The removal of Cr(III) from aqueous Cr(III) using Arthrobacter nicotianae cells was examined. Cr(III) removal was strongly affected by the pH of the solution and the amounts of Cr(III) removed increased as the pH (1 - 5) of the solution increased. The removal of Cr(III) using the cells was also strongly affected by the Cr(III) concentration of the solution, and obeyed the Langmuir isotherm. The percentage of Cr increased as the cell quantity increased, whereas the amount of Cr (μmol/g dry wt. cells) decreased. The removal of Cr(III) using the cells was very fast, and reached an equilibrium within 6 h from the supply of Cr(III) in the solution. A small amount of Cr(III) absorbed by immobilized cells was desorbed at 30 oC; however, most was desorbed at reflux temperature using diluted HCl. Cr(III) adsorption-desorption cycles can be repeated 5 times using immobilized cells. These results have practical implications for industrial wastewater management.
Chromium is used in the textile, leather tanning, electroplating, metal finishing, wood treatment, corrosion control, oxidation, and anodizing industries [
Adsorption is the most effective and widely used technique for the removal of toxic heavy metals from wastewater [
We previously demonstrated that microorganisms are able to remove many toxic and useful metals, such as lithium [
Despite of the Cr(III) removal using persimmon tannin gel under various experimental conditions, little improvement in the removal efficiency has been observed.
Therefore, the removal of Cr(III) using microorganism, Arthrobacter nicotianae which can remove a large amount of metals [
Microorganisms were grown in medium containing 4 g/L meat extract, 5 g/L peptone, and 5 g/L NaCl in deionized water. The cultures of microorganisms, maintained on agar slants, were grown in 300 mL of the medium in a 500 mL flask with continuous shaking (120 rpm) at 30˚C. To ensure a sufficient amount of resting microorganisms after separation from the growth medium, the cultures were grown for 72 h.
Cells were collected by centrifugation (10,000 rpm) at 20˚C for 10 min, washed thoroughly with deionized water, and used in subsequent removal experiments.
Five grams of precultured cells were suspended in 4.5 mL isotonic sodium chloride solution, and 680 mg of acrylamide monomer, 34 mg of N,N’-methy- lene-bis(acrylamide), 0.3 mL of 3-dimethylaminopropionitrile solution (5%), and 0.34 mL of potassium persulfate solution (2.5%) were added to the suspension.
After solidification, the gel was crushed into small pieces (50 - 100 mesh), washed thoroughly with isotonic sodium chloride solution followed by deionized water, and used for adsorption experiments.
Cr(III) nitrate was used. The pH of the solution was adjusted to the desired value (1.0 - 5.0) using 0.1 M HCl. Resting cells (15 mg dry wt. basis) were suspended in 100 mL solutions containing 100 μM (5 ppm) Cr(III) (pH 1 - 5) for 1 h at 30˚C to examine the effect of pH. Similar experiments containing 19 - 960 μM (1.0 - 50 ppm) of Cr(III) (pH 5), or resting cells (5.0 - 60 mg dry wt. basis) were also performed to examine the effect of concentration or cell amount, respectively. Microorganisms were then collected by filtration through a nitrocellulose membrane filter (pore size 0.2 μm). Control studies confirmed that the free metal was not adsorbed on the filter.
The amount of Cr(III) removed by cells was determined by measuring the difference between the initial and final metal content in the filtrate using an atomic absorption quantometer (AA-6300; Shimadzu Corporation, Kyoto, Japan).
Resting cells (15 mg dry wt. basis) were suspended in 100 mL solutions containing 5.0 ppm (100 μM) Cr(III) (pH 5) for 5 min to 24 h at 30˚C.
A. nicotianae cells (15 mg, dry wt. basis) were suspended in 100 mL of a solution (pH 5.0) containing 4 × 10−5 M Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Cr3+ as nitrates for 1 h at 30˚C.
The extent of Cr adsorption/desorption from a Cr(III) nitrate solution using immobilized A. nicotianae cells was investigated. Immobilized A. nicotianae cells (15.4 mg dry wt. cells basis) were suspended with 100 mL of Cr(III) (4.68 ppm, pH 5.0) for 1 h at 30˚C. Immobilized A. nicotianae cells that adsorbed Cr(III) were separated from the suspended solution by filtration through a membrane filter (pore size 0.2 μm) and suspended with diluted HCl or Na2CO3 solution (0.01, 0.1, or 1 M) for 1 h at 30˚C.
Immobilized A. nicotianae cells (15.7 mg dry wt. cells basis) were suspended with 100 mL of Cr(III) (5.19 ppm, pH 5.0) for 1 h at 30˚C. Immobilized A. nicotianae cells that adsorbed Cr(III) were separated following the same method described in Section 2.6 and suspended with diluted HCl (0.1 or 1 M) for 1 h at 30˚C-(refluxed temperature).
Cr(III) solution (5.26 ppm, pH 5.0, 50 mL) was passed through the immobilized A. nicotianae cells (230 mg dry wt. cells basis) column (diameter 8 mm) at 30˚C. Then, immobilized A. nicotianae cells that adsorbed Cr(III) were subjected to desorption by applying 0.1 M HCl at reflux temperature for 1 h using a batch system.
