)3 in the solution (indicated by the formation of a blue-green color and a white precipitate (Cr (OH)3) and his determination for Cromazurol S, (Figures 4 and 6) [19, and 20].

Thus, after 1 h of incubation, the shell biomass caused a drop in Cr (VI) from its initial concentration of 1.0 g/L to almost undetectable levels and the decrease level occurred with no significant change in total Cr content. As expected, total Cr concentration remained constant over time, in solution control. These observations indicate that Litchi shell is able to reduce Cr (VI) to Cr (III) in solution. Furthermore, as the *L. chinensis* Sonn shell contains vitamin C and

**Figure 4.** Formation of blue-green color by different chromium (VI) concentrations at 28 ° C and 60 ° C in the presence of Litchi shell. pH 1.0. 1 g biomass. **1- Chromium (VI) standard solution 2.- Trideionized water 3.- 200 mg/L 4.- 500 mg/L. 5.- 1 000 mg/L**

**Cr (VI) Concentration (mg/L)**

\*\*Not determinated.

of Litchi shell. pH 1.0. 1 g biomass.

**4.1. Effect of biosorbent dose**

**Time (min) 60°C 28°C**

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0\* -------- ------- 200 10 45 300 15 60 400 15 60 500 15 80 1000 20 120 Cystine N.D. \*\* 5 Vitamin C N.D. \*\* 5

**Figure 6.** Cromazurol S Reaction 1.-Trideionized water pH=1.0 2.- K2CrO4 (50 µg/mL) 3.- Cr(NO3)3 9H2O. (50 µg/mL) 4.-

Cr(NO3)3 9H2O. (500 µg/mL) 5.- Problem (50 µg/mL) 6.- Vitamin C (50 µg/mL) 7.- Al2(SO4)3 (50 µg/mL)

**1 2 3 4 5 6 7** 

Removal of Hexavalent Chromium from Solutions and Contaminated Sites by Different Natural Biomasses

**Table 1.** Formation of blue-green color by different chromium (VI) concentrations to 28°C and 60°C, in the presence

The influence of biomass on the removal capacity of Cr (VI) was depicted in Figure 7. If the researchers increase the amount of biomass also increases the removal of Cr (VI) in solution (100% of removal, with 5 g of biomass, 20 minutes), with more biosorption sites of the same, because the amount of added biosorbent determines the number of binding sites available for metal biosorption [27]. Similar results have been reported for modified corn stalks [9], tamarind shell [12], and *Mucor hiemalis* and *Rhizopus nigricans*, although latter with 10 g of biomass [1, 28], but they are different from those reported for biomass wastes from the mandarin (bagasse),

\*Control: 100 mL of trideionized water, pH 1.0. There were no variations in color.

with an optimal concentration of biomass of 100 mg/L [24].

**Figure 5.** Time-course of Cr (VI) decrease and Cr (III) production in solution with 1.0 g/L Cr (VI). 100 rpm, 28°C, pH 1.0

some carbohydrates [32], we found that vitamin C and Cystine quickly reduce Cr (VI) to Cr (III) and could be a very important part in the metal reduction (Table 1), according to some reports in the literature [2, 12, 13, 31, 35, 36, 37, and 38]. There are two mechanisms by which chromate could be reduced to a lower toxic oxidation state by an enzymatic reaction. Currently, we do not know whether the shell biomass used in this study express Cr (VI) reducing enzyme(s). Further studies are necessary to extend our understanding of the effects of coexisting ions on the Cr (VI) reducing activity of the biomass reported in this study. Cr (VI) reducing capability has been described in some reports in the literature [2, 3, 7, 12, 13, 15, 18, 31, 39, and 40]. Biosorption is the second mechanism by which the chromate concentration could be reduced, because the biomass shell can be regarded as a mosaic of different groups that could form coordination complexes with metals and our observations are like to the most of the reports [2, 3, 7, 12, 15, 18, 39, and 40].

