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Experimental and theoretical approaches for the surface interaction between copper and activated sludge microorganisms at molecular scale.

Luo HW, Chen JJ, Sheng GP, Su JH, Wei SQ, Yu HQ - Sci Rep (2014)

Bottom Line: The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis.XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds.To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes.

View Article: PubMed Central - PubMed

Affiliation: CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry.

ABSTRACT
Interactions between metals and activated sludge microorganisms substantially affect the speciation, immobilization, transport, and bioavailability of trace heavy metals in biological wastewater treatment plants. In this study, the interaction of Cu(II), a typical heavy metal, onto activated sludge microorganisms was studied in-depth using a multi-technique approach. The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis. EPR spectra indicated that Cu(II) was held in inner-sphere surface complexes of octahedral coordination with tetragonal distortion of axial elongation. XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds. To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes. These results are useful to better understand the speciation, immobilization, transport, and bioavailability of metals in biological wastewater treatment plants.

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Acid-base titration curve of activated sludge: (a) the corresponding derivative of the titration curve; (b) pKa values of various binding sites; and (c) the corresponding concentrations of functional groups at various pKa values.
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f1: Acid-base titration curve of activated sludge: (a) the corresponding derivative of the titration curve; (b) pKa values of various binding sites; and (c) the corresponding concentrations of functional groups at various pKa values.

Mentions: The titration curve of pH vs. NaOH additions is shown in Fig. 1a, and the corresponding derivative of the titration curve is illustrated in Fig. 1b. The activated sludge showed a certain buffering capacity, as indicated by the weak inflection points (Fig. 1a). The derivative of the titration curve (Fig. 1b) gave the equivalence points and the apparent pKa values for the activated sludge. The peaks indicated a maximum variation in pH corresponding to the equivalence points, and the valleys showed a minimum variation in pH, which was an indicator of buffering. Arrows (at pHs of 5.8 and 8.3) represented the corresponding pH values of the titration curve for each equivalence points (Eq.n)16. Assuming four binding sites according to the derivative of the titration curve, the pKa values of the proton-binding sites as well as their contents were estimated using the PROTOFIT 2.1 software, and are shown in Fig. 1c. The pKa values and their contents of the four binding sites were pKa1 3.57 (0.25 mmol/g), pKa2 5.42 (0.66 mmol/g), pKa3 7.28 (0.37 mmol/g), and pKa4 9.92 (1.12 mmol/g), which were assigned as phosphodiester, carboxyl, phosphoryl and hydroxyl/phenolic groups, respectively171819.


Experimental and theoretical approaches for the surface interaction between copper and activated sludge microorganisms at molecular scale.

Luo HW, Chen JJ, Sheng GP, Su JH, Wei SQ, Yu HQ - Sci Rep (2014)

Acid-base titration curve of activated sludge: (a) the corresponding derivative of the titration curve; (b) pKa values of various binding sites; and (c) the corresponding concentrations of functional groups at various pKa values.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4233339&req=5

f1: Acid-base titration curve of activated sludge: (a) the corresponding derivative of the titration curve; (b) pKa values of various binding sites; and (c) the corresponding concentrations of functional groups at various pKa values.
Mentions: The titration curve of pH vs. NaOH additions is shown in Fig. 1a, and the corresponding derivative of the titration curve is illustrated in Fig. 1b. The activated sludge showed a certain buffering capacity, as indicated by the weak inflection points (Fig. 1a). The derivative of the titration curve (Fig. 1b) gave the equivalence points and the apparent pKa values for the activated sludge. The peaks indicated a maximum variation in pH corresponding to the equivalence points, and the valleys showed a minimum variation in pH, which was an indicator of buffering. Arrows (at pHs of 5.8 and 8.3) represented the corresponding pH values of the titration curve for each equivalence points (Eq.n)16. Assuming four binding sites according to the derivative of the titration curve, the pKa values of the proton-binding sites as well as their contents were estimated using the PROTOFIT 2.1 software, and are shown in Fig. 1c. The pKa values and their contents of the four binding sites were pKa1 3.57 (0.25 mmol/g), pKa2 5.42 (0.66 mmol/g), pKa3 7.28 (0.37 mmol/g), and pKa4 9.92 (1.12 mmol/g), which were assigned as phosphodiester, carboxyl, phosphoryl and hydroxyl/phenolic groups, respectively171819.

Bottom Line: The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis.XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds.To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes.

View Article: PubMed Central - PubMed

Affiliation: CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry.

ABSTRACT
Interactions between metals and activated sludge microorganisms substantially affect the speciation, immobilization, transport, and bioavailability of trace heavy metals in biological wastewater treatment plants. In this study, the interaction of Cu(II), a typical heavy metal, onto activated sludge microorganisms was studied in-depth using a multi-technique approach. The complexing structure of Cu(II) on microbial surface was revealed by X-ray absorption fine structure (XAFS) and electron paramagnetic resonance (EPR) analysis. EPR spectra indicated that Cu(II) was held in inner-sphere surface complexes of octahedral coordination with tetragonal distortion of axial elongation. XAFS analysis further suggested that the surface complexation between Cu(II) and microbial cells was the distorted inner-sphere coordinated octahedra containing four short equatorial bonds and two elongated axial bonds. To further validate the results obtained from the XAFS and EPR analysis, density functional theory calculations were carried out to explore the structural geometry of the Cu complexes. These results are useful to better understand the speciation, immobilization, transport, and bioavailability of metals in biological wastewater treatment plants.

Show MeSH
Related in: MedlinePlus