The effect of pH on Cr(III) removal from aqueous Cr(III) as Cr(NO3)3, using A. nicotianae cells was examined. As shown in
In contrast, the zeta potential of A. nicotianae was decreased as the pH of the solution increased [
The effect of Cr(III) concentration on Cr(III) removal was examined. As shown
in
The relationship between the residual Cr(III) concentration in the solution and the amount of Cr(III) removed is shown in
where Q indicates the amount of Cr(III) removed (μmol Cr(III)/g dry wt. cells), Ce is the residual Cr(III) in the solution (μM Cr(III)), and m and n are Langmuir constants. It was estimated that Ce/Q = 1.38 × 10−3 Ce + 2.25 × 10−2. The maximum amount of Cr(III) removed (μmol Cr(III)/g dry wt. cells) estimated from the slope of the line was 724 μmol Cr(III)/g dry wt. cells.
The effect of cell amounts on Cr(III) removal from aqueous Cr(III) solution using A. nicotianae cells was examined. As shown in
quantitatively reduced, and the amount of Cr(III) (μmol/g dry wt. cells) using less than 20 mg of the cells was approximately 600 μmol Cr(III)/g dry wt. cells.
The removal of Cr(III) using A. nicotianae cells was examined in a time course analysis. These results are summarized in
To determine which heavy metal ion can be most readily removed using A. nicotianae cells at pH 5, the selective removal of heavy metal ions from a solution containing 4 × 10−5 M Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Cr3+ was examined. As shown in
The amount of Cr(III) removed using A. nicotianae cells was strongly affected by the pH of the solution. The amount of Cr(III) removed (%) increased as pH of the solution increased. Therefore, the adsorption of Cr(III) was examined at pH 5 and desorption was examined using both acidic and alkaline conditions by a batch system. As shown in
Desorbent | Adsorbed Cr(III) (mg) | Adsorbed Cr(III) (%) | Desorbed Cr(III) (mg) | Desorbed Cr(III) (%) |
---|---|---|---|---|
0.01 M-HCl | 343 ± 3 | 73.3 ± 0.6 | 122 ± 2 | 35.4 ± 0.8 |
0.1 M-HCl | 334 ± 2 | 71.4 ± 0.5 | 144 ± 3 | 43.1 ± 0.5 |
1 M-HCl | 335 ± 3 | 71.6 ± 0.6 | 151± 2 | 45.2 ± 0.2 |
0.01 M-Na2CO3 | 333 ± 3 | 71.2 ± 0.6 | 14 ± 1 | 4.2 ± 0.2 |
0.1 M-Na2CO3 | 334 ± 2 | 71.4 ± 0.5 | 46 ± 1 | 13.6 ± 0.3 |
1 M-Na2CO3 | 334 ± 3 | 71.4 ± 0.5 | 80 ± 1 | 23.8 ± 0.1 |
73.3%) was adsorbed on A. nicotianae cells. However, only a small amount of adsorbed Cr(III) was desorbed in acidic conditions (i.e., 35% using 0.01 M- and 45% using 1 M HCl at 30˚C) and alkaline conditions (i.e., 4% using 0.01 M- and 24% using 1 M Na2CO3 at 30˚C).
The amount of Cr(III) desorbed was very low using A. nicotianae cells at 30˚C. Therefore, the effect of temperature on the desorption of adsorbed Cr(III) was examined. As shown in
To obtain basic information on the recovery of Cr(III) using immobilized A. nicotianae cells, cycles of Cr(III) adsorption and desorption was repeated five times.
As shown in
The removal of Cr(III) using A. nicotianae cells was strongly affected by the pH of the solution. The amount of Cr(III) removed increased as the pH of the solution increased. The maximum Cr(III) removed (%) of appropriately 90% was observed at pH 5. As the removal of 2.5 ppm Cr(III) using persimmon tannin gel was about 30% (21), the amount of Cr(III) removed using A. nicotianae was six times higher than that using persimmon tannin gel.
The Cr(III) removed (µmol/g dry wt. cells) increased as the Cr(III) concentration increased, whereas the Cr(III) removed (%) decreased.
The removal of Cr(III) using A. nicotianae cells obeyed the Langmuir isotherm over all concentrations examined.
Cr removed (%) increased as the cell amount increased, whereas the Cr(III) removed (μmol/g dry wt. cells) decreased. The amount of Cr(III) removed using A. nicotianae cells increased very rapidly and 76% of the Cr(III) in the solution was removed during the first 5 min following the supply of Cr(III). The removal of Cr(III) reached an equilibrium within 6 h. The selective removal of 7 kinds of metal ions was examined using A. nicotianae cells; Cr(III) and Cu(II) were removed at much higher rates than the other metal ions. Immobilized A. nicotianae cells can also adsorb Cr(III) at 30˚C and can desorb most Cr(III) with 0.1 M hydrochloric acid at reflux temperature. Repetition of adsorption (column) and desorption (batch) cycles using immobilized A. nicotianae cells can be repeated 5 times.
We observed substantial toxic Cr(VI) removal using persimmon gel; however, some (~20%) Cr(III) was produced, and only a low amount of Cr(III) removed [
Hatano, T. and Tsuruta, T. (2017) Removal and Recovery of Chromium(III) from Aqueous Chromium(III) Using Arthrobacter nicotianae Cells. Advances in Microbiology, 7, 487- 497. https://doi.org/10.4236/aim.2017.76038