Removal of Hexavalent Chromium from Solutions and Contaminated Sites by Different Natural Biomasses http://dx.doi.org/10.5772/56152 213

**Figure 6.** Cromazurol S Reaction 1.-Trideionized water pH=1.0 2.- K2CrO4 (50 µg/mL) 3.- Cr(NO3)3 9H2O. (50 µg/mL) 4.- Cr(NO3)3 9H2O. (500 µg/mL) 5.- Problem (50 µg/mL) 6.- Vitamin C (50 µg/mL) 7.- Al2(SO4)3 (50 µg/mL)


\*Control: 100 mL of trideionized water, pH 1.0. There were no variations in color.

\*\*Not determinated.

some carbohydrates [32], we found that vitamin C and Cystine quickly reduce Cr (VI) to Cr (III) and could be a very important part in the metal reduction (Table 1), according to some reports in the literature [2, 12, 13, 31, 35, 36, 37, and 38]. There are two mechanisms by which chromate could be reduced to a lower toxic oxidation state by an enzymatic reaction. Currently, we do not know whether the shell biomass used in this study express Cr (VI) reducing enzyme(s). Further studies are necessary to extend our understanding of the effects of coexisting ions on the Cr (VI) reducing activity of the biomass reported in this study. Cr (VI) reducing capability has been described in some reports in the literature [2, 3, 7, 12, 13, 15, 18, 31, 39, and 40]. Biosorption is the second mechanism by which the chromate concentration could be reduced, because the biomass shell can be regarded as a mosaic of different groups that could form coordination complexes with metals and our observations are like to the most

**Figure 5.** Time-course of Cr (VI) decrease and Cr (III) production in solution with 1.0 g/L Cr (VI). 100 rpm, 28°C, pH 1.0

0 10 20 30 40 50 60 70

**Time (min)**

% de Cr (VI) % de Cr total % de Cr (III)

**Cr (III) production** 

**Figure 4.** Formation of blue-green color by different chromium (VI) concentrations at 28 ° C and 60 ° C in the presence of Litchi shell. pH 1.0. 1 g biomass. **1- Chromium (VI) standard solution 2.- Trideionized water 3.- 200 mg/L 4.-**

**<sup>1</sup> <sup>2</sup> <sup>3</sup> <sup>4</sup> <sup>5</sup>**

**500 mg/L. 5.- 1 000 mg/L**

of the reports [2, 3, 7, 12, 15, 18, 39, and 40].

**Cr (VI) in solutión**

212 Applied Bioremediation - Active and Passive Approaches

**Table 1.** Formation of blue-green color by different chromium (VI) concentrations to 28°C and 60°C, in the presence of Litchi shell. pH 1.0. 1 g biomass.

#### **4.1. Effect of biosorbent dose**

The influence of biomass on the removal capacity of Cr (VI) was depicted in Figure 7. If the researchers increase the amount of biomass also increases the removal of Cr (VI) in solution (100% of removal, with 5 g of biomass, 20 minutes), with more biosorption sites of the same, because the amount of added biosorbent determines the number of binding sites available for metal biosorption [27]. Similar results have been reported for modified corn stalks [9], tamarind shell [12], and *Mucor hiemalis* and *Rhizopus nigricans*, although latter with 10 g of biomass [1, 28], but they are different from those reported for biomass wastes from the mandarin (bagasse), with an optimal concentration of biomass of 100 mg/L [24].

**4.3. Cr (VI) Removal by different biomasses**

tosan [41] and 1 mg/L for cellulose acetate [42].

Percentage of remotion of Cr (VI)

the soil and water.

peel 28°C.

dry weight of mycelium in 7 days.

The researchers studied the Cr (VI) (100 mg/L) removal, with 1 g of different biomass. Litchi shell was the most efficient, because in 10 min at 28°C remove 100% of the metal, followed by xylan and polygalacturonic acid (150 and 300 min at 60 °C, respectively) and starch and cellulose were less efficient (43.6% at 28°C and 300 min of incubation and 21.83% at 60°C, at the same time of incubation, respectively) (Figure 9). With respect to other biomasses used, most authors report lower removal efficiencies of metal, for exam‐ ple: 45 mg/L for eucalyptus bark [16], 13.4 and 17.2 mg/L for bagasse and sugar cane pulp, 29 mg/L coconut fibers, 8.66 mg/L for wool [22], 25 and 250 mg/L of chitin and chi‐

Removal of Hexavalent Chromium from Solutions and Contaminated Sites by Different Natural Biomasses

Figure 9.- Chromium (VI) removal by different biomasses. 100 mg/L Cr (VI). 1.0 g biomass. pH 1.0. 100 rpm. 60°C, Litchi peel 28°C.

**Figure 9.** Chromium (VI) removal by different biomasses. 100 mg/L Cr (VI). 1.0 g biomass. pH 1.0. 100 rpm. 60°C, Litchi

Litchi peel Paecilomyces sp Xylan

Paecilomyces sp

Polygalacturonic acid Mannose Galactose Chitosan Chitin Inulin Cellulose Pectin

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215

Time (min)

Starch 10 60 150 300 300 300 300 300 300 300 300 0

The researchers adapted a water-phase bioremediation assay to explore possible usefulness of L. chinensis Sonn shell, for eliminating Cr (VI) from industrial wastes, the biomass (5 g) was incubated with 20 and non-sterilized contaminated soil containing 297 mg Cr (VI)/g, suspended in trideionized water, and 100 mL of contaminated water with 373 mg/Cr (VI) /L. It was observed that after five and six days of incubation with the biomass, the Cr (VI) concentration of soil and water samples decrease 100% (Figure 10), and the decrease level occurred without change significant in total Cr content, during the experiments. In the experiment carried out in the absence of the biomass, the Cr (VI) concentration of the soil and water samples decreased by about of 18%, and 8%, respectively (date not shown); this might be caused by indigenous microflora and (or) reducing components present in

The researchers adapted a water-phase bioremediation assay to explore possible usefulness of *L. chinensis* Sonn shell, for eliminating Cr (VI) from industrial wastes, the biomass (5 g) was incubated with 20 and non-sterilized contaminated soil containing 297 mg Cr (VI)/g, suspend‐ ed in trideionized water, and 100 mL of contaminated water with 373 mg/Cr (VI) /L. It was observed that after five and six days of incubation with the biomass, the Cr (VI) concentration of soil and water samples decrease 100% (Figure 10), and the decrease level occurred without change significant in total Cr content, during the experiments. In the experiment carried out in the absence of the biomass, the Cr (VI) concentration of the soil and water samples decreased by about of 18%, and 8%, respectively (date not shown); this might be caused by indigenous

The chromium removal abilities of L. chinensis Sonn shell are equal or better than those of other reported biomass, for example tamarind shell [12], M. americana [38], Candida maltosa RR1 [39]. In particular, this biomass was superior to the other biomass because it has the capacity for efficient chromium reduction under acidic conditions. Many of the Cr (VI) reduction studies were carried out at neutral pH [43]. Aspergillus niger also has the ability to reduce and adsorb Cr (VI) [41]. When the initial concentration of Cr (VI) was 500 ppm, A. niger mycelium removal 8.9 mg/L of chromium/g

The chromium removal abilities of *L. chinensis* Sonn shell are equal or better than those of other reported biomass, for example tamarind shell [12], *M. americana* [38], *Candida maltosa* RR1 [39]. In particular, this biomass was superior to the other biomass because it has the capacity for efficient chromium reduction under acidic conditions. Many of the Cr (VI) reduction studies

Removal of Cr (VI) in industrial wastes with Litchi chinensis Sonn shell

microflora and (or) reducing components present in the soil and water.

**4.4. Removal of Cr (VI) in industrial wastes with** *Litchi chinensis Sonn* **shell**

**Figure 7.** Effect of biomass concentration on Chromium (VI) removal by *L. chinensis* Sonn shell. 1 g/L Cr (VI). 28oC. pH 1.0, 100 rpm.

#### **4.2. Cr (VI) Removal in the presence of different heavy metals**

The researchers analyzed whether the presence of different metals interfere with the Cr (VI) removal (500 mg/L) at a pH of 1.0, with 1 g of Litchi shell, finding that none of the added metals (salts of cadmium, copper, zinc and mercury) interferes with the Cr (VI) removal, but in the presence of zinc and mercury takes 10-20 min longer to remove 100% of the metal (Figure 8). This is consistent with many reports in the literature [1, 12, 13, 16, 31, 32, and 33].

**Figure 8.** Effect of different metals concentration on Chromium (VI) removal by *L. chinensis* Sonn shell. 500 mg/L of metal. 1.0 g biomass. pH 1.0. 100 rpm. 28°C

#### **4.3. Cr (VI) Removal by different biomasses**

**Percentage of remotion of Cr (VI)** 

metal. 1.0 g biomass. pH 1.0. 100 rpm. 28°C

**4.2. Cr (VI) Removal in the presence of different heavy metals**

**Time (min)**

**Figure 7.** Effect of biomass concentration on Chromium (VI) removal by *L. chinensis* Sonn shell. 1 g/L Cr (VI). 28oC. pH

The researchers analyzed whether the presence of different metals interfere with the Cr (VI) removal (500 mg/L) at a pH of 1.0, with 1 g of Litchi shell, finding that none of the added metals (salts of cadmium, copper, zinc and mercury) interferes with the Cr (VI) removal, but in the presence of zinc and mercury takes 10-20 min longer to remove 100% of the metal (Figure 8).

0 10 20 30 40 50 60 70 80 90

**Time (min)**

**Figure 8.** Effect of different metals concentration on Chromium (VI) removal by *L. chinensis* Sonn shell. 500 mg/L of

This is consistent with many reports in the literature [1, 12, 13, 16, 31, 32, and 33].

1 g 2 g 3 g 4 g 5 g

> Cr (VI) Cd Cu Zn Hg

**Percentage of Cr (VI) in solution**

214 Applied Bioremediation - Active and Passive Approaches

1.0, 100 rpm.

The researchers studied the Cr (VI) (100 mg/L) removal, with 1 g of different biomass. Litchi shell was the most efficient, because in 10 min at 28°C remove 100% of the metal, followed by xylan and polygalacturonic acid (150 and 300 min at 60 °C, respectively) and starch and cellulose were less efficient (43.6% at 28°C and 300 min of incubation and 21.83% at 60°C, at the same time of incubation, respectively) (Figure 9). With respect to other biomasses used, most authors report lower removal efficiencies of metal, for exam‐ ple: 45 mg/L for eucalyptus bark [16], 13.4 and 17.2 mg/L for bagasse and sugar cane pulp, 29 mg/L coconut fibers, 8.66 mg/L for wool [22], 25 and 250 mg/L of chitin and chi‐ tosan [41] and 1 mg/L for cellulose acetate [42].

Figure 9.- Chromium (VI) removal by different biomasses. 100 mg/L Cr (VI). 1.0 g biomass. pH 1.0. 100 rpm. 60°C, Litchi peel 28°C. **Figure 9.** Chromium (VI) removal by different biomasses. 100 mg/L Cr (VI). 1.0 g biomass. pH 1.0. 100 rpm. 60°C, Litchi peel 28°C.

The researchers adapted a water-phase bioremediation assay to explore possible usefulness of L.

#### Removal of Cr (VI) in industrial wastes with Litchi chinensis Sonn shell **4.4. Removal of Cr (VI) in industrial wastes with** *Litchi chinensis Sonn* **shell**

chinensis Sonn shell, for eliminating Cr (VI) from industrial wastes, the biomass (5 g) was incubated with 20 and non-sterilized contaminated soil containing 297 mg Cr (VI)/g, suspended in trideionized water, and 100 mL of contaminated water with 373 mg/Cr (VI) /L. It was observed that after five and six days of incubation with the biomass, the Cr (VI) concentration of soil and water samples decrease 100% (Figure 10), and the decrease level occurred without change significant in total Cr content, during the experiments. In the experiment carried out in the absence of the biomass, the Cr (VI) concentration of the soil and water samples decreased by about of 18%, and 8%, respectively (date not shown); this might be caused by indigenous microflora and (or) reducing components present in the soil and water. The chromium removal abilities of L. chinensis Sonn shell are equal or better than those of other reported biomass, for example tamarind shell [12], M. americana [38], Candida maltosa RR1 [39]. In particular, this biomass was superior to the other biomass because it has the capacity for efficient chromium reduction under acidic conditions. Many of the Cr (VI) reduction studies were carried out at neutral pH [43]. Aspergillus niger also has the ability to reduce and adsorb Cr (VI) [41]. When the initial concentration of Cr (VI) was 500 ppm, A. niger mycelium removal 8.9 mg/L of chromium/g The researchers adapted a water-phase bioremediation assay to explore possible usefulness of *L. chinensis* Sonn shell, for eliminating Cr (VI) from industrial wastes, the biomass (5 g) was incubated with 20 and non-sterilized contaminated soil containing 297 mg Cr (VI)/g, suspend‐ ed in trideionized water, and 100 mL of contaminated water with 373 mg/Cr (VI) /L. It was observed that after five and six days of incubation with the biomass, the Cr (VI) concentration of soil and water samples decrease 100% (Figure 10), and the decrease level occurred without change significant in total Cr content, during the experiments. In the experiment carried out in the absence of the biomass, the Cr (VI) concentration of the soil and water samples decreased by about of 18%, and 8%, respectively (date not shown); this might be caused by indigenous microflora and (or) reducing components present in the soil and water.

dry weight of mycelium in 7 days. The chromium removal abilities of *L. chinensis* Sonn shell are equal or better than those of other reported biomass, for example tamarind shell [12], *M. americana* [38], *Candida maltosa* RR1 [39]. In particular, this biomass was superior to the other biomass because it has the capacity for efficient chromium reduction under acidic conditions. Many of the Cr (VI) reduction studies were carried out at neutral pH [43]. *Aspergillus niger* also has the ability to reduce and adsorb Cr (VI) [41]. When the initial concentration of Cr (VI) was 500 ppm, *A. niger* mycelium removal 8.9 mg/L of chromium/g dry weight of mycelium in 7 days.

(VI) of a contaminated site, combined with *Ganoderma lucidum*, the latter used to remove by biosorption Cr (III) formed. The results showed that the reduction of 50 mg/L of Cr (VI) by bacteria was about 80%, with 10 g / L of peptone as a source of electrons and a hydraulic retention time of 8 h. The Cr (III) produced was removed using a column with the fungus *G. lucidum* as absorber. Under these conditions, the specific capacity of adsorption of Cr (III) of *G. Lucidum* in the column was 576 mg/g [47]. In other studies, has been tested the addition of carbon sources in contaminated soil analyzed in column, in one of these studies was found that the addition of tryptone soy to floor with 1000 mg/L of Cr (VI) increase reduction ion, due to the action of microorganisms presents in the soil, although such action is not observed in soil with higher concentrations (10.000 mg/L) of Cr (VI) [48]. Another study showed that the addition of nitrate and molasses accelerates the reduction of Cr (VI) to Cr (III) by a native microbial community in microcosms studied, in batch or columns of unsaturated flow, under similar conditions to those of the contaminated zone. In the case of batch microcosms, the presence of such nutrients caused reduction of 87% (67 mg/L of initial concentration) of Cr (VI) present in the beginning of the experiment, the same nutrients, added to a column of unsatu‐ rated flow of 15 cm, added with 65 mg/L of Cr (VI) caused the reduction and immobilization of 10% of metal, in a period of 45 days [49]. Finally, Cardenas-Gonzalez and Acosta-Rodríguez [40], adapted a water-phase bioremediation assay to explore possible usefulness of strain of *Paecilomyces* sp to eliminate Cr (VI) from industrial wastes, the mycelium biomass was incubated with non-sterilized contaminated soil containing 50 mg Cr (VI)/g, suspended in Lee's minimal medium [50] pH 4.0. It was observed that after eight days of incubation with the *Paecilomyces* sp biomass, the Cr (VI) concentration (50 mg/g) of soil sample decrease fully

Removal of Hexavalent Chromium from Solutions and Contaminated Sites by Different Natural Biomasses

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217

**% of Cr (III) production**

Chromium (VI) in solution

Total Chromium

Chromium (III) production

0 1 2 3 4 5 6 7 8 9 10

**Time (weeks)**

**Figure 11.** Bioremediation of Cr (VI) *in situ*, by *M. americana* biomass. 100 Kg of contaminated soil with 345 mg de Cr

(100%).

**% of Cr (VI) in solution**

(VI)/g soil. (20 Kg biomass. 28oC).

**Figure 10.** Chromium (VI) removal in industrial wastes incubated with the biomass. 100 rpm. 28oC. 5 g Litchi biomass. Contaminated soil and water (297 mg/Cr(VI)/g soil] and 373 mL Cr(VI)/L, respectively.

#### **4.5. Biorremediation assay** *in situ*

100 kg of contaminated soil (345 mg Cr(VI)/ g soil), with 20 g of natural biomass of *M. Americana* were incubated in a greenhouse at 28o C. After 10 weeks of incubation, the natural biomass removal 83% of the metal from contaminated soil (Figure 11), without change significant in total Cr content. In the experiment carried out in the absence of the biomass, the Cr (VI) concentration of the soil sample decreased by about of 15% (date not shown); this might be caused by indigenous microflora and (or) reducing components present in the soil, like microorganisms lactic acid producers, which reduce Cr (VI) to Cr (III) (Figure 12). Reports on applications of microorganisms for studies of bioremediation of soils contaminated with chromates are rare. Such study involved the use of *Pseudomona mendocina* for the removal of the metal from cooling tower effluent [44], and soil microcosms [45]. In the first process when carried out in a 20 liter continuous stirred tank reactor removed 25-100 mg chromate/L, in 4.5-8 hours with >99.9% efficiency in the presence of sugarcane molasses as nutrient, and in soil microcosms could immobilize 100 μg (2mM) chromate/g soil in 8 hours by converting into trivalent form, and the chromate contaminated soil, after microbiological treatment, supported growth of wheat seedlings without exerting any toxic effects. Other study involved the use of unidentified bacteria native from the contaminated site, which is used in bioreactors to treat soil contaminated with Cr (VI). It was found that the maximum reduction of Cr (VI) occurred with the use of 15 mg of bacterial biomass/g of soil (wet weight), 50 mg/g of soil molasses as carbon source, the bioreactor operated under these conditions, completely reduced 5.6 mg/Cr (VI)/g of soil at 20 days [46]. In another study using unidentified native bacteria reducing Cr (VI) of a contaminated site, combined with *Ganoderma lucidum*, the latter used to remove by biosorption Cr (III) formed. The results showed that the reduction of 50 mg/L of Cr (VI) by bacteria was about 80%, with 10 g / L of peptone as a source of electrons and a hydraulic retention time of 8 h. The Cr (III) produced was removed using a column with the fungus *G. lucidum* as absorber. Under these conditions, the specific capacity of adsorption of Cr (III) of *G. Lucidum* in the column was 576 mg/g [47]. In other studies, has been tested the addition of carbon sources in contaminated soil analyzed in column, in one of these studies was found that the addition of tryptone soy to floor with 1000 mg/L of Cr (VI) increase reduction ion, due to the action of microorganisms presents in the soil, although such action is not observed in soil with higher concentrations (10.000 mg/L) of Cr (VI) [48]. Another study showed that the addition of nitrate and molasses accelerates the reduction of Cr (VI) to Cr (III) by a native microbial community in microcosms studied, in batch or columns of unsaturated flow, under similar conditions to those of the contaminated zone. In the case of batch microcosms, the presence of such nutrients caused reduction of 87% (67 mg/L of initial concentration) of Cr (VI) present in the beginning of the experiment, the same nutrients, added to a column of unsatu‐ rated flow of 15 cm, added with 65 mg/L of Cr (VI) caused the reduction and immobilization of 10% of metal, in a period of 45 days [49]. Finally, Cardenas-Gonzalez and Acosta-Rodríguez [40], adapted a water-phase bioremediation assay to explore possible usefulness of strain of *Paecilomyces* sp to eliminate Cr (VI) from industrial wastes, the mycelium biomass was incubated with non-sterilized contaminated soil containing 50 mg Cr (VI)/g, suspended in Lee's minimal medium [50] pH 4.0. It was observed that after eight days of incubation with the *Paecilomyces* sp biomass, the Cr (VI) concentration (50 mg/g) of soil sample decrease fully (100%).

were carried out at neutral pH [43]. *Aspergillus niger* also has the ability to reduce and adsorb Cr (VI) [41]. When the initial concentration of Cr (VI) was 500 ppm, *A. niger* mycelium removal

0 2 4 6 8

Contaminated soil

Contaminated water

C. After 10 weeks of incubation, the natural

**Time (days)**

**Figure 10.** Chromium (VI) removal in industrial wastes incubated with the biomass. 100 rpm. 28oC. 5 g Litchi biomass.

100 kg of contaminated soil (345 mg Cr(VI)/ g soil), with 20 g of natural biomass of *M.*

biomass removal 83% of the metal from contaminated soil (Figure 11), without change significant in total Cr content. In the experiment carried out in the absence of the biomass, the Cr (VI) concentration of the soil sample decreased by about of 15% (date not shown); this might be caused by indigenous microflora and (or) reducing components present in the soil, like microorganisms lactic acid producers, which reduce Cr (VI) to Cr (III) (Figure 12). Reports on applications of microorganisms for studies of bioremediation of soils contaminated with chromates are rare. Such study involved the use of *Pseudomona mendocina* for the removal of the metal from cooling tower effluent [44], and soil microcosms [45]. In the first process when carried out in a 20 liter continuous stirred tank reactor removed 25-100 mg chromate/L, in 4.5-8 hours with >99.9% efficiency in the presence of sugarcane molasses as nutrient, and in soil microcosms could immobilize 100 μg (2mM) chromate/g soil in 8 hours by converting into trivalent form, and the chromate contaminated soil, after microbiological treatment, supported growth of wheat seedlings without exerting any toxic effects. Other study involved the use of unidentified bacteria native from the contaminated site, which is used in bioreactors to treat soil contaminated with Cr (VI). It was found that the maximum reduction of Cr (VI) occurred with the use of 15 mg of bacterial biomass/g of soil (wet weight), 50 mg/g of soil molasses as carbon source, the bioreactor operated under these conditions, completely reduced 5.6 mg/Cr (VI)/g of soil at 20 days [46]. In another study using unidentified native bacteria reducing Cr

Contaminated soil and water (297 mg/Cr(VI)/g soil] and 373 mL Cr(VI)/L, respectively.

8.9 mg/L of chromium/g dry weight of mycelium in 7 days.

*Americana* were incubated in a greenhouse at 28o

**Percentage of Cr (VI) in solution**

216 Applied Bioremediation - Active and Passive Approaches

**4.5. Biorremediation assay** *in situ*

**Figure 11.** Bioremediation of Cr (VI) *in situ*, by *M. americana* biomass. 100 Kg of contaminated soil with 345 mg de Cr (VI)/g soil. (20 Kg biomass. 28oC).

**4.7. Biosorption of Chromium (VI) in solution by different natural biomasses**

*Mammea americana*

Not Interfere

Soil: 5 days Water: 6 days

and 60 minutes, respectively), at pH 1.0 at 50o

*Citrus reticulata*

Not Interfere

Soil: 5 days Water: 6 days

**Table 2.** Chromium (VI) removal of 1.0 g/L with different natural biomasses.

*Litchi chinensis*

Not Interfere

Soil: 5 days Water: 6 days

**Parameter**

Incubation time (100 mg/L,28°C)

Temperature (50oC, 1.0 g/L)

Biomass concentration (5 g. 1.0 g/L)

Presence of different heavy metals (500 mg/L)

Reduction of Cr VI to Cr III

Biorremediation of contaminated sites (100%)

Desorption (7 days)

**5. Conclusion**

In Table 2, the researchers show the biosorption of Chromium (VI) *by* the different biomasses analyzed. It was found that the biomass of L*. chinensis* Sonn, *T. indica*, *M. Americana,* and *C. reticulata*, shells were the most efficient at removing the metal in solution (100% at 20, 40, 50

Removal of Hexavalent Chromium from Solutions and Contaminated Sites by Different Natural Biomasses

they can remove it from contaminated industrial wastes, and can be used six times efficiently.

*Citrus sinensis*

Not Interfere

Soil: 5 days Water: 6 days

The use of biomaterials like natural biomasses has demonstrated to be a promising alternative for removal of Chromium hexavalent from aqueous solution. The screening and selection of the most effective biomaterial (biomasses) with sufficiently high metal binding capacity and selectivity for heavy metal ions, in this case, Chromium (VI), are prerequisite for a full process. The natural biomasses showed complete capacity of biosorption and reduction concentrations of 1.0 g/L Cr (VI) in solution after different incubation times, and *L. chinensis* Sonn, *C. reticu‐*

pH optimum 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

*Citrus limonium*

10 min 40 min 50 min 120 min 80 min 60 min 60 min 230 min

35 min 90 min 110 min 120 min 200 min 140 min 80 min 105 min

20 min 60 min 50 min 75 min 85 min 40 min 25 min 600 min

Yes Yes Yes Yes Yes Yes Yes Yes

81.2% 80.1% 78.3% 83% 79.3% 80% 78% 78%

Not Interfere

Soil: 5 days Water: 6 days

C, the biomasses reduce the metal in solution,

Not Interfere Not Interfere

Soil: 5 days Water: 6 days

Soil: 5 days Water: 6 days

*Musa cavendishii*

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*Cuccumis melo* **L.**

219

Not Interfere

Soil: 5 days Water: 6 days

*Tamarindus indica*

**Figure 12.** Chromium (VI) Reduction by lactic acid. 1. - Lactic acid standard solution (85%) 2. - Chromium (VI) standard solution (1.0 g /L). pH= 1.0 3.-100 mg Cr (VI)/L with lactic acid (100 mL) 4. - 1000 mg Cr (VI)/L with lactic acid (100 mL)

#### **4.6. Desorption of Cr (VI) by different solutions**

Furthermore, the researchers examined the ability of different solutions to desorb the metal bioadsorbed (250 mg/L) for the Litchi biomass, obtaining high efficiency with 0.1 N NaOH and 0.5 N (80 and 61% respectively (Figure 13), which are less those reported for desorption of Chromium (VI) with alkaline solutions (100%, pH 9.5), 1.0 N NaOH (95%) and a hot solution of NaOH/Na2CO3 (90%), respectively, [21, 51], and are higher than that reported (14.2%) using 0.2 M NaOH [52]. This indicates that binding of metal to biomass is not as strong and that it can be used up to 6 desorption cycles of removal, which further lowers the metal removal process of niches contaminated with it.

**Figure 13.** Desorption of Chromium (VI) (250 mg/L) by different solutions (1 g biomass. 28°C, 100 rpm)

### **4.7. Biosorption of Chromium (VI) in solution by different natural biomasses**

In Table 2, the researchers show the biosorption of Chromium (VI) *by* the different biomasses analyzed. It was found that the biomass of L*. chinensis* Sonn, *T. indica*, *M. Americana,* and *C. reticulata*, shells were the most efficient at removing the metal in solution (100% at 20, 40, 50 and 60 minutes, respectively), at pH 1.0 at 50o C, the biomasses reduce the metal in solution, they can remove it from contaminated industrial wastes, and can be used six times efficiently.


**Table 2.** Chromium (VI) removal of 1.0 g/L with different natural biomasses.
